Photon-detectors — report on the history and activities of the IMEKO technical committee on photon-detectors (TC-2)

Photon-detectors - Report on the history and activities of the I M E K O Technical C o m m i t t e e on Photon-detectors (TC-2) J. Schanda* and Miroslav Jedlickaf *Research Institute for Technical Physics of the Hungarian Academy of Sciences, Budapest, Hungary 1"Czechoslovak Scientific and Technical Society, Prague, Czechoslovakia

The paper reviews the developments of the technology of photon-detectors as reflected in the work of the relevant IMEKO Technical Committee.

Introduction

Photovoltaic detectors

At the first Congress of IMEKO, the participants realised the importance and special position of photondetectors among other measurement transducers and decided to establish a technical committee devoted to the task of bridging the gap between photon-detector manufacturers and users. Optical radiation has some peculiarities as a vehicle of information which justify the existence of a special committee for investigating its use in measurement techniques. The Technical Committee at the time of its establishment dealt mainly with the characteristics of vacuum photodetectors (photocells, photoelectric multipliers and image tubes). Over the years the emphasis on photoconductive and photovoltaic transducers has increased, and, in addition, new classes of detectors were invented and implemented, eg, pyroelectric detectors. The Committee had its first meeting in Budapest, Hungary, in 1963. Since then nine meetings have been held, at which over 250 papers have been read. The Proceedings of the IMEKO Symposia on Photondetectors have been regularly published by the Central Secretariat and have always been among the bestsellers of IMEKO publications. In recent years the Committee has built some very fruitful liaison and co-operation with its sistercommittee TC-2.2, 'Detectors', of the International Commission on Illumination (CIE), which is mainly interested in the performance specifications of lightand radiation-measuring devices. Several times this standardising body has held its meetings jointly with a symposium of IMEKO TC-2, boosting the participation at our symposia, at which manufacturers and developers of new photodetectors could learn of the demands of measurement technologists, and people from the measurement community could hear about the latest detectors. In the following a summary is presented of some of the most important activities of TC-2.

At early IMEKO Symposia on Photon-detectors the performances of Se cells were thoroughly reviewed (eg, Lukfics and Rohaly, 1969). Peculiarities, such as the non-additivity of blue and red response, were investigated and explained. Later, the study of the characteristics of heterojunctions became the focus of attention. Many studies dealt with their application as photon-detectors, particularly as they gained importance in light-emitting devices (Schanda, 1971; Kanev, and Constantinova, 1971; Kandilarov, 1971; Gill, 1971; Malachowski et al, 1978; Lukyanchikova, 1980; Bittner et al, 1980). At a p-n junction a current-carrier concentration gradient is introduced by the doping difference on the two sides of the junction. Light absorption produces free current-carriers (Fig 1) which are either swept through the junction by the built-in electric field or are trapped, eventually recombining at defect sites in the bulk of the semiconductor or at surface states. To achieve short wavelength sensitivity, semiconductors have to be chosen with a high-energy band-gap. The position at which the free current carriers are produced is determined by the wavelength dependence of absorption within the semiconductor. Shorter wavelength photons are absorbed nearer to the surface. If the probability of surface recombination is higher than that for carriers reaching the p-n junction, the shortwavelength responsivity will decrease. To produce high short-wavelength responsivity, the junction has to be produced near to the surface. Photons of lower energy will penetrate deeply into the semiconductor. If there is no built-in electric field in this part of the device, the current carriers produced can reach the junction only by diffusion and thus the probability of recombination of minority carriers before reaching the junction increases. This would require semiconductors of steeper band edge or a junction produced farther away from the surface. No photovoltage is produced by photons with energy lower than the band-gap energy.

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materials are absorbed near to the junction and produce a large photosignal (Fig 2). Such detectors with a broad sensitive window were produced, but found no widespread applications. A major problem with these heterojunction detectors is that the lattice mismatch between the materials used introduces surface states at the heterojunction, decreasing the efficiency of the detector. Heterojunctions do, however, promise the possibility of producing detectors with very special characteristics. Back-to-back junctions, for example (see Fig 3a for a possible band scheme), can produce output signals whose polarity depend s on the wavelength of irradiation, as shown in Fig 3b. The technological difficulties of manufacturing practicable heterojunction photovoltaic detectors have still not been mastered. At the same time silicon technology has developed to an extremely high level. Surface recombination problems have been to a large extent eliminated, and the preparation of very shallow but still homogeneous junctions has become possible, so that modern Si cells are highly sensitive from about 200 nm up to the band gap of Si (-1100 nm). Problems are still found with the short-wavelength stability of some of these cells, but despite this they are more stable and permit a higher reproducibility of radiation measurement than any other light detectors. It has also been shown that by coupling Si cells to high-performance operational amplifiers, instruments can be built with light input-voltage output characteristics linear over more than eight decades (Budde, 1978). Also the sensitivity achievable has increased over the years. The quantum efficiency of Si detectors is already near to the theoretical limit. The instrument performance depends on the internal resistance and capacitance of the detectors and the drift properties of the amplifiers (Eppeldauer and L(mc, 1980). Internal resistances in the many-megohm range are now possible, even with large surface ( - 1 cm 2) detectors, so that the ultimate performance depends now on the input drift properties of the amplifier. The best amplifiers, if only low-frequency operation is required, give sensitivities that were possible previously only by instruments using photoelectric multipliers, but with much improved stability. For a number of applications, responsivity in a restricted wavelength range is required. GaAs technology has developed considerably in recent years because of its widespread application in optoelectronic transducers. Photon-detector manufacturers have taken

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Photoemissive detectors IMEKO TC-2 has seen two revolutions in photocathode technology: the introduction of multi-alkaline and negative electron-affinity photocathodes. Over the years a number of papers have been given at the symposia helping to clarify the physical properties of Cs-Ag-O and Cs-Sb photocathodes, which have been used for many years but whose operation was not really understood (eg, Jedlicka, 1967; Vernier, 1967; Nanev, 1967; Hoene and Heimann, 1969; Kansky et al, 1969; Dvorfik, 1969; Jung and Stadlmann, 1969; Feldner et al, 1971; Jedlicka, 1974; Rocca, 1974). Papers given have covered both the basic aspects of photoemission [eg, Jazenko (1967) dealt with photofield effect, Rocca (1971) with quantum statistics, Bedos (1974) with photoemission of metals, etc], as well as its practical application. Some earlier works dealt with photon counting (eg, Schanda, 1967), special photodetectors (eg, UV detectors Lang, 1973; Pressler and Eberhardt, 1974), and with the problem of negative electron affinity (Jedlicka, 1971). Fig 4 shows the band diagram of both positive and negative EVQC

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electron-affinity photocathodes. The big advantage of the latter structure is that high long-wavelength sensitivity can be achieved even with materials with low thermionic emission properties. It was interesting to note how the number of papers dealing with photoemission and photoelectric devices based on the external photoeffect decreased over the years. At the last two meetings only very few papers falling into this category were read, and these dealt only with special applications, such as the time control of the gain of photoelectric multipliers (Abramochkin et al, 1980), in which a voltage modulation of the dynodes was used to modulate the sensitivity of the tube.

Photoconductive detectors Modern semiconductor research has had a large impact on the development of photoconductive detectors. Papers in this field have featured at every symposium, their importance in special areas of photoelectric detector application being clearly demonstrated in the proceedings of the symposia. In the early days attention centred on II-VI compound photoresistors (Andreichin et al, 1971, Biger and Kunze, 1974), but has moved over the years to III-V type semiconductors, especially to those that can be used in the infrared spectral region (eg, Sandera, 1976; Igras et al, 1978; Sikula and Vasina, 1978); then, at the last meeting, switched back to II-VI compounds (Snejdar, 1980; Cimpl et al, 1980; Hiie et al, 1980a, b; Altosaar et al, 1980; Sikula et al, 1980; Lukyanchikova et al, 1980) because, in the meantime, a number of technological problems had been solved, and it became possible to construct from II-IV compounds photoresistors with good linearity and reasonable speed of response. 7O 60

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Thermal detectors- absolute radiometry In the early days thermopiles and classical bolometer configurations were the main subjects of symposium

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papers (Kortum, 1967), together with their measurement (Kechlibarov and Zirwer, 1969) and the description of radiation standards. Carbon arcs were used as radiation standards, and their properties were investigated thoroughly (Rutgers, and Schurer, 1969). Fig 7 shows a typical arrangement for such a measurememt. A few years later pyroelectric detectors became the favourites (eg, Berndt, 1974), and were used also in the imaging type of device (Steinhage, 1976), but special and new measuring principles were always being discussed at the symposia: items covered included superconducting (Fr6hlich et al, 1973, 1974) and Ettingshausen-Nernst detectors (Elbel and Soa, 1978), as well as temperature-frequency converting instruments (Donati and Angeleri, 1980). The latter principle was realised in the system shown in Fig 8. Two quartz crystals are cut so as to maximise the temperature coefficient of resonant frequency and are blackened to absorb optical power. One of the crystals is irradiated, the other serves as reference. The two crystals set the frequency of the main and reference oscillator. The difference pulses, after a second mixing stage for zero balancing, are counted and displayed. The main interest in radiation measurement in recent years has been in precision methods and absolute techniques, because the illuminating engineering community decided to change its basic standards to absolute radiation measurement. At the 8th Symposium the organisers invited members of the sister committee, CIE TC-2.2 'Detectors', to discuss this question of mutual interest. F. Hengstberger, chairman of the sister committee, gave a state-of-the-art report (Hengstberger, 1978). He dealt with new instrumental developments using pyroelectric sensing elements for absolute radiometers, and improved bolometers and thermopile sensors. The calculation of instrumental correction factors was also discussed. The basic layouts of an ideal and practical absolute radiometer are depicted in Fig 9. In Fig 9a, the radiant and reference power are alternately switched on to the common heat converter. In practice it is usually necessary to use separate heat converters, as seen in the scheme of Fig 9b. Only at the heat sensor stage are the two signals combined. The sensor signals for the radiant and the reference power are either measured independently, or combined into a difference signal, and the reference

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power being measured separately at the zero value of the difference signal. A number of papers have dealt with the constructional details, accuracy, and application of radiation measuring detectors and equipment (Zatkovic, 1978; Miiller and Ratz, 1980; Vogel, 1980; Giittich, 1980; Zatkovic, 1980). An interesting alternative approach to absolute radiation measurement was discussed by Geist and co-workers (Geist et al, 1980), who proposed to use a Si-photodiode for this purpose: the absolute responsivity of Si can be determined from semiconductor theory and from measurement of the reflectivity and the changes in response under forward and reverse biasing. Detector

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electric multipliers (Luk~ics and Roh~ily, 1969; Jedlicka and Raus, 1969; Beffmek and Nov~kov~i, 1969). It was well known that inherent instabilities in polycrystalline Se cells prevented their application as precision instruments. Long-term drifts, spectral and spatial responsivity changes, non-linearities and lack of additivity discouraged the use of these cells in objective light and radiation measurement. Similar problems were observed in photoelectric multipliers as well, restricting these devices to short-duration and low-intensity measurements. Approximately a decade ago the Si-photovoltaic measuring cell evolved from the solar energy converter and from semiconducting property studies of Si. The technology of these devices advanced considerably: their responsivity was extended into the ultraviolet, their internal resistance increased [an important characteristic for coupling them to current-voltage transducers (Jedlicka et al, 1978)], and their stability was Measurement Vol 1 No 1 ,Jan--Mar 1983

Schanda and Jedlicka also greatlyimproved, so that it became possible to build photoelectric systems using Si-photovoltaic cells whose stability surpassed that of other optical devices used as radiation standards. Present-day Si-cell-based photometers are the workhorses of photometric laboratories (Geutler and Krochmann, 1974; Priu and Budde, 1980; Budde, 1980; Szentiday, 1980). The latest tests appear to show that they can be used even as absolute detectors for determining spectral irradiance (Geist et al, 1980). A p p l i c a t i o n of p h o t o n - d e t e c t o r s

Photon-detector Symposia have been and are held to promote information exchange among developers, manufacturers and users of photon-detectors. Thus papers on different areas of application featured at every meeting. The selection given here can only exemplify the widespread use of these detectors and can by no means try to present a complete picture of applications. Problems of light and radiation measurement were dealt with at almost every symposium [eg, (Bauer, 1969; Krochmann, 1969; Quemerais et al, 1974; Svet and Gavanin, 1974; Hieke and Hahn, 1976; Kaase and Bischoff, 1976; Svet, 1978)], and the use of photondetectors in optical information gathering and transmission (Pohl, 1971; Pohl and Schmidt, 1973; De la Rue, 1974) was also discussed frequently. Industrial measurement problems - both of light and radiation measurement (Fischer and Tannberger, 1974; Krochmann and Geutler, 1976; Czibula et al, 1978) and in cases where optical radiation is only a vehicle of information (Reiter, 1974; Bates and Galan, 1980; Weissenborn et al, 1974; Prydz, 1974) - were also discussed.

Image-forming photon-detectors

Image detectors can be subdivided into two groups: (a) those which convert both the optical signal as well as the optical image (being defined as a planar distribution of one or more parameters of the incident radiation) into an electrical signal; (b) those which convert an optical image into another optical image, usually spectrally transposed and/or intensified. The history of electrical imaging, starting with the first attempt at television (involving the conversion of light to electricity, proposed by G. R. Carey in 1875) up to the present day, is very exciting. The variety of image-detecting techniques and their applications has increased continually. A great many symposia and scientific and technical conferences have been devoted to discussions of the detailed aspects of image-detecting devices. IMEKO TC-2, also, has extended the possibilities for discussion of the results of recent developments and provided a forum for exchange of ideas in the field of photon-detecting devices. I would like to present in this paper my personal observations on the total activity of IMEKO TC-2 in electronic imaging as discussed at the TC-2 Symposia. In the early 1960s, the image-orthicon was the MeasurementVol 1 No 1,Jan--Mar 1983 4*

dominant television camera tube. Measurements on these tubes, without any doubt, presented a very interesting problem. During the 2nd Symposium in Jena in 1965, L. Jung and H. Stadlmann presented a paper devoted not only to the study of the measurement of camera tube properties but also to obtaining further information about the so-called after-image, which occurred in image-orthicons after some period of use. The authors' initial work proved to be successful and stimulated much further research in this area. Indeed, further work was done by the same authors in order to explain the response limitations of camera tubes of that time. The results were based on signal and background fluctuation studies and agreed with practical experience. These results were reported at the 3rd Symposium in Warsaw in 1967. On that occasion Biermann (1967) introduced a new photoconductive camera tube, the 'Endicon', sensitive in the infrared region from about 400 to 1900 nm, with a very low residual output (for that time) of 10% after 40 ms. No pyrovidicons were available at that time, and so the use of this tube for image moving thermal sources at 250-500°C was very attractive. A study of the basic factors governing the detection limit in astronomical imaging was carried out by Gebel (1967). The object of his paper was to analyse from a probabilistic viewpoint the different basic factors which determine the detection limit in imaging by considering the stochastic nature of radiation and of the attenuation and absorption processes, as well as the randomness inherent in energy conversion. It was demonstrated that images obtained by electro-optic image processing contained information which otherwise could not be recognised reliabl3~ by direct visual examination. The 4th Symposium was held in Prague in 1969. At the end of the 1960s, solid state pick-up devices based on thin films seemed to show some advantages in spite of difficulties connected with their design and fabrication. Interesting new possibilities arose in connection with applied television. Problems arose in the scanning system, in the image sensor itself and in combining both these parts into a complete system. Furthermore, many manufacturing problems had to be solved. In the paper presented by Vitovsky (1969), some points of interest concerning this photon-detector were discussed and a deposition method for the complex thin film structure was described. When several image-convertor tubes are cascaded, ie, when using several phosphors, it is often overlooked that a convolution of the phosphor emission responses of the different tubes occurs. Gebel (1969) showed how the convolution of the phosphor responses of cascaded image-convertor tubes can be used to obtain an image time delay which allows for the operation of thresholdcontrollable gating devices designed to protect the highly fragile television image transducer tubes against randomly occurring highly intense light flashes, etc. This protective gating also blanks out the flashes in the reproduced image and thus protects kinescope recordings from accidental overexposure by these flashes. Further work undertaken by Jung and Stadlmann (1971) and presented at the 5th Symposium in Varna in 1971 isolated the properties of the optical components and the camera tube itself which most affected image 19

Schanda and dedlicka contrast in television. The optical image quality, the diffusion of the charge accumulated on the target and the limited size of the scanning electron beam can be considered as the main limiting factors in the case of a stationary object. Besides these, the phosphor decay time must be taken into account with moving objects. Poor edge resolution can occur in images which are obtained from a time sequential signal produced by electron-beam or flying-spot light scanning of photosensitive targets illuminated by an optical image. This lack of edge resolution may be due to the finite thickness of the film, the finite size of the scanning beam, unfavourable lateral-to-transverse ratio of the effective resolution element, insufficient bandwidth in the transmission path, etc. The method described by Gebel and Fettis (1971) in Varna at the same meeting was efficient enough to restore the sharpness of the edges, and utilised a filter with appropriate properties. A round-table discussion on photon-detectors was organised during the 6th IMEKO Congress in Dresden in 1973. There had recently been many detailed investigations of the use of silicon for photoelectronic imaging. Jedlicka (1973) described some new possibilities for applying single-crystal silicon for vidicon targets and CCD devices. Work along these lines was done by Pohl (1971), which yielded interesting results with a matrix containing 64 silicon phototransistors. The next regular Symposium took place at Si6fok in 1974. On this occasion the first experiment in the systematic classification of electro-optic science from the viewpoint of the electro-optical transducers was carried out by Jedlicka and Kostfil (1974). Imaging photon-detectors used as camera tubes and various CCD-CID sensors for video-signal generation, image intensifiers and convertors occupied a very important position in their technique. Pi6tri (1974) solved the problem of the design and performances of the fast vacuum photon-detectors for high-speed imaging, making use of results from LEP (Philips) laboratories. At that time the general trends were: the systematic application of microchannel plates, proximity electron focusing and photocathode transfer techniques. This still holds good. At the 7th Symposium in Brunswick in 1976, methods of electronic image conversion from invisible into visible spectral regions were demonstrated and discussed in some detail. Heimann (1976) discussed procedures for the conversion of UV-intensity distributions into the visible range by the use of microscopic imaging. By employing modern electro-optic image intensification and low-light-level camera tubes, illumination levels were drastically reduced; thus effects on the object became practically negligible and living objects could be imaged undisturbed. An optimum design of highly sensitive UV-microscope was suggested as well as some examples of its application. Jares, (1976a) dealt with the reason for the spurious circular signals caused by secondary emission in vidicon camera tubes and discussed some possibilities for eliminating them by means of a modified electrode system in the tube. The same author (Jfires, 1976b) discussed some problems of grid-shuttered imageconvertor tubes in ultra-high-speed photography. He compared the performance of image convertor tubes with different electSon optics and photocathode resistances with a view to evaluating the inter-dependence of 20

the dynamic range and the time resolution limit in these devices. The principles of operation of pyroelectric image tubes were outlined by Steinhage (1976). Problems of material choice and related technological questions, the contemporary state of the art, and performance data were discussed, and a pyroelectric television set-up displaying an MRTD of 0.2 K was demonstrated. In the middle of the 1970s camera tube targets utilising heterojunctions between n- and p-type semiconductors or insulators began to be applied widely. Jedlicka (1976) determined the operating condition for these heterojunction targets, discussed the properties of these targets in chalnicon, saticon, newvicon and some experimental tubes, and reported the development of spray-techniques for the preparation of a CdSe heterostructure layer instead of its vacuum deposition. At the 8th Symposium in Prague in 1978 the problem of heterojunction vidicon target was again under discussion. Some electrical properties of the heterostructure CdSe-As2Se3 and the optical properties of the sprayed CdSe layer, both used in a vidicon target, were reported by Cimpl et al (1978). The detailed conditions for operation of this target from the viewpoint of technological possibility and the requirements for high image quality were discussed in a further work presented by Jedlicka et al (1978). The problem of low-light-level imaging began to be more and more important. A comprehensive theory of low-light-level image detection was suggested by Coleman (1978) and treated the questions of quantum detection efficiency, information content, least detectable contrast, and application of image photon counting detectors - briefly covering the basic theory of image analysis and evaluation. It was demonstrated that the most efficient instrument available for the detection and photometry of extremely faint imaRes at the present time is an image photon counting system. The most recent Symposium was organised at Visegrfid in 1980. The previous results on CdSe-As2Se3 vidicon target heterostructure were supplemented by new findings of Cimpl and co-workers (1980). In this short report only the most important points can be mentioned, characterising the direction of the activities of IMEKO TC-2 during the last 20 years. In retrospect I may say that our committee has contributed - to some extent - to progress in a field which is of great interest in photon imaging electro-optics. Let us hope that our future work will continue on the same lines.

Summary A report such as this, summarising the proceedings of the Photon-detector Symposia, can never be as complete as one would like. One would wish to include further papers in the different sections but space and time do not permit this. It has, however, been interesting to follow the trends in the development of the different detector types. Some earlier detectors are totally obsolete, while others still struggle for survival. Vacuum photocells are almost obsolete, as are Se-photovoltaic cells. Si cells now dominate the instrumentation field, while new types [avalanche detectors (Wegrzecka, 1978; Cova et al, 1980), prepared from Measurement Vol 1 No 1, Jan--Mar 1983

Schanda and Jedlicka compound semiconductors (Zhingarev et al, 1980)] and other detectors are gaining importance. The introductory papers by Prof G6rlich, for a long time Chairman of the Committee and now its Honorary Chairman (see G6rlich, 1974, 1976, 1978, 1980) are a special feature of the Symposia and provide the best summary of new developments in photon-detectors. There are certainly no better papers than these to which an interested reader could refer for further information.

References* Ahramochkin, A. I., Nolle, P. M. and Tikhomirov, A. A. 1980. 'Photomultiplier with time control of gain'. 9th Symp, Visegrfid, p 92. AItosaar, M., Kukk, P., Meilikov, E. and Valdna, V. 1980. 'CdS and CdSe microphotoresistors for optoelectronics'. 9th Symp, Visegr~d, p 175. Andreichin, R., Ivanova, A. and Stanislavova, U. 1971. 'Evaporated ZnCdS layers as photoresistor in the ultraviolet'. 5th Symp, Varna, p 363. Andreichin, R. 1978. 'A multifunctional medium for photon detecting'. 8th Symp, Prague, p 63. Bates, C. W. Jr and Galan, L. E. 1980. 'X-ray photoemission and Auger electron spectroscopy of multialkali antimonide photocathodes'. 9th Symp, Visegrfid, p 100. Bauer, G. 1969. 'Internationale Vergleichsmessungen an Standard-Lampen und Vakuum-Photozellen und ihre Normung'. 4th Symp, Prague, p 153. Bedos, R. 1974. 'A critical review of computation methods - based on the Fowler theory - used to determine the photoelectric work function of metals'. 6th Symp, Si6fok, p 136. Behrendt, R., Herrmann, K. H. and Wendlandt, R. 1978. 'Design problems with respect to Pbl_xSn×Te homojunction and heterojunction photodiodes'. 8th Symp, Prague, p 72. Ber~inek, I. and Nov~ikov~i, O. 1969. 'Uber die Stabilit~it der Sekund~ir-elektronenvervielfacher im Impulsbetrieb'. 4th Symp, Prague, p 103. Berndt, K. 1974. 'Pyroelectric infrared detectors for lasers based on strontium-barium-niobate'. 6th Symp, Si6fok, p 308. Biermann, M. 1967. 'Praktische Ergebnisse zur Nachweisempfindlichkeit des Ultrarotendikons bei der Beobachtung bewegeter thermischer Eigenstrahler'. 3rd Syrup, Warszawa, p 120. Bittner, H., Bremser, W. and Herrmann, K. H. 1980. 'The spectral photoelectric quantum efficiency of PbSnTe/PbTe heterojunctions - comparison of isotype and anisotype junctions'. 9th Symp, Visegrfid, p 200. Budde, W. 1978. 'Multi-decade linearity measurements on Si-photodiodes'. 8th Symp, Prague, p 466. Budde, W. 1980. 'Measurement of chopped radiation with Si-photodiodes. 2. Linearity'. 9th Symp, Visegr~d, p. 291. Biiger, P. A. and Kunze, O. A. 1974. 'Morphology of * As all references relate to IMEKO Photon-detector Symposia, and the Photon-detector Round Table Meeting, short form referencing has been used. Thus, 4th Symp, Prague means Proceedings of the 4th IMEKO Photon-detectors Symposium, Prague. Measurement Vol 1 No 1, Jan--Mar 1983

lead sulphide formed during the reaction of thiourea with plumbite during the preparation of lead sulphide detectors'. 6th Symp, Si6fok, p 268. Cimpl, Z., Jedlieka, M., Kosek, F. and Schauer, F. 1978. 'CdSe - amorphous chalcogenide layer heterostructure'. 8th Symp, Prague, p 54. Cimpi, Z., Janda, M., Jedlicka, M., Kosek, F., Schauer, F. and Zajic, J. 1980. 'CdSe photoconductive layers in heterostructures'. 9th Syrup, Visegr~id, p 159. Coleman, C. I. 1978. 'The theory of low-light-level image detection'. 8th Symp, Prague, p 21. Cova, S., Longoni, A. and Andreoni, A. 1980. 'Avalanche photodiodes for single-photon detection'. 9th Symp, Visegrfid, p 82. Czibula, G., D6zsi, G., Sz6nyi, L. and Schanda, J. 1978. 'On the determination of parameters of photodetectors used in illuminance meters'. 8th Symp, Prague, p 166. De la Rue, R. M. 1974. 'Integrated optical photodetectors'. 6th Symp, Si6fok, p 237. Donati, S. and Angeleri, A. 1980. 'A simple, digital radiant-power meter based on a quartz oscillator'. 9th Symp, Visegrfid, p 336. Dvor~ik, M. 1969. 'Einige Eigenschaften der zusammengesetzten Photokathode Sb-K-Rb-Cs'. 4th Symp, Prague, p 63. Elbel, T. and Soa, E. A. 1978. 'Ettingshausen-Nernst detectors'. 8th Symp, Prague, p 272. Eppeldauer, G. and L~inc, J. 1980. 'Problems of photocurrent measurements using photovoltaic cells'. 9th Symp, Visegrfid, p 310. Feldner, E., GOrlich, P. and Miiller, T. 1971. 'Zur Technologie von Trialkali-Antimonid-Photokathoden'. 5th Symp, Varna, p 51. Fischer, J. and Tanneberger, T. 1974. 'Some experience gained in VEB Kombinat NARVA in the application of photon detectors in industrial photometry, radiometry, and colorimetry'. 6th Syrup, Si6fok, p 400. Fr6hlich, H., Vodel, W. and W~ichter, D. D. 1973. 'On the influence of electromagnetic radiation on weak supraconducting links'. Round Table, Dresden, p 86. Fr/ihlich, H., Vodel, W. and Waechter, D. D. 1974. 'The possibility of detecting electromagnetic radiation in the spectral region 0.6-40/xm means of narrow superconducting strips'. 6th Symp, Si6fok, p 337. G:il, M. 1971. 'Position sensitive photocell based on Ge-Si heterojunction'. 5th Syrup, Varna, p 426. Gebel, R. K. H. 1967. 'A study of basic factors governing the detection limit in astronomical imaging'. 3rd Symp, Warszawa, p 9. Gebel, R. K. H. 1969. 'Convolution of 0 phosphor responses occurring in cascaded image intensifier tubes and related subjects'. 4th Symp, Prague, p 293. Gebel, R. K. H. and Fettis, H. E. 1971. 'Controllable edge sharpening for time sequential imaging devices'. 5th Symp, Varna, p 187. Geist, J., Schaefer, A. R. and Zalewski, E. F. 1980. 'Silicon photodiode absolute spectral response selfcalibration'. 9th Symp, Visegrfid, p 365. Geutler, G. and Krochmann, J. 1974. 'On the limits of applying silicon-photoelements in photometry'. 6th Symp, Si6fok, p 366. 21

Schanda and Jedlicka G6rlich, P. 1974. 'New results in the field of photondetectors and their application'. 6th Symp, Si6fok, pl. G6rlich, P. 1976. 'Review of the recent results in the field of photon-detectors and their applications'. 7th Symp, Braunschweig, p 1. G6rlich, P. 1978. 'Recent results in the field of photon-detectors and their applications. II'. 8th Symp, Prague, p 4. G6rlich, P. 1980. 'Recent results in the field of photon-detectors and their applications. III'. 9th Symp, Visegrfid, p 3. G/ittich, R. 1980. 'Local distribution of sensitivity (local response) of thermal detectors - measuring technique - results'. 9th Syrup, Visegrfid, p 347. Heimann, W. 1976. 'UV-microscopy utilizing image intensifier and high sensitive camera tube'. 7th Symp, Braunschweig, p 75. Hengstberger, F. 1978. 'The present state of the art in absolute radiometry'. 8th Symp, Prague, p 132. Hieke, H. and Hahn, D. 1976. 'Determination of the quantum efficiency of luminophor standards'. 7th Symp, Braunschweig, p 107. Hiie, J., Iljina, N., Kukk, P., Mellikov, E. and Varema, T. 1980a. 'Cadmium sulphide monograin layers as detectors of visible and X-rays'. 9th Symp, Visegrfid, p 172. Hiie, J., Krunks, M., Meilikov, E. and Veel, E. 1980b. 'Photoconductive CdS and CdSxSej_x layers for microwave range'. 9th Symp, Visegrfid, p 167. Hoene, E. L. and Heimann, W. 1969. 'Optische und photoelektrische Eigenschaften d/inner C~isiumoxydschichten'. 4th Symp, Prague, p 29. lgras, E., Jezykowski, R., Persak, T., Piotrowski, J. and Nowak, Z. 1974. 'Epitaxial CdxHgl_xTe layers as infrared detectors'. 6th Symp, Si6fok, p 221. Igras, E., Nowak, Z., Piotrowski, J. and Piotrowski, T. 1978. 'Narrow band (CdHg)Te photodetectors'. 8th Syrup, Prague, p 83. Jares, V. 1976a. 'Possibilities of eliminating the circular, spurious signals in vidicons caused by secondary emission'. 7th Symp, Braunschweig, p 168. Jares, V. 1976b. 'Some problems of grid-shuttered image-converter tubes in ultra-high speed photography'. 7th Syrup., Braunschweig, p 177. Jazenko, A. F. 1967. 'Photofeldemission von hochohmigen Halbleitern'. 3rd Symp, Warszawa, p 77. Jedlicka, M. 1967. 'Neue Photokathoden'. 3rd Symp, Warszawa, p 38. Jedlieka, M. and Raus, J. 1969. 'Einige Eigenschaften des bei hOheren Temperaturen verwendbaren Photovervielfachers'. 4th Symp, Prague, p 87. Jedlicka, M. 1971. 'Photoelektrische und sekund~ire Emitter mit negativer Elektronenaffinit~t'. 5th Symp, Varna, p 9. Jedlicka, M. 1973. 'New chances for Am-B v and Si in photon-detectors'. Round Table, Dresden, p 17. Jedlicka, M. 1974. 'Current status of photoemitters'. 6th Symp, Si6fok, p 79. Jedlicka, M. and Kost~l, E. 1974. 'Electro-optics and photon-detectors'. 6th Symp, Si6fok, p 126. Jedlicka, M. 1976. 'Heterojunction targets in camera tubes'. 7th Syrup, Braunschweig, p 191. Jedlicka, M, Kulh~inek, P., Mravinac, J. and Lezal, D. 1978. 'Heterojunction structure ScSe-As2Se3_xSx for camera tubes'. 8th Syrup, Prague, p 118. 22

Jung, L. and Stadlmann, H. 1969. 'Uber den Einfluss der optischen Anregung auf die Quantenausbeute von Durchsichts-Multi-alkali-Photokathoden' 4th Syrup, Prague, p 75. Jung, L. and Stadlmann, H. 1971. 'Die Konstrast/ibertragung yon Bildaufnahmr6hren'. 5th Symp, Varna, p 150. Kaase, H. and Bischoff, K. 1976. 'UV and vacuum-UV radiometry'. 7th Symp, Braunschweig, p 117. Kandilarov, B. 1971. 'The heterojunction as a photondetector'. 5th Syrup, Varna, p 408. Kanev, St. and Constantinova, E. 1976. 'Photoelements a la base heterojunction CdS-Cu2_×Te. 5th Syrup, Varna, p 380. Kansky, E., Jeric, D., Heimann, W. and Hoene, E. L. 1969. 'Ein interessanter Ubers~ittigungseffekt mit C/~sium bei der Synthese der Ag-O-Cs Photokathode'. 4th Symp, Prague, p 43. Kechlibarov, T. and Zirwer, D. 1969. 'Uber die Messung der spektralen Empfindlichkeit thermischer Strahlungsempf/mger'. 4th Symp, Prague, p 215. Kortum, It. 1967. 'Betrachtungen tiber M6glichkeiten zur Verbesserung des Signal-Rausch-Verh~ltnisses bei Bolometern'. 3rd Symp, Warszawa, p 166. Kroehmann, J. 1969. 'Uber einige neuere Arbeiten zur Strahlungsund Lichmesstechnik'. 4th Symp, Prague, p 187. Kroehmann J. and Geutler, G. 1976. 'Proposal for the definition of the quality of illumination meters'. 7th Symp, Braunschweig, p 89. Kroehmann, J. and Rattunde, R. 1978. 'The technique of correction of the relative spectral responsivity to photobiological spectral weighting functions and the possibilities of defining the quality of the correction'. 8th Symp, Prague, p 182. Lang, W. 1973. 'On UV-detectors'. Round Table, Dresden, p 60. Luk~ies, G. and Roh~ly, M. 1969. 'Neue Untersuchungen fiber die spektrale Empfindlichkeit von Selen-Photoelementen'. 4th Symp, Prague, p 123. Lukyanchikova, N. B. 1980. 'Characteristic features of energy conversion in the "non-ideal" heterojunctions'. 9th Symp, Visegrfid, p 64. Lukyanchikova, N. B., Pekar, G. S. and Tkachenko, N. N. 1980. 'Photoelectric and noise properties of photon detectors based on ZnS Schottky diodes'. 9th Symp, Visegrfid, p 187. Malachowski, M. J., Rogaiski, A., Bedelek, W. and Zmija, J. 1978. 'Photoresponse of metal-CdS-SnO2 thin film heterojunction structure'. 8th Symp, Prague, p 379. Miskosza, H. 1967. 'Einfluss der Hochenergiequantenstrahlung yon CdS Einkristallen'. 3rd Symp, Warszawa, p 153. Morvic, M., Novfik, J. and Kordos, P. 1978. 'Photoelectric properties of GaAs-Gal_xAlxAs heterodiodes'. 8th Symp, Prague, p 46. Miiller, J. E. and Ratz, P. 1980. 'A radiation thermopile for absolute measurements'. 9th Symp, Visegrfid, p 317. Nanev, K. 1967. 'Der Einfluss der Temperatur und der St6rstellen auf die Photoemission des Z~isiumRubidium-Antimonids'. 3rd Symp, Warszawa, p 64. Pietri, G. 1974. 'Design and performances of fast Measurement Vol 1 No 1, Jan--Mar 1983

Schanda and Jedlicka phototubes for photon counting or for high speed imaging'. 6th Symp, Si6fok, p 142. Pohl, It. J. 1971. 'Photodetektoren in der optischen Informations verarbeitungstechnik'. 5th Symp, Varna, p 128. Pohi, H. J. and Schmidt, D. 1973. 'Photoelectric detection of two-dimensional patterns'. Round Table, Dresden, p 65. Pressler, G. and Eberhardt, W. 1974. 'Ultraviolet sensitive photocells'. 6th Symp, Si6fok, p 65. Priu, J. and Budde, W. 1980. 'Measurement of chopped radiation with Si-photodiodes. 1. Compliance with Talbot's law'. 9th Symp, Visegr~d, p 274. Prydz, S. 1974. 'Some possible principles of position sensitive photon-detectors and a possible application in computers'. 6th Symp, Si6fok, p 193. Quemerais, A., Priol, M. and Robin, S. 1974. 'Detection and light flux calibration in the vacuum ultraviolet'. 6th Symp, Si6fok, p 95. Reiter, H. 1974. 'Photon-detectors used for measuring planks and round timber'. 6th Symp, Si6fok, p 349. Roeca, F. 1971. 'Quantum statistical theory of photodetection'. 5th Symp, Varna, p 1. Rocca, F. 1974. 'Photodetection mechanism in the multi-absorption case'. 6th Symp, Si6fok, p 120. Rutgers, G. A. W. and Schurer, K. 1969. 'Radiation standards'. 4th Symp, Prague, p 225. Sandera, M. 1976. 'Characteristics of IR radiation detectors from InSb at the temperature of 273 K and 194.5 K'. 7th Symp, Braunschweig, p 213. Schanda, J. 1967. 'Photoelektronenvervielfacher in der Messtechnik geringer Strahlungsintensit~iten'. 3rd Symp, Warszawa, p 87. Sehanda, J. 1971. 'A review of heterojunction photodetectors'. 5th Symp, Varna, p 392. Sehanda, J. 1976. 'UV-enhancement of the sensitivity of Si-cells'. 7th Symp, Braunschweig, p 49. Sikula, J. and Vasina, P. 1978. 'Transport and noise characteristics of InSb infrared detectors'. 8th Symp, Prague, p 249. Sikula, J., Schauer, P., Koktavy, B. and Vasina, P.

Measurement Vol 1 No 1 , J a n - - M a r 1983

1980. 'Noise in CdTe detectors induced by illumination'. 9th Symp, Visegr~id, p 180. Snejdar, V. 1980. 'On the speed of response of the photo-conductivity in CdSe films'. 9th Symp, Visegr~id, p 149. Steinhage, P. W. 1976. 'Pyroelectric detectors and imaging devices'. 7th Symp, Braunschweig, p 88. Svet, D. J. and Gavanin, V. A. 1974. 'Optical types of photodetectors in radiation pyrometry'. 6th Symp, Si6fok, p 408. Svet, D. J. 1978. 'Photoelectric detectors in modern optical pyrometry and some feasibilities of evaluating their parameters directly in the process of thermal radiation measurement'. 8th Symp, Prague, p 346. Szentiday, K. 1980. 'On the measurement of the internal resistance and linearity of photovoltaic cells'. 9th Symp, Visegr~id, p 297. Vernier, P. 1967. 'Les ph6nom~nes qui limitent le rendement quantique des photocathodes'. 3rd Symp, Warszawa, p 53. Vitovsky, O. 1969. 'Some aspects of design of solid state image sensors'. 4th Symp, Prague, p 275. Vogel, J. 1980. 'An absolute radiometer for the measurement of the optical radiation scale'. 9th Symp, Visegr~id, p 325. Wegrzeeka, I. 1978. 'Some results on silicon avalanche photodiodes'. 8th Symp, Prague, p 300. Weissenborn, B., Schenker and Fritzsehe, W. 1974. 'Recent results of experiments made in the field of stereoscopic colour-television'. 6th Symp, Si6fok, p 185. Zatkovic, J. 1978. 'Symmetrical radiometer for optical radiation'. 8th Symp, Prague, p 147. Zatkovic, J. 1980. 'Electrically calibrated symmetrical radiometer with two bolometers - theoretical remarks'. 9th Symp, Visegr~id, p 358. Zhingarev, M. Z., Korolkov, V. I., Mikchailova, M. P. and Yassievieh, I. N. 1980. 'Low-noise avalanche photodiodes based on III-V compounds and their alloys'. 9th Symp, Visegr~d, p 141.

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