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Photoelectric properties of p-n heterojunctions between GaP and GaAs
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ABSTRACTS OF PAPERS Di SOVIET PHYSICS-SOLID STATE
1vt.~imum. This type of construction enables one to workbat liquid nitrogen temperatures in vacuum 5 X 10 mm Hg, and a specIal micrometer arrangemeet permits one to shift the crystal In the dlrection ci the rotor axis and back without disturblag the vacuum in the system. The dependence of MCPD~jghton the intensity of monochromatic light, AUk, at various wavelengths shows that the Tn.gnltude of the effect Increases rapidly at small light Intensities, becoming linear at large intensities. It follows from the obtained dependences that the magnitude of the effect is maximum in the interval 350-480 ms&, after which a sharp dorp of m2gn1tude i observed, which reaches zero in the region of 800 mu. In vacuum of the Hg the value of the effect in order of 10of2mm the region 350-520 mu decreases: further reduction in pressure to i0~mm Hg leads to additional weakening of the effect. Heating of the single crystal In air for a few minutes at 400°C leads to changes in the spectral distribution of the effect. Comparison with data obtained prior to heating shows that a considerable change in ~(CPD)J~ht Is observed only in the region of short wavelengths and is reversible with time. Change in the sign of the effect from positive to negative has been discovered for wavelengths above 650 mu. The mechanism of the phenomenon is discussed.
Vol. 3, No. 7
value of the coefficient, I, exceeded unity when a positive surface charge, formed as a result of an auxiliary beam, was present on a target. Current pulses for penetration of a negatively charged target were practically the same as those in the case of an uncharged target. On the basis of this, it was concluded that the films under investigation possessed properties characteristic for emitters capable of ensuring an amplification of the secondary electron emission by the field. All obtained volt-ampere characteristics, K(Uk), where Uk is the collector potential have in common a gradual rise of the coefficIent K with increase in field intensity In the ZnS layer, and also the presence of a sharp maximum. It may be noted that this m~Imumcorresponds to the primary electron energy, E~ 2 keY, obviously insufficient for the penetratton of the beam through the emitter. It is confirmed that, in the given case, two processes are of major Importance; avalanche multiplication of the secondary electrons in the vapors of the semiconducting layer and the soft S-ray emission by the target substrate bombarded by the beam. This emission is regarded as a means of obtaining a low-voltage emitter, which insures large amplification of the primary current. Bibliography: 9 titles.
Bibliography: 22 titles. FIELD-INTENSIFIED SECONDARY ELECTRON EMISSION THROUGH THIN ZnS LAYERS. L. A. Serebrov and V. I. Sali (Vol. 7, No. 4, p. 1233). Some preliminary results of experiments with targets having a ZnS layer are reported. Measurements were made by methods utilizing a pulsed double beam and sealed-off vacuum appax~atus. The targets consisted of thin (-0. 5~ porous semiconducting layers on aluminum substrates about 0. lu thick. The electron energy of the working beam, bombarding the target from the substrate side, could be measured within the limits of 0.05 to 10 key (the beam current did not exceed lua). The gain coefficient, K = I’/l, where I’ and I are the amplitude values of the pulse currents for the penetration of charged and uncharged targets, respectively, was taken as the main indicator characterizing the effectiveness of the secondary electron emission. The magnitude of the primary current was chosen in such a way as to keep the pulse amplitude, I, unchanged throughout the range of energies of the primary electrons of the working beam. The
PHOTOELECTRIC PROPERTIES OF p-n HETEROJUNCTIONS BETWEEN GaP and GaAs. J. I. Alferov, N. S. Zimogorova, M. K. Trukan and V. M. Tutchkevitch (Vol. ‘?, No. 4, p. 1235). Results are reported from a study~of photoelectric properties of p-n heterojunctions between GaP and GaAs obtained by vapor transport in sealed evacuated quartz ampules. The substrate consisted of a single crystal GaAs wafer doped with Te (electron concentration 2 x 1017 cm-3, and room temperature mobility 2500 cm2/Vsec). The source material was polycrystalline GaP of high pj~ity(degree of compensation — 1 x 1017 cm”). Cadmium chloride was used for the transport and doping of the growing GaP epitaxial layer. Films having the following parameters were obtained: hole concentration 5 x 1017 5 x 101~m~3, mobility at 3000K 20-80 cm2/Vsec. Th following properties were studied: photoelectric properties of heterojunctions, the dependence of short-circuit current and photovoltage on light intensity. The following results were obtained: (1) The range of photosensitivity of the GaP-GaAs heterojunction is quite large (0.85 eV) and is bounded by abrupt drops in photosensitivity at photon energies close -
Vol. 3, No. 7
ABSTRACTS OF PAPERS IN SOVIET PHYSICS-SOLID STATE
to the energy gaps ci GaAs and ci GaP. The spectral dependence ci the short-circuit current indicates that the absorption coefficient Is constant in this range ii energies. When the ternperature Is lowered down to 800K, the shape of the photoreaponae changes somewhat: The photosensitivity decreases in the long wavelength region and increases at energies corresponding to pair production near the energy gap of GaP. From the temperature dependent shift of the photovoltaic spectrum, the coefficients dE/dT were evaluated: dE/dT = -4.5 x 104eV/deg for GaAs and -5.2 x i0~ eV/deg for Gap. The dependence of open circuit photoemf on the intensity of incident white light reaches a saharation of 0.5 V (for incident power of —1.5 x i04 watt). Loading characteristics indicate that maximum power is generated for a load of 400 Kohm; then, the efficiency of the photodetector approaches 8 per cent. Bibliography: 8 titles. INTRINSIC RECOMBINATION RADIATION IN HETEROJUNCTIONS. M. V. Kot, L. M. Panaciuk, A. V. Semashkevitch, A. E. Tsurkan and D. A. Sherban (Vol. 7, No. 4, p. 1242). The radiative recombination was studied in p-n beterojunctions of ZnSe-ZnTe prepared into crystalline layers. The V-I characteristics of such heterojunctions look like those of ordinary diodes. The forward current at 2 volts Is a few milliamperes, and the reverse current at 5 V is about 20 uA. Other properties which were measured were: the dependence of short circuit current on illumination and of light emission on current, and the photovoltaic spectrum. In all the samples, the short-circuit current varied linearly with illumination; the open circuit voltage was 0.6-0. 7 V. The samples were photosensitive in the 0.4 to 0. 65u spectral range. Radiative recombinatlon is obtained when a forward current is passed through such a heterojunction. This radiation can be observed visually with currents of the order of 0.2 A/cm2. The dependence of emission on current density is shown in curves: one finds that the emission occurs in the 0.44 to 0. 75 ii spectral range and that the emission intensity grows with the current density. The half width of the emission band is 0. 19u in the range 0.48 to 0.67 u (this corresponds to photon energies of 2.6 and 1.82 eV). On the basis that the experimental data corresponds to the width of the energy gap at room temperahire (2.6 eV for ZnSe and 2. 1 eV for ZnTe) it is proposed that this emission is due to intrinsic
lvii
recomblmtion. The dependence of Integrated emission on current density under pulsed condittons shows that the brightness ci a 1 mm2 area at room temperature Is typically 50 nit and grows to 150 nit at liquid nitrogen. INTRINSIC RADIATIVE RECOMBDiATION Di ZnTe. M. V. Kot, L. U. Panasluk, A. V. Slmashkevltch and A. E. Tsurkan (Vol. 7, No. 4, p. 1244). Special structures were befit in sinjle crystals of ZnTe with areas of up to 1 mm~to study the radiative recombination during injection at a p-n junction. The VI characteristics, the emission spectra at various current densities and the variation of light Intensity with current density were studied. The VI characteristics in the dark have a very assymmetric appearance. The emission is observed during forward bias. The emission spectrum at room temperature lies in the range: 0.5 to 0. 7 u. As the current density is increased, the emission intensity increases and the line width decreases (the long wavelength edge shifting to shorter wavelengths). The energy of the emitted photons (2.1-2.2 eV) corresponds to the width of the energy gap in ZnTe at room temperature. Therefore, the emission is due to intrinsic recombination. The light intensity grows somewhat faster than linearl~ with current density up to 5 A/cm2. When the current density exceeds 1 A/cm2, the emission can be observed visuaiiy in directions parallel and transverse to the plane of the junction. The brightness of such junctions is 5 nit at 20°Cand increases to 50 nit at 77°K. CONCENTRATION DEPENDENCE OF THE ENERGY GAP IN ALLOYS OF InSb-GaSb. I. S. Baukin, V. I. Ivanov-Omsky and B. T. Kolomlets (Vol. 7, No. 4, p. 1261). The composition dependence of the energy gap of alloys of InSb with increasing additions of GaSb was deduced from the optical properties of single crystal alloys. The energy gap Is obtained from the variation of the absorption coefficient with energy. The energy gaps for alloys of different compositions were compared at the same absorption coefficient. The dependence of photon energy on lattice constant was examined for four different levels of absorption. From this it follows that at low absorption coefficients, this dependence Is practically linear in the range of compositions considered, but it becomes quite non-linear as the absorption coefficient increases.
ABSTRACTS OF PAPERS Di SOVIET PHYSICS-SOLID STATE
1vt.~imum. This type of construction enables one to workbat liquid nitrogen temperatures in vacuum 5 X 10 mm Hg, and a specIal micrometer arrangemeet permits one to shift the crystal In the dlrection ci the rotor axis and back without disturblag the vacuum in the system. The dependence of MCPD~jghton the intensity of monochromatic light, AUk, at various wavelengths shows that the Tn.gnltude of the effect Increases rapidly at small light Intensities, becoming linear at large intensities. It follows from the obtained dependences that the magnitude of the effect is maximum in the interval 350-480 ms&, after which a sharp dorp of m2gn1tude i observed, which reaches zero in the region of 800 mu. In vacuum of the Hg the value of the effect in order of 10of2mm the region 350-520 mu decreases: further reduction in pressure to i0~mm Hg leads to additional weakening of the effect. Heating of the single crystal In air for a few minutes at 400°C leads to changes in the spectral distribution of the effect. Comparison with data obtained prior to heating shows that a considerable change in ~(CPD)J~ht Is observed only in the region of short wavelengths and is reversible with time. Change in the sign of the effect from positive to negative has been discovered for wavelengths above 650 mu. The mechanism of the phenomenon is discussed.
Vol. 3, No. 7
value of the coefficient, I, exceeded unity when a positive surface charge, formed as a result of an auxiliary beam, was present on a target. Current pulses for penetration of a negatively charged target were practically the same as those in the case of an uncharged target. On the basis of this, it was concluded that the films under investigation possessed properties characteristic for emitters capable of ensuring an amplification of the secondary electron emission by the field. All obtained volt-ampere characteristics, K(Uk), where Uk is the collector potential have in common a gradual rise of the coefficIent K with increase in field intensity In the ZnS layer, and also the presence of a sharp maximum. It may be noted that this m~Imumcorresponds to the primary electron energy, E~ 2 keY, obviously insufficient for the penetratton of the beam through the emitter. It is confirmed that, in the given case, two processes are of major Importance; avalanche multiplication of the secondary electrons in the vapors of the semiconducting layer and the soft S-ray emission by the target substrate bombarded by the beam. This emission is regarded as a means of obtaining a low-voltage emitter, which insures large amplification of the primary current. Bibliography: 9 titles.
Bibliography: 22 titles. FIELD-INTENSIFIED SECONDARY ELECTRON EMISSION THROUGH THIN ZnS LAYERS. L. A. Serebrov and V. I. Sali (Vol. 7, No. 4, p. 1233). Some preliminary results of experiments with targets having a ZnS layer are reported. Measurements were made by methods utilizing a pulsed double beam and sealed-off vacuum appax~atus. The targets consisted of thin (-0. 5~ porous semiconducting layers on aluminum substrates about 0. lu thick. The electron energy of the working beam, bombarding the target from the substrate side, could be measured within the limits of 0.05 to 10 key (the beam current did not exceed lua). The gain coefficient, K = I’/l, where I’ and I are the amplitude values of the pulse currents for the penetration of charged and uncharged targets, respectively, was taken as the main indicator characterizing the effectiveness of the secondary electron emission. The magnitude of the primary current was chosen in such a way as to keep the pulse amplitude, I, unchanged throughout the range of energies of the primary electrons of the working beam. The
PHOTOELECTRIC PROPERTIES OF p-n HETEROJUNCTIONS BETWEEN GaP and GaAs. J. I. Alferov, N. S. Zimogorova, M. K. Trukan and V. M. Tutchkevitch (Vol. ‘?, No. 4, p. 1235). Results are reported from a study~of photoelectric properties of p-n heterojunctions between GaP and GaAs obtained by vapor transport in sealed evacuated quartz ampules. The substrate consisted of a single crystal GaAs wafer doped with Te (electron concentration 2 x 1017 cm-3, and room temperature mobility 2500 cm2/Vsec). The source material was polycrystalline GaP of high pj~ity(degree of compensation — 1 x 1017 cm”). Cadmium chloride was used for the transport and doping of the growing GaP epitaxial layer. Films having the following parameters were obtained: hole concentration 5 x 1017 5 x 101~m~3, mobility at 3000K 20-80 cm2/Vsec. Th following properties were studied: photoelectric properties of heterojunctions, the dependence of short-circuit current and photovoltage on light intensity. The following results were obtained: (1) The range of photosensitivity of the GaP-GaAs heterojunction is quite large (0.85 eV) and is bounded by abrupt drops in photosensitivity at photon energies close -
Vol. 3, No. 7
ABSTRACTS OF PAPERS IN SOVIET PHYSICS-SOLID STATE
to the energy gaps ci GaAs and ci GaP. The spectral dependence ci the short-circuit current indicates that the absorption coefficient Is constant in this range ii energies. When the ternperature Is lowered down to 800K, the shape of the photoreaponae changes somewhat: The photosensitivity decreases in the long wavelength region and increases at energies corresponding to pair production near the energy gap of GaP. From the temperature dependent shift of the photovoltaic spectrum, the coefficients dE/dT were evaluated: dE/dT = -4.5 x 104eV/deg for GaAs and -5.2 x i0~ eV/deg for Gap. The dependence of open circuit photoemf on the intensity of incident white light reaches a saharation of 0.5 V (for incident power of —1.5 x i04 watt). Loading characteristics indicate that maximum power is generated for a load of 400 Kohm; then, the efficiency of the photodetector approaches 8 per cent. Bibliography: 8 titles. INTRINSIC RECOMBINATION RADIATION IN HETEROJUNCTIONS. M. V. Kot, L. M. Panaciuk, A. V. Semashkevitch, A. E. Tsurkan and D. A. Sherban (Vol. 7, No. 4, p. 1242). The radiative recombination was studied in p-n beterojunctions of ZnSe-ZnTe prepared into crystalline layers. The V-I characteristics of such heterojunctions look like those of ordinary diodes. The forward current at 2 volts Is a few milliamperes, and the reverse current at 5 V is about 20 uA. Other properties which were measured were: the dependence of short circuit current on illumination and of light emission on current, and the photovoltaic spectrum. In all the samples, the short-circuit current varied linearly with illumination; the open circuit voltage was 0.6-0. 7 V. The samples were photosensitive in the 0.4 to 0. 65u spectral range. Radiative recombinatlon is obtained when a forward current is passed through such a heterojunction. This radiation can be observed visually with currents of the order of 0.2 A/cm2. The dependence of emission on current density is shown in curves: one finds that the emission occurs in the 0.44 to 0. 75 ii spectral range and that the emission intensity grows with the current density. The half width of the emission band is 0. 19u in the range 0.48 to 0.67 u (this corresponds to photon energies of 2.6 and 1.82 eV). On the basis that the experimental data corresponds to the width of the energy gap at room temperahire (2.6 eV for ZnSe and 2. 1 eV for ZnTe) it is proposed that this emission is due to intrinsic
lvii
recomblmtion. The dependence of Integrated emission on current density under pulsed condittons shows that the brightness ci a 1 mm2 area at room temperature Is typically 50 nit and grows to 150 nit at liquid nitrogen. INTRINSIC RADIATIVE RECOMBDiATION Di ZnTe. M. V. Kot, L. U. Panasluk, A. V. Slmashkevltch and A. E. Tsurkan (Vol. 7, No. 4, p. 1244). Special structures were befit in sinjle crystals of ZnTe with areas of up to 1 mm~to study the radiative recombination during injection at a p-n junction. The VI characteristics, the emission spectra at various current densities and the variation of light Intensity with current density were studied. The VI characteristics in the dark have a very assymmetric appearance. The emission is observed during forward bias. The emission spectrum at room temperature lies in the range: 0.5 to 0. 7 u. As the current density is increased, the emission intensity increases and the line width decreases (the long wavelength edge shifting to shorter wavelengths). The energy of the emitted photons (2.1-2.2 eV) corresponds to the width of the energy gap in ZnTe at room temperature. Therefore, the emission is due to intrinsic recombination. The light intensity grows somewhat faster than linearl~ with current density up to 5 A/cm2. When the current density exceeds 1 A/cm2, the emission can be observed visuaiiy in directions parallel and transverse to the plane of the junction. The brightness of such junctions is 5 nit at 20°Cand increases to 50 nit at 77°K. CONCENTRATION DEPENDENCE OF THE ENERGY GAP IN ALLOYS OF InSb-GaSb. I. S. Baukin, V. I. Ivanov-Omsky and B. T. Kolomlets (Vol. 7, No. 4, p. 1261). The composition dependence of the energy gap of alloys of InSb with increasing additions of GaSb was deduced from the optical properties of single crystal alloys. The energy gap Is obtained from the variation of the absorption coefficient with energy. The energy gaps for alloys of different compositions were compared at the same absorption coefficient. The dependence of photon energy on lattice constant was examined for four different levels of absorption. From this it follows that at low absorption coefficients, this dependence Is practically linear in the range of compositions considered, but it becomes quite non-linear as the absorption coefficient increases.