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Fixed-interface-charge model for isotype heterojunctions
World Abstracts on Microelectronics and Reliability
One chip controls keyboard and display. LORNE TROTTIER and BRANKO MATIC. Electronics p. 125 (11 May 1978). Device simplifies microprocessor interface to alphanumeric displays. Managing the flow of data is easy with programmable multiplexer. DAVE WYLAND. Electronics p. 132 (11 May 1978). Device dedicated to data management has diode-
231
fuse array that may be programmed with standard PROM techniques to set up bit flow.
Single-chip microcomputer expands its memory. HAROLD W. DOZIERand Robert S. GREEN. Electronics p. 105 (11 May 1978). Over 4 kilobytes of program storage includes 64 bytes of executable RAM to extend the one-chipper into more complex applications.
7. SEMICONDUCTOR INTEGRATED CIRCUITS, DEVICES A N D MATERIALS The role of distributed parameters in the analysis of technological processes of semiconductor technique. W. HEINZE and J. LUDWIG. Nachrichtentechnik Electronik 28, (5) 184 (1978) (in German). Owing to close tolerances admitted for dimensions and the concentration of differently doped regions, distributed parameters must at any rate be taken into account in analysing technological processes in semiconductor technique, as is illustrated by the inverse voltage of p+ pn ÷ power diodes. Their effect can quantitatively be determined by means of their distribution curves if they can be measured as concentrated parameters, or by stating the extent to which measurable parameters depending on them may be modified.
A model of charge injection at metal-insulator contacts. I. CHEN. Solid St. Commun. 26, 359 (1978). A phenomenological model of charge carrier injection at metal-insulator contacts is proposed to quantify the injection property of such contacts, especially of non-Ohmic ones. The model contains two parameters: one is the injection current G at a given field, and the other is the field-dependence power p of the injection. It is shown that the values of G and p for a given contact can be determined from the results of step-voltage experiments. When applied to the data on Au-As2Se3 contact, it is found that the injection current is G ~ 10- 6 A cm- 2 at a field of l0 s V cm- 1, and the field dependence is approximately quadratic, p ~ 2. In addition, the field-dependence and the thickness-independence of the peak current can be explained.
Energy spectrum particularities of gapless semiconductors with impurities. V. K. DUGAEVand P. P. PETROV. Solid St. Commun. 26, 303 (1978). At the T-matrix approximation the possibility of dielectric gap formation in single-particle spectrum of gapless semiconductors in the presence of impurity is shown. Value of the gap depends upon impurity concentration and impurity level position.
For a 001-stress along a (100)-surface one finds that (i) the stress induced subband splitting is a function of the electron density, and (ii) the splitting E1 - E 0 within a subband system depends on the applied stress.
Analysis of static and dynamic characteristics in v.i.I. SHUICHI KATO, OSAMU TOMISAWA, YASUTAKA HORIBA and TAKAO NAKANO. Solid-St. Electron Devices 2, (3) 83 (May 1978). After a survey of the electrical characteristics for vertical injection logic (v.i.l.) structure compared with the conventional i.i.l, structure, static characteristics and dynamic behaviour for the v.i.l, structure are analysed by using a simplified one-dimensional model, and experimental verifications are carried out. The analysis reveals that the minimum propagation delay time is determined by the cutoff frequency of the n-p-n transistor and the effective lifetime of holes injected into the epitaxial layer from the base. The bottom injector in the v.i.1, structure reduces the effective lifetime of the holes, which results in improved minimum propagation delay times. In addition, the improvement in the minimum propagation delay times due to a reduction in the effective lifetime is more pronounced when the cutoff frequency is higher. Experimental results show that the minimum progation delay time for v.i.l, is improved by a factor of 1.6, as predicted from the analysis.
Experimental comparison of lifetime-measurement techniques for m.o.s, capacitors. C. MORANDI and G. SPADINI. Solid-St. Electron Devices 2, (3) 69 (May 1978). Three techniques commonly used to determine lifetime in m.o.s. capacitors are compared experimentally and very good agreement is found. It is shown that, in favourable circumstances, the combined use of the three may help to localise the active defect in the forbidden gap. Finally, some experimental results obtained with two of the techniques over a wide temperature range are discussed.
The assessment of the formal semiconductor device theory. Conductivity increase of amorphous Si and Ge by Mn. T. SHIMIZU, M. KUMEDA, I. WATANABEand K, KAMONO. Solid St. Commun. 26, 445 (1978). Amorphous Si and Ge are doped with Mn by co-sputtering. The electrical conductivity is increased by as much as a factor of 10° ~ 107 in some cases by the addition of several at % Mn. The temperature dependence of the conductivity shows the variable range hopping conduction for both samples with and without Mn. The results can be interpreted by the presence of two conduction processes; the variable range hopping through dangling bonds and that through Mn sites.
Hartree calculations for n-inversion layers on stressed silicon surfaces. H. TEWS. Solid St. Commun. 26, 349 (1978). The energy splittings and occupation number densities in n-type inversion layers are estimated in a Hartree calculation with a parametrized exponential potential, Good agreement with experiment is obtained for low temperatures and for electron concentrations 1 x 1012cm -2 =< Ns =< 1 x 1013 cm -2. On the basis of these calculations the influence of uniaxial stress is considered.
A. CHIABRERA,R. DELF1NO, D. PONTA, G. VERNAZZAand R. VIVIANI. Alta Frequenza XLVI1, (5) 265 (March 1978). The paper gives a contribution to the assessment of the formal semiconductor device theory. The analysis of an extrinsic semiconductor region, which is bounded by junctions, ohmic contacts and interfaces with dielectrics, is performed, taking into account doping gradient effects, nonuniform spatial distribution of minority carrier lifetimes and surface recombination velocities. The general properties of the network matrix that models the semiconductor regions are found. The generation-recombination currents in the junctions and the voltage drops in the quasi-neutral region are evaluated. The approach is suitable to implement the model in CAD programs, provided that the region overall parameters are experimentally identified on real devices.
Fixed-interface.-eharge
model for isotype heterojunctions.
D, DELAGEBEAUDEUFand M. LESCROEL Solid-St. Electron Devices 2, (3) 91 (May 1978). Numerous anomalies have been observed in the electrical characteristics of isotype n-Ge/n-GaAs heterojunctions which cannot be explained
232
World Abstracts on Microelectronics and Reliability
by the existing models. These are (al the "apparent" inverse barrier in I / V experiments is often abnormally high (b) the dependence of the barrier on doping concentration is opposite to predicted behaviour (c) the I~ V intercept voltage is always higher than the apparent inverse barrier resulting from I/V experiments (d) the slope dC/dV can be normally inversed or even flat. The proposed model assumes a given fixed negative interface charge to allow the existence of depletion layers in both semiconductors. The different anomalies are then explained by assuming an interface negative charge corresponding to the trapping of about two electrons by each interface impurity atom.
An exact derivation of contact resistance to planar devices. S. B. SCHULDT. Solid-St. Electron. 21, 715 (1978). An imperfect, rectangular contact to a semiconducting sheet is formulated as a mixed boundary-value problem, This problem is solved by conformal mapping to yield the complex potential function as an eigenfunction expansion. The result can be used to calculate exact contact resistance if specific contact resistivity is known. With voltage probing data, it can also be used to confirm estimates of specific contact resistivity. The expression for contact resistance resembles that for a perfect (lossless) contact but includes an extra term involving the lowest-order coefficient ao from the expansion. Contact resistances are calculated and compared with the values obtained from three approximate models; the lossless contact, transmission line, and extended transmission line models. U p to a c o m m o n normalization constant, the contact resistances predicted by all models are completely determined by two dimensionless parameters. These define the validity ranges for the approximate models. Compared to the present model, the extended transmission line model appears to be a very satisfactory approximation if the ratio of electrode length to sheet thickness is not less than 0.5. Thermal evolution of gas from a solid following detrapping and diffusion during a linear tempering schedule. S. E. DONNELLY and D. C. INGRAM. Vacuum 28, (2) 69 (1978). A numerical analysis has been performed to determine the form of evolution rate transients resulting from detrapping and diffusion of gas implanted into a solid substrate (socalled substitutional pop-out) during a linear tempering schedule of the form T = To + at. The way in which the temperature for m a x i m u m release rate and the e ~ width of the transient vary as a function of the ratio of migration energy, E, to detrapping energy, Q, has been determined for a range of values of detrapping energy, Q, and diffusion starting depth, p. A general criterion has been derived which indicates that the diffusion process plays a significant role whenE/Q~> I 0.161ogp. Polycrystalline silicon p - n junctions. T. L. CHU, SHIRLEY S. CHt:, G. A. VAN DER LEEDEN, C. J. LIy and J. R. BOYD. Solid-St. Electron. 21,781 (1978). Silicon films deposited on recrystallized metallurgical silicon substrates have been used for the fabrication of low cost solar cells. The substrate is polycrystalline, and the active region of the solar cell is epitaxial with respect to the substrate. Since the dark current-voltage characteristics of a solar cell are important factors affecting its conversion efficiency, the characteristics of a number of epitaxial mesa diodes of the configuration n*-silicon/p-silicon/p+-metallurgical silicon,/ graphite have been measured over a wide temperature range to study the effects of grain boundaries. The results were analyzed on the basis of the two-exponential model. Analysis of the deep depletion MOSFET and the use of the d.c. characteristics for determining bulk-channel chargecoupled device parameters. ROGER A. HAKEN. Solid-St. Electron. 21, 753 (1978). A qualitative and quantitative analysis of the deep depletion M O S F E T operated in the
regimes of depletion, enhancement and depletion/enhancement, is presented. The quantitative analysis presented here does not make any of the simplifications made in some earlier papers, applicable to shallow channel depletion MOSFETs, and uses a four terminal device model so as to provide a complete set of characterisation equations for each node of operation~ It is demonstrated that the device parameters of flatband voltage, implanted channel doping and depth, and bulk and surface carrier mobilities, can easily be determined by use of some of the characteristic equations in conjunction with simple measurements made directly from the drain current/drain voltage characteristics. Furthermore these parameters are applicable to bulk-channel charge-coupled devices fabricated under the same implantation and drivein conditions. As the device parameters are determined from the drain current/drain voltage characteristics the techniques presented offer an attractive alternative to the more complicated C l' methods used for bulk-channel chargecoupled device characterisatiou. The validity of the model and the techniques used to determine the device parameters is demonstrated by the good agreement between calculated and measured results obtained from fabricated devices.
Thickness and field dependence of defects in silicon dioxide, D, BAGLEL A. K. ZAKZ{)UK, W. ECCLESTON and R. A, STUART. Solid-St. Elecwon. 21, 763 (1978). The Liquid Crystal Technique is used to determine the variation of saturation defect density with applied field and film thickness, in thermal oxides of silicon. The results are consistent with trap controlled space charge limited currents occurring in the region of a defect. Various parameters of the free charge, and traps, are estimated. Entirely diffused vertical channel JFET: Theory and experiment. J. L. MORENZA and D. ESrEVE. Solid-St. Electron. 21, 739 (1978). The experimental electrical properties of a vertical channel JFET fabricated by a double diffusion technique are presented. A table showing its principal characteristics for different values of the diffusion depths is included. The analysis of the "'triode-like" operation revealed by the output characteristics is based on a twodimensional numerical simulation of the device. At high drain currents I~, is proportional to l}]st~.< 1). This behaviour can be attributed mainly to the effect of channel length modulation by the drain voltage. At low drain currents, the potential barrier between the source and the drain determines the current magnitude. This is an exponential function of the barrier height which increases almost linearly when V.s increases and decreases non-linearly when [ , s increases. Measurement of mobility profiles in GaAs at room temperature by the corbino effect. H. POTH. Solid-St. Electron. 21, 801 (1978). A method for obtaining profiles of the carrier mobility in GaAs films utilizing the Corbino effect is introduced. This approach is compared with the conventional methods to measure profiles of shallow density and carrier mobility, The Corbino diode permits applying both methods to the same structure. It will be shown that conventional G V-measurements on n-GaAs at room temperature yield results for the shallow density, which differ numerically from the carrier density. Lifetime control by palladium diffusion in silicon. LINGKON SO, J. STANLEY WH1TEI.EY, SORAB K. GHANDHI and B. JA'~'AN3 BAL1GA. Solid-St. Electron. 21, 887 (1978). This paper will discuss the use of palladium for the control of lifetime in silicon power devices. It is shown that palladium has the advantage over platinum of lower solid solubility (by a factor of 20-50). As a result, greater process control can be achieved for lifetimes in the range that is desirable
One chip controls keyboard and display. LORNE TROTTIER and BRANKO MATIC. Electronics p. 125 (11 May 1978). Device simplifies microprocessor interface to alphanumeric displays. Managing the flow of data is easy with programmable multiplexer. DAVE WYLAND. Electronics p. 132 (11 May 1978). Device dedicated to data management has diode-
231
fuse array that may be programmed with standard PROM techniques to set up bit flow.
Single-chip microcomputer expands its memory. HAROLD W. DOZIERand Robert S. GREEN. Electronics p. 105 (11 May 1978). Over 4 kilobytes of program storage includes 64 bytes of executable RAM to extend the one-chipper into more complex applications.
7. SEMICONDUCTOR INTEGRATED CIRCUITS, DEVICES A N D MATERIALS The role of distributed parameters in the analysis of technological processes of semiconductor technique. W. HEINZE and J. LUDWIG. Nachrichtentechnik Electronik 28, (5) 184 (1978) (in German). Owing to close tolerances admitted for dimensions and the concentration of differently doped regions, distributed parameters must at any rate be taken into account in analysing technological processes in semiconductor technique, as is illustrated by the inverse voltage of p+ pn ÷ power diodes. Their effect can quantitatively be determined by means of their distribution curves if they can be measured as concentrated parameters, or by stating the extent to which measurable parameters depending on them may be modified.
A model of charge injection at metal-insulator contacts. I. CHEN. Solid St. Commun. 26, 359 (1978). A phenomenological model of charge carrier injection at metal-insulator contacts is proposed to quantify the injection property of such contacts, especially of non-Ohmic ones. The model contains two parameters: one is the injection current G at a given field, and the other is the field-dependence power p of the injection. It is shown that the values of G and p for a given contact can be determined from the results of step-voltage experiments. When applied to the data on Au-As2Se3 contact, it is found that the injection current is G ~ 10- 6 A cm- 2 at a field of l0 s V cm- 1, and the field dependence is approximately quadratic, p ~ 2. In addition, the field-dependence and the thickness-independence of the peak current can be explained.
Energy spectrum particularities of gapless semiconductors with impurities. V. K. DUGAEVand P. P. PETROV. Solid St. Commun. 26, 303 (1978). At the T-matrix approximation the possibility of dielectric gap formation in single-particle spectrum of gapless semiconductors in the presence of impurity is shown. Value of the gap depends upon impurity concentration and impurity level position.
For a 001-stress along a (100)-surface one finds that (i) the stress induced subband splitting is a function of the electron density, and (ii) the splitting E1 - E 0 within a subband system depends on the applied stress.
Analysis of static and dynamic characteristics in v.i.I. SHUICHI KATO, OSAMU TOMISAWA, YASUTAKA HORIBA and TAKAO NAKANO. Solid-St. Electron Devices 2, (3) 83 (May 1978). After a survey of the electrical characteristics for vertical injection logic (v.i.l.) structure compared with the conventional i.i.l, structure, static characteristics and dynamic behaviour for the v.i.l, structure are analysed by using a simplified one-dimensional model, and experimental verifications are carried out. The analysis reveals that the minimum propagation delay time is determined by the cutoff frequency of the n-p-n transistor and the effective lifetime of holes injected into the epitaxial layer from the base. The bottom injector in the v.i.1, structure reduces the effective lifetime of the holes, which results in improved minimum propagation delay times. In addition, the improvement in the minimum propagation delay times due to a reduction in the effective lifetime is more pronounced when the cutoff frequency is higher. Experimental results show that the minimum progation delay time for v.i.l, is improved by a factor of 1.6, as predicted from the analysis.
Experimental comparison of lifetime-measurement techniques for m.o.s, capacitors. C. MORANDI and G. SPADINI. Solid-St. Electron Devices 2, (3) 69 (May 1978). Three techniques commonly used to determine lifetime in m.o.s. capacitors are compared experimentally and very good agreement is found. It is shown that, in favourable circumstances, the combined use of the three may help to localise the active defect in the forbidden gap. Finally, some experimental results obtained with two of the techniques over a wide temperature range are discussed.
The assessment of the formal semiconductor device theory. Conductivity increase of amorphous Si and Ge by Mn. T. SHIMIZU, M. KUMEDA, I. WATANABEand K, KAMONO. Solid St. Commun. 26, 445 (1978). Amorphous Si and Ge are doped with Mn by co-sputtering. The electrical conductivity is increased by as much as a factor of 10° ~ 107 in some cases by the addition of several at % Mn. The temperature dependence of the conductivity shows the variable range hopping conduction for both samples with and without Mn. The results can be interpreted by the presence of two conduction processes; the variable range hopping through dangling bonds and that through Mn sites.
Hartree calculations for n-inversion layers on stressed silicon surfaces. H. TEWS. Solid St. Commun. 26, 349 (1978). The energy splittings and occupation number densities in n-type inversion layers are estimated in a Hartree calculation with a parametrized exponential potential, Good agreement with experiment is obtained for low temperatures and for electron concentrations 1 x 1012cm -2 =< Ns =< 1 x 1013 cm -2. On the basis of these calculations the influence of uniaxial stress is considered.
A. CHIABRERA,R. DELF1NO, D. PONTA, G. VERNAZZAand R. VIVIANI. Alta Frequenza XLVI1, (5) 265 (March 1978). The paper gives a contribution to the assessment of the formal semiconductor device theory. The analysis of an extrinsic semiconductor region, which is bounded by junctions, ohmic contacts and interfaces with dielectrics, is performed, taking into account doping gradient effects, nonuniform spatial distribution of minority carrier lifetimes and surface recombination velocities. The general properties of the network matrix that models the semiconductor regions are found. The generation-recombination currents in the junctions and the voltage drops in the quasi-neutral region are evaluated. The approach is suitable to implement the model in CAD programs, provided that the region overall parameters are experimentally identified on real devices.
Fixed-interface.-eharge
model for isotype heterojunctions.
D, DELAGEBEAUDEUFand M. LESCROEL Solid-St. Electron Devices 2, (3) 91 (May 1978). Numerous anomalies have been observed in the electrical characteristics of isotype n-Ge/n-GaAs heterojunctions which cannot be explained
232
World Abstracts on Microelectronics and Reliability
by the existing models. These are (al the "apparent" inverse barrier in I / V experiments is often abnormally high (b) the dependence of the barrier on doping concentration is opposite to predicted behaviour (c) the I~ V intercept voltage is always higher than the apparent inverse barrier resulting from I/V experiments (d) the slope dC/dV can be normally inversed or even flat. The proposed model assumes a given fixed negative interface charge to allow the existence of depletion layers in both semiconductors. The different anomalies are then explained by assuming an interface negative charge corresponding to the trapping of about two electrons by each interface impurity atom.
An exact derivation of contact resistance to planar devices. S. B. SCHULDT. Solid-St. Electron. 21, 715 (1978). An imperfect, rectangular contact to a semiconducting sheet is formulated as a mixed boundary-value problem, This problem is solved by conformal mapping to yield the complex potential function as an eigenfunction expansion. The result can be used to calculate exact contact resistance if specific contact resistivity is known. With voltage probing data, it can also be used to confirm estimates of specific contact resistivity. The expression for contact resistance resembles that for a perfect (lossless) contact but includes an extra term involving the lowest-order coefficient ao from the expansion. Contact resistances are calculated and compared with the values obtained from three approximate models; the lossless contact, transmission line, and extended transmission line models. U p to a c o m m o n normalization constant, the contact resistances predicted by all models are completely determined by two dimensionless parameters. These define the validity ranges for the approximate models. Compared to the present model, the extended transmission line model appears to be a very satisfactory approximation if the ratio of electrode length to sheet thickness is not less than 0.5. Thermal evolution of gas from a solid following detrapping and diffusion during a linear tempering schedule. S. E. DONNELLY and D. C. INGRAM. Vacuum 28, (2) 69 (1978). A numerical analysis has been performed to determine the form of evolution rate transients resulting from detrapping and diffusion of gas implanted into a solid substrate (socalled substitutional pop-out) during a linear tempering schedule of the form T = To + at. The way in which the temperature for m a x i m u m release rate and the e ~ width of the transient vary as a function of the ratio of migration energy, E, to detrapping energy, Q, has been determined for a range of values of detrapping energy, Q, and diffusion starting depth, p. A general criterion has been derived which indicates that the diffusion process plays a significant role whenE/Q~> I 0.161ogp. Polycrystalline silicon p - n junctions. T. L. CHU, SHIRLEY S. CHt:, G. A. VAN DER LEEDEN, C. J. LIy and J. R. BOYD. Solid-St. Electron. 21,781 (1978). Silicon films deposited on recrystallized metallurgical silicon substrates have been used for the fabrication of low cost solar cells. The substrate is polycrystalline, and the active region of the solar cell is epitaxial with respect to the substrate. Since the dark current-voltage characteristics of a solar cell are important factors affecting its conversion efficiency, the characteristics of a number of epitaxial mesa diodes of the configuration n*-silicon/p-silicon/p+-metallurgical silicon,/ graphite have been measured over a wide temperature range to study the effects of grain boundaries. The results were analyzed on the basis of the two-exponential model. Analysis of the deep depletion MOSFET and the use of the d.c. characteristics for determining bulk-channel chargecoupled device parameters. ROGER A. HAKEN. Solid-St. Electron. 21, 753 (1978). A qualitative and quantitative analysis of the deep depletion M O S F E T operated in the
regimes of depletion, enhancement and depletion/enhancement, is presented. The quantitative analysis presented here does not make any of the simplifications made in some earlier papers, applicable to shallow channel depletion MOSFETs, and uses a four terminal device model so as to provide a complete set of characterisation equations for each node of operation~ It is demonstrated that the device parameters of flatband voltage, implanted channel doping and depth, and bulk and surface carrier mobilities, can easily be determined by use of some of the characteristic equations in conjunction with simple measurements made directly from the drain current/drain voltage characteristics. Furthermore these parameters are applicable to bulk-channel charge-coupled devices fabricated under the same implantation and drivein conditions. As the device parameters are determined from the drain current/drain voltage characteristics the techniques presented offer an attractive alternative to the more complicated C l' methods used for bulk-channel chargecoupled device characterisatiou. The validity of the model and the techniques used to determine the device parameters is demonstrated by the good agreement between calculated and measured results obtained from fabricated devices.
Thickness and field dependence of defects in silicon dioxide, D, BAGLEL A. K. ZAKZ{)UK, W. ECCLESTON and R. A, STUART. Solid-St. Elecwon. 21, 763 (1978). The Liquid Crystal Technique is used to determine the variation of saturation defect density with applied field and film thickness, in thermal oxides of silicon. The results are consistent with trap controlled space charge limited currents occurring in the region of a defect. Various parameters of the free charge, and traps, are estimated. Entirely diffused vertical channel JFET: Theory and experiment. J. L. MORENZA and D. ESrEVE. Solid-St. Electron. 21, 739 (1978). The experimental electrical properties of a vertical channel JFET fabricated by a double diffusion technique are presented. A table showing its principal characteristics for different values of the diffusion depths is included. The analysis of the "'triode-like" operation revealed by the output characteristics is based on a twodimensional numerical simulation of the device. At high drain currents I~, is proportional to l}]st~.< 1). This behaviour can be attributed mainly to the effect of channel length modulation by the drain voltage. At low drain currents, the potential barrier between the source and the drain determines the current magnitude. This is an exponential function of the barrier height which increases almost linearly when V.s increases and decreases non-linearly when [ , s increases. Measurement of mobility profiles in GaAs at room temperature by the corbino effect. H. POTH. Solid-St. Electron. 21, 801 (1978). A method for obtaining profiles of the carrier mobility in GaAs films utilizing the Corbino effect is introduced. This approach is compared with the conventional methods to measure profiles of shallow density and carrier mobility, The Corbino diode permits applying both methods to the same structure. It will be shown that conventional G V-measurements on n-GaAs at room temperature yield results for the shallow density, which differ numerically from the carrier density. Lifetime control by palladium diffusion in silicon. LINGKON SO, J. STANLEY WH1TEI.EY, SORAB K. GHANDHI and B. JA'~'AN3 BAL1GA. Solid-St. Electron. 21, 887 (1978). This paper will discuss the use of palladium for the control of lifetime in silicon power devices. It is shown that palladium has the advantage over platinum of lower solid solubility (by a factor of 20-50). As a result, greater process control can be achieved for lifetimes in the range that is desirable