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Theory of nonequilibrium properties of MIS capacitors including charge exchange of interface states with both bands.
314
World Abstracts on Microelectronics and Reliability
lattice modes. Simple expressions are obtained for the transition matrix elements using model free-electron wavefunctions. Determination of the exciton energy from electron beam excited luminescence in direct gap semiconductors. B. SERMAGE. SoIM-St. Electron. 21, 1361 (1978). The exciton radiative recombination spectra of CuCI, ZnSe, CuGaS2 and AgGaSe_, have been investigated at 300 K. The sample was excited by electron beams of different energies. The reabsorption is determined by the ratio rl of the spectra obtained for different electron beam energies such as 5 and 40 kV. This ratio is independent o f h v when the absorption coefficient :~ is small ( < 103 cm ~). It increases when g becomes larger than the inverse of the penetration depth ( -~ 3/~5 of the 40 kV electron beam. In this case, r/is approximately proportional to the absorption coefficient. In particular, its maxima give the excitonic energies E,,.,. We find the following values, in agreement with previous reflectivity and absorption measurements: for CuCI, E,,~(Z3) - 3.26 eV and E~.,(Z, 2) - 3.33 eV: for ZnSe, E,., = 2.7(I eV: for CuGaS2, E,.,(A) = 2.46 eV and /:',,~(B)= 2.59 eV. In the case of AgGaSe2, there is no peak in the q spectrum and we have fitted our data to a broadened exciton model. We obtain E,.~(A) - 1.80 eV. Monte Carlo studies of transitions between excited donor states--resolution. Some open questions in electron-donor recombination. F. BELEZNAY and L. ANDOR. SolM-St. Electron. 21, 1305 (19785. Transition probabilities between excited states of donor energy levels both for simple hydrogenic model and for prolate-spheroid conduction bands are calculated. Monte Carlo simulation of electrondonor rccombination shows that the two orders of magnitude disagreement between experimental and theoretical capture cross sections can be explained by the quasiequilibrium situation which results from the very fast transitions bctwecn excited states. This reinterpreted cascade model is supported by recent non-equilibrium photoconductivity measurements in high purity Ge and the temperature dependence of the photothermal ionization probability in GaAs. Limitations of the applicability of this model and different experimental data on other materials arc discussed. Recombination: A survey. N. F. MOTT. Solid-St. Electron. 21, 1275 (1978). Auger, optical, multiphonon and cascade are the main recombination processes known. Carriers can recombine from band to band. or after they have formed an exciton, or after one or both are trapped at an impurity or defect. This paper gives attention to recombination by bound and free excitons, and wide-gap materials are discussed as well as semiconductors, because the recombinalion mechanisms are often better understood. We-treat particularly the competition between radiative and multiphonon process, including that of Dexter, Klick and Russell. It is pointed out that cascade trapping by a charged centre does not always give rise to a large ( ~ 10 ~~2 cm 2) cross section. Exciton lifetime and fluorescence are described. Configuration diagramsare illustrated by the cases of Va centrcs and similar behaviour in semiconductors where the valence band is of lone pair type and in insulators such as AseTe3 and SiO2. Recombination in some amorphous semiconductors is contrasted with that in crystals: SiO2 presents some special problems. Finally the effect of magnetic field and an ESR signal is described. Gallium nitride epitaxiai growth. G. JA(O~. Aeta eleetronica 21, (25 159 (1978). (In French.) Gallium nitride (GaN) is a potential material for blue light emission due to its large band gap (3.5 eV). As this material cannot be obtained in the shape of large single crystals due to its very high dissociation pressnre ( ~ 10 TM N. m -~) at melting temperature.
GaN heteroepitaxy has been studied on c o r u n d u m with the HCI/Ga/NH3 method. The G a N nucleation phase on c o r u n d u m has been studied as a function of temperature, concentration of reactants, the nature of the carrier gas etc. The growth rate and the properties of the films (crystallographic, electric, luminescent) have been measured as a function of the different growth parameters. The main difficulty encountered with G a N is that until n o u only an N type material could be obtained whereas the 2 types of conductions are needed for obtaining a P/N junction the only really efficient means of realizing luminescent devices. Zinc doping has been studied: the resnlts are discussed. Despite the fact that the conductive P type layers have not been obtained, electroluminescent devices with P type tendancy show interesting characteristics, in particular blue devices with low operating voltage. Thermal conductivity variation of silicon with temperature. CHANDRA PRAKASH. Microeh'ctron. Reliab. 18, 333 11978). In the present paper a mathematical relation has been developed to explain the variation of thermal conductivity of silicon from room temperature to its melting point quite accurately. The theoretical results obtained for various temperatures have been compared with the experimental results. Discharge of m.n.o.s, structures. L. 1, P o p o w , P K VITANOV and B. Z. ANTOV. Solid-St. Electro/1 D~'t'ice.v 3, ( I ) l 7 (January 1979). The discharge behaviour of m.n.o.s. structures with no applied voltage is investigated tit temperatures fl'om - 155 C to 120' C for times from I 0 to I 0 z s. The decay rate is practically independent of the temperature tip to 80:C but increases significantly at 120"C. The discharge curves are explained by direct tunnelling from traps, combined with the thermal excitation of these traps. The time dependence of the charge ccntroid is ascribed to a redistribution of the stored charge in the nitride. A correlation between the decay rate increase after write erase cycling with the increased nitride conductivity is t\mnd. Doping and annealing effects on ESR in chemically vapor deposited amorphous ,silicon. S. HASEGAWA,T. KASAJIMAand T. SHIMIZU. Solid St. Commun. 29, 13 (1979). The efffects of phosphorus doping and annealing on localized states in the gap for CVD a-Si are investigated using ESR. A close relation between the spin density and the lincwidth is found out for undoped samples suggesting that the localized states are uniformly annealed out up to 105OC in spite or" the crystallization of the samples at 700 ~ 8 0 0 C . The spin density also decreases with an increase of doping ratio, but the linewidth remains constant. For a heavily doped sample, a new signal with .q = 2.0043 is observed, and suggested to be due to localized states associated with incorporated phosphorus atoms. Determination of surface state distribution from pulsed M O S capacitor transients. LAHTA MANCHANDA,J. VASl and A. B. BHATTACHARYYA.Solid-St. Eh, ctron. 22, 29 (1979). The transient capacitance plots of metal oxide semiconductor capacitors are numerically computed taking into account the effect of the surlEce state distribution. For negligible minority carrier generation in the bulk and at the surface, the slope of a capacitance (C) vs time (t) curve is proportional to the surface state density. It is shown that a plot of t dC/dt vs In t is a direct measure of the surface state density distribution. Epitaxial silicon, state of the art. k. J. M. BoLI.~!~. Acla e/ectronica 21, (2) 185 (1978). In this article the chemical vapour deposition of mono-crystalline silicon is described including instrumental and basic process conditions and characterization, with particular emphasis on the fabrication of material for semiconductor device applications.
World Abstracts on Microelectronics and Reliability
lattice modes. Simple expressions are obtained for the transition matrix elements using model free-electron wavefunctions. Determination of the exciton energy from electron beam excited luminescence in direct gap semiconductors. B. SERMAGE. SoIM-St. Electron. 21, 1361 (1978). The exciton radiative recombination spectra of CuCI, ZnSe, CuGaS2 and AgGaSe_, have been investigated at 300 K. The sample was excited by electron beams of different energies. The reabsorption is determined by the ratio rl of the spectra obtained for different electron beam energies such as 5 and 40 kV. This ratio is independent o f h v when the absorption coefficient :~ is small ( < 103 cm ~). It increases when g becomes larger than the inverse of the penetration depth ( -~ 3/~5 of the 40 kV electron beam. In this case, r/is approximately proportional to the absorption coefficient. In particular, its maxima give the excitonic energies E,,.,. We find the following values, in agreement with previous reflectivity and absorption measurements: for CuCI, E,,~(Z3) - 3.26 eV and E~.,(Z, 2) - 3.33 eV: for ZnSe, E,., = 2.7(I eV: for CuGaS2, E,.,(A) = 2.46 eV and /:',,~(B)= 2.59 eV. In the case of AgGaSe2, there is no peak in the q spectrum and we have fitted our data to a broadened exciton model. We obtain E,.~(A) - 1.80 eV. Monte Carlo studies of transitions between excited donor states--resolution. Some open questions in electron-donor recombination. F. BELEZNAY and L. ANDOR. SolM-St. Electron. 21, 1305 (19785. Transition probabilities between excited states of donor energy levels both for simple hydrogenic model and for prolate-spheroid conduction bands are calculated. Monte Carlo simulation of electrondonor rccombination shows that the two orders of magnitude disagreement between experimental and theoretical capture cross sections can be explained by the quasiequilibrium situation which results from the very fast transitions bctwecn excited states. This reinterpreted cascade model is supported by recent non-equilibrium photoconductivity measurements in high purity Ge and the temperature dependence of the photothermal ionization probability in GaAs. Limitations of the applicability of this model and different experimental data on other materials arc discussed. Recombination: A survey. N. F. MOTT. Solid-St. Electron. 21, 1275 (1978). Auger, optical, multiphonon and cascade are the main recombination processes known. Carriers can recombine from band to band. or after they have formed an exciton, or after one or both are trapped at an impurity or defect. This paper gives attention to recombination by bound and free excitons, and wide-gap materials are discussed as well as semiconductors, because the recombinalion mechanisms are often better understood. We-treat particularly the competition between radiative and multiphonon process, including that of Dexter, Klick and Russell. It is pointed out that cascade trapping by a charged centre does not always give rise to a large ( ~ 10 ~~2 cm 2) cross section. Exciton lifetime and fluorescence are described. Configuration diagramsare illustrated by the cases of Va centrcs and similar behaviour in semiconductors where the valence band is of lone pair type and in insulators such as AseTe3 and SiO2. Recombination in some amorphous semiconductors is contrasted with that in crystals: SiO2 presents some special problems. Finally the effect of magnetic field and an ESR signal is described. Gallium nitride epitaxiai growth. G. JA(O~. Aeta eleetronica 21, (25 159 (1978). (In French.) Gallium nitride (GaN) is a potential material for blue light emission due to its large band gap (3.5 eV). As this material cannot be obtained in the shape of large single crystals due to its very high dissociation pressnre ( ~ 10 TM N. m -~) at melting temperature.
GaN heteroepitaxy has been studied on c o r u n d u m with the HCI/Ga/NH3 method. The G a N nucleation phase on c o r u n d u m has been studied as a function of temperature, concentration of reactants, the nature of the carrier gas etc. The growth rate and the properties of the films (crystallographic, electric, luminescent) have been measured as a function of the different growth parameters. The main difficulty encountered with G a N is that until n o u only an N type material could be obtained whereas the 2 types of conductions are needed for obtaining a P/N junction the only really efficient means of realizing luminescent devices. Zinc doping has been studied: the resnlts are discussed. Despite the fact that the conductive P type layers have not been obtained, electroluminescent devices with P type tendancy show interesting characteristics, in particular blue devices with low operating voltage. Thermal conductivity variation of silicon with temperature. CHANDRA PRAKASH. Microeh'ctron. Reliab. 18, 333 11978). In the present paper a mathematical relation has been developed to explain the variation of thermal conductivity of silicon from room temperature to its melting point quite accurately. The theoretical results obtained for various temperatures have been compared with the experimental results. Discharge of m.n.o.s, structures. L. 1, P o p o w , P K VITANOV and B. Z. ANTOV. Solid-St. Electro/1 D~'t'ice.v 3, ( I ) l 7 (January 1979). The discharge behaviour of m.n.o.s. structures with no applied voltage is investigated tit temperatures fl'om - 155 C to 120' C for times from I 0 to I 0 z s. The decay rate is practically independent of the temperature tip to 80:C but increases significantly at 120"C. The discharge curves are explained by direct tunnelling from traps, combined with the thermal excitation of these traps. The time dependence of the charge ccntroid is ascribed to a redistribution of the stored charge in the nitride. A correlation between the decay rate increase after write erase cycling with the increased nitride conductivity is t\mnd. Doping and annealing effects on ESR in chemically vapor deposited amorphous ,silicon. S. HASEGAWA,T. KASAJIMAand T. SHIMIZU. Solid St. Commun. 29, 13 (1979). The efffects of phosphorus doping and annealing on localized states in the gap for CVD a-Si are investigated using ESR. A close relation between the spin density and the lincwidth is found out for undoped samples suggesting that the localized states are uniformly annealed out up to 105OC in spite or" the crystallization of the samples at 700 ~ 8 0 0 C . The spin density also decreases with an increase of doping ratio, but the linewidth remains constant. For a heavily doped sample, a new signal with .q = 2.0043 is observed, and suggested to be due to localized states associated with incorporated phosphorus atoms. Determination of surface state distribution from pulsed M O S capacitor transients. LAHTA MANCHANDA,J. VASl and A. B. BHATTACHARYYA.Solid-St. Eh, ctron. 22, 29 (1979). The transient capacitance plots of metal oxide semiconductor capacitors are numerically computed taking into account the effect of the surlEce state distribution. For negligible minority carrier generation in the bulk and at the surface, the slope of a capacitance (C) vs time (t) curve is proportional to the surface state density. It is shown that a plot of t dC/dt vs In t is a direct measure of the surface state density distribution. Epitaxial silicon, state of the art. k. J. M. BoLI.~!~. Acla e/ectronica 21, (2) 185 (1978). In this article the chemical vapour deposition of mono-crystalline silicon is described including instrumental and basic process conditions and characterization, with particular emphasis on the fabrication of material for semiconductor device applications.