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Concentration dependence of the energy gap in alloys of InSb-GaSb
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.
lviii
ABSTRACTS OF PAPERS IN SOVIET PHYSICS-SOLID STATE
The non-linearity is beyond experimental error. The experimental data is compared graphically with a hypothetical linear variation of the energy pp with composition between the values for InSb and GaSb. The experimental results cannot be explained by a crude model in which the variation of the energy gap is due to a simple change in lattice constant without taking into account the nature of the solute and of the solvent. It is further established that, because of the very pronounced non-linearity, the experimental curve for large absorption coefficients tends to become parallel to the hypothetical dependence (excluding the intersection) as expected from the data of
Vol. 3, No. 7
Ivanov-Omsky, and Kolomiets, Dokiady, USSR 127, 135 (1959) and Wolly and Gilleti, .1. Phys. Chem. 17, 34 (1960). From the varlousbehaviors of the various absorption curves, the differentlation in energy increases with the absorption coefficient and with increasing concentration of GaSb. This fact is interpreted as a slower compositional variation of the band edges cornpared to the variation of levels deeper in the band. The mechanism is discussed and a cornparison is made between observation and theory. Bibliography: 5 titles.
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.
lviii
ABSTRACTS OF PAPERS IN SOVIET PHYSICS-SOLID STATE
The non-linearity is beyond experimental error. The experimental data is compared graphically with a hypothetical linear variation of the energy pp with composition between the values for InSb and GaSb. The experimental results cannot be explained by a crude model in which the variation of the energy gap is due to a simple change in lattice constant without taking into account the nature of the solute and of the solvent. It is further established that, because of the very pronounced non-linearity, the experimental curve for large absorption coefficients tends to become parallel to the hypothetical dependence (excluding the intersection) as expected from the data of
Vol. 3, No. 7
Ivanov-Omsky, and Kolomiets, Dokiady, USSR 127, 135 (1959) and Wolly and Gilleti, .1. Phys. Chem. 17, 34 (1960). From the varlousbehaviors of the various absorption curves, the differentlation in energy increases with the absorption coefficient and with increasing concentration of GaSb. This fact is interpreted as a slower compositional variation of the band edges cornpared to the variation of levels deeper in the band. The mechanism is discussed and a cornparison is made between observation and theory. Bibliography: 5 titles.