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Selective optical valley pumping in silicon and germanium
530
World Abstracts on Microelectronics and Reliability
not yet been observed. The interaction of this collective oscillation with the surface plasmons of the semi-metallic film in an MOS structure is calculated in the long wavelength limit. The results indicate large coupling with the tangential surface plasmon and suggest an indirect means of observing the two-dimensional plasmon.
Far-infrared absorption of large electron-hole drops in stressed Ge. R. L. AURBACH,L. EAVES,R. S. MARKIEWICZ and P. L. RICHARDS. Solid-State Commun. 19, 1023 (1976). The far-infrared attentuation spectrum due to a large electron-hole drop in inhomogeneously stressed Ge has been measured and compared to the attenuation by small drops in unstressed Ge. The spectrum is analyzed using the full Mie theory for the absorption due to a large sphere; the experimental results are interpreted as bulk plasma absorption in a drop with pair density considerably lowered by the strain.
Analytical approximations for diffused junctions under highlevel conditions. S. C. CHOO and H. YAMASAKI.Solid-State Electron. 19, 769 (1976). A theoretical study is made of the applicability of a previously-proposed diffused-junction model to diffused junctions with varying degrees of steepness in the impurity profile. This is done by comparing the predictions of the model with the exact numerical solutions obtained for a series of silicon p 4- n diffused junctions, ranging from very gradual junctions to the infinitely steep or ideal step junctions, and with the lightly-doped side of the junction in each case under high-level injection conditions. The results indicate that the range of validity of the model extends from those gradual junctions which are typically found in high-power thyristor structures to relatively steep diffused junctions similar to those that can occur in the emitter regions of UHF transistors.
An observation by photoconductivity of strain splitting of shallow bulk donors located near to the surface in silicon MOS devices. R. J. NICHOLAS, K. VON KLITZING and R. A STRADLING, Solid-State Commun. 20, (1976). Photoconductivity is observed in n-channel inversion Si MOSFETS at 4.2 K at infrared frequencies up to 700 cm-2. Two groups of sharp lines of opposite sign are observed in the regions of 300 and 650 cm-1 together with a continuum of transitions starting at ~ 350 cm-1. The sharp lines are interpreted as bound transitions from shallow neutral phosphorous donors and boron acceptors on either side of the depletion layer, The angular dependence of the Zeeman splitting of the sharp lines demonstrates that the normal 90 ° symmetry of the 100 surface is lifted for devices with thin metal gates due to the presence of a strong uniaxial stress component.
Valley degeneracy of electrons in accumulation and inversion layers on Si(lll) surface. D. C. TsuI and G. KAMINSKV. Solid-State Commun. 20, 93 (1976). We report three experiments exploring the valley degeneracy of electrons in n-channel MOSFETs on the Si(111) surface. The results suggest that the reduction of the valley degeneracy from 6 to 2 can be explained by the existence of highly stressed domains at the Si-SiO2 interface. The stress, being much too large for those known from thermal mismatch between Si-SiOz, is attributed to mismatch between the Si-Si bonds in Si and the Si-O-Si bonds in SiO2.
Selective optical valley pumping in silicon and germanium. A. A. KAPLYANSKIand N. S. SOKOLOV. Solid-State Commun. 20, 27 (1976). The preferential population of conduction band valleys in Si and Ge was observed at T = 1.8 K with linearly polarized optical excitation of crystals via indirect and direct transitions. The concentration of the
photoelectrons in valleys was measured by the cyclotron resonance technique.
Studies of n-Type GaAs material properties by anodic current behavior. ALEXANDER COLQUHOUN and HANS L. HARTNAGEL. Solid-State Electron. 19, 819 (1976). The carrier concentration of n-type GaAs material have been measured by a technique using anodisation in the dark. The results are compared with a theoretical model and with other results based on Schottky barrier reverse breakdown. The technique has also been extended to include surfaces containing more than one type of material and n-type materials of different carrier concentrations. Additionally the technique has been used to make an assessment of the surface quality of the material.
Structure of amorphous Ge alloy films. H. S. RANDHAWA, P. NATH, L. K. MALHOTRAand K. L. CHOPRA. Solid-State Commun. 20, 73 (1976). Structural details of amorphous alloy films of Ge with Al, Cu and Fe up to 30 at °Jo metal concentrations have been studied. As determined by the electron diffraction studies, the short range order in these alloy films is essentially similar to that of amorphous (~)Ge films. Electron microscopy and electrical resistivity measurements show that the concentration of voids and associated dangling bonds in :t-Ge is reduced considerably on alloying. It is concluded from these studies that the metal atoms are accommodated in the tetrahedral network of a-Ge.
Polycrystalline silicon solar cells on metallurgical silicon suhstrates. R. L. CHu and K. N. SINGH, Solid-State Electron. 19, 837 (1976). The use of a polycrystalline silicon p-n junction structure deposited on low*cost substrates is a promising approach for the fabrication of low-cost solar cells. Metallurgical-grade silicon, with a purity of about 98°'o and a cost of about $1/kg, was cast into plates in a boron nitride container and used as substrates for the deposition of solar cell structures. The substrates were polycrystaUine with millimetre size crystallites. Solar cells of the configurations n+-silicon/p-silicon/metallurgical silicon and n+-silicon/p+-silicon/metallurgical silicon were prepared by the thermal decomposition of silane and the thermal reduction of trichlorosilane containing appropriate dopants. The AMO efficiencies of n+-silicon/p-silicon/ metallurgical silicon solar cells were up to 2.8~, (with no anti-reflection coatings) and were limited by the grain boundaries in the p-layer. The grain boundary effects were reduced by increasing the dopant concentration in the p-layer, and AMO efficiencies of about 3.5°0 were obtained from n+-silicon/p+-silicon/metallurgical silicon solar cells.
Direct observation of the ground state splitting of the indirect free exciton in silicon. M. L. W. THEWALT and R. R. PARSONS.Solid-State Commun. 20, 97 (1976). The effect of the splitting of the indirect free exciton ground state on both the photoluminescence and derivative absorption spectra is reported. These results are the first direct observation of this splitting in silicon. The energy of the splitting is found to be 0.2 + 0.05 meV, whereas the only previous experimental estimate was 0.6 (_+0.1. -0.3) meV,
Hot electron microwave conductivity of wide bandgap semiconductors. P. DAS and D. K. FERRY. Solid-State Electron. 19, 851 (1976). Hot electron microwave conductivity of the wide bandgap semiconductors GaN, SiC and Diamond have been calculated using displaced Maxwellian approximation for the electron distribution function. The effects of both the energy and momentum relaxation times due to scattering by acoustical, optical intervalley phonons and by ionized impurities are included in the derivations. Numeri-
World Abstracts on Microelectronics and Reliability
not yet been observed. The interaction of this collective oscillation with the surface plasmons of the semi-metallic film in an MOS structure is calculated in the long wavelength limit. The results indicate large coupling with the tangential surface plasmon and suggest an indirect means of observing the two-dimensional plasmon.
Far-infrared absorption of large electron-hole drops in stressed Ge. R. L. AURBACH,L. EAVES,R. S. MARKIEWICZ and P. L. RICHARDS. Solid-State Commun. 19, 1023 (1976). The far-infrared attentuation spectrum due to a large electron-hole drop in inhomogeneously stressed Ge has been measured and compared to the attenuation by small drops in unstressed Ge. The spectrum is analyzed using the full Mie theory for the absorption due to a large sphere; the experimental results are interpreted as bulk plasma absorption in a drop with pair density considerably lowered by the strain.
Analytical approximations for diffused junctions under highlevel conditions. S. C. CHOO and H. YAMASAKI.Solid-State Electron. 19, 769 (1976). A theoretical study is made of the applicability of a previously-proposed diffused-junction model to diffused junctions with varying degrees of steepness in the impurity profile. This is done by comparing the predictions of the model with the exact numerical solutions obtained for a series of silicon p 4- n diffused junctions, ranging from very gradual junctions to the infinitely steep or ideal step junctions, and with the lightly-doped side of the junction in each case under high-level injection conditions. The results indicate that the range of validity of the model extends from those gradual junctions which are typically found in high-power thyristor structures to relatively steep diffused junctions similar to those that can occur in the emitter regions of UHF transistors.
An observation by photoconductivity of strain splitting of shallow bulk donors located near to the surface in silicon MOS devices. R. J. NICHOLAS, K. VON KLITZING and R. A STRADLING, Solid-State Commun. 20, (1976). Photoconductivity is observed in n-channel inversion Si MOSFETS at 4.2 K at infrared frequencies up to 700 cm-2. Two groups of sharp lines of opposite sign are observed in the regions of 300 and 650 cm-1 together with a continuum of transitions starting at ~ 350 cm-1. The sharp lines are interpreted as bound transitions from shallow neutral phosphorous donors and boron acceptors on either side of the depletion layer, The angular dependence of the Zeeman splitting of the sharp lines demonstrates that the normal 90 ° symmetry of the 100 surface is lifted for devices with thin metal gates due to the presence of a strong uniaxial stress component.
Valley degeneracy of electrons in accumulation and inversion layers on Si(lll) surface. D. C. TsuI and G. KAMINSKV. Solid-State Commun. 20, 93 (1976). We report three experiments exploring the valley degeneracy of electrons in n-channel MOSFETs on the Si(111) surface. The results suggest that the reduction of the valley degeneracy from 6 to 2 can be explained by the existence of highly stressed domains at the Si-SiO2 interface. The stress, being much too large for those known from thermal mismatch between Si-SiOz, is attributed to mismatch between the Si-Si bonds in Si and the Si-O-Si bonds in SiO2.
Selective optical valley pumping in silicon and germanium. A. A. KAPLYANSKIand N. S. SOKOLOV. Solid-State Commun. 20, 27 (1976). The preferential population of conduction band valleys in Si and Ge was observed at T = 1.8 K with linearly polarized optical excitation of crystals via indirect and direct transitions. The concentration of the
photoelectrons in valleys was measured by the cyclotron resonance technique.
Studies of n-Type GaAs material properties by anodic current behavior. ALEXANDER COLQUHOUN and HANS L. HARTNAGEL. Solid-State Electron. 19, 819 (1976). The carrier concentration of n-type GaAs material have been measured by a technique using anodisation in the dark. The results are compared with a theoretical model and with other results based on Schottky barrier reverse breakdown. The technique has also been extended to include surfaces containing more than one type of material and n-type materials of different carrier concentrations. Additionally the technique has been used to make an assessment of the surface quality of the material.
Structure of amorphous Ge alloy films. H. S. RANDHAWA, P. NATH, L. K. MALHOTRAand K. L. CHOPRA. Solid-State Commun. 20, 73 (1976). Structural details of amorphous alloy films of Ge with Al, Cu and Fe up to 30 at °Jo metal concentrations have been studied. As determined by the electron diffraction studies, the short range order in these alloy films is essentially similar to that of amorphous (~)Ge films. Electron microscopy and electrical resistivity measurements show that the concentration of voids and associated dangling bonds in :t-Ge is reduced considerably on alloying. It is concluded from these studies that the metal atoms are accommodated in the tetrahedral network of a-Ge.
Polycrystalline silicon solar cells on metallurgical silicon suhstrates. R. L. CHu and K. N. SINGH, Solid-State Electron. 19, 837 (1976). The use of a polycrystalline silicon p-n junction structure deposited on low*cost substrates is a promising approach for the fabrication of low-cost solar cells. Metallurgical-grade silicon, with a purity of about 98°'o and a cost of about $1/kg, was cast into plates in a boron nitride container and used as substrates for the deposition of solar cell structures. The substrates were polycrystaUine with millimetre size crystallites. Solar cells of the configurations n+-silicon/p-silicon/metallurgical silicon and n+-silicon/p+-silicon/metallurgical silicon were prepared by the thermal decomposition of silane and the thermal reduction of trichlorosilane containing appropriate dopants. The AMO efficiencies of n+-silicon/p-silicon/ metallurgical silicon solar cells were up to 2.8~, (with no anti-reflection coatings) and were limited by the grain boundaries in the p-layer. The grain boundary effects were reduced by increasing the dopant concentration in the p-layer, and AMO efficiencies of about 3.5°0 were obtained from n+-silicon/p+-silicon/metallurgical silicon solar cells.
Direct observation of the ground state splitting of the indirect free exciton in silicon. M. L. W. THEWALT and R. R. PARSONS.Solid-State Commun. 20, 97 (1976). The effect of the splitting of the indirect free exciton ground state on both the photoluminescence and derivative absorption spectra is reported. These results are the first direct observation of this splitting in silicon. The energy of the splitting is found to be 0.2 + 0.05 meV, whereas the only previous experimental estimate was 0.6 (_+0.1. -0.3) meV,
Hot electron microwave conductivity of wide bandgap semiconductors. P. DAS and D. K. FERRY. Solid-State Electron. 19, 851 (1976). Hot electron microwave conductivity of the wide bandgap semiconductors GaN, SiC and Diamond have been calculated using displaced Maxwellian approximation for the electron distribution function. The effects of both the energy and momentum relaxation times due to scattering by acoustical, optical intervalley phonons and by ionized impurities are included in the derivations. Numeri-