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Quantum well model of hydrogenated amorphous silicon
284
World Abstracts on Microelectronics and Reliability
nonequilibrium characteristics are rich in structure and yield useful information on bulk-trap generation rate and interface trap emission.
additional parts to control four IBM-compatible drives.
Chip controls floppy-disk drives. R. COLIN JOHNSON. Electronics p. 175 (4 December 1980). Dedicated microcomputer has menlory-mapped interface, needs very few
7. S E M I C O N D U C T O R
INTEGRATED
Gate arrays--a special report. JOIIN G. POSA. Electronics p. 145 (25 September 1980). Arrays have rushed in to fill the vacuum between high-volunle standard parts and costly custom chips: now their growth depends on new resources for layout, testing+ and packaging.
CIRCUITS,
Diffusion of boron into silicon from doped oxide source. P. M. PRASAD and V. P. SUNDARSINGH. Microelectron..I. 1 ! (6), 21 (1980L This paper describes a new technique for tile preparation of boron doped oxide films on silicon by tile pyrolytic decomposition of tetraethoxysilane and trimethyl borate. The formation of an oxide film is confirmed using an infra-red technique. The effects of flow rate of ambient and time and temperature of deposition on tile formation of oxide film are investigated. A much faster growth rate for oxide film is observed by keeping the tetraethoxysilane at higher temperature. Since the doped oxide is grown at 700°C, the density of dislocations and precipitates will be reduced. The oxide films can be used as boron diffusion sources, especially for shallow junctions. It is observed that the diffusion coefficient is dependent on surface concentration due to source depletion. Comparison of Thai's theory with experimental boron doping profiles in silicon, diffused from boron nitride sources. K. P. FROHMADER and L. BAUMBAUER.Solid-St. Electron. 23, 1263 (1980). Silicon wafers, ( 111 )-oriented, were diffused with BN sources at temperatures from 986 to 1132°C and times from 15rain to 4 h r at various flow rates of ambient gas (N_~l of 2-80 l/hr. Doping profiles were determined. They showed plateaus of nearly constant doping concentration near the silicon surface and great deviations from erfc profiles. From this profiles diffusion coefficient D(c) was derived by means of Boltzmann's method as a function of doping concentration C. Comparison with Thai's theory (corrected by Jain and vail Overstraeten) shows for the nondegenerate case of field-enhanced diffusion good agreement with the experimental results of D(c). A remarkable increase for D(c) is found for boron concentrations C~>10~"cm -3. Preexponential term D O activation energy E. I for diffusion coefficient D(c) are derived and found to be 1.36 cm-'/sec and 3.59 eV respectively. They coincide well with values given by other authors. The longitudinal diffusion coefficient and the mobility of hot electrons in silicon, G. BOSMAN, R. J. J. ZIJLSTRA and F. NAVA. Solid-St. Electron. 24, 5 (1981). The longitudinal diffusion coefficient of electrons in silicon is (i) calculated as a function of electric field strength from noise and current measurements on a n÷ml ÷ planar silicon device and [ii) measured vs field strength with the help of the Time-ofFlight technique at 200, 160 and 77 K. The electric field was oriented along the ( 111 ) direction. The first method yielded results for fields lower than 105 V m -~ whereas the second method yielded results for fields ranging from 2 x 10'* to 2 x 106 V m ~. Values for the mobility obtained with the first method are presented as well and compared with Time-of-Flight data. Heat transfer of modified silicon surfaces. MORTON D. REEBER and RUDOLF G. FRIESER. IEEE Trans. Components, Hybrids Mfilg Technol. C H M T - 3 (3), 387 (September 1980). The heat transfer between silicon surfaces and perfluorohexane has been measured for fluxes ranging from 0 to 2.2 W/cm 2. Data are presented for ten different surface treatments designed to encourage thermal nucleation.
DEVICES
AND
MATERIALS
Resistivity changes of heavily-boron-doped CVD-prepared polycrystalline silicon caused by thermal annealing. T. M AKINO and H. NAKAMURA.Solid-St. Electron. 24, 49 ( 1981 ). Heavilyboron-doped polycrystalline Si films were deposited at 600°C on thermally grown SiO2 by the thermal decomposition of SiH.~-BCI3-H 2 mixture. Resistivity changes with isochronal or sequential annealing were systematically examined. Temperature dependence of equilibrium saturation carrier concentration was determined at 8 0 0 - I I00°C. Since asdeposited polycrystalline Si is in the super-saturated state, carrier concentration decreases fiom the super-saturated to equilibrium saturation value by annealings over 700°C for poly Si doped with over 2 x 10-'° cm - 3 resulting in anomalous resistivity change. Carrier concentration changes reversibly between saturation values with sequential annealing and is determined by the last annealing temperature when the annealing time is long enough. Mobility increases with annealing temperature, however, less increase is found for heavily doped poly Si, which is attributed to the suppression of grain growth caused by electrically inactive Si-B compounds. Quantum well model of hydrogenated amorphous silicon. M. H. BRODSKY. Solid St. Commun. 36, 55 {1980). A model of barrier-separated regions is proposed that leads to quantization and spatial correlation of carriers near tile band gap of hydrogenated amorphous silicon. The size of these regions. which consist of pure Si bounded by potentials emanating from Si-H bonds, is estimated from a classical percolation picture. Near band gap localized states lie in these q u a n t u m well regions and are about 0.3eV more widely separated than in unbounded Si, thereby accounting for a wide variety of hitherto uncorrelated experimental results. Dopants enhance conductivity by providing conduction paths through the barriers. Spatially coincident pairing of conduction with valence band localized states is speculated to be relevant to other amorphous semiconductors as well. Final-state effects in the excitation spectra of deep impurities in semiconductors. SOKRATES T. PANTELIDES and HERMANN G. G RIMMEISS.Solid St. Commun. 35, 653 (1980), Tile excitation spectra of deep impurities have usually been interpreted in terms of transitions to continuum states having the same energy distribution and Bloch-like character as the perfectcrystal band states. Here we provide theoretical analysis and experimental evidence showing that deep-level spectra may in fact be dominated by bound and quasibound final states induced by the strong short-range impurity potentials. The measurement of deep centers in float zone silicon by photovoltage spectroscopy. L. L. JASTRZEBSKIand J. LAGOWSKI. RCA Rev. 41, 181 (June 1980). Derivative (wavelength modulated) photovoltage spectroscopy of MOS and MS structures has been employed for studying band structure transitions and photoionization of deep levels in float zone silicon (p = 2 x 1015 cm - 3). From low temperature (T < 30 K ) photovoltage spectra and photovoltage transient characteristics, it has been established that deep levels of tile energy 0.56 eV above the valence band are present in as-grown high quality float zone silicon and in oxidized wafers. The photovoltage measurements also revealed the presence of shallow
World Abstracts on Microelectronics and Reliability
nonequilibrium characteristics are rich in structure and yield useful information on bulk-trap generation rate and interface trap emission.
additional parts to control four IBM-compatible drives.
Chip controls floppy-disk drives. R. COLIN JOHNSON. Electronics p. 175 (4 December 1980). Dedicated microcomputer has menlory-mapped interface, needs very few
7. S E M I C O N D U C T O R
INTEGRATED
Gate arrays--a special report. JOIIN G. POSA. Electronics p. 145 (25 September 1980). Arrays have rushed in to fill the vacuum between high-volunle standard parts and costly custom chips: now their growth depends on new resources for layout, testing+ and packaging.
CIRCUITS,
Diffusion of boron into silicon from doped oxide source. P. M. PRASAD and V. P. SUNDARSINGH. Microelectron..I. 1 ! (6), 21 (1980L This paper describes a new technique for tile preparation of boron doped oxide films on silicon by tile pyrolytic decomposition of tetraethoxysilane and trimethyl borate. The formation of an oxide film is confirmed using an infra-red technique. The effects of flow rate of ambient and time and temperature of deposition on tile formation of oxide film are investigated. A much faster growth rate for oxide film is observed by keeping the tetraethoxysilane at higher temperature. Since the doped oxide is grown at 700°C, the density of dislocations and precipitates will be reduced. The oxide films can be used as boron diffusion sources, especially for shallow junctions. It is observed that the diffusion coefficient is dependent on surface concentration due to source depletion. Comparison of Thai's theory with experimental boron doping profiles in silicon, diffused from boron nitride sources. K. P. FROHMADER and L. BAUMBAUER.Solid-St. Electron. 23, 1263 (1980). Silicon wafers, ( 111 )-oriented, were diffused with BN sources at temperatures from 986 to 1132°C and times from 15rain to 4 h r at various flow rates of ambient gas (N_~l of 2-80 l/hr. Doping profiles were determined. They showed plateaus of nearly constant doping concentration near the silicon surface and great deviations from erfc profiles. From this profiles diffusion coefficient D(c) was derived by means of Boltzmann's method as a function of doping concentration C. Comparison with Thai's theory (corrected by Jain and vail Overstraeten) shows for the nondegenerate case of field-enhanced diffusion good agreement with the experimental results of D(c). A remarkable increase for D(c) is found for boron concentrations C~>10~"cm -3. Preexponential term D O activation energy E. I for diffusion coefficient D(c) are derived and found to be 1.36 cm-'/sec and 3.59 eV respectively. They coincide well with values given by other authors. The longitudinal diffusion coefficient and the mobility of hot electrons in silicon, G. BOSMAN, R. J. J. ZIJLSTRA and F. NAVA. Solid-St. Electron. 24, 5 (1981). The longitudinal diffusion coefficient of electrons in silicon is (i) calculated as a function of electric field strength from noise and current measurements on a n÷ml ÷ planar silicon device and [ii) measured vs field strength with the help of the Time-ofFlight technique at 200, 160 and 77 K. The electric field was oriented along the ( 111 ) direction. The first method yielded results for fields lower than 105 V m -~ whereas the second method yielded results for fields ranging from 2 x 10'* to 2 x 106 V m ~. Values for the mobility obtained with the first method are presented as well and compared with Time-of-Flight data. Heat transfer of modified silicon surfaces. MORTON D. REEBER and RUDOLF G. FRIESER. IEEE Trans. Components, Hybrids Mfilg Technol. C H M T - 3 (3), 387 (September 1980). The heat transfer between silicon surfaces and perfluorohexane has been measured for fluxes ranging from 0 to 2.2 W/cm 2. Data are presented for ten different surface treatments designed to encourage thermal nucleation.
DEVICES
AND
MATERIALS
Resistivity changes of heavily-boron-doped CVD-prepared polycrystalline silicon caused by thermal annealing. T. M AKINO and H. NAKAMURA.Solid-St. Electron. 24, 49 ( 1981 ). Heavilyboron-doped polycrystalline Si films were deposited at 600°C on thermally grown SiO2 by the thermal decomposition of SiH.~-BCI3-H 2 mixture. Resistivity changes with isochronal or sequential annealing were systematically examined. Temperature dependence of equilibrium saturation carrier concentration was determined at 8 0 0 - I I00°C. Since asdeposited polycrystalline Si is in the super-saturated state, carrier concentration decreases fiom the super-saturated to equilibrium saturation value by annealings over 700°C for poly Si doped with over 2 x 10-'° cm - 3 resulting in anomalous resistivity change. Carrier concentration changes reversibly between saturation values with sequential annealing and is determined by the last annealing temperature when the annealing time is long enough. Mobility increases with annealing temperature, however, less increase is found for heavily doped poly Si, which is attributed to the suppression of grain growth caused by electrically inactive Si-B compounds. Quantum well model of hydrogenated amorphous silicon. M. H. BRODSKY. Solid St. Commun. 36, 55 {1980). A model of barrier-separated regions is proposed that leads to quantization and spatial correlation of carriers near tile band gap of hydrogenated amorphous silicon. The size of these regions. which consist of pure Si bounded by potentials emanating from Si-H bonds, is estimated from a classical percolation picture. Near band gap localized states lie in these q u a n t u m well regions and are about 0.3eV more widely separated than in unbounded Si, thereby accounting for a wide variety of hitherto uncorrelated experimental results. Dopants enhance conductivity by providing conduction paths through the barriers. Spatially coincident pairing of conduction with valence band localized states is speculated to be relevant to other amorphous semiconductors as well. Final-state effects in the excitation spectra of deep impurities in semiconductors. SOKRATES T. PANTELIDES and HERMANN G. G RIMMEISS.Solid St. Commun. 35, 653 (1980), Tile excitation spectra of deep impurities have usually been interpreted in terms of transitions to continuum states having the same energy distribution and Bloch-like character as the perfectcrystal band states. Here we provide theoretical analysis and experimental evidence showing that deep-level spectra may in fact be dominated by bound and quasibound final states induced by the strong short-range impurity potentials. The measurement of deep centers in float zone silicon by photovoltage spectroscopy. L. L. JASTRZEBSKIand J. LAGOWSKI. RCA Rev. 41, 181 (June 1980). Derivative (wavelength modulated) photovoltage spectroscopy of MOS and MS structures has been employed for studying band structure transitions and photoionization of deep levels in float zone silicon (p = 2 x 1015 cm - 3). From low temperature (T < 30 K ) photovoltage spectra and photovoltage transient characteristics, it has been established that deep levels of tile energy 0.56 eV above the valence band are present in as-grown high quality float zone silicon and in oxidized wafers. The photovoltage measurements also revealed the presence of shallow