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Boron diffusion in polycrystalline silicon layers
World Abstracts on Microelectronics and Reliability anomalous variation of the Hall coefficient with Ps2 indicates that the electron concentration increases with increasing Ps2. This is attributed to the formation of anti structure defects Sc~. A complete defect model is proposed, and published solubility and diffusion data for Ag in CdS in equilibrium with (Ag, Cd) alloys are reinterpreted on the basis of this model.
On the lime dependency o! the avalanche process in semiconductors. A. A. WALMA and REUBEN HACKAM. Solid-St. Electron. 18, 511 (1975). A n equation is derived for the time dependent current in the avalanche region of a uniform diode, for the case of one charged carrier of either electron or hole is injected, for unequal ionization rates and drift velocities of electrons and holes. The appearing time-constant differs from earlier results, derived on the basis of the well known intrinsic response time. The noise characteristics of the current are established for a Poissonian injection of an electron or hole. The factor which describes the influence of the statistics of the multiplication for low frequencies, is also found to differ, from previous published results. At high current multiplication factors the present study is in agreement with previous work.
Boron
diffusion in polycrystalline silicon layers. S.
HORIUCHI and R. BLANCHARD. Solid-St. Electron. 18, 529 (1975). Boron was diffused into the poly Si layers of 5.51.Lm thickness with boron nitride and diborane as boron sources. The diffusion depth was found to be proportional to the square root of diffusion time. The boron diffusion in the poly Si layers can be expressed in the well known complementary error function. The diffusion coefficient of boron in the poly Si layers is larger when diborane is used than when boron nitride is used as a boron source and is 10-50 times larger than that in the single crystal silicon substrates in the experimental range. The diffusion coefficients of boron at 1050°C in the single crystal silicon substrates with diborane as a boron source in the poly Si layers with boron nitride and diborane as boron sources are 8.80 x 10 -'4 , 1.17 × 10 -~2 and 1-95 × 10 ,2 cm2/sec, respectively. The activation energies of the diffusion coefficients of boron in each case are 3.42, 2.39 and 2.51 eV, respectively.
Energy levels u d concentration for platinum in silicon. K. P. LISIAK and A. G. MILNES. Solid-St. Electron. 18, 533 (1975). The energy levels and electrically active concentrations of platinum in silicon have been measured by Hall techniques. Analysis shows platinum to have two electrically active sites. The usual site Np,~ (assumed to be substitutional) predominates (>80%) and has two levels, a donor at Eo + 0.28 eV, degeneracy ~,: = 2 in p-type material and an acceptor at E c - 0 . 2 0 e V , 3,~ = 1/6, in n-type material. However a second platinum site exists, and is p r e s e n t t o a concentration Nr~. of about 10 per cent with an acceptor level at Eo + 0.42 eV (TH = 1/8). The physical nature of this Pt associated site is unknown. Neutron activation analysis has been used to determine total atomic platinum concentrations for diffusions from 800 to 1250°C. These results, in conjunction with Hall measurements, show the electrical activity to be very high. Previous studies on platinum are reviewed and compared to the result of this work. A review of the theory and technology ior OHMIC contacts to Group i l I - V compound semiconductors. V. L. RIDEOUT. Solid-St. Electron. 18, 541 (1975). The technology for ohmic contacts to group III-V compound semiconductors is reviewed in this paper. The basic principles of current transport in metal-semiconductor (Schottky barrier) contacts are presented first. The modes of current transport considered are thermionic emission
347
over the barrier, and tunneling through the barrier due to thermionic-field or field emission. Special attention is devoted to the parameters of temperature and doping concentration which determine the dominant mode of conduction. As the primary mode of conduction changes from thermionic emission dominated to tunneling dominated, the current-voltage behavior of the contact changes from rectifying to ohmic in character. The experimental techniques for fabricating ohmic contacts to III-V compound semiconductors are then described. Contact problems as they pertain to specific device applications are considered. Finally, present difficulties with contacts to mixed III-V crystals are discussed.
Reaction of sputtered Pt films on GaAs. V. KUMAR. J. Phys. Chem. Solids 36, 535 (1975). Pt/GaAs interface reaction has been investigated between 250-500°C. Schottky barrier Impatt diodes for microwave applications with this structure have an operating temperature of - 2 5 0 ° C and the solid state reaction at the interface can lead to degradation of the device. Using RF sputtered Pt films on (100) GaAs, the reaction has been investigated with the help of X-ray diffraction, Auger spectroscopy, Rutherford backscattering and electrical resistivity measurements. The reaction starts by a rapid diffusion and dissolution of Ga in Pt and is slowed down by the formation of PtAs2 at the interface which acts as a barrier for further Ga diffusion and reaction. Five different P t - G a phases and PtAs2 were identified at various stages of the reaction. The final reaction products are PtAs2 and GaPt. The reaction becomes self limited (up to 500°C) for Pt films thicker than 2 0 0 0 ~ , probably due to extremely slow diffusion of Ga through the interfacial PtAs2. Electrical resistivity data seem to indicate that Pt3Ga is more resistive than PtGa which is the final equilibrium P t - G a compound observed in this reaction. A solution for melt-level control when growing Czochralski silicon crystals in hemispherical quartz crucibles. T. G. DIGGES JR., Solid-St. Tech. February 1975. p. 44. Equations are given for melt-level control when growing Czochralski Crystals in hemispherical crucibles. Application of the equations to the silicon process has resulted in tight diameter control. Pre-secondary breakdown behaviour of silicon epitaxial diodes. A. BAR-LEv and H. AHARONI. Int. J. Electron. 38, 353 (1975). Diodes built in epitaxial layers can exhibit two distinct modes of behaviour in the avalanche region, prior to the development of secondary breakdown. The mode depends on whether the diode is of the punchthrough type when avalanching, i.e. the depletion layer extends to the nn + substrate-layer interface, or not. A series of epitaxial diodes of the two kinds were made and a method developed for estimation of current density uniformity from light emission of the avalanching diode up to the point of secondary breakdown. In the first case the current density remains uniform across the diode area, including sidewalls, up to the secondary breakdown point, while in the second case it starts to concentrate in the bottom area of the junction, usually at some weak spot, long before secondary breakdown happens. In order to find the reason for this the depletion region was divided into three zones to facilitate analysis, the results of which are used to explain the two modes of behaviour and contribute to the understanding of secondary breakdown in transistors in the cut-off region. Fine structures of indirect exciton absorption in phosphorus-doped silicon. T. NtSHINO and Y. HAMAKAWA. Solid-St. Commun. 16, 1105 (1975). A new indirect exciton absorption structure has been observed in
On the lime dependency o! the avalanche process in semiconductors. A. A. WALMA and REUBEN HACKAM. Solid-St. Electron. 18, 511 (1975). A n equation is derived for the time dependent current in the avalanche region of a uniform diode, for the case of one charged carrier of either electron or hole is injected, for unequal ionization rates and drift velocities of electrons and holes. The appearing time-constant differs from earlier results, derived on the basis of the well known intrinsic response time. The noise characteristics of the current are established for a Poissonian injection of an electron or hole. The factor which describes the influence of the statistics of the multiplication for low frequencies, is also found to differ, from previous published results. At high current multiplication factors the present study is in agreement with previous work.
Boron
diffusion in polycrystalline silicon layers. S.
HORIUCHI and R. BLANCHARD. Solid-St. Electron. 18, 529 (1975). Boron was diffused into the poly Si layers of 5.51.Lm thickness with boron nitride and diborane as boron sources. The diffusion depth was found to be proportional to the square root of diffusion time. The boron diffusion in the poly Si layers can be expressed in the well known complementary error function. The diffusion coefficient of boron in the poly Si layers is larger when diborane is used than when boron nitride is used as a boron source and is 10-50 times larger than that in the single crystal silicon substrates in the experimental range. The diffusion coefficients of boron at 1050°C in the single crystal silicon substrates with diborane as a boron source in the poly Si layers with boron nitride and diborane as boron sources are 8.80 x 10 -'4 , 1.17 × 10 -~2 and 1-95 × 10 ,2 cm2/sec, respectively. The activation energies of the diffusion coefficients of boron in each case are 3.42, 2.39 and 2.51 eV, respectively.
Energy levels u d concentration for platinum in silicon. K. P. LISIAK and A. G. MILNES. Solid-St. Electron. 18, 533 (1975). The energy levels and electrically active concentrations of platinum in silicon have been measured by Hall techniques. Analysis shows platinum to have two electrically active sites. The usual site Np,~ (assumed to be substitutional) predominates (>80%) and has two levels, a donor at Eo + 0.28 eV, degeneracy ~,: = 2 in p-type material and an acceptor at E c - 0 . 2 0 e V , 3,~ = 1/6, in n-type material. However a second platinum site exists, and is p r e s e n t t o a concentration Nr~. of about 10 per cent with an acceptor level at Eo + 0.42 eV (TH = 1/8). The physical nature of this Pt associated site is unknown. Neutron activation analysis has been used to determine total atomic platinum concentrations for diffusions from 800 to 1250°C. These results, in conjunction with Hall measurements, show the electrical activity to be very high. Previous studies on platinum are reviewed and compared to the result of this work. A review of the theory and technology ior OHMIC contacts to Group i l I - V compound semiconductors. V. L. RIDEOUT. Solid-St. Electron. 18, 541 (1975). The technology for ohmic contacts to group III-V compound semiconductors is reviewed in this paper. The basic principles of current transport in metal-semiconductor (Schottky barrier) contacts are presented first. The modes of current transport considered are thermionic emission
347
over the barrier, and tunneling through the barrier due to thermionic-field or field emission. Special attention is devoted to the parameters of temperature and doping concentration which determine the dominant mode of conduction. As the primary mode of conduction changes from thermionic emission dominated to tunneling dominated, the current-voltage behavior of the contact changes from rectifying to ohmic in character. The experimental techniques for fabricating ohmic contacts to III-V compound semiconductors are then described. Contact problems as they pertain to specific device applications are considered. Finally, present difficulties with contacts to mixed III-V crystals are discussed.
Reaction of sputtered Pt films on GaAs. V. KUMAR. J. Phys. Chem. Solids 36, 535 (1975). Pt/GaAs interface reaction has been investigated between 250-500°C. Schottky barrier Impatt diodes for microwave applications with this structure have an operating temperature of - 2 5 0 ° C and the solid state reaction at the interface can lead to degradation of the device. Using RF sputtered Pt films on (100) GaAs, the reaction has been investigated with the help of X-ray diffraction, Auger spectroscopy, Rutherford backscattering and electrical resistivity measurements. The reaction starts by a rapid diffusion and dissolution of Ga in Pt and is slowed down by the formation of PtAs2 at the interface which acts as a barrier for further Ga diffusion and reaction. Five different P t - G a phases and PtAs2 were identified at various stages of the reaction. The final reaction products are PtAs2 and GaPt. The reaction becomes self limited (up to 500°C) for Pt films thicker than 2 0 0 0 ~ , probably due to extremely slow diffusion of Ga through the interfacial PtAs2. Electrical resistivity data seem to indicate that Pt3Ga is more resistive than PtGa which is the final equilibrium P t - G a compound observed in this reaction. A solution for melt-level control when growing Czochralski silicon crystals in hemispherical quartz crucibles. T. G. DIGGES JR., Solid-St. Tech. February 1975. p. 44. Equations are given for melt-level control when growing Czochralski Crystals in hemispherical crucibles. Application of the equations to the silicon process has resulted in tight diameter control. Pre-secondary breakdown behaviour of silicon epitaxial diodes. A. BAR-LEv and H. AHARONI. Int. J. Electron. 38, 353 (1975). Diodes built in epitaxial layers can exhibit two distinct modes of behaviour in the avalanche region, prior to the development of secondary breakdown. The mode depends on whether the diode is of the punchthrough type when avalanching, i.e. the depletion layer extends to the nn + substrate-layer interface, or not. A series of epitaxial diodes of the two kinds were made and a method developed for estimation of current density uniformity from light emission of the avalanching diode up to the point of secondary breakdown. In the first case the current density remains uniform across the diode area, including sidewalls, up to the secondary breakdown point, while in the second case it starts to concentrate in the bottom area of the junction, usually at some weak spot, long before secondary breakdown happens. In order to find the reason for this the depletion region was divided into three zones to facilitate analysis, the results of which are used to explain the two modes of behaviour and contribute to the understanding of secondary breakdown in transistors in the cut-off region. Fine structures of indirect exciton absorption in phosphorus-doped silicon. T. NtSHINO and Y. HAMAKAWA. Solid-St. Commun. 16, 1105 (1975). A new indirect exciton absorption structure has been observed in