Lithium was diffused into Ge and Si at temperatures 300°−400°C and 400°−500°C, respectively. The diffusion was carried out in an inert gas atmosphere by decomposing LiAlH4. The concentration of Li impurities as a function of depth from the surface of the sample was determined by lapping down thin layers of the diffused part of the sample and measuring the conductance of each of these thin layers. An erfc was chosen to fit the experimentally measured concentration curve from which the diffusion constant D for each temperature of diffusion was determined. The following dependence of temperature was found: D=9.10×10−3exp(−13100/RT) for Ge,and D=2.65×10−3exp(−14500/RT) for Si,where D is measured in cm2/sec, T in °K, and R=1.98 cal/°K. The deviation in the experimental values of D was not more than ±10% for Ge and ±20% for Si.
Amorphous silicon films were prepared by plasma decomposition of SiF4.+SiF2 gas. Structural analysis, electronic-transport-property measurements, optical-property measurements, and electronspin-resonance measurements were performed as a function of deposition and annealing temperature. Hydrogenated amorphous silicon (a-Si:H) samples were prepared in a separate identical reactor under similar plasma conditions for reference. The results indicate that compensation of dangling bonds by fluorine alone can be obtained, yielding ESR values of the order of 10' spins/cm . The a-Si:F films can be doped. The dark conductivity of a-Si:F increases with spin density, but the photoconductivity is low and independent of the spin density. The differences between a-Si;F and a-Si:H are interpreted in terms of the different diffusivity and bond strength of fluorine and hydrogen in the a-Si matrix. These differences result in a larger density of tail states in a-Si:F relative to a-Si:H samples of equal spin densities.
Fig. 5. Scanning electron micrograph of precipitation front. Backscattered electron image of alloy is darker than that of Ni matrix Iomellae.logous to an isothermal eutectoid transformation in a homogeneous solid and v is related to the lameUar spacing, 8, bywhere D A is the alloy diffusion coefficient and f is the relative supersaturation (1), which will be here estimated as 0.1. If segregation is achieved by boundary diffusion along the a/d interface, then an approximate growth equation analogous to [3] is obtained by substituting D B b/5 for D A, where D B is the diffusion constant within the boundary of width b. To a first approximation then v = 0.1 DA/8 volume diffusion [4] v = 0.1 DBb/~ ~ boundary diffusion [5] Substitution of the values of v and 5 reported in Fig. 2 into [4] and [5] assuming b = 10A yields D A ~ 10 -9 cm 2 sec -1 or D B ,~ 10 -6 cm 2 sec -1. Extrapolation of high temperature results (17) for volume interdiffusion in the Ni-Mo solid solution yields, at 700~ D A 10 -i s cm ~ sec -1, indicating that segregation must be achieved by the second mechanism of diffusion along the advancing interface. This is almost universally the case with discontinuous precipitation. It is concluded from the simultaneous observations of linear kinetics, uniform lamellar morphology, and a discontinuous change in concentration at the reaction front that the mechanism of internal sulfidation of Ni-20Mo is that of discontinuous precipitation. It is not possible, however, to conclude that the reaction rate is controlled entirely at the precipitation front. Since the kinetics of the over-all reaction are approximately linear, so too are those of external scale growth. Such behavior in an alloy exposed to HeS/H2 atmospheres has frequently been ascribed to rate control by a process occurring at the solid-gas interface. If this is the case in the present instance, then the penetration velocity and interlamellar spacing of the internal precipitation zone may be partially determined by this external constraint.We are undertaking a study of the high temperature deformation of polycrystalline silicon as part of a program to find low cost methods of manufacturing silicon solar cells. The material used as samples in these deformation experiments was commercially available, Permanent address: The Technion, ttaifa, Israel.
Production of silicon films by a silicon fluoride transport reaction is described here. The effect of various deposition parameters including temperature, partial pressure, and gas flow rate on the deposition kinetics was investigated. X‐ray analysis, surface electron spectroscopy, optical absorbance and reflectance, and electrical measurements indicate that the films have properties similar to those of silicon films obtained by CVD from silane.
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