The anisotropy of the surface mobility for oriented, nearly intrinsic n‐type germanium samples were investigated at different temperatures (77 to 300° K) and different states of surface. For the (112) plane the anisotropy coefficient was found to be about 15% at large accumulation bend of bands, Ys ≈︁ 0.15 eV, and zero at small Ys. Values of the length of the intervalley scattering of carriers in the above mentioned temperature region have been obtained. Also calculations on the conductance anisotropy of the space charge region (SCR) for the multivalley current carrier spectrum of n‐germanium are presented. For large accumulation layers the theoretical predicted anisotropy coefficient coincide with experimental ones.
The anisotropy of the surface mobility of electrons p for carriers moving in thin layers of the surface space charge (SSC) and diffuse scattering on the surface was predicted for multivalley semiconductors of the Ge and Si types in (1 to 4). In (4) the anisotropy of ps has been analysed theoretically for different crystallographic orientations assuming absence of intervalley scattering and zero normal component of current for every valley (in (1, 2) the latter was not taken into account).It turned out, particu€arly, that for (100) and (111) planes degenerates into scalars, though for great surface potentials Ys these magnitudes may differ from each other rather noticeably. For other planes the mobility turns out to be anisotropic.The magnitudes calculated are given in Fig. 1. They show the anisotropy degree K = psl/ps2 a s a function of Y using the theory developed in (4). The calculation has been made on a computer f6r intrinsic Ge using the exact dependence Y(z). S S S Experiments aiming at detecting and investigating the anisotropy of have S been carried out. Measurements of the integral field effect (FE) have been made on the same sample of intrinsic Ge by passing a current along different crystallographic directions. FE-curves in the SSC-accumulation region were then compared, and from the ratio of conductivity changes (for fixed electric fields) K(YJ was obtained. Samples cut along the (loo), (lll), and (115 planes were used.To detect the anisotropy of )1 using this method it is convenient to utilize the S ( 1 1 : ) plane: the mutually perpendicular directions on these planes correspond to the main crystallographic axes (il0) and (111) for which a considerable K (% 1.2) is predicted. Thus, the experiment may be carried out on a plate of a simple square form, which essentially simplifies the manufacturing of samples and reduces the masking factors in the utilized method (irreproducibility of the surface properties for different samples as well as inhomogeneity).
No abstract
The dependences of the effective electron mobility (μs) on the band bending at the surface (Ys) are obtained both, for non‐bombarded Ge samples and Ge samples after their bombardment with Ar+ ions under conditions of different bombardment doses (from 1012 to 1014 ions/cm2) and ion energies (from 0.2 to 1.2 keV). The value of μ is found to decrease with increasing bombardment dose and ion energy, and anno‐monotonic dependence of μs on Ys is observed. This non‐monotonic behaviour (the appearance of minimum in the μs(Ys)‐dependence at Ys ≈ (1 to 3) kT/e) is assumed to be connected with an acceptor level at Ec = 1.5kT/e which has a non‐uniform surface density. A model for the effect of the nonuniform acceptor distribution on the behaviour of μs (Ys)‐dependence is developed which describes qualitatively the experimental results obtained. To explain the mobility decrease observed, a calculation of the effective carrier mobility is made which includes the additional carrier scattering in the surface layer with a high defect density.
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