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The polarization anisotropy in the longitudinal surface barrier electroreflectance (ER) of heavily doped Si (110) single crystal is measured as a function of the bias for the 3.4 eV peak ( E i ) .The E R anisotropy under depletion and weak accumulation conditions is found to be characterized by the usual polarization ratio signature of S : 1.35. Both, in the flatband and in the strong sccnmulation regions practically no polarization dependence is observed. The data obtained indicate that the surface-related electrooptic effect contributes essentially to the isotropic behaviour of surface-barrier ER of Si due to surface quantization (flatband region) and to surface amorphism (strong accumulation). The unusual lineshape of the E R spectra taken in the flatband region is shown to be due to the mixing of the depletion-and accumulation-type spectra in the nondifferential E R measurement conditions.

The luminescence intensity of porous silicon layers (PSLs) is investigated as a function of their thickness and temperature. For thin PSLs the emission intensity was found to depend superlinearly on thickness and exponentially on temperature. For thick PSLs no rise in emission intensity with lowering temperature is observed. The data obtained suggest that at room and some lower temperatures the photocreated excitons are free to diffuse in PSL and can be rejected into the silicon substrate. This behavior may also explain some recent experimental results.Also in the present work we report on results of combined PL and capacitance measurements which show that, for PSLs formed at small current densities, the distance between pore centers is, within the experimental uncertainties, the same as that between fluorine ions in the Helmholtz layer. This allows us to conclude that in the region of weak anodic polarizations every fluorine ion gives rise to the growth of individual pore.

A possible cause of the transverse photovoltaic effect (TPE) observed on mechanically polished surfaces /1/ might be the anisotropy of the internal stresses. The work reported here was initiated t o check this point by observing TPE'along with the electroreflectance (ER) effect on etched and mechanically polished surfaces.Measurements were made at T = 300 K on 45 Qcm p-type germanium with the orientation corresponding to the maximum anisotropy of the electron mobility (29' away from the [lll] axis /2/, see Fig. 1). Specimens were polished with 1 pm diamond paste. The ER spectra were taken by the electrolyte method i n the spectral range 1.9 to 2.5 eV (El, El + A1 transitions) using linearly polarized light. In the T P E studies the intense 1.06 p m radiation from a Nd laser was used to excite the excess carriers. In the case of chemically (or electrochemically) etched surface some of the TPE measurements were made under uniaxial stress along the sample y-axis.Our measurements show that the transverse photo-e. m. f. observed on mechanically polished Ge surface (a) is several times greater than that observed on the unstressed etched surface which originates because of the spatial separation of the diffusive electrons along the intervalley scattering length; (b) has a sign opposite t o that for the illuminated etched surface under compressive s t r e s s along y.To elucidate the origin of the TPE observed we have taken the ER spectra from the same surfaces. Fig. 1. Orientation of specimen and the directions of modulating (ExER ) and transverse electric ( E T P E ) fields Y 1 ) prospekt Nauki 115, 252650 Kiev, USSR.