SEMICONDUCTORS VOLUME 33, NUMBER 5 MAY 1999 REVIEW Induced photopleochroism in semiconductors Review F. P. Kesamanly and V. Yu. Rud’* St. Petersburg State Technical University, 195257 St. Petersburg, Russia Yu. V. Rud’ A. F. Ioffe Physicotechnical Institute, Russian Academy of Sciences, 194021 St. Petersburg, Russia ~Submitted August 24, 1998; accepted for publication September 22, 1998! Fiz. Tekh. Poluprovodn. 33, 513–536 ~May 1999! The results of experimental investigations of induced photopleochroism of elementary ~Si, Ge!, binary ~III–V, II–VI!, and more complicated diamond-like semiconductors ~III–V— III–V solid solutions, ternary compounds I–III–VI and II–IV–V compounds! and photosensitive structures based on them are discussed and generalized. The laws of induced photopleochroism, which have been established for various types of phototransducers, and their relation with the parameters of semiconductors are analyzed. The possibilities of practical applications of induced polarization photosensitivity of isotropic semiconductors in polarimetric structures and in the diagnostics of the quality of the semiconductors are discussed. © 1999 American Institute of Physics. @S1063-7826~99!00105-2# 1. INTRODUCTION tors an external polarizing component and by producing uniaxial deformation11 or conditions for photon drag of A complete description of optical radiation includes, in charge carriers12 and for photovoltaic effects.13–16 In the addition to the intensity and photon energy, the state of po- most widely used approach a polarization-insensitive photo- larization of the light wave.1–5 In this respect, the present detector is equipped with an external polarizing component growth of semiconductor optoelectronics based on source-to- and the polarization parameters of the incident radiation are detector information transfer and reception by intensity and determined on the basis of the intensity measured with the wavelength modulation of a light flux is one-sided. It is com- photodetector. In such systems there always arises the prob- pletely obvious that the development of optoelectronic sys- lem of spectral matching of the polarizing component and tems in which the state of polarization also plays the role of the photodetector, and, in addition, the polarizing component an information parameter will make it possible to increase generally introduces additional radiation losses in the optical system capacity substantially. The need to develop polarized channel and thereby lowers the detection power of the sys- optoelectronics is also stimulated by the rapid growth of ap- tem with respect to polarization. It should also be under- plications of linearly polarized light ~LPL! in science and scored that polarimetric systems with an external ~relative to technology.6–8 In this connection, fundamental research on the photodetector! polarizing component are also not widely the anisotropy of photoelectric phenomena is evolving into a used because of structural design complications.17 Polari- central direction in the physics and technology of semicon- zation-sensitive IS photodetectors based on the approaches ductors. considered above have never been demonstrated explicitly. A qualitative breakthrough in this field involved the use A major step forward in this problem appeared only with of natural photopleochroism ~NP! in photoconversion struc- the discovery, in the 1980s at A. F. Ioffe Physicotechnical tures based on oriented anisotropic semiconductors from sev- Institute, of a new type of photopleochroism induced by ob- eral crystal classes.9,10 Thus the first phototransducers, whose lique incidence of LPL on the receiving plane of a quantum efficiency is determined by the position of the po- photodetector.18 This type of photopleochroism is deter- larization plane of LPL relative to the principal crystallo- mined entirely by the optical processes occurring at the in- graphic axes of the semiconductor, were developed.9 The terface between a semiconductor and the medium from still inadequate, for large-scale applications of NP, techno- which the LPL is incident on the semiconductor and, in con- logical familiarity of anisotropic semiconductor materials is trast to NP,10 there are no limitations with respect to the stimulating assessment of the classic cubic semiconductors, structure and phase state of the semiconductor. Thus polari- whose technological base is well-developed, for use in pola- metric photodetectors with record-high azimuthal photosen- rimetric photodetectors. sitivity '0.2 A/W•deg and wide-band or narrowly selective For a long time attempts have been made throughout the regimes of photodetection of natural and linearly polarized world to use isotropic semiconductors ~ISs! for analyzing light, as well as with continuous tuning of the induced pho- polarized radiation, for example, by adding to IS photodetec- topleochroism ~IP! have been developed. The first demon- 1063-7826/99/33(5)/21/$15.00 483 © 1999 American Institute of Physics 484 Semiconductors 33 (5), May 1999 Kesamanly et al. strations of the possibilities of obtaining gigantic induced photopleochroism ~GIP! and using polarization photosensi- tivity spectroscopy for rapid diagnostics of the quality of finished structures have been performed in the structures ob- tained. Many original publications and announcements report- ing the results of investigations of IP in various photosensi- tive structures based on a large group of semiconductor ma- terials from the basic classes have now appeared at various levels of scientific conferences. In our review article the physical mechanisms of the new photoelectric phenomenon are examined and approaches are developed for obtaining and controlling the parameters of polarimetric semiconductor photodetectors based on this effect. The characteristic fea- tures of the observed phenomena, which could find wide application in the development of polarization photoelectron- ics systems and in diagnostics of finished polarimetric struc- tures, are also discussed. 2. PHOTOPLEOCHROISM OF ISOTROPIC FIG. 1. Diagram of optical processes at the air/IS interface and the com- SEMICONDUCTORS WITH OBLIQUE INCIDENCE OF LPL puted dependences PI(a0) for semiconductors with different refractive in- There exists a wide range of semiconductor photoelec- dices ~indicated on the curves!. tric devices based on isotropic materials.19–30 Photodetectors based on elementary, binary, and more complicated crystals, S P as well as glassy semiconductors have long been used to H05H01H0 5A0@m0•a8]2B0n0a8, ~1! record the intensity of optical radiation. This is due to the where A and B are the scalar amplitudes of the incident fact that optical transitions in the energy spectrum of isotro- 0 0 wave with the corresponding polarizations, a , b , and q pic crystal and glassy semiconductors are equally probable 8 8 8 are the unit basis vectors, n is the vector of the wave normal for any polarization of the radiation. Since anisotropy was 0 to the incident wave, n and n are, respectively, the refrac- not observed in investigations of their photosensitivity spec- 0 2 tive indices of air and the semiconductor, and m and m are tra, the possibilities of direct detection of LPL using photo- 0 2 the refraction vectors of the incident and refracted waves detectors consisting of ISs were not discussed at all in the ~Fig. 1!. We can then represent the intensity of the radiation scientific literature before the appearance of Ref. 18, where fluxes with oblique incidence of LPL can be represented in the then unexpected possibility of using isotropic semicon- terms of the radiation power vector P and the unit vector q ductors in a completely new ~for them! function—as a normal to the interface as: photoanalyzer—was predicted and demonstrated. F5 P q 5~C/4p! Re E 2m q 2.1. Photosensitivity anisotropy of isotropic semiconductors ^ i• & ^ i& i• 2 When the surface of an isotropic semiconductor is illu- 5~C/4p!^Re Ei& hi , ~2! minated with LPL along the normal to the front plane ~the where hi5ni cos ai , and i50, 1, 2. angle of incidence of the LPL a050°), the photosensitivity In this case the intensities of the incident wave can be ~PS! is independent of the position of the electric field vector written as E of the light wave relative to the principal crystallographic S 2 P 2 F05~C/4p!A0h0 and F0 5~C/4p!B0h0 , ~3! axes in the semiconductor. For a0.0°, according to the Fresnel relations, nonequivalent reflection and refraction of and the intensities of the refracted wave as rays with different polarization azimuths, which depend on S 2 P 2 the permittivities of the adjoining media, occur at the air/IS F25~C/4p!A2h2 and F2 5~C/4p!B2h2 . ~4! boundary. The intensity of the radiation transmitted into the Using the Fresnel formulas in the covariant representation,32 semiconductor is a function of the azimuthal angle u between we obtain for the refracted waves E and the plane of incidence ~PI! of the radiation. For this A25$~2h0!/~h01h2!%A0 , reason, for a0.0° the density of photogenerated charge car- riers in an isotropic semiconductor depends on u. 2 2 B25$~2n0n2h0!/~n2h01n0h2!%B0 . ~5! We shall consider the simplest case of a flat interface on Substituting the Fresnel formulas ~5! into Eq. ~4! shows that which an LPL beam is incident at angle a0 ~Fig. 1!. The when the intensities of the incident LPL with different polar- electric E0 and magnetic H0 vectors of the incident wave can be written in the covariant representation31,32 as follows: ization azimuths are the same (A05B0), the intensities of the waves refracted into the semiconductor for orthogonal E 5ES1EP5A a81B @n a8#, S P 0 0 0 0 0 0• polarizations F2 and F2 become nonequivalent for all a0 Semiconductors 33 (5), May 1999 Kesamanly et al. 485 Þ0°. Since the density of photogenerated pairs in an IS is determined by the intensity of the absorbed radiation, the photosensitivity ~PS! for each polarization can be written in the form P P S S i 5C•F2 , i 5C•F2 , ~6! where the constant C includes all contributions, which are independent of the polarization of the LPL, to the PS, for example, the optical absorption coefficient, the quantum yield, the electron–hole pair separation factor, and so on.