Characterization of Electronic Structures of Deep Levels in Semiconductors by Magneto-Circular Emission Spectrum

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(1)Survery of electronic structures associated with the deep levels in semiconductorsExperimental and theoretical studies concerning the electronic structures of deep impurity levels in semiconductors were surveyed with particular reference to those introduced by transition atom impurities.(2)Layout, setup and abjusting of apparatus for magneto-circular dichroism spectrumBy combining optical elements purchased by this grant-in-aid, apparatus for the measurement of magneto-circular dichroism spectrum in the near-infrared region was constructed. This apparatus consists of a halogen-tungsten light source, a monochromator, an optical system with ellipsoidal mirrors, a polarizer, a piezo-birefringent modulator, an electromagnet with a perforation through its pole-pieces, a cryostat with helium a refrigerator and a semiconductor photocell for infrared detoction. This apparatus is equipped with an electronic system including two lockin-amplifiers and a microprocessorbased data-acquisition sys … More tem. This apparatus is capable of measuring the MCD for 0.4- 2.4um with magnetic field up to 13kG between temperatures from 20K to 300K.(3)Preparation of specimensChromium-doped semi-insulating GaAs wafers with different concentration of chromium made by the horizontai Bridgmann(HB)-method, an undoped semi-insulating GaAs wafer grown by liquid encapsulated Czochralski(LEC) technique, indium-doped dislocation-free GaAs ingots with different conductivity types(p,i,n) and LEC-grown InP wafers doped with iron were cut and polished to serve as specimens for the measurement of MCD. Heat treatment in arsemic atmosphere or chromium diffusion was also carried out.(4)Measurement and theoretical analysis of MCD spectraAll specimens measured showed MCD structures below the fundamental energy gap characteristic to the nature of the crystal. Among these spectra, MCD spectrum associated with the photoionization transition in HB-grown GaAs:Cr was analyzed in terms of the quantum defect model assuming the transition occurs from spin-orbit-split valence bands to Cr-related deep states. The calculated spectrum fit to the experimental one was satisfactory with the energy threshold 0.89eV and spin-orbit parameter of 0.2eV. The latter value is too small compared with that known for valence band splitting; i.e. 0.35eV. This suggests that a modification of the theory is necessary.(5)MCD as a crystal evaluation techniqueIt was found that MCD spectrum is very sensitive to crystallinity; for example the spectral shape changes drastically by heat treatment. Therefore, it becomes clear that the technique can be used as an evaluation method for crystal properties if we can classify MCD data for crystals with different treatments. Less