A CuInSe2 (CIS) bulk single crystal grown by the directional freezing method from the melt at 1250°C shows superior crystal quality, as evidenced by its (p-type) electrical properties. Photoluminescence at 1.5 K shows a strong and well resolved spectrum with fine structures never before observed from this compound. Free exciton emission exhibits a doublet structure which can either be described as a splitting due to the uniaxial crystal field or as a polariton. The energy gap of the CIS semiconductor as determined from the temperature dependence of the free exciton line is 1.058 eV. Two moderate free-to-bound transitions are assigned to VCu and CuIn acceptors. A weak PL peak corresponding to a deep level is interpreted as arising from the Sei acceptor. Strong phonon replicas are also observed for the first time in a CIS bulk single crystal. The phonon wavelength of 218–237 cm-1 is in good agreement with the reported Raman result of 233 cm-1 for the LO phonon.

Hall measurements were made on selectively Si-doped InSb, GaSb/InSb, and GaAs/InSb heterostructures grown by molecular beam epitaxy using cracker sources. A cap layer had a pronounced influence especially on the low temperature conduction. The measurements showed an apparent increase in free carrier concentration and reduction of mobility due to compensation and/or parallel conduction. The best mobility, 38 700 cm2/V s at room temperature, was measured in a 2-μm-thick InSb layer capped with GaSb and doped with a concentration of 3×1016 cm−3 within 1000 Å from the cap interface. The variation of carrier concentration with temperature in doped samples revealed singularities at 50 and 90 K due to conduction from an unintentional p-background doping.

Layers of InxGa1−xAs with In-mole fraction ranging from 0 to 1 were grown on GaAs by molecular beam epitaxy. The electron mobility was measured by Hall effect as a function of both In concentration and temperature. The mobility was found to depend strongly on the composition. These experimental results were accurately calculated based on scattering from ionized impurities, polar optical phonons, the disordered alloy, and dislocations. In addition, the effect of space charge scattering is discussed. For layers with 0.2≤x≤0.85 the mobility monotonically declined with reduced temperature below 300 K as an effect of increased ionized impurity and space charge scattering. Free-carrier concentration due to Si-doping of InAs layers was also investigated. This was found to vary exponentially from the 1016 to 1019 cm−3 with the inverse Si-source temperature. The highest measured value was 3.3×1019 cm−3 and the carrier concentration saturated above this. For such high values the surface was deteriorated which we attributed to precipitation of silicon.

A melt growth CuInSe2 bulk single crystal was shown to be very high quality from its sharp and strong photoluminescence (PL) emissions. Photoreflectance (PR) measurement on a selected sample were performed from 12 K to room temperature. The PR line shape depends on surface treatment of the sample. Sharp features of PR spectra were obtained from bromine-methanol etched surface. PR spectra measured from 12 K to 140 K were analyzed by using both the well known Aspnes' relation and the confluent hypergeometric function suitable for exciton with Gaussian line shape. Result of the line-shape analysis shows that transitions involved are derived from two excitons with Gaussian line shape. By comparison with excitonic emission from its PL result, the two excitons are identified as the A- and the B-exciton which result from the splitting of the uppermost of the valence band. The energy difference of the two excitons computed from the PR spectrum at 12 K is 3.7 meV which agrees fairly well with 3.2 meV from PL result. The Gaussian exciton line shape at low temperature also indicates that the exciton-phonon coupling in a high quality CuInSe2 bulk single crystal is strong. PR spectra measured from an as-polished surface are weak and exhibit broader spectral lines which are well fitted by two excitons with the Lorentzian line shape. In addition, by carefully etching and polishing, the PR spectrum at 40 K exhibits a spectral line which can be interpreted as a superposition of the two spectra of different line shapes. The spectrum is well fitted by two Gaussian excitons and two Lorentzian excitons with two sets of transition energies. The presence of Lorentzian excitons indicates that excitons near the as-polished surface are weakly coupled to phonon which may be a result of residual strain left over by mechanical polishing.

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