INFRARED OPTICAL STUDIES OF MERCURY-TELLURIDE - CADMIUM-TELLURIDE SUPERLATTICES AND GALLIUM-ARSENIDE (PHOTOLUMINESCENCE, DOUBLE ACCEPTOR, RAMAN SCATTERING, EXCITED STATES, LUMINESCENCE)

This thesis presents two different studies of the infrared optical properties of two different semiconductors. Chapter 2 describes the results of the first infrared photoluminescence (IRPL) measurements of a HgTe-CdTe superlattice. IRPL spectra of two different HgTe-CdTe superlattices from two different sources were measured from 100 to 270 K. The luminescence from both samples occurred at significantly lower energies than that from Hg(,1-x)Cd(,x)Te alloys with the same Cd concentrations as the average Cd concentrations of the superlattices. Analysis of the luminescence lineshape from sample 1 showed it to be consistent with wave-vector conserving band-to-band recombination. In this case, the band-gap energy of the superlattice would be near the low energy threshold of the luminescence peak. A comparison of the lineshapes from both samples with those measured in GaAs-Ga(,1-x)Al(,x)As superlattices showed evidence for fluctuations in the layer thicknesses of both the HgTe-CdTe superlattice samples. A simple theory of the band gaps of HgTe-CdTe superlattices was shown to be consistent with the experiments, if there were small errors in the measurements of the superlattice layer thicknesses of each sample. The differences in the luminescence properties of the two samples show that it is possible to tailor the band gaps of HgTe-CdTe superlattices.;Chapter 3 describes the first observation of s-like excited states of a double acceptor in a semiconductor. Measurements on two different liquid encapsulated Czochralski GaAs samples showed two s-like excited state transitions of equal magnitude, separated by 4.0 meV. A simple effective mass-like model of a double acceptor was developed to account for the two s-like excited states. This model predicted a splitting of the 1s('1)2s('1) excited state of a double acceptor to be 2.6 meV, in good agreement with the observed value of 4.0 meV. This proved that the 78-meV acceptor in GaAs is due to the first ionization of a double acceptor, the first such identification to made based on the s-like excited state spectrum. It is therefore possible to identify the valency of an acceptor in a semiconductor by measuring the s-like excited state spectrum.