Photoluminescence (PL) studies of bulk and epitaxial CdTe samples obtained from several sources are discussed. Steady state PL measurements were carried out at temperatures ranging from 16–300 K. The effects of surface preparation, substrate temperature, and film thickness were studied in detail for homoepitaxial films grown on the (111)A and (100) planes of CdTe. PL studies of epitaxial CdTe films grown on (0001) sapphire by molecular beam epitaxy (MBE), by hot wall MBE, and by metal-organic chemical vapor deposition (MOCVD), and on the (111)B and (100) planes of GaAs by MBE have also been completed. The CdTe epilayers on sapphire and GaAs substrates typically display a bright PL spectrum dominated by the near edge peak at 1.58 eV (77 K). In addition, a number of films exhibit a near edge peak at 1.503 eV at 300 K, which is indicative of high quality epitaxy and which allowed direct measurement of the room temperature band gap of CdTe. PL studies of epitaxial Cd1−x MnxTe films grown by MBE on 5.0 μm thick CdTe buffer layers on GaAs substrates reveal shifts of the band gap into the visible spectral region with increasing x accompanied by a significant increase in edge peak magnitude.

Single-crystal multilayers of the dilute magnetic semiconductor Cd1−x Mnx Te (x∼0.2) alternating with CdTe have been successfully grown for the first time using the molecular beam epitaxy technique. Four sets of superlattices have been prepared consisting of 14, 60, 90, and 240 double layers of average thickness 460, 140, 75, and 37 Å, respectively. Each set consists of two samples grown simultaneously using 7×15×1-mm thick (0001) sapphire substrates onto which 5.0-μm-thick CdTe buffer layers were first deposited. X-ray diffraction techniques were employed to verify that epitaxy had been achieved and to obtain the average lattice constant of each of the multilayer structures. X-ray diffraction satellites were observed on both sides of the (111) diffraction peak of the superlattices composed of 14 and 60 alternating layers, respectively, which allowed an accurate estimate of the superlattice period, or double-layer thickness, for these samples. Results of UV reflectance studies and photoluminescence experiments at liquid nitrogen temperatures are also presented and discussed.

Quantum-size effects and strain effects have been calculated for the CdMnTe–CdTe superlattice. Unlike previous theories dealing with materials grown in the [100] direction, this work applies to CdMnTe–CdTe superlattices oriented in the [111] direction. A Kronig–Penney analysis is used to obtain the quantized conduction-band energies. Pikus–Bir deformation theory is employed to calculate the strain-induced splitting of the heavy and light-hole valence bands. Excitation luminescence spectra obtained for several CdMnTe–CdTe superlattices exhibit sharp peaks which correspond to heavy and light-hole excitonic transitions from the quantized conduction-band states. Observed transition energies from the n=1 conduction band state are used with the theory to obtain the heavy and light-hold exciton binding energies for the supperlattices. An increase in binding energies over the values for bulk CdTe is obtained and is attributed to the 2D nature of the quantum wells and possibly strain-induced distortion of the valence bands. The calculated transition energies from higher level (n=2,3,...) conduction-band states agree closely with the experimental data.

Growth of bulk crystals of CdTe, Mn~Cd,_~Te, Zn~Cd,_xTe, and CdSe, Te,_, by zone leveling and the vertical Bridgman technique is described. The twinning probability P increases in the order P(CdSe~Te, ~) < P(Zn~Cd~ ~Te) < P(Mn~Cdl_xTe). The Vicker hardness H increases in the order H(CdTe) < H(Mn~.Cd~_xTe) < H(CdSeyTe~ ~) < H(Zn~Cd, ~.Te) for 90% CdTe alloys. Pure CdTe exhibiting room-temperature luminescence has been prepared that does not show the usually observed 1.42 eV emission. Photoluminescence spectra of the alloys are presented that reveal a proportional shift in the deep emission to the bandgap change with composition. Mn~Cd, ~Te does not exhibit deep emission for x = 0.2.

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