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.
We report details of the successful controlled substitutional doping of CdTe films with indium. These n-type films were prepared using a new technique, photoassisted molecular beam epitaxy, in which the substrate is illuminated during the deposition process. In the present work, an argon ion laser was used as an illumination source. The incident light was found to produce immediate and significant changes in the electrical properties of the films. In particular, highly activated n-type CdTe:In layers resulted.
Results of initial attempts to grow cubic-phase CdTe films on sapphire by molecular beam epitaxy are reported. Depositions have been completed on (11̄02) R-plane, (12̄10) A-plane, and (0001) basal plane substrates. Substrate temperatures in the range 260–350 °C were employed along with deposition rates of 1.5–7.5 Å/s. Depositions on (11̄02) sapphire generally produced films containing some elements of the hexagonal phase, as disclosed by x-ray diffraction and UV reflectance measurements. Sharp cubic-phase epitaxy was obtained for thick (∼5 μm) CdTe films grown on (12̄10) and (0001) sapphire substrates. The epitaxial films are smooth and mirrorlike in appearance. Nomarski micrographs show a featureless CdTe surface.
High quality growth of InSe on Si(111) was achieved by insertion of GaSe buffer layer. Rhombohedral polytypes were formed in both the InSe and GaSe layers. Twinning and stacking disorder was often detected in these materials due to their layered structure. Moreover, in samples with a thin GaSe layer, strong interdiffusion of indium into the GaSe layer was detected that resulted in the formation of an InxGaySe phase. The dominant threading defects present in these InSe/GaSe heterostructures were screw dislocations, which may act as nonradiative recombination centers.
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