Low Temperature Photoluminescence Study of Doped CdTe and CdMnte Films Grown by Photoassisted Molecular Beam Epitaxy
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LOW TEMPERATURE PHOTOLUMINESCENCE STUDY OF DOPED CdTe AND CdMnTe FILMS GROWN BY PHOTOASSISTED MOLECULAR BEAM EPITAXY N. C. GILES, R. N. BICKNELL, AND J. F. SCHETZINA Department of Physics, North Carolina State University, Raleigh, North Carolina, 27695-8202 ABSTRACT N-type and p-type (100) CdTe films have been grown on (100) CdTe substrates by photoassisted molecular beam epitaxy, using indium and antimony as n-type and p-type dopants, respectively. The application of this growth technique to substitutionally dope another II-VI material is demonstrated by the successful n-type doping of (100) CdMnTe films with indium. Modulationdoped superlattices consisting of barrier layers of CdMnTe:In alternating with CdTe have also been grown. The point defect nature of these in situ doped films and multilayers is studied with low temperature (1.6-5 K) photoluminescence and excitation photoluminescence measurements. The introduction of the dopant atoms using this new growth technique produces immediate changes in the photoluminescence spectra of the epilayers. Photoluminescence studies of the superlattices show the effects of quantum well confinement and band filling due to free carriers. INTRODUCTION One of the principal problems that has hindered the use of II-VI compounds in device applications has been the tendency for these materials to self-compensate. As a consequence, the intentional introduction of either n-type or p-type dopants usually results in low activation of the impurity, yielding high resistivity as-grown material. The recent development of a thin film growth technique, compatible with molecular beam epitaxy (MBE), in which control of the electrical properties of layers of both conductivity types is demonstrated has been reported 11,21. This new doping technique which was developed at North Carolina State University, photoassisted MBE, allows introduction of selected dopant species during the actual film growth. This procedure differs from conventional MBE in that the substrate is illuminated during the growth of the epilayers. We find that this process produces immediate changes in both the electrical and optical properties of the as-grown films. In fact, only those films grown under illumination are conducting. A description of the growth details, and structural and electrical properties of the doped CdTe and CdMnTe films can be found in the literature [3,4]. In this paper, we report the results of a low temperature (1.6-5 K) photoluminescence (PL) study of the as-grown, electrically active, in situ doped CdTe and CdMnTe epilayers, and n-type CdMnTe-CdTe modulation-doped superlattices (SLs). Indium and antimony were used as dopant atoms for the n-type and p-type layers, respectively. The characteristic low temperature PL spectra normally associated with as-grown CdTe containing these dopants, which is often high resistivity, is dominated by defect band emission (1.4-1.45 eV). In contrast, the PL spectra from conducting epilayers grown by photoassisted MBE are dominated by shaop, near-edge radiative transiti
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