Doping of epitaxial layers and heterostructures based on HgCdTe
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Doping of Epitaxial Layers and Heterostructures Based on HgCdTe K. D. Mynbaev^ and V. I. Ivanov-Omskiœ Ioffe Physicotechnical Institute, Russian Academy of Sciences, Politekhnicheskaya ul. 26, St. Petersburg, 194021 Russia ^e-mail: [email protected] Submitted April 27, 2005; accepted for publication April 28, 2005
Abstract—Available publications concerned with doping of epitaxial layers of HgCdTe alloys and heterostructures based on these alloys are reviewed. The main changes in technology of HgCdTe doping, which occurred when device structures fabricated on the basis of bulk material were replaced by those based on epitaxial layers are analyzed. The specific features of the doping of HgCdTe epitaxial layers in the course of the growth of these layers by the liquid-phase epitaxy, metal–organic chemical vapor deposition, and molecular-beam epitaxy are considered. The electrical properties of the doped material are analyzed. The current concepts of the intrinsic defects in HgCdTe and the effect of these defects on the properties of HgCdTe are briefly considered. PACS numbers: 61.72.Ss, 61.72.Yx, 66.30.Tt, 66.30.Lw, 68.55.Ln DOI: 10.1134/S1063782606010015
1. INTRODUCTION
being used instead of those based on the bulk material. This technological change required the revision of the approaches to doping, taking into account the modern method developments of growth such as molecularbeam epitaxy (MBE) and postgrowth treatment. The methods for doping and the concepts of controlling the electrical and physical properties of the thin epitaxial layers differ from those used previously in relation to the bulk material. For example, in the first stage, the transition to epitaxial layers significantly limited the temperature range within which the doping occurred; this limitation was related to the diffusion of components and impurities from the substrate into the layer. As a result, MCT epitaxial layers and, especially, multiple-layer structures had to be doped at temperatures no higher than 500°C. Simultaneously, the use of impurities with large diffusion coefficients (first of all, the Group-I elements, such as Cu, Ag, and Au) was partially abandoned. These trends were mentioned in a previous review concerned with doping of MCT, published in 1996 [5]. Later on, the Group-V elements (As, N) were used almost exclusively to dope the epitaxial layers with acceptor impurities because, the epitaxial layers became increasingly thinner and, accordingly, the requirements imposed on the diffusion coefficients even at relatively low (180–200°C) MBE temperatures became more and more stringent. Since the above impurities are amphoteric in the MCT epitaxial layers grown under the conditions corresponding to the Te corner of the phase diagram, special methods for activating these impurities had to be developed; these methods will be considered in detail in what follows. A similar tendency was observed in the development of donor doping of the MCT epitaxial layers grown using
Technology of the HgCdTe (MCT) alloy, which is one of the m
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