Strained CdZnTe/CdTe Superlattices As Threading Dislocation Filters in Lattice Mismatched MBE Growth of CdTe on GaSb
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https://doi.org/10.1007/s11664-020-08406-1 Ó 2020 The Minerals, Metals & Materials Society
TOPICAL COLLECTION: U.S. WORKSHOP ON PHYSICS AND CHEMISTRY OF II-VI MATERIALS 2019
Strained CdZnTe/CdTe Superlattices As Threading Dislocation Filters in Lattice Mismatched MBE Growth of CdTe on GaSb W.W. PAN,1 R.J. GU,1 Z.K. ZHANG,1 J.L. LIU,1 W. LEI,1,2 and L. FARAONE1 1.—Department of Electrical, Electronic and Computer Engineering, The University of Western Australia, Perth, WA 6009, Australia. 2.—e-mail: [email protected]
In this work, multiple sets of CdZnTe/CdTe strained-layer superlattices have been used as dislocation filtering layers for reducing the threading dislocations and improving the material quality of CdTe buffer layers grown by molecular beam epitaxy (MBE) on GaSb (211)B substrates. By incorporating a CdZnTe/CdTe superlattice filtering structure, a significant improvement in material quality has been achieved, with a low etch pit density of 1 9 105 cm2 demonstrated for CdTe grown on GaSb, which is two orders of magnitude lower than previously reported values for CdTe grown directly on lattice mismatched substrates, and is comparable to values for state-of-the-art CdTe grown on lattice matched CdZnTe substrates. The filtering efficiency for each set of dislocation filtering layers has been determined to be approximately 70%. This approach provides a promising pathway towards achieving hetero-epitaxy of high quality HgCdTe on large-area lattice-mismatched alternative substrates with a low dislocation density for the fabrication of next generation infrared detectors with features of lower cost and larger array format size. Key words: CdTe, CdZnTe, GaSb substrates, dislocation filters, etch pit density
INTRODUCTION Recently, considerable attention has been devoted to the epitaxial growth of CdTe layers on alternative substrates such as Si,1,2 Ge,3,4 and GaAs,5 to act as buffer layers for the subsequent growth of HgCdTe infrared materials and detector device structures. These studies on lattice mismatched hetero-epitaxial growth have been motivated by the potential for growing high quality HgCdTe infrared materials on large-area, cost-effective substrates for next generation HgCdTe infrared detectors and focal plane arrays (FPAs) with features of lower cost and larger array format size,6,7 in comparison to current stateof-the-art HgCdTe infrared detectors grown on lattice matched CdZnTe substrates that are higher
(Received December 28, 2019; accepted August 11, 2020)
cost, lower crystal quality and smaller wafer size.8 Although such an approach is attractive and presents great potential, the large lattice mismatch between (Hg)CdTe and these alternative substrates (19%, 14.3%, 14.4% and 6.1% lattice mismatch for Si, Ge, GaAs, and GaSb, respectively) inevitably generates misfit dislocations in the vicinity of the CdTe/substrate interface that form threading dislocations (TD) that propagate into the CdTe and subsequently grown HgCdTe epitaxial layers.9,10 These defects will degrade the optical and electr
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