Direct Heteroepitaxial Growth of ZnTe(100) and CdZnTe(100)/ZnTe(100) on Si(100) Substrates by MBE
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DIRECT HETEROEPITAXIAL GROWTH OF ZnTe(100) AND CdZnTe(100)/ZnTe(100) ON Si(100) SUBSTRATES BY MBE T. J. de LYON*, S. M. JOHNSON**, C. A. COCKRUM**, 0. K. WU*, AND J. A. ROTH* *Hughes Research Labs, 3011 Malibu Canyon Rd., Malibu, California 90265 **Santa Barbara Research Center, 75 Coromar Drive, Goleta, California 93117
ABSTRACT Epitaxial films of ZnTe(100) and CdZnTe(100)/ZnTe(l00) have been deposited by molecular-beam epitaxy onto Si(100) substrates misoriented from 0-8 degrees towards the [011] direction. The films were characterized with x ray diffraction, photoluminescence spectroscopy, optical microscopy, and stylus profilometry. Through use of ZnTe buffer layers, single crystal CdZnTe(100) films have been demonstrated on both 40 and 8* misoriented Si with structural quality comparable to that obtained with GaAs/Si composite substrates. X ray rocking curves for ZnTe(400) with FWHM less than 300 arcseconds and for CdZnTe(400) with FWHM less than 160 arcseconds have been obtained for as-grown films. The observed surface morphologies are superior to those obtained on GaAs/Si composite substrates. HgCdTe(100) films with x ray FWHM as low as 55 arcseconds and average etch pit densities of 5 x 106 cm"2 have been deposited by liquid phase epitaxy on these MBE CdZnTe/ZnTe/Si substrates.
INTRODUCTION Bulk, single-crystal CdZnTe substrates are currently utilized for the epitaxial growth 1 of HgCdTe infrared detector structures that are used in second-generation infrared focal-plane arrays (IRFPA's) designed for thermal imaging applications. Although the technology for producing high-quality CdZnTe substrates has greatly improved in recent years, 2 a fundamental problem with use of CdZnTe substrates for large area arrays remains due to the hybrid structure of the completed IRFPA in which the array is indium bump-bonded to a Si readout electronics chip. Thermal expansion mismatch between the Si readout chip and the IRFPA's CdZnTe substrate results in considerable strain localized in the indium bumps upon cooling from room temperature to the IRFPA's operating temperature (40-180K). It will be essential to provide a means of matching the detector array thermal expansion to that of Si if acceptable long-term thermal cycle reliability is to be achieved in large-area HgCdTe IRFPA's hybridized to Si readout chips. For this reason, there is considerable current interest in replacing bulk CdZnTe substrates with Si-based alternative substrates, which offer the additional advantages of larger available size, lower cost, and superior mechanical strength. The ultimate technical challenge with this approach is to grow low dislocation density HgCdTe detector structures on these Si-based alternative substrates, and therefore growth of CdZnTe buffer layers on Si-based substrates has been pursued as a first step. Most prior efforts to develop Si-based starting substrates for LPE or vaporphase HgCdTe growth have focused on CdZnTe(100) growth on composite GaAs/Si substrates by congruent evaporation, 3 MOCVD, 4 MBE, 5 or hot-wall epitaxy
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