Growth and Characterization of UHV/CVD Si/SiGe Strained-Layer Superlattices on Bulk Crystal SiGe Substrates
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Growth and characterization of UHV/CVD Si/SiGe strained-layer superlattices on bulk crystal SiGe substrates S.R. Sheng 1, M. Dion 2, S.P. McAlister 1, and N.L. Rowell 3 1 Device Physics, Institute for Microstructural Sciences, National Research Council of Canada, Ottawa, ON K1A 0R6, Canada; 2 SiGe Semiconductor, 2680 Queensview Drive, Ottawa, ON K2B 8J9, Canada; 3 Institute for National Measurement Standards, National Research Council of Canada, Ottawa, ON K1A 0R6, Canada ABSTRACT High-quality short-period Si/SiGe strained-layer superlattices have been grown on bulk singlecrystal SiGe substrates using a commercial low-temperature ultrahigh vacuum chemical vapor deposition (UHV/CVD) reactor. These superlattices were characterized by high-resolution x-ray diffraction (HRXRD), Auger electron spectroscopy (AES), atomic force microscopy (AFM), crosssectional transmission electron microscopy (XTEM) and photoluminescence (PL). HRXRD, AES, and XTEM results confirm that the materials deposited are high crystal-quality superlattice layers with abrupt interfaces and excellent thickness and composition uniformity across superlattices of 5 periods. AFM images show similar surface RMS roughness of much less than 1 nm for both the top layer surface and the starting substrate surface, indicating very smooth surfaces. PL measurements further confirm material quality and composition, and show sharp, well-resolved near band-edge BE and FE PL and strong broad sub-gap PL perhaps related to direct-gap superlattice transitions. The materials grown here are very promising for applications of both high-speed electronic devices and high-efficiency optoelectronic devices. INTRODUCTION Over the past several years, SiGe technology has demonstrated an impressive potential for the development of advanced Si-based electronic and optical devices, and thermoelectric generators incorporating Ge. In particular, SiGe heterostructure technology is beginning to rival that of III-V semiconductors in a number of electronic applications [1]. The scope for SiGe devices will be broadened if high quality, low-defect-density substrates, with an adjustable lattice parameter and band gap between Si and Ge, could be implemented. Such substrates provide a unique possibility for band engineering to tailor band offsets or band gaps [2,3] and for strain adjustment of strainedlayer superlattices [4] which suggest high potential for integrated optoelectronics on Si. These substrates are also useful for the growth of thick lattice-matched and strained SiGe epilayers and heterostructures because of the reduced lattice mismatch [5]. Thick layers are important to optical devices such as detectors and solar cells with deep active regions required to optimize device quantum efficiency. Moreover, they can be a suitable substrate material for lattice-matched heteroepitaxy with III-V semiconductors [3]. Currently, such matching is obtained with so-called “virtual SiGe substrates” formed by overgrowing a very thick relaxed SiGe layer on a Si wafer. However, SiGe virtual substrate
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