Materials Science and Engineering B21 (1993) 307-311 307 Photoluminescence and electroluminescence processes in Si I _ xGex/Si heterostructures grown by chemical vapor deposition J. C. Sturm, X. Xiao, Q. Mi, C. W. Liu, A. St. Amour and Z. Matutinovic-Krstelj Department of Electrical Engineering, Princeton University, Princeton, NJ 08544 (USA) L. C. Lenchyshyn and M. L. W. Thewalt Simon Fraser University, Burnaby, B.C. V5A 1S6 (Canada) Abstract Well-resolved band-edge exciton photoluminescence has been observed in strained Si I xGexquantum wells on Si(100). A growth technique which provides material with a low density of non-radiative centers and a uniform microstructure is necessary for observing such luminescence. The luminescence exhibits a characteristic no-phonon line due to the alloy randomness, and a threefold splitting of the transverse optical phonon mode due to different nearest neighbor inter- actions. The luminescence has been observed from 2 to 300 K, and can also be electrically pumped (electroluminescence) to over 300 K, with peak emission from 1.3 to 1.5/~m. 1. Introduction Very-large-scale integrated circuits are made in sili- con because of the excellent manufacturability of sili- con devices and resulting low defect density over large areas. The intrinsic electrical and optical properties of silicon are rather poor, however (low mobilities, in- direct band gap, etc.). Therefore considerable effort has been focused over the last 10 years on developing a silicon-based heterojunction technology for overcom- ing these inherent limitations of silicon integrated cir- cuits, with the most effective approach being that of commensurately strained Sil_xGe x alloys on Si(100) substrates. Heterojunction bipolar transistors made in this material system at present exhibit fT values in excess of 90 GHz at room temperature [1]. Although the growth of strained Sil_xGe x on Si(100) has been actively pursued by many groups for nearly a decade, it is only within the past 3 years that well-resolved band-edge exciton luminescence has been observed in this material. In 1990, exciton photo- luminescence (PL) was reported from a fairly thick strained layer with only 4 at.% Ge (x= 0.04) [2]. In 1991, such PL was clearly observed for the first time in quantum wells (QWs) and superlattices (with x~ 0.2) [3]. These latter samples were grown not by molecular beam epitaxy, as in most of the previous Si-Ge lumin- escence work, but rather by rapid thermal chemical vapor deposition (RTCVD). This paper reviews the RTCVD growth technique and the resulting Si-Ge layer PL and electroluminescence (EL) from 2 to 300 K and then finally suggests some future directions for continuing research. 2. Rapid thermal chemical vapor deposition RTCVD is a straightforward combination of rapid thermal processing with conventional chemical vapor deposition (CVD) (Fig. 1). A single 100 mm silicon wafer is suspended on quartz pins inside a load-locked quartz reaction tube and is heated by a bank of tungsten-halogen lamps located outside the reactor chamber. The typical source gases are dichlorosilane, germane, diborane and phosphine in a hydrogen carrier, and growth temperatures vary from 500 to 1200°C. (Unless otherwise noted, all results in this paper are for Sil_xGe x grown at 625°C and Si at 700°C, at a pressure of 6 Tort.) The reactor has several unusual features which are important to the growth of high quality films. First, although the reactor is not of an "ultrahigh vacuum" type (O-ring seals are used and only a mechanical rotary vane pump is used in normal operation), through the use of the load-lock and ultrahigh purity gas handling, high quality epitaxial layers with low oxygen concentrations (10 ~s cm 3 or less) can be achieved at growth temperatures as low as 550 °C. (Oxygen contamination (concentrations levels in excess of 10 ~8 cm -3) and related defects are a common problem in silicon-based CVD at tempera- tures below 900 °C.) Second, there is no possible source of extrinsic contamination (such as metal wafer heaters 0921-5107/93/$6.00 © 1993 - Elsevier Sequoia. All rights reserved