279 EPITAXIAL FILMS OF GERMANIUM BY MOCVD ALTAF H. KHAN AND JORGE J. SANTIAGO Center for Sensor Technologies, The Moore School of Electrical Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6390 ABSTRACT A simple and easily expandable atmospheric pressure MOCVD (metal organic chemical vapor deposition) reactor for the growth of germanium films is proposed and implemented. It employs a resistively heated horizontal quartz reaction chamber. The organometallic compound tetramethylgermanium (TMGe) is used as the germanium source, and hydrogen as the carrier gas. Using this reactor, epitaxial films of germanium on < 111> germanium substrates were grown at 550-650'C. The growth rate was found to increase with temperature. The single crystallinity of these films was evaluated by x-ray rocking curves, and the interface strain between the film and substrate was found to be less than 1%. These Ge/Ge samples have the same morphology as the bare substrate and their sheet resistance is 30% higher than the bare substrate value. INTRODUCTION Infrared sensors are a necessary part of the lightwave networks, and germanium avalanche photo-detectors (APD), because of their low cost, occupy a major portion of the infrared (1.0 - 1.7 gim) sensors market. The technique of metal organic chemical vapor deposition (MOCVD) has been used for the deposition of epitaxial, polycrystalline, and amorphous films. The major thrust of this method has been in the deposition of II-VI, III-V, and IV-VI compounds. [1-5]. This technology lends itself perfectly as a very efficient means of producing thin epitaxial films of intrinsic and doped germanium, which in turn can be used to fabricate APDs. The same technique can also be applied for the fabrication of high electron mobility transistors (HEMT), Ge-Si alloys for more tailored band-gap detectors and other heterostructure devices [6] such as Si/Ge/GaAs devices [7]. A schematic diagram of our MOCVD reactor in the operational state is shown in Fig. 1. The hydrogen handling tubing is made of 0.25" low carbon 316L stainless steel. The inside of this tubing is microcleaned to avoid any chemical deposits. VCR fittings are used for all stainless steel- to-stainless steel joints. All of the welding was done in an inert (argon) atmosphere. Hydrogen and nitrogen are fed to the system through 2-jim particulate filters. For spark-free operation, air FLOW CONTROL VALVE H2REACTOR EXHAUST 2 REFRIGERATOR CONTROLLE N 2 Fig. 1. Schematic diagram of the MOCVD reactor. Mat. Res. Soc. Symp. Proc. Vol. 102. ' 1988 Materials Research Society