Epitaxy Of GaAs on Si: MBE and OMCVD
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EPITAXY OF GaAs on Si: MBE AND OMCVD Jhang W. Lee,
Jack P.
KOPIN Corporation,
Salerno,
Ron P.
Gale,
695 Myles Standish Blvd.,
and John C.C. Taunton,
HA
Fan 02780
ABSTRACT Growth technique dependent factors are compared for molecular beam epitaxy (MBE) and organometallic chemical vapor deposition (OMCVD) that are related to the GaAs on Si epitaxy. The comparison, both for growth processes and as-grown material characteristics, indicates that material qualities of these layers provided by the two growth techniques are comparable in many aspects, but differ in morphological texture, residual stress, and occasionally Schottky barrier height. These issues are discussed further with our recent OMCVD results in order to ensure the OMCVD advantages for GaAs on Si wafer engineering, which are referred as an easy scale-up and a large throughput. INTRODUCTION Historically, the first GaAs epitaxy on Si was demonstrated by vapor phase epitaxy (VPE) in 1981 with a Ge-coated Si substrate [1]. However, this VPE work was discontinued because it was not suitable for direct GaAs growth on Si or for growth of AIGaAs heterostructures. VPE was followed by MBE [2,3] and OMCVD [4]. In the last few years, many discrete GaAs devices have been demonstrated using the GaAs on Si materials grown by either MBE or OMCVD. Monolithic integration of Si MOSFET and GaAs LEDs [5], and large scale integration of GaAs devices such as ring oscillators [6] and 1 Kbit static RAM (SRAM) chips [7] have been achieved successfully up to this time. Optoelectronic devices, including laser diodes [8], have also been demonstrated. At the present, both MBE and OMCVD have grown reasonably good quality GaAs on Si device structures. The overall material properties appear to be similar to each other. However, MBE has achieved better surface morphology and lower background doping level in GaAs layers grown on Si than OMCVD has. These factors may partially explain why MBE grown GaAs on Si wafers have been more successful in GaAs IC fabrication, such as 1 K SRAM, and other electronic devices. since OMCVD is considered to be a more viable technique to bring this technology into practical applications, it is important to identify an OMCVD process for GaAs on Si epitaxy yielding material quality comparable to MBE. This paper compares the two growth techniques as related to the growth of GaAs on Si wafers. The differences and similarities of the two growth processes from the substrate preparation step to final material characteristics are described. Also critical issues related in material characterization are addressed. SUBSTRATE CLEANING Substrate cleaning was a common problem in both MBE and OMCVD processes in the early period of GaAs on Si epitaxy works. A difficulty in the cleaning procedure was to protect the chemically cleaned Si surface from natural oxidation until actual growth was initiated. Several different chemical cleaning procedures have been developed to avoid this problem. These procedures start with a conventional Si wafer cleaning step which consis
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