Wafer Fusion ofGaSb to GaAs
- PDF / 793,136 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 45 Downloads / 146 Views
G4.3.1
Wafer Fusion of GaSb to GaAs C.A. Wang, Z.L. Liau, D.A. Shiau, and P.M. Nitishin Lincoln Laboratory, Massachusetts Institute of Technology, Lexington, MA 02420-9108 ABSTRACT Atomic wafer fusion of GaSb to GaAs, and the transfer of epitaxial GaSb/GaInAsSb/GaSb heterostructures to GaAs by fusion and substrate removal are demonstrated for the first time. Wafers and epilayers were fused with or without application of mechanical pressure at temperatures as low as 350 °C. A periodic pattern of grooves etched into the GaAs wafer and an overpressure of As and Sb vapor were used to improve covalent bonding. Varying degrees of mass transport and covalent bond formation between wafers were observed in cleaved crosssections under high-resolution scanning electron microscopy. Epilayers fused without pressure application exhibited significantly better structural and optical properties compared to those fused with pressure. INTRODUCTION GaSb-based III-V semiconductors are of significant interest for high-speed, low-power electronics and mid-infrared optoelectronics. The performance and functionality of these devices could be improved if the epilayer structures were grown on a semi-insulating (SI) GaSb substrate [1-8]. However, since these substrates are not available, a variety of alternative approaches such as growth on specially designed buffer layers [1-2,7]; GaSb transfer by hydrogen implantation [3-4]; lateral epitaxial overgrowth [5]; and wafer bonding with intermediate layers [6,8] have been pursued. Atomic fusion by covalent bond formation is a promising approach for monolithic integration and has been successfully demonstrated for GaAs, InP, and GaP wafers [9-12]. These As- and P-based materials have a significant dissociation vapor pressure, and atomic fusion occurs by mass transport [9]. GaSb, however, has a relatively low melting point of 712 °C and a considerably lower vapor pressure compared to the As- and P-based alloys. Therefore, GaSb wafer fusion may be quite different and more difficult. In this paper, we report successful wafer fusion of GaSb to SI GaAs. Fusion to SI GaAs was selected since its thermal expansion coefficient α is more closely matched to GaSb than InP: α(GaSb) = 6.9 x 10-6 K-1; α(GaAs) = 5.7 x 10-6 K-1; α(InP) = 4.6 x 10-6 K-1. EXPERIMENTAL APPROACH Since the success of wafer fusion can be limited by surface roughness, defects, contamination, and wafer bow, wafer fusion was initially studied by using commercially available polished GaSb and SI GaAs wafers. The mirror-smooth GaAs wafer was first coated with pyrolytic silicon dioxide, then mechanically lapped to a thickness of less than 200 µm to aid in surface-tension pulling as discussed below. In addition, in some fusion experiments, the GaAs wafer was first patterned with a periodic pattern of grooves. The grooves, which were photolithographically defined and chemically etched, were typically 1 µm deep and 25 µm wide with periodicity of 250 µm. Both wafers were then cleaved into 1 x 1 cm pieces. To prepare for fusion, GaSb and GaAs wafe
Data Loading...
