Wet oxidation kinetics of AlAs at elevated temperatures
- PDF / 149,447 Bytes
- 4 Pages / 612 x 792 pts (letter) Page_size
- 87 Downloads / 182 Views
Wet oxidation kinetics of AlAs at elevated temperatures Sun-Chien Ko and Sanboh Lee Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan, Republic of China
Hai-Lin Wang Advanced Technology Research Laboratory, Telecommunication Laboratories, Chunghwa Telecom Company, Taoyuan, Taiwan, Republic of China
Y.T. Chou Department of Chemical Engineering and Materials Science, University of California, Irvine, California 92697 (Received 21 November 2002; accepted 6 February 2003)
Wet oxidation in the AlAs layer sandwiched between two GaAs plates was investigated for the temperature range of 400 to 480 °C. The oxidation rate increased with increasing thickness of the AlAs layer. Theoretical analysis based on the boundary layer diffusion was performed to account for the thickness effect. The theory is in excellent agreement with the experimental measurement.
The thermal oxidation of AlAs in water vapor forms a stable low refraction oxide suitable for the current and optical confinement in laser structures.1–3 The AlAs/ GaAs structure with lateral oxidation layers is used in vertical cavity surface emitting lasers (VCSELs) as a Bragg reflector, which would lower the threshold current and promote quantum efficiency.4–7 Nickel8 found that the oxide depth in AlxGa1−xAs layer was linear with oxidation time for an excessive supply of water vapor, and the activation energy of wet oxidation increased with decreasing Al content. Ochiai et al.9 observed that the oxide growth in AlAs layers was reaction controlled for short times at low temperatures and diffusion controlled for longer times at high temperatures. These authors suggested that the temporal dependence of the oxide depth xd in AlAs is given by the phenomenon equation as x2d xd + =t , kd kr
(1)
where kd and kr are the rate parameters. Eq. (1) reduces to a linear oxide growth (or reaction controlled; kd ⳱ 0) at the short times and thin oxide layers, and to a parabolic growth (or diffusion controlled; kr ⳱ 0) at the long times and thicker oxide layers. However, like many other authors,10–12 they did not discuss the thickness dependence of kd and kp. Later, Naone and Coldren,13 using the surface energy concept, developed a quantitative model for the thickness dependence of parameter kr and found that the J. Mater. Res., Vol. 18, No. 5, May 2003
linear oxidation rate of AlAs increases with increasing thickness. Although the surface energy model effectively explains the thickness effect on wet oxidation in AlAs, it does not include the parabolic oxidation rate and the basic contribution of the diffusion flow. In the present study, this system is re-examined in detail, and a new model based on the boundary layer diffusion is proposed for the thickness effect. Samples for the wet oxidation study were grown by low-pressure metal organic chemical vapor deposition (LP-MOCVD) with the following structure: 500 Å GaAs cap/AlAs/(100) GaAs substructure. Five thicknesses— 300, 400, 500, 700, and 1000 Å—of AlAs were prepared. Before the latera
Data Loading...
