GAAs High-Speed Devices: Physics, Technology, and Circuit Applications

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EPITAXIAL GROWTH PROCESSES

3.1 INTRODUCTION TO EPITAXIAL GROWTH PROCESSES

There are four main techniques by which GaAs and AlGaAs epitaxial films are grown: chloride transport vapor phase epitaxy (VPE) (Jai70], liquid phase epitaxy (LPE) [Hei80], molecular beam epitaxy (MBE) [Pan83], and metalorganic chemical vapor deposition (MOCVD) [Man81]. These epitaxial growth techniques are compared in Table 3.1 [Che87].

In the chloride transport VPE growth system, any silicon contamination is serious for it creates unfavorable thermodynamics in the compound and alloy containing Al, making it very difficult for growth to occur. The LPE technique, through it has been successfully used in compound semiconductors, is not suitable for mass production by substrate limitation. The abruptness of the interface in LPE growth is unsatisfactory for GaAs high-speed device fabrication.

MBE is considered to be the most promising future growth technique because it allows for precise thickness control, dopant control, and pattern drawing. Growth is performed under an ultra-high vacuum chamber with a low growth rate (0.1 to 10 μm/h). This permits one to accurately control the impinging atoms or molecules and thus the thickness of the film. The system has multiple sources that allow accurate stoichiometric growth. The straight-line beam impinging on the substrate also prevents collision, scattering, or diffusion during beam flight.

The MOCVD technique has demonstrated its effectiveness for growing the widest ...