Preparation of gallium arsenide materials
Like silicon, GaAs materials can also be divided into bulk single crystal and epitaxial materials. Bulk single crystal can be used as epitaxial substrate material, or ion implantation doping process can be used to directly manufacture integrated circuits (using high-quality, large cross-section, semi insulated gallium arsenide single crystal). The emphasis is on the liquid sealed Czochralski method (i.e. liquid sealed johrasky method, LEC Method for short), but the horizontal boat growth method (i.e. horizontal Bridgman method) still receives some attention because of the good quality and uniformity of single crystals.In addition, the method of using quartz crucible and aqueous boron oxide as liquid sealing agent at atmospheric pressure has also been tested successfully. Regardless of the horizontal boat growth method or the liquid sealed Czochralski method, the crystal diameter can reach 100 ~ 150 mm, which is similar to that of silicon single crystal.
The epitaxial growth of GaAs can be divided into gas phase epitaxy and liquid phase epitaxy. The obtained epitaxial layer is superior to bulk single crystal materials in purity and crystal integrity. The general vapor phase epitaxy process is GA / ascl3 / H2 method, and the alternative processes of this method are GA / HCl / AsH3 / H2 and GA / ascl3 / N2 method. In order to improve the quality of gas phase epitaxial layer in GA / ascl3 / H2 system, epitaxial growth processes at low temperature and low pressure were also studied. The liquid phase epitaxy process is to cover the substrate surface with GA / GaAs molten pool, and then grow the epitaxial layer by cooling. It can also adopt the temperature gradient growth method or the electric epitaxy method with DC applied. Vapor phase epitaxy is more widely used than liquid phase epitaxy in the manufacture of devices, especially microwave devices. Liquid phase epitaxy can be used to manufacture heterojunctions (such as GaAs / alxga1 XAS), so it is an important means to manufacture GaAs double heterojunction lasers and solar cells.