Preparation process of gallium arsenide material
Since the 1950s, a variety of gallium arsenide single crystal growth methods have been developed. Current mainstream industrial growth processes include liquid-sealed straight-drawing (LEC), horizontal Brijman method (HB), vertical Brijman method (VB), and vertical gradient solidification (VGF).
1. Liquid Sealed Czochralski (LEC)
The LEC method is the main process for growing non-doped semi-insulating gallium arsenide single crystal (SI GaAs). Currently, more than 80% of semi-insulating gallium arsenide single crystals on the market are grown by the LEC method. The LEC method uses a graphite heater and a PBN crucible, and uses B2O3 as a liquid sealing agent to carry out gallium arsenide crystal growth in an argon atmosphere of 2 MPa. The main advantage of the LEC process is that it has high reliability and is easy to grow long-diameter single crystals. The crystal carbon content is controllable and the semi-insulating properties of the crystals are good. The main disadvantages are: the chemical dose is difficult to control, the temperature gradient of the thermal field is large (100~150 K/cm), and the dislocation density of the crystal is up and uneven. Japan's Hitachi Cable Co., Ltd. first established a 6-inch LEC GaAs single crystal production line in 1998. The company installed the world's largest GaAs single crystal furnace at that time, with a diameter of 400mm, a feeding capacity of 50 kg, and a 6-inch single growth. The crystal length reaches 350 mm. In 2000, Freiberger reported the 8-inch gallium arsenide single crystal developed by the world's first LEC process.
2. Horizontal Bridgman (HB)
The HB method was once the main process for mass production of semiconductor (low-resistance) gallium arsenide single crystal (SC GaAs), using quartz boats and quartz tubes to grow under normal pressure, with high reliability and stability. The advantage of the HB method is that the arsenic vapor can be used to precisely control the stoichiometric ratio of the body, and the temperature gradient is small to achieve the purpose of reducing dislocations. The dislocation density of HB gallium arsenide single crystal is more than an order of magnitude lower than that of LEC gallium arsenide single crystal. The main disadvantage is that males grow non-doped semi-insulating gallium arsenide single crystals, and the crystal interface grown is D surname, which will cause a large material waste in the process of processing into wafers. At the same time, it is difficult to grow large diameter crystals due to the load-bearing capacity of quartz boats at high temperatures. At present, the mass production of the HB process is mainly in the case of 2 inch and 3 inch crystals, and the reported maximum gallium arsenide of the gallium arsenide is 4 inches. At present, there are not many companies that use the HB process for the production of gallium arsenide materials. With the maturity of the VB and VGF processes, the HB process has been gradually replaced.
3. Vertical Bridgman (VB)
The VB method is a crystal growth process that was developed in the late 1980s. The synthesized gallium arsenide polycrystal, B2O3 and seed crystals were packed into PBN crucible and sealed in a vacuumed quartz bottle. The furnace body was placed vertically. The wire is heated by a resistance wire, and the quartz bottle is vertically placed in the middle of the furnace body. At a high temperature, the gallium arsenide polycrystal is melted and then fused with the seed crystal, and then the quartz cylinder and the crucible are moved downward by the support rod through a maneuvering mechanism. Under a certain temperature gradient, the single crystal grows slowly from the seed crystal end. The VB method can grow a low-resistance gallium arsenide single crystal or a high-resistance semi-insulating gallium arsenide single crystal. The average EPD of the crystal is below 5,000/cm-2.
4. Vertical Gradient Solidification (Vertical Gradient Freeze, referred to as VGF)
The principle and application field of the VGF process and the VB process are basically similar. The biggest difference is that the VGF method cancels the crystal falling carriage mechanism and the rotating mechanism. The computer precisely controls the thermal field to slowly cool down, and the growth interface moves upward from the lower end of the melt to complete the crystal growth. This process makes the crystal growth interface more stable due to the elimination of the mechanical transmission mechanism, and is suitable for growing ultra-low dislocation GaAs single crystal. The disadvantage of the VB and VGF processes is that the crystal growth cannot be observed and judged during the crystal growth process, and the crystal growth period is long. At present, the international commercial level has been able to mass produce 6-inch VB/VGF gallium arsenide crystals. In 2002, Freiberger reported the world's first 8-inch gallium arsenide single crystal developed by VGF process.