SBIR-STTR Award

We propose to use the vertical-gradient-freeze method developed at American Xtal Technology (AXT) for the growth of large diameter GaAs crystals. The VGF method is chosen because the low thermal gradient employed in the growth system can produce GaAs with very low EDPS and good uniformity which are essential for opto electronic applications. AXT has extensive experience in the VGF method and has successfully developed the crystal growth technology for 2" and 3" diameter GaAs crystals with very good results. The VGF crystal growth process is controlled by a precisely controlled axisym metric furnace heater, which can be reproduced with minimum operator supervision and an excellent potential for size upscaling. In the Phase I of the program, we will modify the existing furnaces at AXT for the growth of 4" diameter GaAs crystal. A small melt volume run will be targeted at the end of Phase I program. Anticipated benefits/potential commercial applications - the industries in lasers, opto electronics, integrated opto electronic devices and large scale integrated circuits will all benefit from the large diameter GaAs wafers with low dislocations and good uniformity.Key words: large diameter GaAs, vertical-gradient-freeze.

In the Phase I program of large diameter crystal growth of GaAs using the vertical-gradient-freeze (VFG) method, we at american xtal technology (AXT) have designed and fabricated a furnace system capable of growing 4" diameter GaAs single crystals. The system includes the furnace heater, temperature control system, crystal growth crucible, ampoule, and the pressure vessel. A vgf 4" diameter single crystal, 1.25" Long was obtained, which is a first in the GaAs industry. The E.P.D. Was 1,700/cm2. The resistivity was 2.26 X 10 ohm-cm and very uniform across the whole wafer. Cost analysis shows that cost per wafer is very competitive, compared with the LEC method. In the Phase II program, we propose to grow longer (5.5 Kg.) 4" Diameter GaAs crystals, to optimize crystal growth parameters and to consistently produce chemically and electrically uniform wafers. Effort will also be put on increasing the single crystal yield by eliminating the sources of twinning, lineage and polycrystal formations. Doping experiments will be performed to provide different doping level wafers. After test marketing, we will identify resources for implementing commercial scale production of 4" VGF wafers, which is expected in the Phase III program. Anticipated benefits/potential commercial applications - the industries in lasers, optoelectronics, integrated optoelectronic devices and large scale integrated circuits will all benefit from the large diameter gaas wafers with low dislocations and good uniformity.