GROWTH OF GAAS CRYSTALS BY TEM FOR MICROWAVE DEVICE APPLICATIONS

LARGE GAAS CRYSTALS WITH UNIFORM PROPERTIES AND LOW DEFECT DENSITIES ARE REQUIRED FOR MICROWAVE DEVICES FABRICATED FOR MILITARY SYSTEMS. THE VARIABLE QUALITY OF THE AVAILABLE GAAS, WAFER-TO-WAFER, INTRA WAFER, BOULE-TO-BOULE, AND INTRA BOULE IS UNSATISFACTORY FOR HIGHYIELD DEVICE PROCESSING. WHILE THE ELECTRONIC PROPERTIES OF LEC GAAS CRYSTALS ARE SATISFACTORY, THESE WAFERS SHOW VERY HIGH DEFECT DENSITY. INDIUM-DOPED GAAS CRYSTALS SHOW LOW DEFECT DENSITY BUT EXHIBIT GROWTH STRIATIONS. THESE WAFERS ARE NOT SUITABLE FOR MICROWAVE DEVICES. THE HEAT EXCHANGER METHOD (HEMTM) HAS BEEN ADAPTED FOR THE GROWTH OF 2" DIAMETER AND 3" DIAMETER GAAS CRYSTALS. IT HAS BEEN DEMONSTRATED THAT UNDOPED (100) SEMI-INSULATING GAAS CRYSTALS CAN BE GROWN BY HEM WITH REMARKABLE UNIFORM ELECTRONIC PROPERTIES. IT HAS ALSO BEEN DEMONSTRATED THAT UPDOPED DISLOCATIONFREE GAAS CRYSTALS CAN BE GROWN BY HEM. AT THE PRESENT TIME, LINEAGE AND TWINNING ARE OBSERVED IN THE STRUCTURE OF 3" DIAMETER BOULES. THE LINEAGE IS ASSOCIATED WITH INCOMPLETE SEEDING AT THE OUTER EDGE OF THE SEED. THE PRESENT PROPOSAL IS TO OPTIMIZE SEEDING PARAMETERS WITH HEM TO ACHEIVE COMPLETE AND REPRODUCABLE SEEDING. THE PRODUCTION OF UNDOPED SEMI-INSULATING 3" DIAMETER (100) GAAS BOULES WITH UNIFORM CARRIER CONCENTRATION, EL2, AND MOBILITY ACROSS THE WAFER WILL BE RETAINED.