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An approach to fabricating X-band power FETs by direct implantation into MBE-grown GaAs/Si incorporating low-temperature buffer layers is described. Devices fabricated on GaAs-on-Si wafers were compared directly to GaAs ion-implanted FET wafers that were processed in the same lot. The MBE low-temperature buffer layer was adapted to GaAs-on-Si to provide a high-resistivity layer to prevent Si out-diffusion from the Si substrate and to reduce strain in the GaAs layer. Excellent DC and RF device performance was obtained from both the GaAs/Si wafers and the GaAs/GaAs wafers. The wafers were put through a standard 0.5- mu m power FET production process. The sheet resistivity, the transconductance, the I/sub dss/ channel current, and the pinch-off voltages of the GaAs/Si devices were comparable to those of the GaAs/GaAs wafers. On-wafer DC and RF testing and mapping were performed to correlate material characteristics with device RF performance. The functional RF yield from on-wafer RF probing tests was very high for both GaAs/Si and GaAs/GaAs wafers, varying between 68 and 90% for GaAs/Si wafers and 94 and 97% for GaAs/GaAs wafers. Although the DC characteristics of the GaAs/Si wafers were comparable to those of the GaAs wafers, the RF characteristics were slightly worse, showing 2 dB less maximum available gain than the GAs/GaAs wafers. > |
