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At this time, GaAs PHEMTs exhibit higher power output than InP HEMTs at 60 and 94 GHz. InP HEMTs, however, feature power-added efficiency values that exceed GaAs PHEMTs by about 5 to 20 percentage points at 94 GHz. As a consequence, InP HEMTs remain a superior candidate for millimeter-wave power applications. The reason for the inferior output power of InP HEMTs lies in their relatively small on-state and off-state breakdown voltages. This paper reviews the state of the art of millimeter-wave power HEMT technology as well as recent advances in understanding of breakdown phenomena. It also discusses the prospects and challenges facing InP HEMTs in performance, reliability and low-cost manufacturing.

We have developed a methodology to diagnose the physical mechanisms limiting the manufacturing yield of millimeter-wave power InAlAs/InGaAs HEMTs on InP. A statistical analysis was carried out on DC figures of merit obtained from a large number of actual devices on an experimental wafer. Correlation studies and a Principal Component Analysis (PCA) of the results indicated that variations in Si delta-doping concentration introduced during MBE accounted for more than half of the manufacturing variance. Variations in the gate-source distance that is determined by the electron-beam alignment in the gate formation process were the second leading source of manufacturing variance.