The dc, small-signal, and microwave power output characteristics of AlGaN/GaN HEMTs are presented. A maximum drain current greater than 1 A/mm and a gate-drain breakdown voltage over 80V have been attained. For a 0.4 m gate length, an of 30 GHz and an max of 70 GHz have been demonstrated. Trapping effects, attributed to surface and buffer layers, and their relationship to microwave power performance are discussed. It is demonstrated that gate lag is related to surface trapping and drain current collapse is associated with the properties of the GaN buffer layer. Through a reduction of these trapping effects, a CW power density of 3.3 W/mm and a pulsed power density of 6.7 W/mm have been achieved at 3.8 GHz.

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The effect of ion-implantation-induced damage on the resistivity of n-type GaN has been investigated. H, He, and N ions were studied. The resistivity as a function of temperature, implant concentration, and post-implant annealing temperature has been examined. Helium implantation produced material with an as-implanted resistivity of 1010 Ω-cm. He-implanted material remained highly resistive after an 800 °C furnace anneal. The damage associated with H implantation had a significant anneal stage at 250 °C and the details of the as-implanted resistivity were sample dependent. N implants had to be annealed at 400 °C to optimize the resulting resistivity but were then thermally stable to over 800 °C. The 300 °C resistivity of thermally stabilized He- and N- implanted layers was 104 Ω-cm, whereas for H-implanted layers the 300 °C resistivity was less than 10 Ω-cm.

The design, fabrication, and characterization of 0.1 m AlSb/InAs HEMT's are reported. These devices have an In 0:4 Al 0:6 As/AlSb composite barrier above the InAs channel and a p + + + GaSb layer within the AlSb buffer layer. The HEMT's exhibit a transconductance of 600 mS/mm and an f f f T T T of 120 GHz at V V V DS DS DS = 0:6 V. An intrinsic f f f T T T of 160 GHz is obtained after the gate bonding pad capacitance is removed from an equivalent circuit. The present HEMT's have a noise figure of 1 dB with 14 dB associated gain at 4 GHz and V V V DS DS DS = 0:4 V. Noise equivalent circuit simulation indicates that this noise figure is primarily limited by gate leakage current and that a noise figure of 0.3 dB at 4 GHz is achievable with expected technological improvements. HEMT's with a 0.5 m gate length on the same wafer exhibit a transconductance of 1 S/mm and an intrinsic fT Lg fT Lg fT Lg product of 50 GHz-m.Index Terms-InAs, MODFET's, quantum wells, semiconductor device fabrication, semiconductor device noise. There he worked on a wide range of projects dealing with electronic materials modification and device fabrication and testing. In particular, he pioneered the use of ion implantation for III-V microwave device development. In 1981, he was made head of the Ion Implantation and Devices Section and in 1992, he became head of the High Frequency Devices and Materials Section. His research efforts have included MeV implantation for novel analog microwave devices, III-V MBE for microwave and millimeter-wave devices, quantum transport for electronic functions, wide band-gap materials and devices for high-temperature and high-power microwave devices, III-V MBE material for optical correlators, and a variety of related topics. He has co-authored more than 85 papers and holds eight patents. He has been extensively involved in the Navy's contractual efforts for electronic device research. Dr. Dietrich represented the Navy as a member of the tri-service team that supported DARPA in both the MIMIC and MAFET programs.