We report on room temperature terahertz generation by a submicron size AlGaN/GaN-based high electron mobility transistors. The emission peak is found to be tunable by the gate voltage between 0.75 and 2.1 THz. Radiation frequencies correspond to the lowest fundamental plasma mode in the gated region of the transistor channel. Emission appears at a certain drain bias in a thresholdlike manner. Observed emission is interpreted as a result of Dyakonov–Shur plasma wave instability in the gated two-dimensional electron gas.

The high temperature stability of AlGaN/GaN and lattice-matched InAlN/GaN heterostructure FETs has been evaluated by a stepped temperature test routine under large-signal operation. While AlGaN/GaN high-electron mobility transistors (HEMTs) have failed in an operating temperature range of 500°C, InAlN/GaN HEMTs have been operated up to 900°C for 50 h (in vacuum). Failure is thought to be still contact metallization stability related, indicating an extremely robust InAlN/GaN heterostructure configuration.

Current dispersion effects have been experimentally investigated in a variety of AlGaN/GaN heterostructure FETs with large signal and switching measurements including HEMTs with doped and undoped barrier layer. A range of dispersion frequencies from 10/sup -3/ Hz to 10 GHz were observed, where the output current amplitude is drastically reduced. Through this effect the full channel charge of an AlGaN/GaN heterostructure FET may be completely depleted under specific bias conditions. This indicates that this phenomena cannot be related to deep traps alone, but is also connected to piezorelated charge states and conduction to these states.

The performance of novel AlInN/GaN HEMTs for high power / high temperature applications is discussed. With 0.25 mum gate length the highest maximum output current density of more than 2 A/mm at room temperature and more than 3 A/mm at 77 K have been obtained even with sapphire substrates. Cut-off frequencies were f_T = 50 GHz and f_MAX = 60 GHz for 0.15 mum gate length without T-gate. Pulsed measurements reveal a less unstable surface than in the case of AlGaN/GaN structures. Although limited by buffer layer leakage, with field plates a maximum drain bias of 100 V has been reached with these devices. The high chemical stability of this unstrained heterostructure and its surface has been demonstrated with successful operation at 1000 degC in vacuum

Microwave frequency capabilities of AlGaN/GaN high electron mobility transistors (HEMTs) on high resistive silicon (111) substrate for power applications are demonstrated in this letter. A maximum dc current density of 1 A/mm and an extrinsic current gain cutoff frequency (F/sub T/) of 50 GHz are achieved for a 0.25 /spl mu/m gate length device. Pulsed and large signal measurements show the good quality of the epilayer and the device processing. The trapping phenomena are minimized and consequently an output power density of 5.1 W/mm is reached at 18 GHz on a 2/spl times/50/spl times/0.25 /spl mu/m/sup 2/ HEMT with a power gain of 9.1dB.

High-frequency high-electron-mobility transistors (HEMTs) were fabricated on AlInN/AlN/GaN heterostructures grown by low-pressure metal-organic chemical vapor deposition on a SiC substrate. The results presented in this letter confirm the high performance that is reachable by AlInN-based technology with an output power of 10.3 W/mm and a power-added efficiency of 51% at 10 GHz with a gate length of 0.25 ¿m. A good extrinsic transconductance value that is greater than 450 mS/mm and exceeding AlGaN/GaN HEMT results was also measured on these transistors. To our knowledge, these results are the best power results published on AlInN/GaN HEMTs. These good results were attributed to optimized heterostructure properties associated with low-resistance ohmic contacts and an effective passivation layer minimizing drain current slump in high-frequency operations.