Electrical stress experiments under different bias configurations for AlGaN/GaN high electron mobility transistors were performed and analyzed.The electric field applied was found to be the extrinsic cause for the device instability,while the traps were recognized as the main intrinsic factor.The effect of the traps on the device degradation was identified by recovery experiments and pulsed I-V measurements.The total degradation of the devices consists of two parts：recoverable degradation and unrecoverable degradation.The electric field induced traps combined with the inherent ones in the device bulk are mainly responsible for the recoverable degradation.
InGaAs high electron mobility transistors （HEMTs） on InP substrate with very good device performance have been grown by mental organic chemical vapor deposition （MOCVD）. Room temperature Hall mobilities of the 2-DEG are measured to be over 8 700 cm^2/V-s with sheet carrier densities larger than 4.6× 10^12 cm^ 2. Transistors with 1.0 μm gate length exhibits transconductance up to 842 mS/ram. Excellent depletion-mode operation, with a threshold voltage of-0.3 V and IDss of 673 mA/mm, is realized. The non-alloyed ohmic contact special resistance is as low as 1.66×10^-8 Ω/cm^2, which is so far the lowest ohmic contact special resistance. The unity current gain cut off frequency （fT） and the maximum oscillation frequency （fmax） are 42.7 and 61.3 GHz, respectively. These results are very encouraging toward manufacturing InP-based HEMT by MOCVD.
Ni/Au Schottky contacts on A1N/GaN and A1GaN/GaN heterostructures are fabricated. Based on the measured current-voltage and capacitance-voltage curves, the electrical characteristics of AlN/GaN Schottky diode, such as Schottky barrier height, turn-on voltage, reverse breakdown voltage, ideal factor, and the current-transport mechanism, are analyzed and then compared with those of an A1GaN/GaN diode by self-consistently solving Schrodinger＇s and Poisson＇s equations. It is found that the dislocation-governed tunneling is dominant for both AlN/GaN and AlGaN/GaN Schottky diodes. However, more dislocation defects and a thinner barrier layer for AlN/GaN heterostrncture results in a larger tunneling probability, and causes a larger leakage current and lower reverse breakdown voltage, even though the Schottky barrier height of AlN/GaN Schottky diode is calculated to be higher that of an A1GaN/GaN diode.
Ni/Au Schottky contacts on AlN/GaN and AlGaN/GaN heterostructures are fabricated. Based on the measured current-voltage and capacitance-voltage curves, the polarization sheet charge density and relative permittivity are analyzed and calculated by self-consistently solving Schrodinger＇s and Poisson＇s equations. It is found that the values of relative permittivity and polarization sheet charge density of AlN/GaN diode are both much smaller than the ones of AlGaN/GaN diode, and also much lower than the theoretical values. Moreover, by fitting the measured forward 1-V curves, the extracted dislocations existing in the barrier layer of the AlN/GaN diode are found to be much more than those of the AlGaN/GaN diode. As a result, the conclusion can be made that compared with AlGaN/GaN diode the Schottky metal has an enhanced influence on the strain of the extremely thinner AlN barrier layer, which is attributed to the more dislocations.
An Ni/Au Schottky contact on an AlGaN/GaN heterostructure has been prepared. By using the peak-conductance model, the threshold voltage and the series resistance of the AlGaN/GaN diode are simultaneously extracted from the conductance-voltage （G-V） curve and found to be in good agreement with the ones obtained by using the capacitance-voltage （C-V） curve integration and the plot of dV/d（ln I） versus current I. Thus, a method of directly and simultaneously extracting both the threshold voltage and the series resistance from the conductance-voltage curve for the AlGaN/GaN Schottky diode is developed.
Lattice-matched InAlN/AlN/GaN high electron mobility transistors (HEMTs) grown on sapphire substrate by using low-pressure metallorganic chemical vapor deposition were prepared, and the comprehensive DC characteristics were implemented by Keithley 4200 Semiconductor Characterization System. The experimental results indicated that a maximum drain current over 400 mA/mm and a peak external transconductance of 215 mS/mm can be achieved in the initial HEMTs. However, after the devices endured a 10-h thermal aging in furnace under nitrogen condition at 300 ℃, the maximum reduction of saturation drain current and external transconductance at high gate-source voltage and drain-source voltage were 30% and 35%, respectively. Additionally, an increased drain-source leakage current was observed at three-terminal off-state. It was inferred that the degradation was mainly related to electron-trapping defects in the InAlN barrier layer.
Monolithic integration of resonant tunneling diodes (RTDs) and high electron mobility transistors (HEMTs) is an important development direction of ultra-high speed integrated circuit. A kind of top-RTD and bottom-HEMT material structure is epitaxied on InP substrate through molecular beam epitaxy. Based on wet chemical etching, metal lift-off and air bridge interconnection technology, RTD and HEMT are fabricated simultaneously. The peak-to-valley current ratio of RTD is 7.7 and the peak voltage is 0.33 V at room temperature. The pinch-off voltage is -0.5 V and the current gain cut-frequency is 30 GHz for a 1.0 μm gate length depletion mode HEMT. The two devices are conformable in current magnitude, which is suitable for the construction of various RTD/HEMT monolithic integration logic circuits.
We report the DC and RF performance of InAlN/GaN high-electron mobility transistors with AlGaN back barrier grown on SiC substrates. These presented results confirm the high performance that is reachable by InAlN-based technology. The InAlN/GaN HEMT sample showed a high 2DEG mobility of 1550 cmE/（V-s） at a 2DEG density of 1.7 × 1013 cm-2. DC and RF measurements were performed on the unpassivated device with 0.2 μm ＂T＂ gate. The maximum drain current density at Vcs = 2 V is close to 1.05 A/mm in a reproducible way. The reduction in gate leakage current helps to increase the frequency performance of AlGaN back barrier devices. The power gain cut-off frequency of a transistor with an A1GaN back barrier is 105 GHz, which is much higher than that of the device without an A1GaN back barrier at the same gate length. These results indicate InAlN/GaN HEMT is a promising candidate for millimeter-wave application.
