Temperature-dependent nonlinearities in GaN/AlGaN HEMTs

Temperature-dependent nonlinearities of GaN/AlGaN HEMTs are reported. The large-signal device model of the transistor is obtained by using a physics-based analysis. The model parameters are obtained as functions of bias voltages and temperature. The analysis of the device has been carried out using a time-domain technique. f(max) for a 0.23 mum x 100 mum Al0.13Ga0.87N/GaN FET is calculated as 69 GHz at 300 K, while at 500 K, f(max) decreases to 30 GHz, which are in agreement with the experimental data within 7% error. f(max) as obtained from calculated unilateral gain, decreases monotonically with increasing temperature. For shorter gate lengths irrespective of the operating temperature f(max) is less sensitive to bias voltage scaling. For longer gate length devices, f(max) becomes less sensitive to the bias voltage scaling at elevated temperatures. 1-dB compression point (PI-dB) at 4 GHz for a I pm x 500 pin Al0.15Ga0.85N/GaN FET is 13 dBm at 300 K. At 500 K, PI-dB decreases to 2.5 dBm for the same operating frequency. Similar results for output referred third intercept point (OIP3) are reported for different gate length devices. Third-order intermodulation (IM3) and carrier-to-IM3 ratio at 10 GHz for 0.45 mum x 250 mum Al0.14Ga0.86N/GaN FET operating at an output power level of 5.3 W/mm, which corresponds to the peak power added efficiency are -12 dB and 11 dBc, respectively, at 300 K. At 500 K, the corresponding quantities are -9 dB and 8 dBc, respectively. The calculated values of output power, gain, and power-added efficiency for the for 0.45 mum x 250 mum Al0.14Ga0.86N/GaN FET for input power varying up to 25 dBm are in good agreement with experimental data with maximum error not exceeding 3%.