Correlation of Drain Current Pulsed Response with Microwave Power Output in AlGaN/GaN HEMTs

Abstract

The drain-current response to short (<lps) gate pulses has been measured for a series of GaN HEMT wafers that have similar dc and small-signal characteristics. This response has been found to correlate well with the measured microwave power output. For example, for devices where the pulsed drain current is greater than 70% of the dc value, output power densities of up to 2.3 W/mm are attained. This is in contrast with 0.5 W/mm measured for devices with low pulse response (less than 20% of the dc value). These results, which can be explained by the presence of traps in the device structure, provide a convenient test which is predictive of power performance.

Photoionization spectroscopy of traps in GaN metal-semiconductor field-effect transistors

“…First, the gate lag response, which is generally associated with surfaces, 27 shows little dependence on the magnitude of the applied drain-source voltage in GaN high electron mobility transistors ͑HEMTs͒. 28 This is unlike the current collapse mechanism reported here, that requires a high drain-source voltage. Furthermore, silicon nitride passivation of GaN HEMTs has resulted in a change of the gate lag response, 29 with no effect on the observed current collapse behavior.…”

Trapping effects and microwave power performance in AlGaN/GaN HEMTs

“…An estimate of the maximum microwave power output obtainable from an FET can be determined from the dc drain characteristics and the operating point. It is frequently observed, however, that the microwave power output of GaN HEMTs is significantly less than that predicted from this estimate [11], [12]. This discrepancy is due in part to trapping effects.…”

“…Historically, a variety of trapping effects have been observed. These include transconductance frequency dispersion [6], current collapse of the drain characteristics [7], light sensitivity [7], gate-and drain-lag transients [8]- [10], and restricted microwave power output [11], [12]. The research activity that is directed toward understanding and eliminating these effects parallels that of the GaAs-based technology, Manuscript received April 13, 2000; revised September 1, 2000.…”

Trapping effects in GaN and SiC microwave FETs

“…Correlation with power output with gate lag for AlGaN/GaN HEMTs. The maximum microwave power output at 2 GHz is plotted against the ratio of the pulsed drain current to the dc drain current [54].…”

“…Binari et al [52]- [54] associated gate lag with the presence of surface trapping in the access region between gate and drain. They found that annealing unpassivated AlGaN/GaN HEMTS at 300 C reduced or eliminated gate lag and dispersion, possibly due to the passivation of surface traps during the annealing process.…”