Analysis of GaN-Based HEMTs Operating as RF Detectors Over a Wide Temperature Range

This article presents an analysis of detection in the microwave region with AlGaN/GaN high-electron-mobility transistors (HEMTs) in terms of the key figures of merit: responsivity and noise equivalent power (NEP), in the temperature range between 20 and 400 K. Transistors with three different gates lengths (75, 150, and 250 nm) have been measured and favorably compared with a simple quasi-static (QS) model extracted from the dc curves, which is able to reproduce the zero-bias experiments at 1 GHz in the entire gate-bias sweep and operating temperature range. Such a model allows to explain the detection experiments performed both with the devices operating in zero-current or zero-voltage conditions and demonstrates that the bowing coefficient of the
$I_{D}$
–
$V_{\mathrm {DS}}$
curves is the parameter that determines the performances of the devices as RF detectors. The voltage responsivity increases when the gate bias approaches the threshold voltage but shows different behaviors in subthreshold conditions. Depending on whether the zero-current bias point is near zero drain voltage (for leaky devices, when the channel is not well pinched off due to the short gate or to the conduction through the buffer at low temperature) or shifted to the point where the third quadrant conduction (TQC) starts (for well-behaved devices), the responsivity presents a decrease or an approximately constant value, respectively. On the other hand, when the detector is biased, the curves of current responsivity show a characteristic bell shape with a maximum, which is approximately the same for all tested devices and hardly depends on the gate bias.