AlGaN/GaN-Based laterally gated high-electron-mobility transistors with optimized linearity

Abstract

In this work, highly linear AlGaN/GaN laterally gated (or buried gate) high-electron-mobility transistors (HEMTs) are reported. The effect of gate dimensions on source-access resistance and the linearity of laterally gated devices are investigated experimentally in detail for the first time. Transistors with different gate dimensions and conventional planar devices are fabricated using two-step electron beam lithography (EBL). Current-voltage, source-access resistance, small-signal, and two-tone measurements are performed to evaluate the linearity of devices. Contrary to conventional planar HEMTs, the intrinsic transconductance of laterally gated devices monotonically increases with increasing gate voltage, showing a similar behavior as junction field-effect transistors (FETs). The source-access resistance shows a polynomial increase with the drain current, which can be reduced by decreasing the filling ratio of the buried gates. Through the optimization of these two competing factors, i.e., intrinsic transconductance and the source-access resistance, flat transconductance with high linearity is achieved experimentally. The laterally gated structure shows flat transconductance and small-signal power gain over a larger span of gate voltage that is 2.5 times higher than a planar device. Moreover, 6.9-dB improvement in output intercept point (OIP3)/P DC is achieved. This approach can be used to improve the linearity of AlGaN/GaN HEMTs at the device level.