Electrostatic Gates for GaN/AlGaN Quantum Point Contacts

We report on AlGaN/GaN quantum point contacts fabricated by using e-beam lithography and dry ion etching. The tunable nano-constrictions are defined by the integration of side and top gates in a single device. In this configuration, the planar gates are located on the both sides of a quantum channel and the metallic top gates, which cover the active region, are separated from the substrate by an insulating and passivating layers of $HfO_2$ or $Al_2O_3//HfO_2$ composite. The properties of devices have been tested at T = 4.2 K. For side gates we have obtained a very small surface leakage current $I_g < 10^{-11}$ A at gate voltages $|V_g|$ < 2 V, however, it is not enough to close the quantum channel. With top gates we have been able to reach the pinch-off voltage at $V_g$ = - 3.5 V at a cost of $I_g ≈ 10^{-6} A$, which has been identified as a bulk leakage current.