Cubic AlGaN/GaN Hetero-Field Effect Transistors with Normally On and Normally Off Operation

Non-polar cubic AlGaN/GaN HFETs were grown by plasma assisted MBE on 3C-SiC substrates. Both normally-on and normally-off HFETs were fabricated using contact lithography. Our devices have a gate length of 2 μm, a gate width of 25 μm, and source-to-drain spacing of 8 μm. For the source and drain contacts the Al0.36Ga0.64N top layer was removed by reactive ion etching (RIE) with SiCl4 and Ti/Al/Ni/Au ohmic contacts were thermally evaporated. The gate metal was Pd/Ni/Au. At room temperature the DC-characteristics clearly demonstrate enhancement and depletion mode operation with threshold voltages of +0.7 V and −8.0 V, respectively. A transconductance of about 5 mS/mm was measured at a drain source voltage of 10 V for our cubic AlGaN/GaN HFETs, which is comparable to that observed in non-polar a-plane devices. From capacity voltage measurements a 2D carrier concentration of about 7×1012 cm-2 is estimated. The influence of source and drain contact resistance, leakage current through the gate contact and parallel conductivity in the underlaying GaN buffer are discussed.