Effect of Ar ion beam channeling on AlGaN/GaN heterostructures during the ion beam etching process

The effect of Ar+ ion beam etching of AlGaN/GaN heterostructures at a bias voltage of 250 V was investigated with respect to different ion incident angles. The samples were measured before and after etching with respect to mobility, sheet electron concentration, and sheet resistance. We found a pronounced dependency of the electrical characteristics after etching on the ion incident angle. Especially at zero degree, the mobility of the two-dimensional electron gas (2DEG), which is located at the AlGaN/GaN interface, decreases dramatically after etching. The sheet resistance increases in the same way. At larger ion incidence angles, the effect vanished. We attribute this behavior predominantly to channeling of the ions through the AlGaN layer down to the 2DEG. An annealing step after etching shows improvement of the electrical characteristic. These results show that gate-recessed GaN field effect transistors can be limited in their device performance by etch-process-induced ion channeling effects. The results also show how etch-induced defects in the gate recess step can minimized. (C) 2000 American Institute of Physics. [S0003-6951(00)04514-9].