Plasma-chemical treatment effect observed during the fabrication of AlGaN/GaN devices

The results obtained when AlGaN/GaN heterostructure surfaces with undoped i-AlGaN and i-GaN upper layers are treated by two types of oxygen plasma created in a two-electrode medium-frequency diode assembly and an electrodeless high-frequency (HF) system and irradiated with an argon ion beam are analyzed. The studies are performed using Rutherford backscattering spectroscopy, and changes in the structural parameters are estimated by means of the HF capacitance-voltage characteristic method. It is demonstrated that nanoregions (10–20 A) of the initial i-AlGaN and i-GaN surface layers have different degrees of crystalline-structure ordering, in particular, i-AlGaN layers, which contain a large number of displaced Ga and Al atoms and, what is most important, nitrogen and oxygen atoms. This leads to an increase in the concentration of donor-like surface traps. A purely chemical interaction between ions and the surface can occur depending on the oxygen-plasma treatment modes; moreover, the chemical cleaning process can be accompanied by the impact action of ions on the surface. It is shown that structures with dissimilar surface layers respond differently to plasma treatment. The greatest change in the state of surface nanolayers is observed upon argon-ion bombardment. The analyzed electrical characteristics of test samples indicate that argon-ion treatment performed immediately before metallization makes it possible to create lower-resistance ohmic contacts and Schottky barriers with the smallest leakage currents.