Characteristics of N2 and O2 Plasma-Induced Damages on AlGaN Thin Film Surfaces.

A fundamental understanding of N2 and O2 plasma-induced damage on AlGaN surface is needed in order not to severely degrade electrical characteristics and in order to intelligently achieve the normally-off operation of AlGaN/GaN-based electronic devices. A difference between the damage characteristics of Al0.24Ga0.76N thin film surfaces irradiated with N2 and O2 plasmas is reported, from the perspective of impact of ultraviolet (UV) photons emitted from the plasmas. With the lengthening irradiation time, N2 plasma irradiation introduced a large degree of nitrogen deficiency under the influence of near-UV photons with energies of 3.68 and 3.93 eV larger than the AlGaN band-gap energy, compared to O2 plasma irradiation without the emission of near-UV photons. In a short irradiation time, O2 plasma irradiation introduced a larger degree of nitrogen deficiency. With increasing gas pressure, O2 plasma-induced damage on the surface was more enhanced than N2 plasma-induced damage. The degree of aluminum deficiency was more enhanced than that of gallium deficiency, the amount of oxides incorporated into the surface was suppressed, and the etch-pit density comparable to the dislocation density was introduced on the surface. These findings can be attributed to the impacts of vacuum ultraviolet photons and energetic O+ ions from the O2 plasma. [ABSTRACT FROM AUTHOR]