Capacitively coupled radio frequency nitrogen plasma etch damage to N-type gallium nitride

Characteristics of N2 plasma etch damage to n-GaN are studied by comparing it with that for the Ar plasma etch damage. The characteristics of N2 plasma etch damage are different from those of the Ar plasma etch damage depending on gas pressure; SEM images show dark dots or curves on the surfaces etched by the Ar plasma at 6.7–13.3 Pa during long etch times, which seem to be due to additional chemical effect resulting from UV light emitted from the plasma, whereas at 1.3 Pa no dark dots or curves occur. The N2 plasma etch damage occurs independently of gas pressure. Although there is UV emission (from vibrationally excited N2 states in the N2 plasma), the physical etch contributes to degradation of n-GaN regardless of gas pressure (no chemical effect occurs): N atoms are preferentially etched from the surface. In contrast, the morphology of surface etched by the N2 plasma does not change from that of the as-grown material regardless of gas pressure, even when the etch time increases. ► Characteristic of N2 plasma etch damage to n-GaN was compared with that for Ar. ► n-GaN etch damage characteristics for N2 and Ar plasmas are different. ► N2 plasma etch damage occurs independent of gas pressure. ► Although UV is emitted from N2, physical etch effect contributes to the damage. ► The surface morphology for N2 does not change from that of the as-grown sample.