Proton irradiation effects on GaN-based high electron-mobility transistors with Si-doped [Al.sub.x][Ga.sub.1-x]N and thick GaN cap layers

1.8 MeV proton radiation-induced degradation in high electron mobility transistors with Si-doped [Al.sub.x][Ga.sub.1] - x N and thick GaN cap layers is studied up to a fluence of 1 x [10.sup.15] protons/[cm.sup.2]. The thick GaN cap layer reduces sheet charge modulation induced by the surface states, as it electrostatically separates the active device layers from the surface, thereby enhancing the device performance. The devices exhibit good tolerance up to [10.sup.14] protons/[cm.sup.2], with displacement damage being the primary degradation mechanism. Charged defect centers introduced by proton radiation in the active device layers degrade carrier mobility and sheet carrier density. Proton radiation alters the barrier height at the Schottky gate and increases the resistance of the thin film structure. Index Terms--Gallium alloys, modulation-doped field effect transistors (MODFETs), proton radiation effects.