Roles of lightly doped carbon in the drift layers of vertical n-GaN Schottky diode structures on freestanding GaN substrates

Abstract

We studied the roles of lightly doped carbon in a series of n-GaN Schottky diode epitaxial structures on freestanding GaN substrates, and evaluated the effects of the doping on diode performances. A large variation of compensation ratio was observed for carbon doping at (1–2) × 1016 cm−3. A model was proposed to explain this phenomenon, in which a vulnerable balance between donor-type CGa and deep acceptor CN strongly affected the free-carrier generation. Application of Norde plots and reverse biased leakage current in current–voltage measurements suggested provisional optimization for a free-carrier concentration of 8 × 1015 cm−3 to achieve a tradeoff between breakdown voltage and on-resistance of the n-GaN diodes.