(Invited) Vertical GaN p-i-n Diodes Formed by Mg Ion Implantation
A 8 μm thick unintentionally doped GaN layer was grown by metal organic chemical vapor deposition (MOCVD) on a n+ Ga-face c-oriented GaN substrate. The p-GaN anode and termination regions were formed by Mg implantation to a concentration of 2x1019 cm-3 following a box profile to a depth of 500nm. The implanted dopants were activated using the multicycle rapid thermal annealing (MRTA) technique described elsewhere . After activation and removal of the protective cap structure , a 1 μm SiO2 field oxide layer was deposited by plasma enhanced chemical vapor deposition (PECVD). Contact windows were opened by reactive ion etching in a CHF3-based plasma. The anode metal was formed by lift-off of Pd/Au (20/100nm), followed by rapid thermal annealing in a N2atmosphere, and the cathode metal was a blanket film of e-beam deposited Al on the back side of the sample.
Rectifying behavior was observed, a first for a p-i-n structure formed by Mg ion implantation in GaN. The turn-on voltage is consistent with a p-n junction, and the ideality factor of 2.6 is consistent with a recombination/generation-based transport mechanism, confirmed by temperature-dependent I-V. Additional non-ideal behavior is associated with recombination in the drift layer due to crystalline defects. The devices suffer from high ON-resistance due to high contact resistance and recombination in the drift layer, which limited the forward current to 1 A/cm2. Capacitance-voltage measurements indicated the presence of a p-GaN layer, with a depletion layer thickness ~500nm and a doping density of 2x1018 cm-3, corresponding to an activation ratio of 10%.
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