Abstract
In this work appropriate activation and passivation techniques have been introduced to p-GaN and applied to improve the electric characteristics of GaN p-i-n diodes. In order to better activate the p-GaN to further reduce the contact resistance, the rapid thermal annealing (RTA) and laser annealing system are studied. It is shown that RTA or laser annealing of Mg-doped GaN (about 0.5 um in thickness) in general helps activate acceptors and increase the average hole concentration by a factor of about 2 from low to mid of 1017/cm3 determined by the Hall measurement. Use of laser annealing of p-GaN coated with Ni and removal afterwards prior to depositing conventional Ni/Au ohmic-contact films, however, greatly improves the contact resistance from 10-2 to 1.6×10-4 Ωcm2. As a result, the forward voltage of p-i-n diodes can be as low as 3.7 V with a current density at 100 A/cm2 which is a 7.5 % reduction compared with control sample. The trifluoromethane-containing plasma is used to passivate the mesa surfaces and suppress the surface current leakage of GaN p-i-n rectifiers. Reduction of surface leakage enhances the reverse blocking voltage by 20% (from 509 to 630 V) measured at J＝1 A/cm2. Differential forward resistances of control samples and plasma-treated ones are 0.5 mΩ-cm2 and 0.48 mΩ-cm2, respectively, and an excellent Baliga’s Figure-of-merit of 827 MW/cm2 is achieved for GaN diodes fabricated on sapphire substrates.