Surface recombination and sulfide passivation of GaN

The surface recombination velocity in n-type heteroepitaxial GaN(0001) is s hown to decrease dramatically when the surface is chemically treated with a queous and alcoholic solutions of inorganic sulfides, such as ammonium or s odium sulfide ((NH4)(2)S-x and Na2S). The room-temperature excitonic photol uminescence (PL) intensity increases by a factor of four to six after treat ment, and improvements persist for at least seven months in room air. Vario us other chemicals commonly used in device processing are investigated and shown to change the PL intensity by factors ranging from 0.7 to 2.5, buffer ed oxide etching being the most beneficial. Schottky barrier diodes using g old as the contact metal are fabricated using a sulfide treatment prior to evaporation. The barrier height from capacitance-voltage measurements is as high as 1.63 +/- 0.07 V, the highest value ever achieved on n-GaN. This re sult is evidence that the effect of surface states on the Fermi level has b een substantially reduced by the treatment.