Characteristics of GaN-Based Bipolar Transistors on Sapphire Substrates With the n-Type Emitter Region Formed Using Si-Ion Implantation

We have investigated the possibility of being able to create gallium nitride bipolar junction transistors (GaN BJTs) whose n-type emitter region is formed using a conventional Si-ion implantation technology. The thermal stability of the p-GaN layer, which was the most important technique in creating GaN BJTs, was found to be maintained even after annealing at 1100 °C. A Hall-effect measurement revealed that the n-type emitter region, which was formed using 2.0 × 10¹⁵ cm^-2 Si-ion implantation within the p-GaN base layer, has a sheet carrier density of 1.59 × 10¹⁴ cm^-2 (i.e., a carrier activation ratio of 8%), an electron mobility of 41.0 cm²/Vs, and a sheet resistance of 958 Q/sq. The fabricated GaN BJTs had a maximum dc current gain of 160 and a maximum differential current gain of 238. These results show that Si-ion implantation is a promising technique for forming an n-type emitter of GaN BJTs. However, some of the transistor characteristics were found to be limited possibly by the Si-ion implantation-induced large base resistance.