The analysis of contact resistivity between a p-type GaN layer and electrode in InGaN MQW laser diodes

The individual elements attributing to the excess voltage drop in the nitride-based laser diodes were investigated. The specific contact resistivity ρc to p-type GaN was estimated by transmission line model (TLM) method and was estimated to slightly vary from 3.2×10−3 to 6×10−4 Ω cm2 in the current range of 1–10 kA cm−2. It is found that a low specific contact resistivity was obtained by optimizing both the acceptor density of p-type GaN and the contact metals. The respective voltage drop at the p-side contact in our laser diodes was found to be 5.6 V for a device with a threshold current density of 6.7 kA cm−2 (Ith=100 mA) at 14 V under pulsed current injection at room temperature. It is found that the excess voltage drop in these devices is mainly due to the p-side contact resistance.