Barrier and well thickness designing of InGaN/GaN multiple quantum well for better performances of GaN based laser diode

The effects of barrier and well thickness in InGaN/GaN (with in content of 15%) multiple quantum well (MQW) on the performances of GaN based laser diode (LD) are investigated by using LASTIP software, and the relevant physical mechanisms are discussed. It is found that when the barrier-thickness in InGaN/GaN MQW is fixed to be 7 nm, for the well thickness values of 3.0, 3.5, 4.0, 4.5, and 5.0 nm, the threshold currents of LD are 76.31, 67.96, 57.60, 64.62, and 74.59 mA, and the output light powers of LD are 12.05, 15.64, 24.70, 18.21, and 11.35 mW under an injection current of 100 mA, respectively. It indicates that too thick or too thin well may lead to a higher threshold current and a lower output power of GaN based LD. A high performance device can be obtained by using an optimized well thickness of around 4.0 nm. It is found that the LD performance is degraded by using too thin well in the device structure mainly due to the high leakage current, while strong polarization will lead to the decrease of overlap integral and luminescence intensity if the well layer is too thick, and thus a poor performance is obtained. It is found that the LD performance can be improved obviously by appropriately increasing barrier thickness from 7 nm to 15 nm. When the barrier thickness in InGaN/GaN MQW is fixed at 15 nm and the well thickness values are 3.0, 3.5, 4.0, 4.5 and 5.0 nm, the threshold currents of LD are 59.54, 52.42, 52.17, 51.38, and 58.99 mA, and the output light powers of LD are 36.12, 39.69, 40.79, 40.27, and 33.19 mW under an injection current of 100 mA, respectively, i.e., LD device parameters are improved. It suggests that the higher performances of GaN based laser diode can be realized by appropriately increasing the thickness of barrier when the thickness of well is optimized to be around 4 nm.