Effects of a step-graded Al_xGa_1−xN electron blocking layer in InGaN-based laser diodes

A step-graded Al_xGa_1-xN electron blocking layer (EBL) is studied on InGaN-based laser diodes (LDs). Its efficacy on device performance is investigated with respect to stimulated emission properties, internal quantum efficiency, internal loss, and temperature-dependent characteristics. When compared to a LD structure with an abrupt Al_0.18Ga_0.82N EBL design, the LD with the step-graded Al_xGa_1-xN EBL design demonstrates lower threshold current density and higher slope efficiency. The threshold current density is reduced from 4.6 kA/cm² to 2.5 kA/cm² under pulsed-current operation and the corresponding slope efficiency is increased from 0.72 W/A to 1.03 W/A. The insertion of the step-graded Al_xGa_1−xN EBL leads to a dramatic enhancement in internal quantum efficiency from 0.60 to 0.92, while internal loss keeps at 9 ∼ 10 cm⁻¹. The temperature-dependent measurement also shows that the step-graded Al_xGa_1−xN EBL can improve the thermal stability with reduced red-shift from 0.05 nm/K to 0.034 nm/K. This simple yet efficient structural design change provides an effective way to achieve high-performance InGaN-based LDs with higher optical-output power and lower electric-power consumption.