Theoretical and experimental analysis on InAlGaAs/AlGaAs active region of 850-nm vertical-cavity surface-emitting lasers

In this study, the gain-carrier characteristics of In_0.02Ga_0.98As and InAlGaAs quantum wells (QWs) of variant In and Al compositions with an emission wavelength of 838 nm are theoretically investigated. More compressive strain, caused by higher In and Al compositions in InAlGaAs QW, is found to provide higher material gain, lower transparency carrier concentration, and transparency radiative current density over the temperature range of 25-95°C. To improve the output characteristics and high-temperature performance of 850-nm vertical-cavity surface-emitting laser (VCSEL), In_0.15Al_0.08Ga_0.77As/Al_0.3Ga_0.7As is utilized as the active region, and a high-bandgap 10-nm-thick Al_0.75Ga_0.25As electronic blocking layer is employed for the first time. The threshold current and slope efficiency of the VCSEL with Al_0.75Ga_0.25As at 25°C are 1.33 mA and 0.53 W/A, respectively. When this VCSEL is operated at an elevated temperature of 95°C, the increase in threshold current is less than 21% and the decrease in slope efficiency is approximately 24.5%. A modulation bandwidth of 9.2 GHz biased at 4 mA is demonstrated.