Fabrication and performance of bottom-emitting flip-chip bonded 980 nm vertical-cavity lasers with copper- and indium-plated heat-sinks

Abstract

Bottom-emitting, flip-chip bonded, oxide-confined, 980 nm vertical-cavity surface-emitting lasers (VCSELs) with improved performance were fabricated and characterized. Flip-chip bonding, bottom-emitting VCSELs with 20 µm active area diameter on copper- and indium-plated heat spreaders reduced the devices’ thermal resistance by 35% and increased the bias current density at which the output optical power saturates by 19%, which increased the maximum output optical power achieved by 26%. Bonded VCSELs with active area diameters of 20 µm demonstrated an ∼30% decrease in the active region temperature at the maximum output optical power. A 10% improvement in the devices’ modulation bandwidth is calculated due to reduced temperature and increased power. Devices with different active area diameters exhibited a threshold current density and differential quantum efficiency of (0.88 ± 10%) kA cm−2 and 0.57 ± 8%, respectively, implying good active area scaling. A simple rate-equation-based thermal VCSEL model was used to extract different VCSELs’ parameters, which enabled the estimation of internal temperature for different device sizes at different bias currents. A genetic algorithm was utilized in model parameter extraction and optimization. Good agreement between measured and simulated characteristics for different device sizes was obtained. Detailed protocols for critical fabrication steps are presented.