Improved performance of top-emitting oxide-confined polyimide-planarized 980 nm VCSELs with copper-plated heat sinks

Top-emitting, oxide-confined, copper-plated 980 nm vertical-cavity surface-emitting lasers (VCSELs) with improved performance were fabricated and characterized. Annular copper-plated heat sinks reduced the device's thermal resistance and increased the output optical power and the bias current density at which the output optical power saturates. Increasing the plated heat sink radii from 0 to 8 μm greater than the mesa diameter for VCSELs with 26 μm mesa diameter and 8 μm active area diameter reduced the measured thermal resistance by 65% and increased the bias current density at which the output optical power saturates by 62%, which increased the maximum output optical power achieved by 162%. VCSELs with active area diameter and heat sink overlap of 8 μm demonstrated ∼64% decrease in active region temperature at the maximum output optical power compared with devices with no heat sink overlap. A 29% improvement in the devices' modulation bandwidth was calculated due to reduced temperature and increased power. Devices with identical mesa diameters of 26 μm and different heat sink overlaps exhibited a threshold current density and a total series resistance of (1.25 ± 4%) kA cm^-2 and ∼95 ω, respectively. Simple VCSEL L-I and thermal models were used to simulate the VCSEL's L-I performance at elevated ambient temperatures. Good agreement between measured and simulated characteristics was obtained. Detailed protocols for critical fabrication steps are presented.