Low current density, inverted polarity, high-speed, top-emitting 850 nm vertical-cavity surface-emitting lasers

High-speed, oxide-confined, inverted polarity (n-up), polyimide-planarised 850 nm vertical-cavity surface-emitting lasers (VCSELs) were fabricated and characterised. The lasers exhibit a -3 dB frequency modulation bandwidth (f_3dB) up to 15.2 GHz with a 10 mum oxide aperture diameter, at the lowest current density (/bias) ever reported of 6.4 kA/cm². The ratio f_3dB ²/J_bias = 36.1 (GHz²/kA/cm²) represents a 21% increase when compared with the highest previously reported ratio. The threshold voltage and current were as low as 1.45 V and 0.9 mA, respectively, with a series resistance of 65 Omega. A rate-equation-based thermal VCSEL model was used to predict the device performance at different temperatures. Good agreements between measured and simulated DC characteristics were obtained.