High-speed vertical -cavity surface -emitting lasers with reduced electrical and thermal constraints on modulation bandwidth.

摘要

High-speed oxide-confined VCSELs were fabricated and characterized. Fabrication processes for top-emitting self-aligned and non-self-aligned 850nm and 980nm as well as for bottom-emitting, non-self-aligned, flip-chip bonded 980nm VCSELs were developed. The effect of heat-sinking on high-speed VCSELs performance was demonstrated for 850nm and 980nm devices.;Two generations of devices were designed, fabricated and characterized. In the first generation, self-aligned top-emitting 850nm high-speed VCSELs were fabricated and characterized. The self-aligned process allowed smaller mesa diameters, decreasing capacitance by 49% and reducing the distance for heat flow to sidewalls. Au-wrapped and Cu-plated heat-spreading layers reduced the thermal resistance (Rth) by 25% and 44%, respectively, and the output power was increased by 17% and 38%, respectively. The fabricated devices exhibited a f3dB of 16.3GHz at 8.9kA/cm 2. Using the second generation design and fabrication process, the effect of improved heat-sinking on the performance of a 10mum active diameter Cu-plated high-speed VCSELs demonstrated a reduction in Rth by up to 57%. The 850nm lasers exhibited a f3dB of ∼18GHz at 8kA/cm 2 and a MCEF of 15GHz/mA1/2.;The effect of heat-sinking on the performance of high-speed, non-self-aligned top-emitting 980nm VCSELs was also demonstrated. Increasing Cu-plated heatsink radii from 0mum to 4mum greater than the mesa in 980nm VCSELs reduced Rth by 50% for top-emitting VCSELs over a range of device sizes. For a 9mum active diameter, the 4mum heatsink increased output power and f3dB by 131% and 40%, respectively. The measured f3dB was 9.8GHz at 10.5kA/cm2.;Bottom-emitting non-self-aligned flip-chip bonded 980nm devices were fabricated and characterized. VCSELs with 10mum active area have a threshold current and a slope efficiency of 0.6mA and 80%, respectively. The flip-chip bonding increased the maximum output power for VCSELs by up to 25%.;The effect of external heating on the VCSELs resonance frequency and damping factor was examined for top-emitting, self-aligned 980nm VCSELs. Increasing temperature reduced the resonance frequency and damping factor, limiting the bandwidth of VCSELs. The damping and resonance frequency relationship revealed a maximum intrinsic bandwidth of 24.7GHz.;Dielectric properties of four different spin-on dielectrics were investigated. The pad capacitance circuit model was obtained based on geometrical and physical considerations.