VCSEL Quick Fabrication for Assessment of Large Diameter Epitaxial Wafers

Stripped-back representative VCSEL devices with a simple fabrication process that very closely approaches the performance of standard BCB-planarised devices have been produced. These VCSEL Quick Fabrication (VQF) devices achieve threshold currents only 0.3 mA higher than that of a standard device produced from the same material. The predictability of standard performance from VQF performance is also robustly assessed in terms of temperature effects to account for the observed disparities. These VQF devices are then processed across a 6-inch (152 mm) wafer and the resulting device-level characteristics are mapped. From this, it is apparent that there is an approximately radial decrease in oxide aperture diameter from centre to edge, found to be driven by the strain-induced wafer bow. After corrections, a residual spatial variation across the wafer remains, which, in conjunction with temperature dependent measurements, is shown to be a result of epi-material variation. By observation at 50 °C, that is, at a temperature closely resembling that of intended application, the residual centre-to-edge variation in threshold current density is found to be only 0.2 kA/cm2, compared to 1.3 kA/cm2 when observing the room temperature variation of devices of nominally equivalent active volumes.