Selective oxidation produces top- and bottom-emitting vertical-cavity lasers
A spatially selective oxidation technique produced arrays of vertical-cavity lasers (VCLs) consisting of surface-emitting devices interleaved with substrate-emitting ones. Researchers at the University of Southern California (USC; Los Angeles, CA) developed the arrays as part of their work on smart pixels for free-space optical systems. Vertical-cavity lasers are attractive for this application because two-dimensional arrays can be made relatively easily. For a smart pixel, the researchers want to incorporate lasers emitting in both the surface and substrate directions with field-effect transistors and detectors.
Aaron Bond and Daniel Dapkus grew VCLs with symmetric and novel distributed-Bragg-reflector stacks on the to¥and bottom of the cavity, then used spatially selective oxidation to change the reflectivities of either the to¥or bottom mirrors, thus creating either top- or bottom-emitting lasers. The researchers created a 9 ¥ 13 array with apertures of differing sizes--more than 95% of the devices lased with good characteristics. Both the top- and bottom-emitting lasers had current thresholds from 65 to 70 µA, slope efficiencies from 16% to 18%, output powers u¥to 0.4 mW, and far-field FWHM beams of 9° to 18°, depending on the aperture size. Peak slope efficiency for a device with an 80-µA threshold is 18%.