Low-threshold cw top-surface-emitting lasers at 850 nm

Abstract

We report new self-aligned top-surface-emitting lasers in which top mirrors are used as output mirrors and deep-ion implantation is used for current funneling. The laser structure, grown with molecular-beam epitaxy, is a vertical pin junction in which electric current is injected through the bottom and top mirrors. The undoped active region consists of four 100 Å thick GaAs quantum wells. 300 keV protons are used to introduce a buried damage layer that is concentrated around a depth of 2.3 µm from the surface, but the topmost 1.5 µm is left relatively conductive. Only those areas under the output windows are not damaged, and current is forced to flow predominantly through the active region. A 10 µm diameter laser has a 1.7 mA cw threshold at room temperature. Initially, the laser light is mostly horizontally polarized with a Gaussian mode profile. At higher current, TEM 01* modes show up with both polarizations. We have observed cw output power of as great as 1.5 mW from a 15 µm diameter top-surface-emitting laser. The cw differential quantum efficiency is approximately 20%. Measured spectral linewidth is 0.02 Å as measured by a scanning Fabry-Perot étalon.