INGAAS(0.98 MU-M)/GAAS VERTICAL-CAVITY SURFACE-EMITTING LASER GROWN BY GAS-SOURCE MOLECULAR-BEAM EPITAXY

We report the growth of InGaAs/GaAs vertical cavity surface emitting lasers (VCSELs) with an emission wavelength at 0.98 mum by gas-source molecular beam epitaxy (GSMBE). The surface emitting laser diodes are composed of a 15-pair p+ GaAs/AlAs graded mirror with a 3-quantum well In0.2Ga0.8As active region and a 16.5-pair n+ GaAs/AlAs grade mirror on an n+ GaAs substrate. We use a simple interferometric technique for in-situ monitoring and feedback control of layer thickness to obtain a highly reproducible Bragg reflector. This technique uses an optical pyrometer to measure apparent temperature oscillations of the growing epi-layer surface. These measurements can be performed with continuous substrate rotation and without any growth interruption. The growing layer thickness can then be related to the apparent temperature oscillation spectrum. When the layer reaches the desired thickness, the growth of the subsequent layer is then initiated. By making layer thickness measurements and control in real-time throughout the entire growth cycle of the structure, the center of the mirror reflectivity and the Fabry-Perot resonance at the desired wavelength can be reproducibly obtained. The reproducibility of the center wavelength and FWHM of the reflectivity stop-band with a variation of less-than-or-equal-to 0.2% was achieved in the AlAs/GaAs mirror stacks grown using this technique. The VCSEL structures with a variation of the Fabry-Perot wavelength of less-than-or-equal-to 0.4% have been grown. Bottom-emitting laser diodes were fabricated and operated CW at room temperature. CW threshold currents of 3 and 6 mA are measured at room temperature for 10 and 25 mum diameter lasers, respectively. Output powers higher than 15 mW are obtained from these devices. These devices have an external quantum efficiency higher than 40%.