Molecular beam epitaxy of vertically compact laser-HEMT structures for monolithic integration

Abstract

Vertically compact Al x Ga 1-x As/GaAs laser structures with Al 0.3 Ga 0.7 As/AlAs SPSL-cladding layers were grown on top of HEMT structures by MBE and investigated with regard to series resistance. We found an exponential dependence of series resistance R s with AlAs and Al 0.3 Ga 0.7 As SPSL-layer thicknesses at ambient temperature. Laser-HEMT structures for monolithic integration were grown and lasers were processed. For 3 x 200 μm 2 3-QW-lasers, suitable for high-frequency performance, threshold currents of 20 mA and series resistances below 12 Ω were obtained. The slope of the linear regression of the I th values as a function of mesa width yielded a low threshold current density j th of 480 A/cm 2 . Reduction of the p-cladding thickness from 600 nm down to 450 nm shows no increase in threshold current density if the p-dopants are kept from diffusing into the active region. This clearly demonstrates that laser structures for monolithic integration can be designed very compact without loosing performance.