Molecular beam epitaxy of vertically compact Al(x)Ga(1-x)As/GaAs laser-HEMT structures for monolithic integration

Vertically compact Al(x)Gal(1-x)As/GaAs laser structures with Al(0.3)Ga(0.7)As/AlAs SPSL-cladding layers were grown top of HEMT structures by MBE and investigated with regard to series resistance. We found an exponential dependence of series resistance Rs 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 mu m(exp 2) 3-QW-lasers, suitable for high-frequency performance, threshold currents of 20 mA and series resistances below 12 ohm 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/cm2. Reduction of the p-cladding thickness from 600 mn down to 450 mn 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 compac t without loosing performance.