STRAINED-LAYER INGAAS-GAAS-ALGAAS LASERS GROWN BY MOLECULAR-BEAM EPITAXY FOR HIGH-SPEED MODULATION

A study of strained InGaAs quantum wells grown on GaAs by molecular beam epitaxy was performed in order to optimize the growth conditions for strained-layer single- and multiple-quantum-well lasers. Photoluminescence of the quantum wells show a rapid degradation in material quality as the substrate temperature is reduced below 500-degrees-C. Single-quantum-well (SQW) laser structures contain a 55 angstrom 35% InGaAs quantum well, while multiple-quantum-well (MQW) lasers contain four 25% or 35% InAs mole fraction 55 angstrom quantum wells. The 35% SQW lasers emit at 1.06-mu-m, while the 25% InGaAs MQW lasers emit at a wavelength of 995 nm and the 35% MQW lasers emit at 1.07-mu-m. The SQW lasers have threshold current densities as low as 83 A/cm2 for 150 x 1000-mu-m devices. Microwave modulation bandwidths increase with an increasing In mole fraction and number of quantum wells, as predicted by theory. A differential gain of 5.0 x 10(-15) cm2 is calculated from the microwave response measurements for the 35% MQW devices, and it is more than 16 times greater than values reported for InGaAsP bulk lasers. The -3 dB bandwidth of 10 x 200-mu-m 35% MQW devices exceeds 15 GHz, and it is the highest continuous-wave direct-modulation band-width reported for a quantum-well laser.