EXPERIMENTAL-DETERMINATION OF THE INFLUENCE OF GAIN SATURATION ON THE TEMPERATURE-DEPENDENCE OF THRESHOLD CURRENT IN SHORT ALGAAS-GAAS QUANTUM-WELL LASERS

In GaAs-AlGaAs single and multiple quantum-well (SQW and MQW) ridge lasers, grown by molecular beam epitaxy, the temperature dependence of the threshold current, expressed by the characteristic temperature T0, is investigated as a function of the cavity length (L) at temperatures between 20-degrees-C and 93-degrees-C. SQW lasers, in contrast to MQWs, show at room temperature a strong decrease in T0 from 250 K to about 100 K when the length is reduced from 400 to 200-mu-m. We found that by further reducing L to about 130-mu-m, a strong increase in T0 up to 250 K occurs and T0 decreases again to 80 K for 60-mu-m SQW lasers. This T0 behavior in SQW lasers is directly correlated to the gain saturation of the n = 1 transition and the switch of the laser emission to the n = 2 transition. In MQW lasers, T0 is constant at all cavity lengths, even at high temperatures, indicating that no gain saturation occurs.