EFFECTS OF NONRADIATIVE RECOMBINATION ON THE TEMPERATURE CHARACTERISTICS OF THRESHOLD CURRENT-DENSITY IN 670 NM GAINASP-ALGAAS VISIBLE LASERS

In order to investigate the effect of nonradiative recombinations on the temperature characteristics of threshold, 670 nm GaInAsP-AlGaAs visible light lasers with different heterobarrier heights were fabricated. In these lasers, the heterobarrier (DELTA-E(g)) can be easily varied merely by changing the Al contents (X(Al)) of AlGaAs cladding layers. The threshold current densities (J(th)) as a function of temperature were evaluated. The resultant characteristic temperature of threshold (T0) was increased from 45 ot 90 K with increasing X(Al) from 0.7 to 0.95 (i.e., the barrier heights, 0.2-0.3 eV), while the J(th) decreased from 5.6 to 1.7 kA/cm2. The results of experiments conducted on the dependency of J(th) on the active layer thickness agreed well with theory. By subtracting the calculated pure radiative recombination component of J(th) from the experimental J(th) values, the nonradiative recombination current densities were obtained as a function of inverse temperature. The thermal activation energies E0 were evaluated for different DELTA-E(g), and as a result we found that the nonradiative recombinations were governed by the heterobarrier heights. On the other hand, the increase of J(th) with decreasing X(Al) was explained theoretically in terms of the carrier leakage over heterobarriers. From these facts, we can say that the carrier leakage components are the main nonradiative recombination processes in these lasers. Finally, 670 nm GaInAsP-AlGaAs VSIS lasers (X(Al) = 0.85) were fabricated to realize low threshold currents (34 mA) and high power operation (82 mW/facet, uncoated).