Abstract
High pressure and spontaneous emission analysis techniques have been used to probe the recombination mechanisms in mid-infrared semiconductor lasers for the 2-4 mum wavelength range. Analysis of the spontaneous emission collected through a window in the substrate contact of two type-I GalnAsSb / AlGaAsSb, compressively strained, quantum well lasers emitting at lambda ~2.11 mum and lambda ~2.37 mum reveals that the threshold current of both devices is dominated by Auger recombination at room- temperature. Further analysis shows that approximately 80% of the room-temperature threshold current of the 2.37 devices can be attributed to Auger recombination. Comparison with larger band gap near-infrared devices suggests that the CHSH Auger process (involving the generation of hot holes in the spin-orbit split-off band) is suppressed in the 2.37 mum lasers as the spin-orbit splitting energy is greater than the band gap in these structures. However, other types of Auger process, such as CHLH and CHCC, persist and dominate the room-temperature threshold current of these lasers. Hydrostatic pressure measurements on the 2.37 mum devices indicate that as pressure is applied, the band gap increases and approaches the spin-orbit splitting energy and at pressures above 6 kbar the CHSH process becomes important. This is also evident in the larger band gap 2.11mum lasers where the pressure dependence indicates that the CHSH process is important at atmospheric pressure. The loss processes in GaSb-based "W" diode lasers operating at lambda ~ 3.25 /mum (at T = 80 K) are also investigated through analysis of their spontaneous emission characteristics and the pressure dependence of their threshold currents. Spontaneous emission analysis shows that defect/impurity recombination, which had been of concern in these structures, does not have a significant influence on the threshold current. Results suggest that a substantial contribution from Auger recombination exists at 80 K and increases strongly with increasing temperature. It is estimated that Auger recombination accounts for about 87% of the threshold current at 200 K and is the main cause of the poor temperature performance in these lasers.