Effects of internal loss on power efficiency of mid-infrared InAs-GaInSb-AlSb quantum-well lasers and comparison with InAsSb lasers

Experimental studies of the lasing efficiency of optically pumped 4-μm GaInSb-InAs-AlSb multiple-quantum-well (MQW) lasers that emitted >1-W peak power/facet at 80 K indicated that internal loss is the main factor that limits the power output. The internal loss coefficient and internal quantum efficiency were determined by measuring the lasing efficiency versus temperature for devices of different facet reflectivities and lengths. The internal loss coefficient was found to increase from ~18 cm^-1 near 70 K to ~60-100 cm^-1 near 180 K, while the internal quantum efficiency remained constant at ~47% (or ~67% with the correction for the finite absorption of the active region) from 70 to 130 K. The increase of internal loss and the decrease of external quantum efficiency versus temperature were found very similar to those of double-heterostructure InAsSb-GaSb lasers and were similarly interpreted in terms of intervalence band carrier absorption. Extrapolation of power performance for improved devices with lower internal loss indicated that high-efficiency multi-watt quasi-CW output with a broad-area brightness of ~1 MW/cm².sterad is possible