We explored the evolution of the photoluminescence (PL) properties versus molecular beam epitaxy growth conditions for a series of type II "W" quantum well [InAs/GaInSb/InAs/AlAsSb] structures. The highest PL intensities are obtained when the quantum wells are grown in a temperature range between 487 and 507 degreesC. Cross-sectional scanning tunneling microscopy was used to explain the temperature evolution of the PL. AlAs clustering within the AlAsSb barrier was observed at low growth temperature. The PL intensity decrease at high temperature was related to In clustering in the GaInSb layer. Laser structures grown at both 425 and 500 degreesC displayed lower lasing thresholds, lower internal losses, and longer Shockley-Read lifetimes than any similar structures grown previously at NRL. A thicker optical cladding layer of 3.5 mum suppressed mode leakage into the substrate and reduced the internal loss to 2.1 cm(-1) at 78 K.