| Popis: |
For many years, mid-infrared (2-5μm) semiconductor lasers operating at or near room temperature have been sought for use in LADAR, gas sensing, and spectroscopy. Smaller bandgap materials necessary for this range are more susceptible to non-radiative Auger recombination. Further, as laser structures become more complicated, like quantum cascade intersubband and interband lasers, Shockley-Read-Hall losses increase. The simplest structure is Type-I multiple quantum well (MQW), but few QW III-V heterojunction material systems capable of 2-5μm emission have a Type-I offset. One such system with InAsSb wells and AlInAsSb barriers has been unable to exceed 175K under CW operation partially due to poor carrier confinement associated with small valence band offsets. This paper describes the growth and performance of AlInAsSb/InAsSb lasers using a 0.3 mole fraction of Al in the Group III elements. Increased Al content enhances the valence and conduction band offsets, but the AlInAsSb alloy exhibits a miscibility gap above 0.06 Al mole fraction, so a digital alloy technique was used to grow high quality 0.3-2μm thick quaternary films. As Al mole fraction in the barriers was increased from 0.20 to 0.30 an 80-fold increase in photoluminescence (PL) was observed. The corresponding lasers were grown and tested demonstrating lasing at 3.9μm and 50K. Theoretical studies suggest that adding Ga to the barriers, forming an AlGaInAsSb quinary alloy, results in band structures more favorable towards minimizing Auger effects and realizing Type I offset behavior over a wider range of alloy compositions. PL structures were grown and tested, again using a digital alloy technique for the quinary alloy. Preliminary results show promise. |
