Proceedings Article | 27 February 2014
Proc. SPIE. 9002, Novel In-Plane Semiconductor Lasers XIII
KEYWORDS: Indium gallium arsenide, Scattering, Composites, Electrons, Interfaces, Laser scattering, Quantum cascade lasers, Thermal effects, Epitaxy, Heterojunctions
Active region designs of QCLs containing composite barriers based on AlAs allow short wavelength emission, improved injection efficiency, and high values of T<sub>0</sub> and T<sub>1</sub>. On the other hand, AlAs introduces challenges, not only in strain compensation and growth, but also in effects on thermal management, thermal stability, and scattering. Leakage current, allowing electrons to bypass transitions between upper and lower laser levels occur due to scattering of electrons into higher-lying states via phonons and interface roughness scattering. This interface roughness scattering is exacerbated by large values of ΔE<sub>c</sub> and by the rms roughness itself, both of which are pronounced at the AlAs/InGaAs interface. The resulting leakage current noticeably reduces the slope efficiency, leading to more heating to achieve a given emission power. Efficient thermal management requires a buried heterostructure design; the re-growth of InP:Fe, however, needs to be carried out at temperatures consistent with maintaining the highly strained AlAs/InGaAs interfaces. This paper describes the physics of intersubband electron scattering due to strained interfaces and some partially optimized structures with J<sub>th</sub> = 1.7 kA/cm<sup>2</sup> at 300 K, slope efficiency η = 1.4 W/A, T<sub>0</sub> = 175 K, and T<sub>1</sub> = 550 K. Re-growth of InP:Fe using gas-source MBE at substrate temperatures below 550°C results in packaged lasers with 7 μm width having high thermal conductance.
