Improved InAs/AlSb/GaSb heterostructures for quantum cascade laser applications

We describe some key growth issues for Mid-Infrared electroluminescent devices based on a quantum-cascade design using InAs/AlSb heterostructures grown on GaSb substrates. Structural and optical properties of antimonide/arsenide interfaces are first investigated on InAs/AlSb multiple quantum well samples with different types of Sb-like interfaces and various InAs thicknesses. We show that X-ray reflectometry is a powerful complementary tool to High Resolution X-ray Diffraction (HRXRD) to extract both individual layer thicknesses and interface roughnesses using only electronic densities as input parameters. The good structural quality of samples is evidenced by the persistence of sharp high order satellite peaks on HRXRD spectra. The associated optical properties are studied by photo-induced intersubband absorption. Strong E-12 p-polarized intersubband absorptions are observed with a full-width-at-half-maximum (FWHM) around 12 meV at 77K showing good material quality. Absorption peak positions are compared to theoretical simulations based on a 2x9-band k.p calculation. These results allow us to properly design and fabricate InAs/AlSb quantum cascade light emitting devices in the 3-5 gm wavelength window taking into account the growth constraints. Well-resolved Mid-Infrared (3.7-5.3 lam) electroluminescence peaks are observed up to 300 K with FWHM to emission energy ratio (DeltaE/E) around 8%.