High-mobility AlAs quantum wells with out-of-plane valley occupation

Employing state-of-the-art molecular beam epitaxy techniques to grow thin, modulation-doped AlAs quantum wells, we have achieved a low temperature mobility of 5.5 m2 V s with out-of-plane occupation, an order of magnitude improvement over previous studies. However, from the narrow well width, mobilities are still limited by scattering due to interface roughness disorder. We demonstrate the implementation of a technique utilizing thermally induced, biaxial, tensile strain that forces electrons to occupy the out-of-plane valley in thicker quantum wells, reducing interface roughness scattering and allowing us to achieve mobilities as high as 8.8 m2 V s.