Metamorphic InAs/InGaAs QWs with electron mobilities exceeding 7 × 105 cm2/Vs

We present a study on the influence of strain-relieving InAlAs buffer layers on metamorphic InAs/InGaAs quantum wells grown by molecular beam epitaxy on GaAs. Residual strain in the buffer layer, the InGaAs barrier and the InAs wells were assessed by X-ray diffraction and high-resolution transmission electron microscopy. By carefully choosing the composition profile and thicknesses of the buffer layer, virtually unstrained InGaAs barriers embedding an InAs quantum well with thickness up to 7 nm can be grown. This allows reaching low-temperature electron mobilities much higher than previously reported for samples obtained by metamorphic growth on GaAs, and comparable to the values achieved for samples grown on InP substrates.