Metamorphic InAs/InGaAs QWs with electron mobilities exceeding $7\times10^5cm^2/Vs$

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 7nm 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.