Characterization of heavily Sn-doped GaAs grown by migration-enhanced epitaxy

The saturation of electron concentration and mobility at high doping concentration observed in the samples grown by low-temperature migration-enhanced epitaxy (MEE) is found to be strongly related to the morphology change in the film. The structural characteristics of the heavily Sn-doped GaAs have been further investigated by means of X-ray diffraction (XRD) measurement and transmission electron microscopy (TEM). The results indicate that the (GaAs)1-x(Sn2)x alloy is formed in the Sn-doped GaAs with the doping concentration higher than 1×1019 cm−3. However, when the Sn concentration exceeds 1×1021 cm−3, the formation of Sn-rich clusters becomes dominant. This formation of (GaAs)1-x(Sn2)x alloy and Sn clusters is found to be responsible for the saturation of the electron concentration and mobility in the heavily doped samples.