Evolution of the amount of InAs in wetting layers in an InAs/GaAs quantum-dot system studied by reflectance difference spectroscopy

摘要

The wetting layer (WL) in InAs/GaAs quantum-dot systems has been studied by reflectance difference spectroscopy (RDS). Two structures related to the heavy-hole (HH) and light-hole (LH) related transitions in the WL have been observed. On the basis of a calculation model that takes into account the segregation effect and exciton binding energies, the amount of InAs in the WL (t_(WL)) and its segregation coefficient (R) have been determined from the HH and LH transition energies. The evolutions of t_(WL) and R exhibit a close relation to the growth modes. Before the formation of InAs dots, t_(WL) increases linearly from approx 1 to approx 1.6 monolayer (ML), while R increases almost linearly from ~0.8 to ~0.85. After the onset of dot formation, t_(WL) is saturated at approx 1.6 ML and R decreases slightly from 0.85 to 0.825. The variation of t_(WL) can be interpreted by using an equilibrium model. Different variations of in-plane optical anisotropy before and after dot formation have been observed.