Deep and shallow electronic states at ultrathin InAs insertions in GaAs investigated by capacitance spectroscopy

Single, ultrathin InAs insertions in GaAs are investigated by deep-level transient Fourier spectroscopy and capacitance–voltage measurements near the transition from layer-by-layer to three-dimensional growth. The formation of a broad band of deep levels between 0.60 and 0.80 eV below the GaAs conduction band edge is shown to be related to the incorporation of the strained InAs layer. The defect density can be as high as 5×1010 cm−2. In addition, distinct interfacial levels, the formation of which is correlated to the GaAs growth conditions, are found at the position of the ultrathin InAs sheet. Due to their short-range potential, these interfacial deep-level defects are suitable to probe the local properties of the ultrathin InAs insertion. It is experimentally verified that the small InAs islands which are formed at the onset of three-dimensional growth give rise to laterally confined quantum states in the InAs insertion.