Capacitance spectroscopy of deep states in InAs/GaAs quantum dot heterostructures

The results of a study of a structure with a single array of InAs quantum dots in a GaAs matrix using capacitance-voltage measurements, deep-level transient spectroscopy (DLTS), photoluminescence spectroscopy, and transmission electron microscopy are reported. Clusters of interacting bistable defects are discovered in GaAs layers grown at low temperature. Controllable and reversible metastable populating of quantum-dot energy states and monoenergetic surface states, which depends on the temperature and conditions of a preliminary isochronal anneal, is observed. This effect is associated with the presence of bistable traps with self-trapped holes. The DLTS measurements reveal variation of the energy for the thermal ionization of holes from surface states of the InAs/GaAs heterointerface and the wetting layer as the reverse bias voltage is increased. It is theorized that these changes are caused by the built-in electric field of a dipole, which can be formed either by wetting-layer holes or by ionized levels located near the heterointerface.