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 d ots in a GaAs matrix using capacitance-voltage measurements, deep-level tra nsient spectroscopy (DLTS), photoluminescence spectroscopy, and transmissio n electron microscopy are reported. Clusters of interacting bistable defect s are discovered in GaAs layers grown at low temperature. Controllable and reversible metastable populating of quantum-dot energy states and monoenerg etic surface states, which depends on the temperature and conditions of a p reliminary isochronal anneal, is observed. This effect is associated with t he presence of bistable traps with self-trapped holes. The DLTS measurement s reveal variation of the energy for the thermal ionization of holes from s urface 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 eith er by wetting-layer holes or by ionized levels located near the heterointer face. (C) 1999 American Institute of Physics. [S1063-7826(99)00702-4].