Deep-level transient spectroscopy in InAs/GaAs laser structures with vertically coupled quantum dots

Indium arsenide/gallium arsenide structures with vertically coupled quantum dots imbedded in the active zone of a laser diode are investigated by deep-level transient spectroscopy (DLTS), and the capacitance-voltage characteristics are analyzed. The DLTS spectrum was found to undergo significant changes, depending on the temperature of preliminary isochronous annealing of the sample, T-a<T-ac=245 K or T-a>T-ac, and on the cooling conditions, with a bias voltage V-b=0 or with an applied carrier pulse V-f>0. The changes are attributed to the onset of Coulomb interaction of carriers trapped in a quantum dot with point defects localized in the nearest neighborhoods of the quantum dots and also to the formation of a dipole when T-a<T-ac and cooling takes place with V-f>0, or to the absence of a dipole when T-a>T-ac and V-b=0. It is discovered that the tunneling of carriers from the deeper states of defects to the shallower states of quantum dots takes place in the dipole, and the carriers are subsequently emitted from the dots into bands. (C) 1997 American Institute of Physics. [S1063-7825(97)02610-0].