Observation of carrier depletion and emission effects on capacitance dispersion in relaxed In0.2Ga0.8As/GaAs quantum wells

Strong changes in capacitance over frequency are found for highly relaxed I n0.2Ga0.8As/GaAs quantum well. The high-frequency dispersion is explained b y a resistance-capacitance time constant effect due to the existence of a h igh resistive layer while the low-frequency dispersion is due to carrier em ission from traps. The high-resistance layer is created by carrier depletio n when InGaAs thickness increases beyond the critical thickness. Excellent agreement is found between the data from capacitance-frequency spectra and deep-level transient spectroscopy, permitting us to conclude that both the carrier depletion and emission effects observed in capacitance-frequency sp ectra are due to the existence of an acceptor trap at 0.33 eV. This trap is generated when the InGaAs thickness is beyond its critical thickness and i s due to defect states associated with misfit dislocations. (C) 1999 Americ an Institute of Physics. [S0003-6951(99)02342-6].