A study on the energy bands of multi-quantum wells in the quantum cascade laser structure by deep-level transient spectroscopy

Abstract

We have investigated the defect states and confined energy levels of three quantum wells (QWs) in the quantum cascade laser (QCL) structure by capacitance-voltage and deep-level transient spectroscopy methods. Defect states with activation energies in the range of 0.49-0.88 eV were obtained in the GaAs capping layer, and their origins were considered as EL3 and EL2 families, which are well-known deep levels of GaAs materials. The densities of these defects in the GaAs capping layer of the QCL structure were about 3-12% of the donor concentration. The confined energy levels of QWs showed activation energies of about 130 meV and 230 meV from the top of the AlGaAs barrier, and their carrier confinement ability was measured to be about 0.5% of the donor concentration.