Quaternary GaInAsSb epilayer was grown by MOCVD on GaSb substrate, and the crystalline state and mismatch relaxation are studied by scanning transmission electron microscopy (STEM), bright field images and convergent beam electron diffraction (CBED) patterns. Mismatch dislocations are generated from the interface, and Lomer 908 dislocations induce surface ridges, and the shift of Kikuchi lines can determine relaxation quantitatively which is similar to the value calculated from electron probe microanalysis.

Photoluminescence (PL) of quantum dots embedded in high potential barriers is studied as functions of barrier thickness and temperature. With the increase of barrier thickness, both the strengthened two-dimensional electron gas (2DEG) structure and strongly localized electron wave functions can increase the carrier recombination. The optical properties of two different-barrier-thickness samples exhibit different characteristics with the decreased measurement temperatures. The PL recombination characteristic of the samples with the barriers adjacent to a Si-doping GaAs layer is different fromthat of samples with the barrier adjacent to an i-GaAs layer.

A quantum dot (QD) can capture and emit carriers, the behavior of which is similar to that of a giant trap, and stacked QDs with a size-controlled growth show a strong tendency to align vertically. The discrete energy level properties of the self-assembled vertically stacked InAs QDs in Al0.5Ga0.5As are studied by means of deep level transient spectroscopy (DLTS) and photoluminescence (PL) spectroscopy. The DLTS measurement displays the spectra of hole and electron discrete energy levels as positive and negative peaks, respectively, which illustrates that the DLTS is a capable tool to study the optical and electrical properties of the QDs. The PL emission peaks are found to completely correspond to the DLTS signals.

An attractive feature of vertically stacked InAs/AlGaAs quantum dots (QDs), which were buried in AlGaAs high potential barrier and spacer epilayer and grown by molecular-beam epitaxy with size-controlled growth, exhibits an unknown macroscopic quantum phenomenon (i.e., phase-change splitting of the ground state). In the vertically aligned QDs, due to many-body effect and quantum-mechanical renormalization, the electron ground state splits into a series of peaks of which the intensity gradually, systematically decreases to redshift direction with a wavelength constant. By the way, energy levels of electrons and holes might really be "seen" by deep level transient spectroscopy to which the photoluminescence experiment is in an excellent agreement.

Quantum dots (QDs), which capture and emit carriers like a giant trap, are studied using deep level transient spectroscopy (DLTS). The electrons and holes in the QDs are emitted from the relevant energy levels to the conduction and valence bands, respectively, of the barrier layers with increasing temperature. The thermal emission energies from the QDs are related to their initial energy levels. In this paper, five-period vertically stacked InAs QDs in the barrier layers of a field-effect type structure are measured. The results agree well with capacitance-voltage and photoluminescence measurements. In addition, the dependence of DLTS signal on the pulse voltage and light illumination is presented. The results prove that DLTS is a powerful tool for the study of the electronic structure of QDs.