Optical anisotropy in type-II quantum wells (QWs) on high-index substrates is studied theoretically. We analyze GaAs1−XSbX/GaAs type-II QWs and calculate the degree ρ of polarization. Compared to type-I QWs, the optical anisotropy is enhanced in the type-II QW due to the spatial overlap of holes in the QW and electrons outside. We also evaluate ρ in the QW as a function of the diffusion length to clarify how the optical anisotropy is affected by the interface grading due to the Sb/As interdiffusion. In an initial stage of grading where the diffusion process tends to increase the effective size of the repulsive potential, the electron is more repelled by the QW, leading to an increase in ρ. In later stages, however, the hole confinement and the electron repulsion by the QW both weaken, leading to a decrease in ρ. We also examine the effect of excited carrier concentration on the optical anisotropy in the type-II QW.Highlights► Type-II quantum wells (QWs) on high-index substrates are studied theoretically. ► We show that compared to type-I QWs, optical anisotropy is enhanced in type-II QWs. ► Optical anisotropy is calculated for different diffusion and carrier conditions.

We investigate effects of annealing on GaSb quantum dots (QDs) formed by droplet epitaxy. Ga droplets grown on GaAs are exposed to Sb molecular beam and then annealed at Ta=340–450 °C for 1 min to form GaSb QDs. An atomic force microscope study shows that with the increase of Ta, the average diameter of dots increases by about 60%, while their density decreases to about 1/3. The photoluminescence (PL) of GaSb QDs is observed at around 1 eV only for those samples annealed above Ta=380 °C, which indicates that the annealing process plays an important role in forming high quality GaSb QDs.

We have studied the growth of GaSb quantum dots (QDs) by droplet epitaxy and found two different growth modes. In one mode, GaSb QDs are directly formed from Ga droplets by supplying Sb molecules (PSb∼1.1×10−6 Torr) at a relatively high temperature (Ts=300 °C). In the second mode, dots are formed in two steps; Ga droplets are exposed to Sb flux (PSb∼1.3×10−6 Torr) at a low temperature (Ts=200 °C) to be clad by large granular crystals of Sb and then GaSb QDs are formed by desorbing the Sb polycrystalline grain layer at Ts=310 °C. GaSb QDs grown in the second mode are larger than original Ga droplets, whereas QDs grown in the first mode are smaller. The proper setting of the Sb flux and the substrate temperature to select either one of the modes is presented.