We report on AlGaN multiple-quantum-well separate confinement laser heterostructures grown by plasma-assisted molecular-beam epitaxy directly on c-sapphire at low temperatures (<800 °C). Threading dislocation density was reduced down to 109–1010 cm−2 owing to both intentionally introduced strained AlGaN/AlN superlattices and self-organized blocking structures in the AlGaN step-graded buffer layers. The quantum wells were fabricated by a submonolayer digital alloying technique. Calculations of the optical gain and confinement in the optically pumped laser structures yielded its optimum design comprising an asymmetric waveguide. Lasing at 303 nm with the relatively low threshold excitation density of 0.8 MW/cm2 at 295K has been achieved.

The violet-green laser converter based on a molecular-beamepitaxy (MBE) grown CdSe quantum dot (QD) laser heterostructure pumped by a commercial InGaN laser diode (LD) emission has been fabricated and studied in detail. The optimized II-VI laser heterostructure consists of asymmetrical ZnSe/ZnSSe superlattice (SL) waveguide and active region comprising five CdSe QD sheets (QDS) placed in the centre of 2-nm-thick ZnSe quantum wells. The new laser structure design provides both a high homogeneity of optical pumping of the CdSe QDS due to tunnelling of charge carriers between the QDS separated by 5-nm-thick ZnSe/ZnSSe/ZnSe barriers and high optical confinement factor. Optimization of both cavity length of the II-VI laser and parameters of optical focusing system to obtain a narrow stripe with the length slightly exceeding the cavity length has been performed. As a result, the maximum achieved quantum efficiency and pulse output power in green have been as high as 8% and 65 mW, respectively.

We have used the variable stripe technique and pump-probe spectroscopy to investigate both gain and the dynamics of amplified spontaneous emission from CdSe quantum dot structures. We have found modal gain coefficients of 75 and 32 cm −1 for asymmetric and symmetric waveguide structures, respectively. Amplified spontaneous emission decay times of 150 and 300 ps and carrier capture times of 15 and 40 ps were measured for the structures with high and low material gains respectively. The difference in the capture times are related to the fact that for the symmetric waveguide, carriers diffuse into the active region from the uppermost ZnMgSSe cladding layer, yielding a longer rise time for the pump-probe signals for this sample.

We report on the molecular beam epitaxy growth of optically pumped Cd(Zn)Se/ZnMgSSe laser heterostructures with CdSe/ZnSe quantum dots in the active region, emitting in the green spectral range. The lasing threshold as low as 2.5 kW/cm 2 and the external quantum efficiency of 43%, maximum pulse power of 22.35 W is demonstrated.

A series of double heterojunction AlGaN/GaN/AlGaN high electron mobility transistor (HEMT) heterostructures are grown by ammonia MBE on sapphire substrates using AlN buffer layers with varying thicknesses and growth conditions. The grown heterostructures are investigated by atomic force microscopy as well as photoluminescence (PL), stimulated emission (SE), and photoreflectance (PR) measurements. It is shown that PL intensity cannot be used as a reliable criterion for quality control of HEMT heterostructures because of an influence of surface roughness. A new method of quality control of the active GaN layer in HEMTs is proposed based on determination of the SE threshold excitation level. An advantage of the method is that no reference sample is needed for comparison of different HEMT structures. Internal electric field strength values are determined from PR spectra and their correlation with 2DEG density is demonstrated.