E. V. Lutsenko

Low-threshold 303 nm lasing in AlGaN-based multiple-quantum well structures with an asymmetric waveguide grown by plasma-assisted molecular beam epitaxy on c-sapphire

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.

Lasing in Cd(Zn)Se/ZnMgSSe heterostructures pumped by nitrogen and InGaN/GaN lasers

Photoluminescence and lasing at a wavelength of λ=510–530 nm (green spectral region) in Cd(Zn)Se/ZnMgSSe structures with a different design of the active region are studied in a wide range of temperatures and nitrogen laser pump intensities. A minimal lasing threshold of 10 kW/cm2, a maximal external quantum efficiency of 12%, and a maximal output power of 20 W were obtained for the structure with the active region composed of three ZnSe quantum wells with fractional-monolayer CdSe inserts. The lasers exhibited a high temperature stability of the lasing threshold (characteristic temperature T0=330 K up to 100°C). For the first time, an integrated converter composed of a green Cd(Zn)Se/ZnMgSSe laser optically pumped by a blue InGaN/GaN laser that is grown on a Si (111) substrate and incorporates multiple quantum wells is suggested and studied.

Blue InGaN/GaN multiple-quantum-well optically pumped lasers with emission wavelength in the spectral range of 450–470 nm

Optically pumped lasing in the wavelength range of 450–470 nm in InGaN/GaN multiple-quantum-well heterostructures grown by metalorganic vapor phase epitaxy was achieved and investigated. The energy and power per pulse of the laser were 80 nJ and 10 W correspondingly for one facet at room temperature. The far-field patterns of the laser emission consisted of three light spots near the angles of +30°, −15°, and −45°. The highest operating temperature was 450 K. The photoluminescence and photoluminescence excitation spectrum structures suggest that the quantum dots inside the quantum wells are involved in the recombination mechanism.

Recombination dynamics and lasing in ZnO/ZnMgO single quantum well structures

We report a time-resolved study of the recombination dynamics in molecular beam epitaxy grown ZnO∕ZnMgO single quantum wells (SQWs) of 1.0–4.5nm width. The SQWs exhibit different emission properties, depending on both the well width and defect density. Stimulated emission has been achieved at room temperature in a separate confinement double heterostructure having a 3nm wide SQW as an active region. It has been found that a critical parameter for the lasing is the inhomogeneous broadening of both QW and barrier emission bands.

Low-threshold green laser heterostructures with Zn(Mg)SSe/ZnSe graded-index superlattice waveguide: Structural and optical properties

We report on structural and optical properties of green (λ∼520 nm) ZnCdSe/ZnMgSSe optically pumped laser heterostructures with a Zn(Mg)SSe/ZnSe graded-index superlattice (SL) waveguide, grown by molecular beam epitaxy. The pseudomorphic 400 nm thick waveguide comprising a set of strained ZnMgSSe/ZnSe and ZnSSe/ZnSe SLs of different periods and barrier-to-well thickness ratios at each side of a ZnCdSe quantum well (QW) active region provides efficient transport of nonequilibrium carriers to the QW. This results in reduction in laser threshold down to the extremely low value of 1.5 kW/cm2 at 300 K and increasing the external quantum efficiency above 44%.

Luminescence and lasing in InGaN∕GaN multiple quantum well heterostructures grown at different temperatures

It was found that the decrease of the InGaN∕GaN multiple quantum well (MQW) growth temperature from 865 to 810 °C leads to a MQW emission wavelength shift from the violet to the green spectral region. The lowering of the growth temperature also promotes a decrease of the MQW photoluminescence (PL) intensity at high excitation and a disappearance of the excitonic features from the low-temperature reflection and PL spectra of GaN barriers and claddings. The laser threshold dependence on Tg is not monotonic, with the lowest value of 270kW∕cm2 at Tg=830°C. High-temperature annealing (900 °C, 30 min) leads to a twofold increase of the PL efficiency only from the InGaN QWs grown at the lowest temperature. The results allow one to explain the laser threshold behavior in terms of the heterostructure quality, the defect concentration, In clusterization, and the piezoelectric field dependence on the MQW growth temperature.

Multiple quantum well InGaN/GaN blue optically pumped lasers operating in the spectral range of 450-470 nm

Lasing under optical pumping by N 2 -laser radiation in InGaN/GaN multiple quantum well heterostructures grown in AIXTRON MOVPE reactors was achieved and investigated in the wavelength range of 450-470 nm. The laser operation wavelength depends most strongly on V/III ratio during quantum well barrier growth. The total energy and power per pulse of the laser were 300 nJ and 40 W, respectively, with differential quantum efficiency of 3% at room temperature. The laser threshold increases exponentially with increasing operation wavelength which is mainly due to the decreasing efficiency of the spontaneous emission and due to an increase of its spectral width.

Influence of UV Light-Assisted Annealing on Optical Properties of InGaN/GaN Heterostructures Grown by MOVPE

The influence of ultraviolet light-assisted annealing on the optical properties of InGaN/GaN single quantum wells (SQW), and thick single and double heterostructures (SH, DH) was investigated. It was shown that annealing promotes an increase of the photoluminescence (PL) intensity from the active layers of the SQW and double heterostructures by as much as one order of magnitude. This is effected mainly by a diminishing of the defect concentration and a smoothing of the potential fluctuations in the upper cladding layer. The operating temperature of the DH lasers was lifted from 220 up to 300 K after annealing. Using nitrogen laser irradiation during annealing led both to a PL efficiency increase and to a phase separation in the SH with a thick active layer.

HIGH-TEMPERATURE OPTICALLY PUMPED LASING IN ZNMGSSE/ZNSE HETEROSTRUCTURES GROWN BY METALORGANIC VAPOR PHASE EPITAXY

Lasing and optical properties of ZnMgSSe/ZnSe-, ZnMgSSe/ZnSSe/ZnSe-, and ZnMgSSe/ZnMgSSe/ZnSe-based single- and multiple-quantum-well heterostructures grown by metalorganic vapor phase epitaxy were studied, and the characteristics were found to depend on the excitation intensity Iexc, temperature, and well width. Laser action under transverse optical pumping was achieved only for well widths Lz⩾4 nm and optical confinement factors Γ>0.04. In separate confinement heterostructures, lasing with the lowest threshold (Ithr=10–30 kW/cm2 at T=78 K) was achieved and device characteristics were studied up to T=577 K.

Irregular spectral position of E || c component of polarized photoluminescence from m-plane InGaN/GaN multiple quantum wells grown on LiAlO2

Polarized temperature dependent photoluminescence (PL) and room temperature (RT) photocurrent spectra of m-plane InGaN/GaN multiple quantum wells grown on LiAlO2 with In content xIn = 5%-30% were studied. As expected, higher xIn leads to larger strain in the wells and enhances both the splitting between the two highest valence subbands and the RT PL degree of polarization. At low temperatures, an irregular red-shift of the PL component with polarization E || c relative to E ⊥ c is observed, which is ascribed to the contribution of recombination of holes localized at band tails within the second highest valence subband.