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The optical characteristics of vertical cylindrical micropillars with AlGaAs distributed Bragg reflectors and InAs/GaAs quantum dots, which are designed for the fabrication of single-photon sources, have been studied. The effect of parameters such as the inclination angle of sidewalls, partial oxidation of AlGaAs layers, and deviation of quantum dots from the central axis of a micropillar on the Purcell factor and the radiation extraction efficiency has been numerically simulated by the finite-difference time-domain method. The allowable ranges of the listed parameters have been determined for cylindrical vertical 920-nm micropillars. The comparison of the calculations performed with the refined refractive indices of the used materials at cryogenic temperatures with the measured characteristics of the fabricated micropillar structures has confirmed the adequacy of the used models.

GaInP microdisks contained InP/GaInP quantum dots having lateral size ∼150 nm and 1-5 μm−2 were investigated with help of microphotoluminescence technique. Experiments carried out in confocal, time-resolved and low-temperature modes. Comparison of results allowed to conclude that overlap of quantum dot emission area with whispering gallery mode antinode results in faster luminescence lifetime (Purcell effect). Whispering gallery mode lasing was detected. Obtained threshold power values were following 6 µW (Q=4500, T=8.5 K) and 0.4 µW (Q=7400, T=80 K).

AbstractWe report on fabrication and studies of composite heterostuctures consisting of an Al_0.55Ga_0.45N/A_l0.8Ga_0.2N quantum well and surface Al nanoislands, grown by plasma-assisted molecularbeam epitaxy on c-sapphire substrates. The influence of a substrate temperature varied between 320 and 700ºC on the size and density of the deposited Al nanoislands is evaluated. The effect of Al nanoislands on decay kinetics of the quantum well middle-ultraviolet photoluminescence has been investigated by time resolved photoluminescence. The samples with the maximum density of Al nanoislands of 10^8 cm^–2 and lateral dimensions in the range of 100–500 nm demonstrated shortening of the photoluminescence lifetime, induced by interaction of the emitting quantum well and the plasmonic metal particles.

We report a realization of room temperature lasing threshold of 1 μW in GaInP microdisk containing a few self-aggregated InP/GaInP quantum dots (QDs) grown by metal-organic vapor phase epitaxy. InP/GaInP QD microdisk cavities emitting in the spectral range of 700–800 nm and having the size of ~2 μm, free spectral range of ~35 nm and quality factors Q ~ 4000 were formed by wet chemical etching. Low dot density (~2 μm–2) and large dot size (~150 nm), suggesting a single dot lasing and maximum overlap of QD and cavity mode, were achieved using deposition of 3 ML of InP layer at 700°C.

The heterostructure design for 1.55 μm range VCSELs is proposed and realized. The wafer fusion technique was used to form the final heterostructure. The growth of AlGaAs/GaAs distributed Bragg reflectors (DBRs) on GaAs substrate and the optical cavity with an active region on InP substrate as well as a tunnel junction (TJ) regrowth was performed by molecular beam epitaxy (MBE). A key feature of the proposed design is the use of n++-InGaAs/p++-InGaAs/p++-InAlGaAs TJ, which allows, due to the effective removal of oxide from the InGaAs surface, to use MBE for re-growth of the TJ surface relief. Despite of the presence in heterostructure a narrow-gap InGaAs layers, a noticeable increase in internal optical loss in lasers can be avoided due to the short-wavelength shift of the edge of interband light absorption in ++-InGaAs layers (Burshtein-Moss effect). Fabricated VCSELs demonstrate single-mode operation with a threshold current less than 2 mA and a slope efficiency of ~ 0.46 W/A, which are comparable with characteristics of VCSELs with n++/p++-InAlGaAs TJ with a similar level of mirror losses.

We report on suppression of the Stark effect in (1.5-2)-monolayer(ML)-thick (GaN/AlN)100 multiple quantum well (MQW) structures grown on AlN/c-Al2O3 templates by plasma-assisted molecular beam epitaxy. Different stress relaxation mechanisms are revealed in these structures by using a multi-beam optical stress sensor in comparison with the 5ML-MQW structure. The former (with well thicknesses ⩽2MLs) demonstrate the nearly stress-free growth, whereas the latter structure with thicker wells exhibits the slow stress evolution from the high initial compressive stress to the nearly relaxed state with zero stress. Moreover, the former structures demonstrate a bright room-temperature cathodoluminescence (CL) with the single peak at the shortest wavelength 240 nm (1.5ML-QWs), while the latter shows much weaker multi-peak CL spectra in the spectral range of 270-360 nm.

We describe stress evolution during plasma-assisted molecular beam epitaxy (PAMBE) of AlN nucleation and buffer layers on c-Al2O3 substrates at varying growth temperatures of 780 and 850°C. Moreover, different mechanisms of stress generation in the growing AlN films, related to the processes of grain coalescence and impact of Me-excess during PA MBE by migration enhanced epitaxy and metal-modulated epitaxy, are considered.

Microdisk lasers based on three InGaAsN/GaAs quantum wells with different types of surface passivation are fabricated and studied under optical pumping. Room temperature lasing at 1.3 μm in 7 μm in diameter microdisks with InGaAsN/GaAs QW is demonstrated. We evaluated the thermal resistance as 1 °C/mW. publishedVersion

In this work we report, to the best of our knowledge, the first quantum well electrically-pumped microdisk lasers monolithically deposited on (001)-oriented Si substrate. The III-V laser structure was epitaxially grown by MOCVD on silicon with an intermediate MBE-grown Ge buffer. Microlasers with an InGaAs/GaAs quantum well active region were tested at room temperature. Under pulsed injection, lasing is achieved in microlasers with diameters of 23, 27, and 31 µm with a minimal threshold current density of 28 kA/cm2. Lasing spectrum is predominantly single-mode with a dominant mode linewidth as narrow as 35 pm.

Formation, emission, and lasing properties of strain-free InP(As)/AlInAs quantum dots (QDs) embedded in AlInAs microdisk (MD) cavity were investigated using transmission electron microscopy and photoluminescence (PL) techniques. In MD structures, the QDs have the nano-pan-cake shape with the height of similar to 2 nm, the lateral size of 20-50 nm, and the density of similar to 5-10(9) cm(-2). Their emission observed at similar to 940 nm revealed strong temperature quenching, which points to exciton decomposition. It also showed unexpected type-I character, indicating In-As intermixing as confirmed by band structure calculations. We observed lasing of InP(As) QD excitons into whispering gallery modes in MD having the diameter of similar to 3.2 lm and providing a free spectral range of similar to 27 nm and quality factors up to Q similar to 13 000. Threshold of similar to 50 W/cm(2Y) and spontaneous emission coupling coefficient of similar to 0.2 were measured for this MD-QD system. Published by AIP Publishing.

We report on microdisk lasers based on GaInNAs(Sb)/GaAs(N) quantum well active region. Their characteristics were studied under electrical and optical pumping. Small-sized microdisks (minimal diameter 2.3 μm) with unprotected sidewalls show lasing only at temperatures below 220 K. Sulfide passivation followed by SiNx encapsulation allowed us achieving room temperature lasing at 1270 nm in 3 μm GaInNAs/GaAs microdisk and at 1550 nm in 2.3 μm GaInNAsSb/GaAsN microdisk under optical pumping. Injection microdisk with a diameter of 31 μm based on three GaInNAs/GaAs quantum wells and fabricated without passivation show lasing up to 170 K with a characteristic temperature of T0 = 60 K. publishedVersion

We demonstrate that quantum dot microdisk lasers are able to operate under continuous wave current injection at 100 °C. We also present a novel method for increasing a side mode suppression ratio in microdisk lasers. publishedVersion

AlInAs microdisk cavities having quality factor Q ~ 15 000 were fabricated from lattice-matched InP/AlInAs (interface/aggregation) quantum dot (QD) structures using wet chemical etching. The QD emission coupled to whispering gallery modes was observed at spectral range 920 - 1000 nm at temperatures of 10 - 160 K. The laser generation with threshold power density of 50 W/cm2 at T = 10 K was observed under optical pumping. It was found that the spontaneous emission coupling factor β equals 0.23 for these microdisks. The low temperature lasing operation and the small coupling factors observed suggest the existence of small QDs formed at the InP/InAlAs interface as the main active elements.

The paper describes experimental study of stress relaxation and generation in (1-2)-μm-thick GaN and AlGaN layers grown on AlN/c-Al2O3 buffer layers by low temperature (

We demonstrate a Schottky ultraviolet photodiode (UV-PD) and a UV light-emitting diode (UV-LED) based on AlGaN heterostructures grown by plasma-assisted molecular beam epitaxy. The spectral responsivity of the Schottky UV-PD is 3 mA/W at 271 nm at zero bias and decreases by two orders of magnitude for the spectral range of longer wavelengths ( > 300 nm). The sub-monolayer digital alloying technique was used for growing the AlGaN quantum wells in UV-LEDs emitting a single electroluminescence peak at 273 nm.

Authors represent utilizing UHV Ga FIB for preparing a Si3N4/GaN substrate for submicron selective-area epitaxy. In result, GaN submicron stripes were grown in the 100, 200 and 500 nm windows of a Si3N4 mask layer. SEM investigations show good crystalline perfection of the grown stripes.

A 31 µm in diameter microdisk laser with an InAs/InGaAs quantum dot active region has been tested in the continuous-wave regime at elevated temperatures. Lasing is achieved up to 100°C with a threshold current of 13.8 mA. The emission spectrum demonstrates single-mode lasing at 1304 nm with a side mode suppression ratio of 24 dB and a dominant mode linewidth of 35 pm.

The possible mechanisms of the polarization control in single-mode intracavity- contacted vertical-cavity surface-emitting lasers (IC-VCSELs) with the rhomboidal selectively- oxidized current aperture were investigated. It was found that the lasing emission polarization of all single-mode VCSELs is fixed along the minor diagonal of the rhomboidal-shape aperture (the [110] direction). Numerical modelling of carrier transport did not reveal any sufficient injection anisotropy in the laser active region, while the transverse optical confinement factors calculated for the fundamental mode with two orthogonal polarizations are identical. Optical loss anisotropy and/or gain anisotropy are the most likely mechanisms of inducing the polarization fixation.

Complex influence of photon lifetime (controlled by the mirror loss) and aperture size on the performance of 850 nm InGaAlAs oxide-confined vertical-cavity surface-emitting lasers (VCSELs) with fully doped AlGaAs-based distributed Bragg reflectors (DBR) was investigated. We find a tradeoff between photon lifetime and gain nonlinearity for maximizing the optical bandwidth, leading to the optimum aperture size close to 4-6 μm. In spite of the reduced photon lifetime (from 4 ps to 1 ps), the excess damping caused by the current-induced self-heating limits the ultimate modulation bandwidth for the given VCSELs design at 24-25 GHz. Further improvement in high frequency characteristics can be facilitated by decrease of the heat generation and improvement of the heat removal from the active region as well as by proper engineering of the scattering loss at the oxide aperture while keeping the low capacitance optimizing design of the oxide aperture.

Multifractal analysis was applied to characterize quantitatively nanostructural disordering in HVPE-grown AlGaN/GaN UV LED structures. A higher level of leakage currents shunting the active region of LEDs by an extended defect system is correlated with higher values of multifractal parameters (MFs). As a result, the concentration of injected carriers participating in radiative recombination in the active region is reduced. MFs and the conductivity of quasi-ohmic shunts localized in an extended defect system are higher in AlGaN/GaN structures than in InGaN/GaN structures. It is one of the reasons behind the low external quantum efficiency of AlGaN/GaN UV LEDs.

Microdisk lasers based on novel InGaAsNSb/GaAsN quantum well active region are developed and studied under optical pumping. Room temperature lasing at 1.55 μm in 2.3 μm in diameter microdisks with InGaAsNSb/GaAsN QW is demonstrated.

Sulphide passivation was used for reducing the surface recombination velocity of microdisk mesas based on (AlGaIn)As/GaAs heterostructures with active region formed either by ten GaAs/AlAs quantum wells or by 1 layer of InAs/In0.15Ga0.85As quantum dots. It was demonstrated that the sulfide passivation results in substantial increase of photoluminescence intensity in all types of the mesa-structures studied.

International audience; The results of the some practical applications of InAlN layers in a device hetrostructures grown by MOVPE is presented. It is shown that use of InAlN allows not only create high-quality DBRs and HEMT structures, but also effectively modify properties of InAlN/GaN/InGaN light-emitting devices.

In this paper we present a new technological approach for GaN nanowires synthesis using metal-organic chemical vapor deposition. This aproach is to use thin titanium film, which promote nanowires seeds formation. Such an approach allows to synthesis nanowires with diametr in the range of 30 nm- 3 mkm, strongly oriented along saphire c axis and with regular hexagonal shape. A good quality of the nanowires material is confirmed by low temperature micro-photoluminescence spectrum of single nanowire, where spectral lines, corresponded to free and bound excitons, are observed.

Focused ion beam is applied to quantum dot based microresonators to form pits or groove on their surface. The emission spectra of the resonators based lasers are significantly thinned out after the ion beam milling, and one or two modes become dominant instead of a group of modes having comparable intensities. The linewidth of the lasing mode is kept unchanged, whereas the lasing threshold demonstrates an insignificant growth.