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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.

An investigation has been performed of 1.55-μm vertical-cavity surface-emitting lasers based on heterostructures with a buried tunnel junction (BTJ) with a height difference of 15 nm. The devices are obtained by wafer fusion of heterostructures grown by molecular beam epitaxy and provide single-mode lasing at a BTJ diameter of up to 8 μm. A decrease in the BTJ size leads to a sharp increase in the threshold current, the output optical power, and the resonance frequency at the lasing threshold. Stable single-mode lasing takes place due to the smoothed boundary of the buried surface relief, which induces a gradual change in the profile of the effective refractive index in the lateral direction with the effective current confinement retained. This makes it possible to reduce significantly the transverse optical confinement factor for the higher-order modes even at a large BTJ size. However, at a small BTJ size, it leads to the formation of a saturable absorber in unpumped parts of the active region.

The results are presented of a study and optimization of the conditions under which heterointerfaces of the GaAs–InGaAsP type are formed via the direct intermolecular wafer bonding (fusion) of a heterostructure of an active region on an InP substrate and distributed Bragg reflectors on GaAs substrates upon the fabrication of hybrid heterostructures for long-wavelength vertical-cavity surface-emitting lasers (VCSELs). The heterostructures are grown by solid-source molecular-beam epitaxy. It is shown that, in the case of the incomplete removal of oxide films during preparation of the wafers before fusion and/or in the presence of adsorbed water on the wafer surfaces, the fused interface contains a large number of amorphous inclusions, which are most likely oxides of Group-III elements. Optimization of the conditions in which a buried tunnel junction is formed on the surface of the heterostructure on an InP wafer made it possible to reduce the surface roughness to 1 nm and to ensure that the thickness of the GaAs–InGaAsP fused interface does not exceed 5 nm, with no dislocations or other extended defects found at the fused heterointerfaces. The 1.55-μm VCSELs fabricated from the hybrid heterostructures created using the developed technology demonstrate efficient lasing under continuous-wave pumping in a wide temperature range, which is indicative of the high optical quality of the fused heterointerfaces in the VCSEL structure.

A design of a tunnel junction (TJ) based on n++-InGaAs/p++-InGaAs/p++-InAlGaAs layers for vertical-cavity surface-emission lasers (VCSELs) for the 1.55-μm spectral range fabricated by wafer fusion of an InAlGaAsP/InP optical cavity and wafers with AlGaAs/GaAs distributed Bragg reflectors has been suggested and tested. The presence of the oxidation-resistant InGaAs layers makes it possible to employ the molecular-beam epitaxy in all stages of the fabrication technology of VCSELs, including the overgrowth of the surface profile in the TJ layer. Owing to the Burstein–Moss effect and to the thickness minimization of the p++-InGaAs layer, it was possible to avoid a buildup of the internal optical loss. As a result, the characteristics of the thus fabricated devices are comparable with those of VCSELs having an n++-/p++-InAlGaAs TJ and a similar level of the mirror losses.

A high-electron-mobility transistor (HEMT) based on InAlAs/InGaAs/InP heterostructures possessing higher breakdown characteristics is developed. An InGaAs composite channel structure, combined with completely selective forming of the double recess structure, is used in the devices. HEMTs with a T‑shaped gate 120 nm in length consist of four fingers, each 30 μm in width, exhibit a maximum transconductance of 810 mS/mm, 460-mA/mm maximum density of drain current and 8- to 10-V drain-to-gate breackdown voltage. The current-amplification cut-off frequency of transistors is over 115 GHz. Due to the enhanced breakdown voltage and the forming of a double recess structure by selective etching, the elaborated transistors are promising for application in the monolithic integrated circuits of the millimeter-wave medium power amplifiers.

Optimum shape of the capacitance–voltage (C–V) characteristic is a critical parameter determining the efficiency of frequency multiplication in heterobarrier varactors (HBVs) operating in the millimeter and submillimeter frequency ranges. A numerical model for calculating the C–V characteristics and leakage currents of HBV heterostructures with arbitrary composition and doping profiles has been verified on the basis of published and original experimental data. A specially designed HBV heterostructure with three undoped InAlAs/AlAs/InAlAs barriers surrounded by nonuniformly doped n-InGaAs modulation layers has been grown by molecular beam epitaxy on InP substrate. Prototype HBVs manufactured using the proposed heterostructure demonstrated a nearly cosine shape of the C–V curve at bias voltages up to 2 V, increased overlap capacitance, and low leakage currents.

The results of studying the dynamic characteristics of 1.55-μm single-mode vertical-cavity surface-emitting lasers (VCSELs) formed by the fusion of wafers of high-quality Bragg reflectors and an active region based on thin highly strained InGaAs/InAlGaAs quantum wells are presented. It is found that the proposed design of the active region and optical microcavity of the laser make it possible in principle to attain a high level of differential laser gain in the temperature range of 20°C–85°C, but weak electron localization leads to an increase in gain compression at elevated temperatures. Due to this fact, the VCSEL modulation bandwidth at 20°C can be increased from 9.2 to 11.5 GHz due to an increase in output optical losses, while the modulation bandwidth at 85°C does not exceed 8.5 GHz, depends weakly on the output optical losses, and is mainly limited by the optical-gain saturation.

The results of a study of internal optical losses and current injection efficiency in vertical-emitting lasers of a spectral range of 1.55 µm obtained by sintering plates of high-q Bragg reflectors and the active region on the basis of thin strained InGaAs/InAlGaAs quantum wells have been presented. It has been shown that the proposed design of the laser provides a record low level of internal optical losses (less than 6.5 cm–1) and high efficiency of current injection (more than 90%) at room temperature, which allows the realization of submilliampere threshold currents. As the temperature rises to 85°C, the current injection efficiency drops to 70% due to the thermal emission of charge carriers from the active region, accompanied by an increase in internal optical losses to 9.1 cm–1 because of an increase in absorption on free carriers and/or intersubband absorption in the valence band.

© 2021 Optica Publishing Group. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for non-commercial purposes and appropriate attribution is maintained. All other rights are reserved. A combination of advanced light engineering concepts enables a substantial improvement in photon extraction efficiency of micro–cavity–based single–photon sources in the telecom O–band at ∼1.3 µm. We employ a broadband bottom distributed Bragg reflector (DBR) and a top DBR formed in a dielectric micropillar with an additional circular Bragg grating in the lateral plane. This device design includes a doped layer in pin–configuration to allow for electric carrier injection. It provides broadband (∼8–10 nm) emission enhancement with an overall photon–extraction efficiency of ∼83% into the upper hemisphere and photon–extraction efficiency of ∼79% within numerical aperture NA=0.7. The efficiency of photon coupling to a single–mode fiber reaches 11% for SMF28 fiber (with NA=0.12), exceeds 22% for 980HP fiber (with NA=0.2) and reaches ∼40% for HNA fiber (with NA=0.42) as demonstrated by 3D finite–difference time–domain modeling.

We propose a hybrid microcavity design of a 1.3 μm range electrically driven single-photon source (SPS) consisting of two high-contrast dielectric distributed Bragg reflectors which surround a 3λ-thick semiconductor cavity with two intra-cavity contact layers and four 40-nm-thick oxide-confined apertures. According to 3D finite-difference time-domain modelling, the overall photon-extraction efficiency of ~74% and the Purcell factor of ~13 can be obtained by properly adjusting the position of oxide-confined apertures relative to the electric field of the fundamental optical mode. The studied SPS design also demonstrates a coupling efficiency of up to 13% within numerical aperture 0.12 in contrast to ~5% reached for a conventional semiconductor micropillar.

A combination of advanced concepts is applied for designing micro-cavity structures aimed for single-photon sources with high photon-extraction efficiency in the telecom O-band at ~1.3 μm. The device design consists of a broad stop-band bottom distributed Bragg reflector (DBR), a top DBR formed in a dielectric micropillar with additional circular Bragg grating and a central dielectric passive cavity. This combination of photonic elements is compatible with electric carrier injection and provides overall photon-extraction efficiency of ~83% as shown by 3D finite-difference time-domain simulations.

The characteristics of lasers of the 1.44–1.46-μm optical range grown on GaAs substrates using a metamorphic buffer are studied. The active region of the laser contains 10 rows of InAs/In0.4Ga0.6As/In0.2Ga0.8As quantum dots. It is shown that the use of special selective high-temperature annealing along with the application of short-period In0.2Ga0.8As/In0.2Al0.3Ga0.5As short-period superlattices makes it possible to substantially decrease the density of threading dislocations in the active region. A threshold current density of 1300 A cm–2, external differential quantum efficiency of 38%, and maximal pulsed-mode output power of 13 W are attained for a laser with a broad area 3 mm in length.

Vertical-cavity surface-emitting lasers (VCSELs) of 895 nm spectral range, with fixed direction of output polarization have been developed. These lasers provide single-mode output power of over 1 mW at an operational temperature of 60°С, at orthogonal polarization suppression ratio (OPSR) about 20 dB. The designed VCSELs were used in a laser source for a perspective compact nuclear magnetic resonance gyroscope. The designed laser source provides precise tuning of wavelength to the Cs133 D1 spectral line, and formation of collimated output beam.

The main problems of providing a high-speed operation semiconductor lasers with a vertical microcavity (so-called “vertical-cavity surface-emitting lasers”) under amplitude modulation and ways to solve them have been considered. The influence of the internal properties of the radiating active region and the electrical parasitic elements of the equivalent circuit of lasers are discussed. An overview of approaches that lead to an increase of the cutoff parasitic frequency, an increase of the differential gain of the active region, the possibility of the management of mode emission composition and the lifetime of photons in the optical microcavities, and reduction of the influence of thermal effects have been presented. The achieved level of modulation bandwidth of ∼30 GHz is close to the maximum achievable for the classical scheme of the direct-current modulation, which makes it necessary to use a multilevel modulation format to further increase the information capacity of optical channels constructed on the basis of vertical-cavity surface-emitting lasers.

The emission-line width for 850-nm single-mode vertical-cavity surface-emitting lasers based on InGaAs/AlGaAs quantum wells is studied. The width of the emission line for a laser with a 2-μm oxide current aperture attains it minimum (~110 MHz) at an output power of 0.8 mW. As the optical output power is further increased, anomalous broadening of the emission line is observed; this is apparently caused by an increase in the α-factor as a result of a decrease in the differential gain in the active region under conditions of increased concentration of charge carriers and of high internal optical losses in the microcavity. The α-factor is estimated using two independent methods.

The studies of the emission linewidth for single-mode near-IR vertical-cavity surface-emitting lasers with an active region based on InGaAs/AlGaAs quantum wells and different optical microcavity design. For low mirror loss, lasers with a 1λ cavity and carrier injection through distributed Bragg reflectors demonstrate a linewidth of 70 MHz and its growth to 110 MHz with increasing mirror loss (corresponding differential of efficiency ∼0.65 W/A). The design of the optical cavity with carrier injection through intracavity contacts and low-Q composition Bragg lattices reduces the linewidth to 40 MHz in spite of high mirror loss (corresponding differential efficiency of ∼0.6 W/A).

We demonstrate noise characterization of novel 894.4 nm vertical-cavity surface emitting lasers with intracavity contacts and a rhomboidal oxide current aperture (IC-VCSELs), dedicated to 133Cs D1 line compact optically pumped atomic magnetometers (OPM). The laser relative intensity noise, measured to be -139 dB/Hz at 10 kHz frequency in 1 Hz bandwidth for a laser optical power of 0.8 mW, is decreased with optical power growth. The IC-VCSELs polarization-resolved relative intensity noise is 143 dB/Hz at 10 kHz frequency in 1 Hz bandwidth for 0.8 mW. The emission linewidth of the VCSEL is about 55 MHz. The IC-VCSEL parameters are determined, such as emission linewidth ~ 50-60 MHz, optical power ~ 0.5-1.0 mW, at which the polarization-resolved RIN becomes close to the RIN, which makes it possible to use these lasers in various OPM Mz and Mx schemes. The ultimate sensitivity of OPM was estimated by the ratio of the magnetic resonance to the signal to noise level. It is shown that a OPM based on the IC-VCSELs, assuming magnetic resonance FWHM ~ 1 kHz, can achieve a shot noise-limited sensitivity around 20 fT in 1 Hz bandwidth without any polarization improvements by polarizer or polarization beam splitter cube (PBC). Developed IC-VCSELs is acceptable for use in compact OPM for magnetoencephalography.

The molecular-beam epitaxy of InGaAs/InAlAs/AlAs structures for heterobarrier varactors is studied and optimized. The choice of the substrate-holder temperature, growth rate and III/V ratio in the synthesis of individual heterostructure regions, the thickness of AlAs inserts and barrier-layer quality are critical parameters to achieve the optimal characteristics of heterobarrier varactors. The proposed triple-barrier structures of heterobarrier varactors with thin InGaAs strained layers immediately adjacent to an InAlAs/AlAs/InAlAs heterobarrier, mismatched with respect to the InP lattice constant at an AlAs insert thickness of 2.5 nm, provides a leakage current density at the level of the best values for heterobarrier varactor structures with 12 barriers and an insert thickness of 3 nm.

The electron transport in superlattices based on GaAs/AlAs heterostructures with a small number of periods (6 periods) is calculated by the Monte Carlo method. These superlattices are used in terahertz diodes for the frequency stabilization of quantum cascade lasers in the range up to 4.7 THz. The band structure of superlattices with different numbers of AlAs monolayers is considered and their current–voltage characteristics are calculated. The calculated current–voltage characteristics are compared with the experimental data. The possibility of the efficient application of these superlattices in the THz frequency range is established both theoretically and experimentally.

The quality of heteroboundaries and optimal conditions for epitaxial growth are critical parameters for obtaining low leakage currents of heterobarrier varactors in the InGaAs/InAlAs/AlAs material system. Grown by molecular-beam epitaxy, three-barrier heterobarrier varactor structures adjacent to InAlAs/AlAs/InAlAs barrier layers by additional mismatched InGaAs layers subjected to compressive stress show, under optimal epitaxy conditions, extremely low levels of leakage current density (not more than 0.06 A/cm2 at a voltage of 5 V and 85°C) with relatively thin AlAs inserts (with a thickness of 2 nm).

We report on room-temperature generation at the 4.8-μm wavelength in a lattice-matched structure of a quantum cascade laser (QCL) grown on indium phosphide (InP) substrate. Laser heterostructures grown by molecular beam epitaxy (MBE) comprised 30 cascades and were designed to generate at the 4.80 μm wavelength corresponding to an atmospheric transparency window. Experiments demonstrated effective lasing at temperatures from 80 to 300 K on a wavelength coinciding with the calculated value, which confirmed the high quality of interfaces, high precision of layer thicknesses, and high accuracy of active region doping.

Vertical-cavity surface-emitting lasers with an active region based on submonolayer InGaAs quantum dots with an oxide-aperture diameter of ~1 μm have been studied. It is established that peaking of the output optical pulses to 50–100 ps can be achieved by pumping these lasers with 10–100 ns electric pulses at a repetition frequency of 10–100 kHz.

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 demonstrate the possibility of using vertical-cavity surface emitting lasers with intracavity contacts and a rhomboidal oxide current aperture for creating compact optically pumped 133Cs atomic magnetometer operating in non-zero magnetic fields, which is promising to use in magnetoencephalographic systems. The magnetic resonance parameters were studied in a two-beam MX optically pumped magnetic field sensor scheme based on the effect of the magnetic resonance line narrowing at high laser pumping and high concentrations of alkali-metal atoms. The ultimate sensitivity of OPM was estimated by the ratio of the magnetic resonance steepness to the probe light shot noise level. It is shown that a magnetic sensor based on the vertical-cavity surface emitting lasers and a compact (0.125 cm3 volume) Cs vapor cell can achieve a shot noise-limited sensitivity better than 15 fT in 1 Hz bandwidth. Developed intracavity contacted VCSELs suitable for use in compact atomic magnetometers for magnetoencephalographic systems.

The static characteristics of 1.5 μm wafer-fused VCSEL with the thin n++-InGaAs/p++-InGaAs/p++-InAlGaAs tunnel junction (TJ) were investigated. The devices with the 8 μm diameter of the buried tunnel junction (BTJ) demonstrate effective single-mode lasing. A rapid increase in the threshold current, accompanied by an abrupt change in the output optical power is observed for devices with BTJ-diameter less than 7 μm. The observed behavior can be explained by increasing in the overlap of the optical mode with the unpumped (passive) part of the active region, which leads to the additional optical absorption. On the one hand, since the high-order transverse modes have the higher optical losses due to larger overlap with the unpumped part of the active region, then lasing via fundamental mode is more preferable even at large size of BTJ region. On the other hand, the reduction of effective index step between the BTJ region and the regions outside BTJ (caused by using small TJ etching depth) and the lateral smoothing of the difference in the height of the surface relief after TJ regrowth results in the significant drop of the transverse optical confinement factor and rise of absorption. Moreover, the absorption effect can be also strongly enhanced by increasing the heatsink temperature due to decreasing in the gain-to-cavity detuning.

Studies aimed at optimization of the design of a dielectric distributed Bragg reflector (DBR) produced by the reactive magnetron sputtering method for applications in near-IR vertical-cavity surface-emitting lasers with intracavity contacts (ICC-VCSELs) are carried out. It is shown that the reflectivity of the dielectric DBRs based on SiO2/TiO2 decreases due to the polycrystalline structure of the TiO2 layers, which causes diffusive scattering of light. In contrast, amorphous Ta2O5 layers is characterized by a low surface roughness and low fluctuation in the refractive index. Single-mode ICC-VCSELs in the 980-nm spectral range with dielectric DBR based on SiO2/Ta2O5 with a threshold current less than 0.27 mA, electric resistance of less than 200 Ω, and differential efficiency of more than 0.8 W/A are demonstrated.

The fundamental possibility of achieving temperature stability of laser emitters of 1.3-μm spectral range exhibiting a vertical microcavity and an active region based on InAs/InGaAs quantum dots (QDs) is investigated. It is demonstrated that using an undoped hybrid vertical optical microcavity formed by a lower undoped semiconductor and an upper distributed dielectric Bragg reflectors allows obtaining laser oscillation up to a temperature of ~100°C at nearly constant threshold optical pump power for an active region consisting of QD layers under optimal spectral mismatch between the position of maximum gain of the QD ground state and the resonance wavelength.

The effect of the layer thickness and composition in AlGaN/AlN/GaN and InAlN/AlN/GaN transistor heterostructures with a two-dimensional electron gas on their electrical and the static parameters of test transistors fabricated from such heterostructures are experimentally and theoretically studied. It is shown that the use of an InAlN barrier layer instead of AlGaN results in a more than twofold increase in the carrier concentration in the channel, which leads to a corresponding increase in the saturation current. In situ dielectric-coating deposition on the InAlN/AlN/GaN heterostructure surface during growth process allows an increase in the maximum saturation current and breakdown voltages while retaining high transconductance.

The polarization characteristics of 850-nm vertical-cavity surface-emitting lasers (VCSELs) with intracavity contacts and a rhomboidal oxide current aperture are studied. It is found that radiation polarization is always directed along the minor diagonal of the rhomboidal aperture (along the [ $$\overline 1 $$ 10] direction) for all single-mode VCSELs. The numerical simulation of carrier transport does not reveal the significant anisotropy of carrier injection to the active region. Furthermore, an analysis of the spatial distribution of the fundamental mode for two orthogonal polarizations within an effective waveguide model shows close transverse optical-confinement factors. Optical loss anisotropy in the asymmetric microcavity and/or gain anisotropy in the strained active region are the most likely mechanisms responsible for fixing the polarization.

Microdisk injection lasers on GaAs substrates, with a minimum diameter of 15 μm and an active region based on InAs/InGaAs quantum dots, are fabricated. The lasers operate in the continuous-wave mode at room temperature without external cooling. The lasing wavelength is around 1.27 μm at a minimum threshold current of 1.6 mA. The specific thermal resistance is estimated to be 5 × 10–3 °C cm2/W.

cited By 9; International audience; The numerical simulation, and theoretical and experimental optimization of field-effect microwave high-electron-mobility transistors (HEMTs) based on GaN/AlN/AlGaN heterostructures are performed. The results of the study showed that the optimal thicknesses and compositions of the heterostructure layers, allowing high microwave power implementation, are in relatively narrow ranges. It is shown that numerical simulation can be efficiently applied to the development of microwave HEMTs, taking into account basic physical phenomena and features of actual device structures.

The coherent light–matter interaction in a 4-level cascade-type subband system of an asymmetric GaAs/AlGaAs quantum well structure is studied in pump-probe transmission experiments with picosecond (ps) time resolution. Coupling two excited subbands by an intense mid-infrared laser pulse at low sample temperatures is found to result in a substantially increased transparency of the fundamental e 1 –e 2 transition. We find a reduction of the absorption coefficient by ~80%, which is one of the most pronounced electromagnetically induced transparency in solid state systems observed so far.

An approach to precision calibration of the silicon doping level in gallium arsenide epitaxial layers is discussed that is based on studying the dependence of the carrier density in the test GaAs layer on the silicon- source temperature using the Hall-effect and CV profiling techniques. The parameters are measured by standard or certified measuring techniques and approved measuring instruments. It is demonstrated that the use of CV profiling for controlling the carrier density in the test GaAs layer at the thorough optimization of the measuring procedure ensures the highest accuracy and reliability of doping level calibration in the epitaxial layers with a relative error of no larger than 2.5%.

Detail measurements and full-vector three-dimensional FDTD technique were used to analyze anomalous mode behavior in double-aperture oxide-confined 850 nm VCSELs with large gain-to-cavity detuning.

Miniature laser source based on intracavity-contacted vertical-cavity surface-emitting laser with rhomboidal oxide current aperture was investigated for coherent population trapping (CPT) resonance excitation in microfabricated 133Cs gas cell filled with Ne buffer gas under the pressure of 300 torr. The cell operation temperature was 90°C. The laser output power was 550 μW at bias current of 3.2 mA and 65°C. The short-term stability of ∼2.5·10-11 at the measurement time of 1 sec was estimated from CPT resonance signal measurements.

The thermal properties, including thermal resistance R th , capacitance C th and time constant τ th of highpower AlGaInN LEDs have been investigated and analyzed. The transient thermal behavior was expressed as a multiexponential function with time constants associated with a specific R th,i and C th,i components of LED structure.

The spectral characteristics of a laser with an active region based on a ten-layer system of In(Ga)As/GaAs vertically correlated quantum dots with 4.5-nm GaAs spacer layers between InAs quantum dots are studied under the conditions of spontaneous and stimulated emission, depending on the current and the duration of pump pulses. Data obtained by transmission electron microscopy and electroluminescence and absorption polarization anisotropy measurements make it possible to demonstrate that the investigated system of tunnel-coupled InAs quantum dots separated by thin GaAs barriers represents a quantum-dot superlattice. With an increase in the laser pump current, the electroluminescence intensity increases linearly and the spectral position of the electroluminescence maximum shifts to higher energies, which is caused by the dependence of the miniband density-of-states distribution on the pump current. Upon exceeding the threshold current, multimode lasing via the miniband ground state is observed. One of the lasing modes can be attributed to the zero-phonon line, and the other is determined by the longitudinal-optical phonon replica of quantum-dot emission. The results obtained give evidence that, under conditions of the laser pumping of an In(Ga)As/GaAs quantum-dot superlattice, strong coupling between the discrete electron states in the miniband and optical phonons takes place. This leads to the formation of quantum-dot polarons, resulting from the resonant mixing of electronic states whose energy separation is comparable to the optical-phonon energy.

The paper presents results on optimizing the MOVPE technology of light-emitting diode (LED) structures in a Dragon-125 system to accelerate the technological cycle. Due to the high growth rate of GaN layers and optimization of the initial GaN growth phase, the total duration of the epitaxial process is reduced from 4 h 45 min to 2 h 44 min. The LED diode structures grown by this technique compare well in quality with LEDs grown by the standard method in the commercially available AIX2000HT system.

The effect of the spectral detuning between the spectral gain maximum of an active region based on AlInGaAs nanoheterostructures and vertical microcavity resonance (gain-cavity detuning) on the steady-state- and dynamic characteristics of high-speed vertical-cavity surface-emitting lasers (VCSELs) for the 850-nm spectral range with two selectively oxidized current apertures is studied. For multimode devices with gain-cavity detuning exceeding 20 nm and a comparatively large current aperture (>6 μm), anomalous lasing onset via higher order modes is observed, with subsequent switching to lower order modes at high currents. Simultaneous lasing via both types of transverse modes, observed at intermediate pumping levels, leads to a nonclassical dependence of the maximum effective-modulation frequency on the pump current. An increase in the working temperature, as well as a decrease in the size of the current aperture of a VCSEL, leads to classical multimode lasing behavior. The observed phenomena are to be taken into account when optimizing the design of high-speed VCSELs.

The effect of the photon lifetime in an optical microcavity on the characteristics of 850-nm vertical-cavity surface-emitting lasers (VCSELs) with fully doped distributed Bragg reflectors (DBRs) and an oxide current aperture is studied. The photon lifetime in the microcavity is controlled by varying the upper DBR reflectance. It is found that the speed of VCSELs with a current-aperture diameter of 10 μm is mainly limited by the self-heating effect, despite an increase in the relaxation-oscillation damping coefficient with increasing photon lifetime in the microcavity. At the same time, the higher level of internal optical loss in lasers with a current-aperture diameter of 1.5 μm leads to dominance of the effect of relaxation-oscillation damping independently of the radiation output loss. In the case of devices with a current-aperture diameter of 5.5 μm, both mechanisms limiting the speed operate, which allow an increase in the VCSEL effective modulation frequency from 21 to 24 GHz as the photon lifetime decreases from 3.7 to 0.8 ps.

We have studied the possibility of determining the actual thicknesses and compositions of separate layers in AlGaAs heterostructures with vertical-cavity optical microresonators by the combined use of optical reflectance spectroscopy and X-ray diffraction. It is established that a self-consistent solution of two inverse problems with the aid of a special test heterostructure partly removes the problem of solution ambiguity and increases the absolute accuracy of determination of the parameters of individual epitaxial layers.

The miniband conductivity in short-period GaAs/AlAs superlattices with a terahertz cavity has been studied. A stepwise decrease in the current caused by the formation of the electrical domains has been observed in current–voltage characteristics at a certain threshold voltage. It has been found that this threshold voltage changes considerably under the variation of the cavity parameters. The shift of the threshold has been explained by the excitation of high-amplitude oscillations in the cavity.

Performance of a detector based on AlGaAs/InGaAs/GaAs-material system was studied. The detector was comprised of large serpentine array of high-electron mobility transistors (HEMTs) connected in series. The floating drain contact of each transistor (except the last one) served as a source for the next one. Detection of terahertz (THz) radiation was based on the excitation of electron plasma oscillations in the HEMT's channel. The peculiarities of THz response of the detector in question including an enhanced noise-equivalent power were demonstrated.