Search

Semiconductor lasers have developed rapidly with the steady growth of the global laser market. The use of semiconductor laser diodes is currently considered to be the most advanced option for achieving the optimal combination of efficiency, energy consumption, and cost parameters of high-power solid-state and fiber lasers. In this work, an approach for optical mode engineering in planar waveguides is investigated. The approach referred to as Coupled Large Optical Cavity (CLOC) is based on the resonant optical coupling between waveguides and allows the selection of high-order modes. The state-of-art of the CLOC operation is reviewed and discussed. We apply the CLOC concept in our waveguide design strategy. The results in both numerical simulation and experiment show that the CLOC approach can be considered a simple and cost-efficient solution for improving diode laser performance.

Edge-emitting lasers with active regions based on novel InGaAs/GaAs quantum heterostructures of transitional dimensionality, i.e., quantum well-dots, which are intermediate in properties between quantum wells and quantum dots, are studied. It is shown that the rate of the lasing-wavelength blue shift decreases with increasing number of quantum well-dot layers in the active region and with increasing optical confinement factor as the cavity length decreases. In a laser with 10 quantum well-dot layers, the lasing-wavelength position remains within the limits of the fundamental optical transition down to the smallest cavity lengths (100 μm). In devices with a single quantum well-dot layer and/or with a low optical confinement factor, lasing directly switches from the ground state to waveguide states omitting excited states below ≤200 μm. Such an effect has not been observed in quantum-well- and quantum-dot lasers and can be attributed to the abnormally low density of excited states in quantum well-dots.

Analytical expressions are presented, and, through them, the analysis of component parts of the electrical resistance of injection microdisk lasers is carried out depending on the size of the microdisk resonator, parameters of the substrate, and configuration of the contact to it.

High-speed photodetectors (PDs) based on InGaAs/GaAs quantum well-dot (QWD) nanostructures with the frontal-end and back-end input of radiation have been studied. A PD with 40 rows of QWDs exhibited a spectral responsivity of up to 0.4 A/W in the 950–1100 nm optical range at a –5-V bias voltage. The decay time constant of pulsed response for PDs with an input area of 1.4 × 10–4 cm2 was ~250 ps.

We discuss the effect of self-heating on performance of injection microdisk lasers operating in continuous-wave (CW) regime at room and elevated temperature. A model is developed that allows one to obtain analytical expressions for the peak optical power limited by the thermal rollover effect, the corresponding injection current and excess temperature of the device. The model predicts, there exists the maximum temperature of microlaser operation in CW regime and the minimum mircrodisk diameter, at which CW lasing is possible. The model allows one to determine the dependence of the device characteristics on its diameter and the inherent parameters, such as thermal resistance, electrical resistance, non-radiative recombination and characteristic temperature of the threshold current. It is found that a rapid growth of the threshold current density with decreasing the diameter (which takes place even in the absence of the self-heating effect) is the main internal reason leading to the dependence of the temperature characteristics of the mirodisk laser on its size. In the calculations, we used a set of parameters extracted from experiments with InGaAs quantum dot microdisk lasers. The simulation results (in particular, the light-current curve and the dependence of the minimum microdisk diameter on ambient temperature) comply well with the measured dependences.

Data on the synthesis of structures for a quantum cascade terahertz laser in the AlGaAs/GaAs material system on GaAs substrates using the molecular-beam-epitaxy method and their characterization are presented. The specific features necessary for the implementation of such structures are considered. It is shown that, for this configuration, almost single-mode lasing is observed at a frequency of ~3 THz up to a temperature of ~60 K.

AlGaAs/GaAs microdisk lasers with InAs/InGaAs quantum dots have been transferred to the surface of a silicon wafer using an indium solder. The microlasers have a common electric contact deposited on top of the residual n+-GaAs substrate and individual addressing is ensured by placing the microdisks with the p contact down onto separate contact pads formed on silicon. No effect of a non-native substrate on the electrical, threshold, thermal, and spectral characteristics has been established. The microdisks can operate in continuous-wave regime without forced cooling at a threshold current density of ~0.7 kA/cm2. The lasing wavelength is stable (

The feasibility of detecting the emission of a microdisk laser with a diameter of 23 μm with an active region based on InGaAs/GaAs quantum well-dots using a nearby photodetector (100 × 4000 μm) with a similar active region is demonstrated. For continuous lasing, a pump current of 20 mA, and a distance between the faces of the microlaser and the photodetector of about 100 μm, a photocurrent of ~10 μA was obtained, which corresponds to a photodetector sensitivity of ~0.9 μA/μW.

A model is developed that makes it possible to analytically determine the threshold current of a microdisk laser with consideration for its self-heating as a function of the ambient temperature and the microlaser diameter. It is shown that there exists a minimum microdisk diameter determined by self-heating, up to which continuous-wave lasing can be reached at a given temperature. Another manifestation of the self-heating effect is the existence of the ultimate working temperature, which is lower, the smaller the microlaser diameter. Reasonable agreement between the predictions of the model and the available experimental data is shown.

The operation speed of microdisk lasers with quantum dots working at room temperature without thermal stabilization has been experimentally examined, and the widest modulation bandwidth of microdisks with various diameters has been calculated. It was shown that taking into account the effect of self-heating of a microlaser at high bias currents, which is manifested in a decrease of the ultimate operation speed and in an increase in the current at which the widest modulation bandwidth is reached, enables a good description of the experimental data. The self-heating most strongly affects microlasers with a small diameter (less than 20 μm).

Solar cells based on a new type of nanostructure (quantum well-dots) have been studied. These quantum well-dots (QWDs) are In0.4Ga0.6As layers with marked composition and thickness modulations. The energies of the observed optical transitions in QWDs turn out to be close to the energies of transitions involving a light hole and a heavy one in a two-dimensional quantum well of the same nominal thickness and composition. The ground-state peak is characterized by strong TE polarization (>70%), while the shorter-wavelength peak is almost unpolarized (

Evolution of photoluminescence (PL) and PL excitation spectra in structures containing InAs/InGaAs/GaAs quantum-dot (QD) arrays is investigated in detail as a function of detection energy in the temperature range from 20 to 300 K. Detailed analysis of PL excitation spectra enabled identification of peaks corresponding to excited QD states. The transition probability from the latter to the ground state is higher than in states the transition probability from which to the ground state is low but considerably increases due to effective carrier relaxation involving LO phonons. The dependence of the energy difference of the spectral position of the peaks corresponding to the ground and excited states on ground-state energy (i.e., on QD size) that is characteristic for QDs is found to be violated at 140–160 K, the temperature at which transport of carriers between QDs becomes activated.

Half-disk lasers fabricated by cleaving initial full-disk lasers have an advantage of directional light outcoupling as well as increased output power and efficiency as compared to full-disk lasers of the same diameter. The continuous wave output power of a 200 µm diameter half-disk laser exceeds 70 mW. Quasi single-mode lasing with a high side-mode suppression ratio more than 20 dB is demonstrated for half-disk lasers of various diameters. A maximum 3 dB small signal modulation frequency of 4.9 GHz was measured for a 100 µm in diameter half-disk laser.

Spontaneous emission in a vertical cavity surface emitting laser (VCSEL) have been studied. It was estimated that a significant part of the spontaneous emission (~1/3) in a conventional VCSEL goes into a waveguide mode that propagates in the plane of the Bragg mirrors. The theoretical study of a recently proposed anti-waveguide VCSEL design is presented and the damping of the waveguide mode emission is shown. Moreover we calculate that 3λ/2-cavity AVCSEL has almost the same gain value for vertical mode as conventional λ-VCSEL despite the higher cavity width due to the light redistribution effect while λ/2-cavity AVCSEL has 19% higher gain.

The radiation power from active area into the planar waveguide has been studied theoretically in order to model VCSEL characteristics. Exact and simple quantitative connection between modal gain and spontaneous emission into planar waveguide has been established. The possibility of the in-plane lasing in the conventional VCSEL with gain area laterally limited by gain aperture has been examined and condition required for this has been found.

InGaAs/InGaAlAs laser diodes operating in the 1.55-μm spectral range are studied. It is demonstrated that a certain level of carbon doping (1012 cm–2 per a single quantum well) allows one to reduce the temperature coefficient of variation of the lasing wavelength in such structures and raise the characteristic temperature of threshold current and differential efficiency at temperatures from 16 to ~50°C. These changes are accompanied by an increase in threshold current density and a reduction in differential efficiency.

The development of a fast semiconductor laser is required for the realization of next-generation telecommunication applications. Since lasers operating on quantum dot ground state transitions exhibit only limited gain due to the saturation effect, we investigate lasing from excited states and compare its corresponding static and dynamic behavior to the one from the ground state. InAs quantum dots (QDs) grown in dot-in-well (DWELL) structures allowed to obtain light emission from ground and three excited states in a spectral range of 1.0–1.3 μm. This emission was coupled to whispering gallery modes (WGMs) of a 6 μm microdisk resonator and studied at room temperature by steady-state and time-resolved micro-photoluminescence. We demonstrate a cascade development of lasing arising from the ladder of quantum dot states, and compare the lasing behavior of ground and excited state emission. While the lasing threshold is being increased from the ground state to the highest excited state, the dynamic behavior is improved: turn-on times and lifetimes of WGMs become shorter paving the way towards high frequency direct driven microlasers.

In the last decades, significant efforts have been devoted to developing semiconductors III-V lasers on silicon substrates, due to the prospects for the implementation of the high-speed lasers for optical communication systems integrated with silicon electronics and transistor logic. Low-threshold ridge-waveguide and microdisk/microring lasers based on AlGaAs heterostructures with self-organizing quantum dots In(Ga)As grown on Si substrates were demonstrated [1] , [2] . However, lasers synthesized on silicon are still inferior to analogs grown on native substrates (GaAs) [3] , due to higher defect densities caused by differences in polarity, lattice constants and coefficients thermal expansion of III-V materials and silicon. The epitaxial growth of laser heterostructures on native substrates (e.g. GaAs) and subsequent transfer of ready-made microlasers to silicon can help to avoid problems associated with monolithic integration of III-V and Si. Ring and disk microlasers have attracted more and more attention and are considered as promising sources of emission for inter-chip data transmission. The advantages of such microcavities are the high Q-factor of the whispering gallery (WG) modes, small size and, accordingly, low threshold currents and power consumption. In this work we study integration of InAs/GaAs quantum dot microdisk lasers on silicon either retaining the native substrate or separating from the substrate using a sacrificial layer.

A method of hybrid integration of quantum dot microdisk lasers with silicon wafer is proposed and realized. In addition to the possibility of combining microlasers with various silicon-based electronic and photonic devices, this makes it possible to significantly improve heat removal from the active region of the microlaser. The thermal resistance normalized to the mesa area reaches the level of about 0.002 (K/W)*cm2, which is significantly lower than the corresponding values of QD microlasers on GaAs substrate and monolithically grown on Si. As a result, the threshold current as well as current-induced shift of emission wavelength are reduced in continuous-wave regime.

The transition from frequency-modulated to amplitude-modulated frequency comb operation is studied experimentally in a multi-section InAs/InGaAs quantum dot frequency comb laser. Temporally and spectrally-resolved intensity and phase as well as time and frequency domain analysis allow to identify frequency-modulated and amplitude-modulated comb operation regimes in dependence on the laser gain current and absorber reverse bias voltage.

An original design of ring semiconductor lasers based on InAs/InGaAs/GaAs quantum dots, promising for clock pulse generation, optical sensing, biological and medical applications, and microwave photonics, has been proposed and tested. Lasing was obtained at room temperature with a nominal threshold current density as low as 150 A cm−2. The output power in continuous wave mode was 45 mW.

The subject of this paper is microlasers with the emission spectra determined by the whispering gallery modes. Owing to the total internal reflection of light on the sidewalls, a high Q-factor is achieved until the diameter is comparable to the wavelength. The light emission predominantly occurs in the plane of the structure, which facilitates the microlaser integration with other elements. We focus on microdisk lasers with various types of the In(Ga)As quantum dots (QDs). Deep localization of charge carriers in spatially separated regions suppresses the lateral diffusion and makes it possible to overcome the undesirable effect of non-radiative recombination in deep mesas. Thus, using conventional epitaxial structures and relatively simple post-growth processing methods, it is possible to realize small microlasers capable of operating without temperature stabilization at elevated temperatures. The low sensitivity of QDs to epitaxial and manufacturing defects allows fabricating microlasers using III–V heterostructures grown on silicon., The use of epitaxial In (Ga)As quantum dots and relatively simple post growth methods make it possible to realize microdisk lasers capable of operating without temperature stabilization at elevated temperatures.

We report on lasers based on InGaAs/GaAs quantum well-dots (QWDs). The density of states in QWDs is unique and different from that of quantum well and quantum dots. Modal gain of QWD ground state transition is as high as 75 cm-1 per layer. Output power of 14.2 W and 50 W in CW and in pulsed modes, respectively were obtained.

A strip-loaded slot waveguide is used for collecting, confining, and guiding the emission of a microdisk laser with InAs/InGaAs/GaAs quantum dot (QD) active region operating in continuous wave mode under optical pumping. An analytical model was developed to determine the vertical coupling conditions between the microdisk laser and strip-loaded slot waveguide using the model of 5-layers horizontal planar structure. The scanning near-field optical microscope measurements performed on the 10-micron in diameter microdisk covered by a TiO 2 /SiO 2 /TiO 2 strip-loaded slot waveguide confirmed the mode coupling into and guiding along the loading strip.

An InAs/InGaAs quantum dot laser with a heterostructure epitaxially grown on a silicon substrate was used to fabricate injection microdisk lasers of different diameters (15&ndash, 31 &micro, m). A post-growth process includes photolithography and deep dry etching. No surface protection/passivation is applied. The microlasers are capable of operating heatsink-free in a continuous-wave regime at room and elevated temperatures. A record-low threshold current density of 0.36 kA/cm2 was achieved in 31 &micro, m diameter microdisks operating uncooled. In microlasers with a diameter of 15 &micro, m, the minimum threshold current density was found to be 0.68 kA/cm2. Thermal resistance of microdisk lasers monolithically grown on silicon agrees well with that of microdisks on GaAs substrates. The ageing test performed for microdisk lasers on silicon during 1000 h at a constant current revealed that the output power dropped by only ~9%. A preliminary estimate of the lifetime for quantum-dot (QD) microlasers on silicon (defined by a double drop of the power) is 83,000 h. Quantum dot microdisk lasers made of a heterostructure grown on GaAs were transferred onto a silicon wafer using indium bonding. Microlasers have a joint electrical contact over a residual n+ GaAs substrate, whereas their individual addressing is achieved by placing them down on a p-contact to separate contact pads. These microdisks hybridly integrated to silicon laser at room temperature in a continuous-wave mode. No effect of non-native substrate on device characteristics was found.

We report on broad-area lasers, mode-locked lasers (MLLs), and superluminescent light-emitting diodes (SLDs) based on a recently developed novel type of nanostructures that we refer to as quantum well-dots (QWDs). The QWDs are intermediate in properties between quantum wells and quantum dots and combine some useful properties of both. 1.08 μm InGaAs/GaAs QWDs broad area edge-emitting lasers based on coupled large optical cavity waveguides show high internal quantum efficiency of 92%, low internal loss of 0.9 cm-1 and material gain of ~1.1∙104 cm-1 per one QWD layer. CW output power of 14.2 W is demonstrated at room temperature. Superluminescent light-emitting diodes with one QWD layer in the active region exhibit stimulated emission spectra centered at 1050 nm with the maximal full width at half maximum of 36 nm and the output power of 17 mW. First results on mode-locked operation in QWD lasers are also presented. 2 mm long two-section devices demonstrate the pulse repetition rate of 19.3 GHz and the pulse duration of 3.5 ps. The width of the radio frequency spectrum is 0.2 MHz.

Lasers based on semiconductor whispering gallery mode (WGM) resonators represent a perfect platform for active small footprint high-sensitive devices for biodetection. Biochemical samples typically require aqueous solution, and the resonator should be placed into a cuvette with water or in a microfluidic chip. The characteristics of modern semiconductor WGM lasers with an active region based on InAs/InGaAs quantum dots (QDs) make them promising for creating compact highly sensitive devices for biodetection. Deep localization of carriers in InAs/InGaAs QDs and suppressed lateral migration helps us to obtain room-temperature lasing in microdisk lasers immersed in an aqueous medium. In this work, we studied the sensitivity of the microdisk laser resonance spectral position to the refractive index of the surrounding material by changing the salinity of the water solution. We also successfully detected model proteins (secondary antibodies attached to the microdisk surface) via measurement of the lasing threshold power. The proteinprotein interaction on the microdisk surface manifests itself by an increase in the laser threshold power. Thus, in this work we demonstrated, for the first time, the possibility of using QD semiconductor microdisk lasers for detection of proteins in a microfluidic device.

The results of studying edge-emitting quantum-well lasers with a layered design having coupled planar waveguides, capable of suppressing the generation of excited transverse modes, are presented. In this case, a low internal loss (0.4 cm–1) is provided, combined with a small depth (~0.9 μm) of the active region, which results in a low thermal resistance of 6.0 (K/W) mm without a submount.

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.

GaAs photovoltaic converters containing quantum well-dot (QWD) heterostructures are studied. The QWD properties are intermediate between those of quantum wells (QWs) and quantum dots. The QWDs are obtained by the epitaxial deposition of In0.4Ga0.6As with a nominal thickness of 8 single layers by metal-organic vapor phase epitaxy. QWDs are a dense array of elastically strained islands that localize carriers in three directions and are formed by a local increase in the indium concentration and/ or InGaAs-layer thickness. There are two quantum-well levels of varied nature in structures with QWDs. These levels are manifested in the spectral characteristics of GaAs photovoltaic converters. A short-wavelength peak with a maximum at around 935 nm is associated with absorption in the residual QW, and the long-wavelength peak (1015–1030 nm) is due to absorption in the QWDs. Investigation by transmission electron microscopy demonstrates that an increase in the number of InGaAs layers leads to stronger elastic stresses, which, in turn, increases the carrier confinement energy in the QWDs and lead to a corresponding long-wavelength shift of the internal quantum efficiency spectrum.

We realized the excellent confinement of carriers in single-layer InAs quantum dots (QDs) via introducing two AlGaAs confining layers (CLs), and then fabricated the corresponding rolled-up InGaAs/GaAs QD microtubes by conventional photolithography and wet-etching. Subsequently, the as-fabricated AlGaAs confined QD microtubes were transferred to a Si-based SiOx substrate using a simple liquid-assisted substrate-on-substrate transfer process, thus obtaining the microtube ring resonators. Through micro-photoluminescence (µPL) measurement, optical modes were observed at room temperature and a maximum Q-factor of ~ 550 was demonstrated. In order to clearly show the effect of AlGaAs CLs, we also fabricated and transferred QD microtubes without AlGaAs CLs for comparison. µPL spectra collected at 80 K confirmed that the PL intensity of the central optical mode was increased ~ 10 times with the assistance of AlGaAs CLs. We have confidence that QD microtube ring resonators can be further improved through the incorporation of double-layer QDs together with AlGaAs CLs.

Hybrid quantum-confined heterostructures grown by metal-organic vapor-phase epitaxy (MOVPE) via the deposition of In0.4Ga0.6As layers with various nominal thicknesses onto vicinal GaAs substrates are studied by photoluminescence spectroscopy and transmission electron microscopy. The photoluminescence spectra of these structures show the superposition of two spectral lines, which is indicative of the bimodal distribution of the size and/or shape of light-emitting objects in an array. The dominant spectral line is attributed to the luminescence of hybrid “quantum well–dot” nanostructures in the form of a dense array of relatively small quantum dots (QDs) with weak electron and hole localization. The second, lower intensity line is attributed to luminescence from a less dense array of comparatively larger QDs. Analysis of the behavior of the spectral line intensities at various temperatures showed that the density of larger QDs grows with increasing thickness of the InGaAs layer.

The small-signal amplitude modulation, threshold, and spectral characteristics of microdisk lasers with InGaAs/GaAs quantum well-dots active region were studied jointly with the spectral and threshold parameters of edge-emitting lasers made from the same epitaxial heterostructure. Using the obtained material parameters, the relative intensity noise of the microdisk lasers was calculated as a function of the bias current and side-mode suppression ratio. It is shown that the integral noise is low enough for error-free optical data transmission with the maximum possible bitrate limited by the microdisk modulation bandwidth, if the bias current is above 1.7× threshold current (for side mode suppression ratio > 20 dB).

p-i-n photodiodes comprising dense arrays of InGaAs quantum dots (referred to as quantum well-dots) were fabricated, and the basic physical processes affecting their high-speed performance were studied for the first time by measuring the frequency response under illumination with photons absorbed either in the quantum well-dots (905-nm illumination) or mainly in GaAs layers (860-nm illumination). A GaAs p-i-n photodiode of similar design was also measured for comparison. A maximum −3 dB bandwidth of 8.2 GHz was measured for the 905-nm light illumination, and maximum internal −3 dB bandwidth of 12.5 GHz was estimated taking into account the effect of RC-parasitic by the equivalent circuit model. It was found that the internal response is mainly controlled by the carrier drift time in the depletion region; this process can be characterized by a field-dependent effective velocity of charge carriers in the layered heterostructure, which is approximately half the saturation velocity in GaAs. The carrier escape from the InGaAs quantum well-dots was found to has less effect; the escape time was estimated to be 12–17 ps depending on the reverse-bias voltage applied.

We study the impact of improved heat removal on the performance of InGaAs/GaAs microdisk lasers epi-side down bonded onto a silicon substrate. Unlike the initial characteristics of microlasers on a GaAs substrate, the former’s bonding results in a decrease in thermal resistance by a factor of 2.3 (1.8) in microdisks with a diameter of 19 (31) µm, attributed to a thinner layered structure between the active region and the substrate and the better thermal conductivity of Si than GaAs. Bonded microdisk lasers show a 2.4–3.4-fold higher maximum output power, up to 21.7 mW, and an approximately 20% reduction in the threshold current. A record high 3 dB small-signal modulation bandwidth of 7.9 GHz for InGaAs/GaAs microdisk lasers is achieved.

We report on a study of lasers with an emission wavelength of about 1.5 μm and high temperature stability, synthesized on an InP (001) substrate. Self-organized InAs quantum dots capped with a thin GaAs layer are used as the active region of the laser. A quaternary InGaAsP solid solution with a band-gap width of 1.15 eV serves as the waveguide/matrix layer. A high characteristic temperature of the threshold current, T 0 = 205 K, is reached in the temperature range 20–50°C in ridge-waveguide laser diodes. A correlation between the values of T 0 and the band-gap width of the waveguide layers is found.

The deposition of In x Ga1–x As with an indium content of 0.3–0.5 and an average thickness of 3–27 single layers on a GaAs wafer by metalorganic chemical vapor deposition (MOCVD) at low temperatures results in the appearance of thickness and composition modulations in the layers being formed. Such structures can be considered to be intermediate nanostructures between ideal quantum wells and quantum dots. Depending on the average thickness and composition of the layers, the wavelength of the photoluminescence peak for the hybrid InGaAs quantum well–dots nanostructures varies from 950 to 1100 nm. The optimal average In x Ga1–x As thicknesses and compositions at which the emission wavelength is the longest with a high quantum efficiency retained are determined.

Microdisk lasers demonstrate high performance and low threshold characteristics due to supporting of whispering gallery modes with a high quality factor. One of the challenging problems impeding some practical applications of whispering gallery mode lasers is that they have isotropic emission predominantly lying in the plane of the cavity. In this work, we present a novel method that provides both enhancement of the laser emission and modifies its directivity, making the vertical direction favorable. Electromagnetic energy outcouples from the cavity through the platinum–carbon plasmonic wire nanoantenna grown by electron-beam assisted deposition right up the side wall of the cavity. Evanescent field of whispering gallery mode excites surface plasmon polariton which propagates along the nanoantenna and scatters at its tip. We demonstrate 20× enhancement of the dominant mode intensity with 24 dB of side mode suppression increment without essential worsening of the Q-factor which remains over 3 × 104. The pr...

Lasing in the orange spectral range (599–605 nm) is demonstrated for (AlxGa1 –x)0.5In0.5P–GaAs laser diodes grown by metalorganic vapor-phase epitaxy (MOVPE) on GaAs (211)A and (322)A substrates. The active region consists of four layers of InxGa1 –xP vertically coupled quantum dots. The leakage of nonequilibrium electrons from the active region is suppressed by barriers consisting of four quantum-confinement layers of the InGaAlP solid solution with a high Ga content. The maximal optical output power in the pulsed regime is 800 mW and is limited by the catastrophic optical degradation of mirrors. The lasers fabricated from structures grown on (322)A substrates have a lower threshold current density, higher differential quantum efficiency, and smaller internal losses when compared with lasers fabricated from structures grown on (211)A substrates, which is explained by the higher barrier for nonequilibrium electrons in the first case.

We report simulation of the conduction band alignment in tensile–strained GaP–enriched barrier structures and experimental results on injection lasing in the green–orange spectral range (558–605 nm) in (AlxGa1–x)0.5In0.5P–GaAs diodes containing such barriers. The wafers were grown by metal–organic vapor phase epitaxy side–by–side on (8 1 1)A, (2 1 1)A and (3 2 2)A GaAs substrates, which surface orientations were strongly tilted towards the [1 1 1]A direction with respect to the (1 0 0) plane. Four sheets of GaP–rich quantum barrier insertions were applied to suppress the leakage of non–equilibrium electrons from the gain medium. Two types of the gain medium were applied. In one case 4–fold stacked tensile–strained (In,Ga)P insertions were used. Experimental data shows that self–organized vertically–correlated quantum dots (QDs) are formed on (2 1 1)A– and (3 2 2)A–oriented substrates, while corrugated quantum wires are formed on the (8 1 1)A surface. In the other case a short–period superlattice (SPSL) composed of 16–fold stacked quasi–lattice–matched 1.4 nm–thick In0.5Ga0.5P layers separated by 4 nm–thick (Al0.6Ga0.4)0.5In0.5P layers was applied. Laser diodes with 4–fold stacked QDs having a threshold current densities of ∼7–10 kA/cm2 at room temperature were realized for both (2 1 1)A and (3 2 2)A surface orientations at cavity lengths of ∼1 mm. Emission wavelength at room temperature was ∼599–603 nm. Threshold current density for the stimulated emission was as low as ∼1 kA/cm2. For (8 1 1)A–grown structures no room temperature lasing was observed. SPSL structures demonstrated lasing only at low temperatures

Electronic states in a novel type of quantum-size heterostructures referred to as InGaAs quantum well-dots (QWDs) were experimentally studied using absorption in stripe waveguides of different lengths based on a single, double, five, and ten QWD layers. The value of the modal absorption was measured to be 70 cm−1 and 90 cm−1 for ground-state transition and high-energy one, respectively. The structure of electronic states in the QWDs is also analyzed by polarization-resolved waveguide absorption and the dependence of a polarization degree on the chip length is discussed. TM polarization of the heavy-hole-based optical transition photoresponse observed in the long waveguides is attributed to the light depolarization due to the scattering on the QWD heterointerfaces.