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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.

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 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).

In a laser with asymmetric barrier layers (ABLs) two thin barrier layers adjacent to the active region on both sides are intended to prevent bipolar population of the waveguide layers, hence, to suppress parasitic recombination in them. A theoretical model of a laser with ABLs, based on rate equations which acknowledge undesirable carrier leakage inevitable in lasers of this type implemented in practice, is proposed. Solutions to equations are obtained for the steady-state case. By the example of an InGaAs/GaAs quantum-well laser (lasing wavelength λ = 980 nm), the effect of leakages through ABLs on the device characteristics is studied. The parasitic-flux suppression ratios C of ABLs which are required to prevent the adverse effect of waveguide recombination are estimated. In the case at hand, the effect of ABLs becomes appreciable at suppression ratios of C ≥ 102. To suppress 90% of the parasitic current, C should be 2.3 × 104. The effect of ABLs on useful carrier fluxes arriving at the active region is also studied.

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.

We demonstrate a record low threshold current density of 250 A/cm2 in a quantum dot microdisk laser with a 31-μm diameter operating at room temperature in continuous wave regime without temperature stabilization. This low threshold current density is very close to the transparency current density estimated in broad-area edge-emitting lasers made of the same epitaxial wafer.

Microdisk lasers 10–30 μm in diameter operating at room temperature without thermal stabilization and with an active region based on nanostructures of hybrid dimensionality—quantum wells–dots—are investigated. High-frequency measurements of the microlaser response are performed in the direct small-signal modulation mode, which makes it possible to establish the parameters of the operating speed and analyze their dependence on the microlaser diameter. It is found that the K factor is (0.8 ± 0.2) ns, which corresponds to optical losses of ~6 cm–1, and no regular dependence on the diameter is observed. It is found that the low-frequency component of the damping coefficient of relaxation oscillations is inversely proportional to the diameter. This character of the dependence evidences a decrease in the carrier lifetime in small-diameter microcavities, which can be associated with the prevalence of nonradiative recombination on their side walls.

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.

Epi-side down bonding on a silicon substrate of AlGaAs/GaAs microdisk lasers is presented. A heterostructure with coupled large optical cavities enables location of an InGaAs quantum dot active region at a distance of ∼1 µm from the heterostructure surface. The thermal resistance was reduced to 0.2 and 0.1 K mW−1 for disks of 30 and 50 µm in diameter, respectively. The maximum continuous-wave power limited by the thermal rollover is more than doubled after bonding.

A search for materials suitable for implementation of 1.55 µm Al-free diode lasers based on InP with asymmetric barrier (AB) layers is conducted. It is shown that a very high (over 106) suppression ratio of the parasitic electron flux can be achieved using common III–V alloys for the ABs. Hence placing such ABs in the immediate vicinity of the active region should completely suppress the parasitic recombination in the waveguide. Several optimal AB designs are proposed that are based on one of the following alloys: Al-free GaInPSb, ternary AlInAs, or quaternary AlGaInAs with a low Al-content. As an important and beneficial byproduct of utilization of such ABs, an improvement of majority carrier capture into the active region occurs.

A self-consistent model for calculating the threshold and high-power characteristics of semiconductor quantum well lasers with asymmetric barrier layers is developed. The model, which is based on a system of rate equations, uses the universal condition of global charge neutrality in the laser structure. The electron and hole concentrations in the waveguide region and in the quantum well (QW) and the concentration of photons of stimulated emission are calculated. The local neutrality in the QW is shown to be strongly violated, especially at high injection currents. The violation of neutrality in a QW makes the electron and hole concentrations there dependent on the injection current under lasing conditions: in the structures under consideration, the electron concentration in the QW decreases while the hole concentration increases with increasing injection current. In the case of the ideal functioning of asymmetric barrier layers, when electron–hole recombination in the waveguide region is completely suppressed, the violation of neutrality in the QW has almost no effect on the dependence of the output optical power on the injection current: the quantum efficiency is close to unity and the light–current characteristic is linear. Nevertheless, the violation of neutrality in the QW causes weakening of the temperature dependence of the threshold current and, hence, an increase in the characteristic temperature T0 of the laser.

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.

A semiconductor-laser design is proposed in which parasitic recombination in the waveguide region is suppressed by means of double asymmetric barriers adjacent to the active region. Double asymmetric barriers block the undesirable transport of one type of charge carrier while allowing the transport of the other type of carrier. The spacer in the double asymmetric barrier can serve to compensate the elastic strain introduced by the barrier layers as well as to control the energy spectrum of charge carriers and, thus, the transmission coefficient. By the example of a laser with Al0.2Ga0.8As waveguide layers, it is shown that the design with double asymmetric barriers makes it possible to suppress undesirable electron transport by a factor of 4 in comparison to the design using single asymmetric barriers.

Injection microlasers with an active region based on arrays of InGaAs/GaAs quantum well-dots, formed by deep etching, have been studied. The manner in which the current–voltage characteristic changes when the diameter microlaser is reduced shows that a nonelectrically conducting layer with thickness of about 1.5 μm is formed near the side surface, which leads to a decrease in the effective current flow area.

We have studied characteristics of a 23-μm-diameter microdisk laser operating in a regime of direct high-frequency modulation at a stabilized heat-sink temperature of 18°C. It is found that the minimum energy consumption in this regime amounts to ~1.6 pJ/bit and is achieved at a modulation frequency of 4.2 GHz. The maximum modulation frequency is 6.7 GHz, at which the minimum energy consumption is 3.3 pJ/bit.

In this paper, results are presented on III-V quantum well dot microring diode lasers tested at elevated temperatures. To the best of our knowledge, the first uncooled microdisk lasers with diameter of 40 μm with 3-dB bandwidth above 2 GHz at 55°C are demonstrated.

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 dependences of the electronic-level positions and transition oscillator strengths on an applied electric field are studied for a terahertz quantum-cascade laser (THz QCL) with the resonant-phonon depopulation scheme, based on a cascade consisting of three quantum wells. The electric-field strengths for two characteristic states of the THz QCL under study are calculated: (i) “parasitic” current flow in the structure when the lasing threshold has not yet been reached; (ii) the lasing threshold is reached. Heat-transfer processes in the THz QCL under study are simulated to determine the optimum supply and cooling conditions. The conditions of thermocompression bonding of the laser ridge stripe with an n +-GaAs conductive substrate based on Au–Au are selected to produce a mechanically stronger contact with a higher thermal conductivity.

I–V and radiative characteristics of multilayer quantum-cascade GaAs/AlGaAs heterostructures with a double metal waveguide are investigated. The I–V characteristics typical of the quantum-cascade lasers are seen. The observed threshold-intensity growth and narrow radiation spectrum are characteristic of laser generation. The measured radiation frequency was found to be about 3 THz, which coincides with the calculated value. Thus, fully domestic terahertz quantum-cascade lasers are demonstrated for the first time.

The spatial distribution of the intensity of the emission caused by recombination appearing at a high injection level (up to 30 kA/cm2) in the waveguide layer of a GaAs/AlGaAs laser structure with GaInP and AlGaInAs asymmetric barrier layers is studied by means of near-field scanning optical microscopy. It is found that the waveguide luminescence in such a laser, which is on the whole less intense as compared to that observed in a similar laser without asymmetric barriers, is non-uniformly distributed in the waveguide, so that the distribution maximum is shifted closer to the p-type cladding layer. This can be attributed to the ability of the GaInP barrier adjoining the quantum well on the side of the n-type cladding layer to suppress the hole transport.

We present the design, fabrication, and characterization of a MEMS VCSEL which utilized a silicon on insulator wafer for the microelectromechanical system and encapsulates the MEMS by direct InP wafer bonding in order to improve the protection and control of the tuning element. This can enable more robust fabrication, a larger free spectral range, and bidirectional tuning of the MEMS element. The proposed device uses a high contrast grating mirror on a MEMS stage as the bottom mirror, wafer bondind InP with quantum wells for amplification and a deposited dielectric DBR. A tuning range of 40 nm and a mechanical resonance frequency of $>$ 2 MHz is demonstrated. We present design, fabrication, and characterization of an optically pumped MEMS VCSEL which utilizes a silicon-on-insulator wafer for the microelectromechanical system and encapsulates the MEMS by direct InP wafer bonding, which improves the protection and control of the tuning element. This procedure enables a more robust fabrication, a larger free spectral range, and facilitates bidirectional tuning of the MEMS element. The MEMS VCSEL device uses a high contrast grating mirror on a MEMS stage as the bottom mirror, a wafer-bonded InP with quantum wells for amplification and a deposited dielectric DBR as the top mirror. A 40-nm tuning range and a mechanical resonance frequency in excess of 2 MHz are demonstrated.

We present an analysis of spectral and threshold characteristics of InGaAs/GaAs quantum well-dot microdisk laser operated under cw current injection at room temperature without external cooling. The experimental values of the threshold current for the disk and ring microlasers are compared. We observe that the threshold current can be significantly decreased in devices with large diameters (more than 30 μm) by using the ring geometry.

We studied a far-field emission pattern for microlasers with InGaAs/GaAs quantum well-dots in the active region. Angular-resolved electroluminescence spectra measurement revealed various far-field patterns depending on current and resonance mode.

The spectral, threshold, and power characteristics of a microdisk laser 31 μm in diameter with an active region based on InAs/InGaAs quantum dots, operating in the continuous-wave (cw) mode at room temperature are studied. The minimum threshold current density is 0.58 kA/cm2, the subthreshold linewidth of the whispering-gallery mode is 50 pm at a wavelength lying in the range of 1.26–1.27 μm. The total power emitted into free space reaches ~0.1 mW in the cw mode, whereas the radiation power of the whispering-gallery modes is ~2.8%.

The Postgrowth processing of GaAs/AlGaAs multilayer heterostructures for terahertz quantumcascade lasers (QCLs) are studied. This procedure includes the thermocompression bonding of In–Au multilayer heterostructures with a doped n +-GaAs substrate, mechanical grinding, and selective wet etching of the substrate, and dry etching of QCL ridge mesastripes through a Ti/Au metallization mask 50 and 100 μm wide. Reactive-ion-etching modes with an inductively coupled plasma source in a BCl3/Ar gas mixture are selected to obtain vertical walls of the QCL ridge mesastripes with minimum Ti/Au mask sputtering.

The power characteristics of quantum-well lasers with asymmetric barrier layers, which represent a novel type of injection laser, are calculated on the basis of an extended model taking into account asymmetry in the filling of electron and hole states. The electron–hole asymmetry is shown to have no significant effect on the characteristics of these lasers. Even in the presence of intermediate layers (located between the quantum well and each of the two asymmetric barrier layers), where parasitic electron–hole recombination does occur, the internal differential quantum efficiency of such a laser exhibits only a weak dependence on the pump current and remains close to unity; therefore, the light–current characteristic remains linear up to high pumping levels.

We review epitaxial formation, basic properties, and device applications of a novel type of nanostructures of mixed (0D/2D) dimensionality that we refer to as quantum well-dots (QWDs). QWDs are formed by metalorganic vapor phase epitaxial deposition of 4−16 monolayers of InxGa1−xAs of moderate indium composition (0.3 < x < 0.5) on GaAs substrates and represent dense arrays of carrier localizing indium-rich regions inside In-depleted residual quantum wells. QWDs are intermediate in properties between 2D quantum wells and 0D quantum dots and show some advantages of both of those. In particular, they offer high optical gain/absorption coefficients as well as reduced carrier diffusion in the plane of the active region. Edge-emitting QWD lasers demonstrate low internal loss of 0.7 cm−1 and high internal quantum efficiency of 87%. as well as a reasonably high level of continuous wave (CW) power at room temperature. Due to the high optical gain and suppressed non-radiative recombination at processed sidewalls, QWDs are especially advantageous for microlasers. Thirty-one μm in diameter microdisk lasers show a high record for this type of devices output power of 18 mW. The CW lasing is observed up to 110 °C. A maximum 3-dB modulation bandwidth of 6.7 GHz is measured in the 23 μm in diameter microdisks operating uncooled without a heatsink. The open eye diagram is observed up to 12.5 Gbit/s, and error-free 10 Gbit/s data transmission at 30 °C without using an external optical amplifier, and temperature stabilization is demonstrated.

We study injection GaAs-based microdisk lasers capable of operating at room and elevated temperatures. A novel type of active region is used, namely InGaAs quantum well-dots representing a dense array of indium-rich islands formed inside an indium-depleted residual quantum well by metalorganic vapor phase epitaxy. We demonstrate a high output power of 18 mW, a differential efficiency of about 31%, and a peak electrical-to-optical power conversion efficiency of 15% in a 31 μm diameter microdisk laser. The continuous-wave lasing is observed up to 110°C.

The optical gain performance of 1530-1565 nm laser diodes with active regions containing p-doped barrier layers has been investigated. We have studied the threshold current density and differential quantum efficiency in wide temperature range and compared modal gain behaviour of laser diodes made of heterostructure with delta-doped barrier layers by carbon at level of 1012 cm-2 and heterostructure with undoped barrier layers.

We study the possibility of realization of the asymmetric barrier layers (ABL) concept in an 808-nm Al-free GaInAsP/InGaP/GaAs semiconductor laser. Two ABLs on both sides of the active region are aimed to suppress the parasitic recombination in the optical confinement layers. It is shown that such ABL-laser can be made fully Al-free having high suppression ratios for parasitic charge carrier flows (60 and 207 times for electrons and holes, respectively, as compared to a conventional SCH heterostructure).

Significant interest in compact InAs/InGaAs quantum dot (QD) lasers emitting near 1.3 mkm is caused by the diversity of their applications including non-invasive medicine and ultra-fast data transmission. In such lasers, lasing typically starts at the ground-state (GS) optical transitions of QDs. A further increase in injection may result in the appearance of an additional, short-wavelength spectral line associated with the excited-state (ES) optical transitions of QDs – a simultaneous lasing via QD GS and ES, i.e. multi-state lasing, takes place. The appearance of the ES-line may sufficiently affect the useful GS component. As injection current exceeds the multi-state lasing threshold, a decrease and even a complete quenching of GS-lasing may take place. As it was shown in [V.V. Korenev et. al, Appl. Phys. Lett. 102, 112101 (2013)], the usage of modulation p-doping has a positive influence on the hole concentration in QDs making GS-lasing quenching less pronounced. However, the influence of the concentration of p-dopant on multi-state lasing in general – and on the GS-lasing quenching in particular – has not been yet studied. To clarify this question experimentally, a series of InAs/InGaAs QD laser wafers was grown by molecular beam epitaxy. The active region of each sample was comprised of 10 layers of InAs/InGaAs QDs separated by 35 nm-thick GaAs spacers. Each spacer was p-doped into its central part of 10 nm using carbon atoms. Dependent on the sample, the carbon concentration was equal to 0, 3·10^17 cm^(-3), or 5·10^17 cm^(-3). A series of light-current curves corresponding to the GS component of output power was studied both theoretically and experimentally for “short” (0.5-mm-long) and for “long” (1.0-mm-long) samples. The experiment shows that in case of the short samples, the increase in p-doping level from 0 to 5·10^17 cm^(-3) results in the increase in maximum output power corresponding to the GS of QDs (WGS) from 0.8 to 2.2W, while in case of the longer samples the situation is opposite and WGS decreases from 4.5 to 3.7W correspondingly [V.V. Korenev et. al, Appl. Phys. Lett. 111, 132103 (2017)]. Qualitatively, such a discrepancy can be explained as follows. In case of the short samples, the higher p-doping level results in the faster hole capture into QDs mitigating the competition for the common holes between GS and ES optical transitions, which is an important reason for the GS-lasing quenching. In longer samples, optical loss is small and GS gain is far from its saturated value. Consequently, the ES energy level is weakly occupied and p-doping is not necessary to apply. However, even a small increment in the internal loss due to the p-dopant may lead to a noticeable decrease in laser`s differential efficiency. As a result, the higher p-doping level does not necessarily lead to the higher GS power as it was previously expected. However, if the sample is sufficiently short, the usage of modulation p-doping increases GS power. For a given cavity length, there is a certain p-doping level improving GS lasing characteristics.

The feasibility of implementation of asymmetric barriers (ABs) made of common materials for completely aluminum-free diode lasers is studied. The ABs adjoining a low-dimensional active region on both sides aim to prevent bipolar population in the waveguide layers and thus to suppress parasitic recombination therein, which in turn would enhance the efficiency and temperature-stability of the device. Our search algorithm for appropriate AB materials relies on the minimization of undesired carrier flow (electrons or holes passing through the active region toward the p- or n-type doped cladding layer, respectively), while maintaining the useful flows of hole and electron injection into the active region. Using an example of an 808-nm GaInAsP laser, it is shown that the n- and p-side ABs can be made, for instance, of GaInPSb and GaInP, respectively. In such a laser, the parasitic recombination flux can be suppressed by a factor of 60 for electrons and 200 for holes. It is found that the contribution of the indirect valleys to the electron flow through the p-side AB can be significant and even decisive in some cases. The contribution of light holes to the transmission through the ABs can also be considerable. The optimal thicknesses of the AB layers are determined and the chemical composition tolerances are estimated for a given flux suppression ratio. Published by AIP Publishing.

Band offsets at the heterointerface are calculated for various combinations of InAlGaAs/AlGaAs heteropairs that can be synthesized on GaAs substrates in the layer-by-layer pseudomorphic growth mode. Patterns which make it possible to obtain an asymmetric barrier layer providing the almost obstruction-free transport of holes and the highest possible barrier height for electrons are found. The optimal compositions of both compounds (In0.232Al0.594Ga0.174As/Al0.355Ga0.645As) at which the flux of electrons across the barrier is at a minimum are determined with consideration for the critical thickness of the indium-containing quaternary solid solution.

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

The energy-to-data ratio (EDR) was evaluated for quantum-dot based microdisk laser directly modulated without external cooling. The experimental values of EDR decrease with decreasing diameter of the microdisk and reach 1.5 pJ/bit for the smallest diameter under study (10.5 μm). In larger microdisks (with a diameter greater than 20 μm), the EDR varies in proportion to the square of the diameter. If this relationship were true for smaller microdisks as well, an EDR value of about 100 fJ would be achieved with a diameter of 4 μm. The observed deviation of EDR from the quadratic dependence on the diameter is associated with an increase in the threshold current density in smaller devices, which in turn may be caused by the contribution of nonradiative recombination on the microresonator sidewalls formed by deep etching.The energy-to-data ratio (EDR) was evaluated for quantum-dot based microdisk laser directly modulated without external cooling. The experimental values of EDR decrease with decreasing diameter of the microdisk and reach 1.5 pJ/bit for the smallest diameter under study (10.5 μm). In larger microdisks (with a diameter greater than 20 μm), the EDR varies in proportion to the square of the diameter. If this relationship were true for smaller microdisks as well, an EDR value of about 100 fJ would be achieved with a diameter of 4 μm. The observed deviation of EDR from the quadratic dependence on the diameter is associated with an increase in the threshold current density in smaller devices, which in turn may be caused by the contribution of nonradiative recombination on the microresonator sidewalls formed by deep etching.

The spectral analysis of amplified spontaneous emission is used to determine the linewidth enhancement factor (α-factor) in lasers based on InAs/InGaAs quantum dots (QDs) in a wide spectral range near the ground-state optical transition energy. The effect of the pump current and number of QDs on the spectral dependences of the α-factor is examined. The temperature dependence of the spectra of the α-factor is experimentally determined for the first time for lasers with InAs/InGaAs QDs. An explanation is suggested for the observed anomalous decrease in the α-factor with increasing temperature.

The linewidth enhancement factor (LEF) of an InAs/InGaAs quantum dot Fabry-Perot laser in a wide wavelength range from 1110 to 1300 nm, including ground state (GS) and exited state (ES) bands, is studied. LEF spectra were derived from amplified spontaneous emission spectra measured below the threshold in the pulse regime. The ES optical transition is characterised by significantly lower values of the LEF (≤0.54) as compared to the GS (≥1.21). Moreover, a zero LEF is observed within the ES spectral band. At sufficiently high currents, a near-zero LEF (|α| ≤ 0.1) is achieved in a wide spectral interval from 1146 to 1175 nm, in which the optical gain is not less than 9 cm−1.

An AlGaAs/GaAs quantum well (QW) laser is fabricated with GaInP and AlGaInAs asymmetric barrier layers (ABLs) and its light–current characteristic (LCC) is compared with that of a reference conventional QW laser without ABLs. It was found that the use of the ABLs suppresses the sublinearity of the LCC at high current densities. As a result, the maximum lasing power of 9.2 W, being limited by catastrophic optical mirror damage, is achieved at a considerably lower operating current in the laser with ABLs as compared to the reference laser (12.5 against 20.2 A). The ABL effect is associated with the suppression of the parasitic recombination in the optical confinement layer, as confirmed by a decrease of the intensity of the spontaneous emission from the layer.

Microring cavities (diameter D = 2.7–7 μm) with an active region based on InAs/InGaAs quantum dots are fabricated and their characteristics are studied by the microphotoluminescence method and near-field optical microscopy. A value of 22 000 is obtained for the Q factor of a microring cavity with the diameter D = 6 μm. Lasing up to room temperature is obtained in an optically pumped ring microlaser with a diameter of D = 2.7 μm.

Heat dissipation under the high-speed modulation of quantum dot edge-emitting lasers is considered. It is shown that, for a given laser diode, there is a bias current at which the heat-to-bitrate ratio is minimized. Moreover, there exists a certain optimal optical loss of the laser cavity at which the lowest heat-to-bitrate ratio is provided for any design of edge-emitting lasers that can be fabricated from an epitaxial structure. The heat-to-bitrate ratio and the corresponding bitrate are numerically calculated and analytical expressions are derived. It is demonstrated that the heat-to-bitrate ratio of quantum dot edge-emitting lasers can be less than 0.4 pJ/bit at a bitrate exceeding 10 Gbit/s.