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Experiments on the growth of self-assembled InP/GaInP2 quantum dots in dielectric mask 0.1–1 μm apertures by MOVPE epitaxy have been carried out. A sequence of operations for the implementation of the lift-off lithography method is proposed and implemented. The possibility of obtaining apertures with 100 nm diameter and less is shown. Combination of thermally deposited SiO2 and wet etching is shown to produce minimal amount of nonradiative defects and results in a stable PL signal from single QDs in the aperture. [ABSTRACT FROM AUTHOR]

The effect of lattice relaxation instability (martensitic transition) on piezoelectric fields (EPE) in spontaneously ordered GaInP2/GaAs epitaxial layers was demonstrated using scanning Kelvin probe microscopy in combination with electron microscopy and optical spectroscopy measurements. The transition manifests itself in the dependence of the surface potential of the epi-layer on the mechanical (cleavage) and thermal (annealing) impacts. This is associated with a switching of the crystal lattice between relaxed and strained martensitic states, corresponding to a change in EPE in the epi-layer. The measured surface potential values (0.2–2.4 V) correspond to EPE within ±100 kV/cm and a strong decrease in |EPE| with increasing layer thickness, indicating the pinning of the Fermi level and piezoelectric doping. Our results open up the prospects for using spontaneously ordered semiconductor alloys to control electronic states in semiconductor nanostructures by controlling their piezoelectric fields. [ABSTRACT FROM AUTHOR]

A model is proposed that makes it possible to analytically analyze the speed performance of a waveguide p–i–n photodiode with a light-absorbing region representing a multilayered array of quantum dots separated by undoped spacers. It is shown that there is an optimal number of layers of quantum dots, as well as an optimal thickness of the spacers, which provide the widest bandwidth. The possibility of achieving a frequency range (at the level of –3 dB) above 20 GHz for waveguide photodiodes based on InGaAs/GaAs quantum well-dots is shown. [ABSTRACT FROM AUTHOR]

We have studied superluminescent diodes with simplified design and active region based on 5 or 7 layers of InGaAs/GaAs quantum well-dots (QWDs). Emission peaks of the individual QWD layers are shifted with respect to each other by 15–35 nm to provide as wide as possible emission line in a superluminescent mode with central wavelength of about 1 μm without significant spectral dips. For superluminescent diodes with the active region based on 5 and 7 QWD layers, the maximal value of full width at half maximum of emission spectrum was 92 and 103 nm respectively. [ABSTRACT FROM AUTHOR]

The static and dynamic characteristics of waveguide photodetectors with an absorbing region based on InGaAs/GaAs quantum well-dots were studied at room temperature. The absorption band of InGaAs/GaAs quantum well-dots is in the spectral range from 900 to 1100 nm. The waveguide photodetectors have a width of 50 μm and a length of the absorbing region from 92 μm to 400 μm. A low dark current density (1.1 and 22 μA/cm2 at –1 and –20 V) and cut off frequency of 5.6 GHz, limited by the time constant of a parasitic equivalent electric RC-circuit, were obtained. [ABSTRACT FROM AUTHOR]

A systematic study of a series of InGaAs/GaAs lasers in the 1–1.3 μm optical range based on quantum wells (2D), quantum dots (0D), and quantum well-dots of transitional (0D/2D) dimensionality is presented. In a wide range of pump currents, the dependences of the lasing wavelength on the layer gain constant, a parameter which allows comparing lasers with different types of active region and various waveguide designs, are measured and analyzed. It is shown that the maximum optical gain of the quantum well-dots is significantly higher, and the range of lasing rawavelengths achievable in edge-emitting lasers without external resonators is wider than in lasers based on quantum wells and quantum dots. [ABSTRACT FROM AUTHOR]

We consider structure with single quantum well InP 5 nm thick grown by vapor phase epitaxy on n-GaP wafer. By classical capacitance-voltage profiling of Schottky diode on sample and electrochemical profiling, electron accumulation were detected in InP layer so existence of quantum well is confirmed. Results of admittance spectroscopy and deep-level transient spectroscopy showed defect formation in GaP layers above InP with energy position of Ec-0.21, 0.30 and 0.93 eV. [ABSTRACT FROM AUTHOR]

A relationship has been established between the energy gap width of GaInAs p–n homojunctions and the saturation current. For this purpose, a method was suggested and substantiated for determining the energy gap width of a p–n junction from the spectrum of the photocurrent quantum efficiency. The method was applied to Ga1 –xInxAs p–n junctions grown by metal-organic vapor-phase epitaxy on metamorphic buffers. The difference between the energy gap width determined by using the suggested method and that found from the peak of the electroluminescence spectrum did not exceed 3 meV. It was found that the saturation current exponentially depends on the energy gap width, and this dependence is characterized by a current invariant. [ABSTRACT FROM AUTHOR]

Abstract: Photovoltaic structures on the basis of GaAs p-i-n junctions with a different number of In0.4Ga0.6As layers in the space-charge region forming quantum-confined objects are experimentally and theoretically investigated. For all structures, the dependences of the open-circuit voltage on the solar-irradiation concentration are analyzed. It is shown that the implantation of quantum objects leads to the dominance of recombination in them over recombination in the matrix, which manifests itself in a drop in the open-circuit-voltage. An increase in the number of In0.4Ga0.6As layers leads to a proportional increase in the recombination rate, which is expressed in a proportional increase in the “saturation” current and corresponds to the model proposed in the study. [ABSTRACT FROM AUTHOR]

We investigated structural and emission properties of self-organized InP/GaInP quantum dots (QD) grown by metal organic chemical vapor deposition using an amount of deposited In from 7 to 2 monolayers (ML). In the uncapped samples, using atomic force microscopy (AFM), we observed lateral sizes of 100-200 nm, together with a bimodal height distribution having maxima at ∼5 and ∼15 nm, which we denoted as QDs of type A and B, respectively; and reduction of the density of the type-B dots from 4.4 to 1.6 μm-2. The reduction of the density of B-type dots were observed also using transmission electron microscopy of the capped samples. Using single dot low-temperature photoluminescence (PL) spectroscopy we demonstrated effects of Wigner localization for the electrons accumulated in these dots. [ABSTRACT FROM AUTHOR]

The internal loss at the lasing threshold were studied experimentally and numerically in laser cavities comprising dense arrays of InGaAs/GaAs quantum dots (quantum well-dots) as a function of the number of their planes and the output loss. Numerical values of the parameters were found that determine the free-carrier absorption in the active region and in the waveguiding layer. The optimal design of the laser diode was determined to achieve the highest external differential efficiency. [ABSTRACT FROM AUTHOR]

Heterostructure with InGaAs/GaAs quantum well-dots was investigated in temperature range 10–300 K using photoluminescence spectroscopy in CW mode as well with time resolution. Obtained decay times were splitted into radiative and nonradiative components of carrier lifetime. It is found that radiative lifetime demonstrates exponential growth with temperature rise, while temperature dependence of nonradiative one is much weaker. [ABSTRACT FROM AUTHOR]

An anomaly appearing in the photovoltaic characteristics of triple-junction GaInP/GaAs/Ge and of the corresponding double-junction GaInP/GaAs solar cells at ultrahigh concentrations (more than 2000 suns) of incident light has been studied. The light current–voltage characteristics at various concentration ratios of incident light and the dependence of the open-circuit voltage on the photogenerated current were analyzed. It was shown that the anomaly is observed due to the tunnel diode connected back-to-back between the GaInP and GaAs subcells. This diode absorbs photons that pass across the GaInP layers and creates a counter photovoltage. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In semiconductors under tightly-focused photocarrier excitation, the lateral variation of carrier concentration induces a lateral variation of photovoltage. In chemically-passivated p-type GaAs films at 300 K, we show experimentally and theoretically that the photovoltage lateral dependence is able to block the photoelectron diffusion, thus reducing the effective charge diffusion constant by a factor of ≈ 5 with respect to surface-free conditions and producing a self-trapping of photoelectrons. This effect is not present for surface-free and for oxidized samples, for which the photovoltage magnitude is strongly reduced. The photovoltage lateral variation also induces a coupling between charge and spin diffusion. Because of this coupling, the effective spin diffusion constant is significantly larger than the effective charge one. [ABSTRACT FROM AUTHOR]

The methods of photoluminescence and photoconductivity spectroscopy and the spectroscopy of photocurrent of a p-i-n structure are used to study samples with hybrid quantum-confined medium 'quantum well-dots' (QWD) structures grown on GaAs substrates. The significant contribution of QWD states, which extends the GaAs absorption range to 1075 nm, is found in the photoconductivity and photocurrent spectra. The absorption and luminescence of the quantum-confined structures possess characteristic features of quantum wells. Analysis of the photocurrent and photoconductivity spectra demonstrate that the excitation of carriers from localized QWD states has a combined nature: at temperatures lower than 100 K and an electric-field strength of below 40 kV/cm, excitation is possible via tunneling to the matrix, while at higher temperatures thermal activation coming into play. Also, lateral photoconductivity is observed in the layers of quantum-confined structures. [ABSTRACT FROM AUTHOR]

Photovoltaic laser-power converters for a wavelength of λ = 809 nm are developed and fabricated on the basis of single-junction AlGaAs/GaAs structures grown by metal-organic vapor-phase epitaxy. The parameters of the photovoltaic structure constituted by an optical 'window' and a cladding layer are optimized by mathematical simulation. Photovoltaic converters with areas of S = 10.2 and 12.2 mm and 4 cm are fabricated and studied. For photocells with S = 10.2 mm, the monochromatic efficiency (η) was 60% at a current density of 5.9 A/cm. A photovoltaic module with a working voltage of 4 V (η = 56.3% at 0.34 A/cm) is assembled. [ABSTRACT FROM AUTHOR]

The phenomenon of current spreading is essential for concentrator solar cells since it limits the conversion efficiency at high sunlight-concentration ratios. A model, which describes the regularities of the above phenomenon, is proposed and developed. The model uses a stylized representation of current lines and, respectively, of current tubes; it includes two resistive parameters accounting for the variable lateral (horizontal) component and the constant vertical component of the resistance of each tube. In the model the fact that the thickness of the spreading region is much less than the distance between the contact grid strips is taken into account. The calculated current-voltage ( I-V) characteristics of a solar cell in the resistive and a nonresistive cases are obtained. The spreading-resistance I-V characteristic obtained by the voltage subtraction of these characteristics is nonlinear and depends on the photogenerated current. Thus, the equivalent electrical circuit of a solar cell includes a lumped nonlinear resistance, which depends parametrically on the photogenerated current. The comparison of experimental and calculated I-V characteristics by the example of Ge, GaAs, and GaInP solar cells is performed and both resistive parameters of the model are determined. The model describes correctly the regularities of spreading in single-junction solar cells and can be extended to multijunction solar cells. [ABSTRACT FROM AUTHOR]

The polarization-resolved electroluminescence spectra of waveguide structures based on quantum well–dots are investigated in the temperature range of 60–300 K. It is found that the ground-state emission consists of two peaks with different degrees of TE polarization. The spectral separation of these peaks decreases with a decrease in temperature. The observed bimodality is attributed to the existence of two different types of objects in the active region, namely, quantum well–dots, whose emission is only partially TE polarized, and quantum dots, which emit nearly fully TE polarized light. [ABSTRACT FROM AUTHOR]

The power of radiation in the continuous-wave mode of microdisk lasers with InGaAs/GaAs quantum-well dots hybrid integrated with a silicon substrate with the epitaxial side down using a thermocompression compound has been investigated. Because of a decrease in thermal resistance and suppression of self-heating, there is an increase in the current values at which power saturation and laser generation quenching occur, as well as an increase in the maximum power. In microdisks with a diameter of 19 μm, the largest value of the optical output power was 9.4 mW in the continuous-wave mode. [ABSTRACT FROM AUTHOR]

The possibility of creating a lower junction for the multijunction A3B5/Si-type solar cells based on the n-GaP/p-Si heterostructure grown by the combined method of plasma enhanced atomic-layer deposition and metalorganic vapor-phase epitaxy is demonstrated for the first time at temperature Ts not exceeding 650°C. The photoelectric properties of the structures grown at Ts ≤ 650°C depend on the process conditions—in particular, on the use of additional treatment in Ar plasma. [ABSTRACT FROM AUTHOR]

The energy consumption of a microdisk laser with InGaAs/GaAs quantum well-dots at high-frequency modulation without forced cooling has been investigated. The lowest energy consumption for a microlaser 20 μm in diameter is estimated to be 1.6 pJ per data bit transferred using an optical signal. [ABSTRACT FROM AUTHOR]

Investigation of IR light emitting diodes (wavelength 850 nm) based on AlGaAs/GaAs heterostructures with multiple quantum wells in the region generating radiation grown by the MOCVD technique has been carried out. Post-growth technologies for removing the substrate and for transfer the heterostructure on an alien carrier with an optical reflector have been developed. Technological regimes for fabricating the reflector have been optimized, and the increase of the IR radiation reflection coefficient up to 92–93% has been achieved. Light-emitting diodes with the external quantum efficiency 28.5% have been fabricated. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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). [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: Edge-emitting diode lasers with shallow location of a quantum-well active region at a depth of 0.92 μm were developed and their thermal resistance was evaluated from the analysis of true spontaneous emission spectra through the top contact window. Owing to a close spacing between the active region and laser heatsink, effective heat removal is achieved under continuous wave operation that is characterized by a low value of specific thermal resistance of 6 × 10-3 K/(W cm2). [ABSTRACT FROM AUTHOR]

Abstract: The conditions for the growth of epitaxial layers are considered and the resistance of alloyed ohmic contacts to tellurium-doped gallium arsenide layers is studied. The use of the (AuGe eutectic alloy)-Ni-Au composition alloy of ohmic contacts to the gallium arsenide layers with electron conductivity, including use as a contact layer of a narrow-band (In0.5Ga0.5As), makes it possible to achieve a resistance of 10-7 Ohm cm2, in the best case; however, this leads to a deterioration of the surface morphology. In this paper, we study the issues of doping the GaAs contact layer by tellurium to the maximum concentration of 2.5 × 1019 cm-3. In this case, the resistance of the ohmic contacts proves to be less than 5 × 10-8 Оhm cm2, simultaneously with the improvement of the semiconductor's surface morphology. [ABSTRACT FROM AUTHOR]

Abstract: 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Results are presented of a study of light-current characteristics and far-field patterns of emission of stripe lasers with coupled planar waveguides. This configuration makes it possible to suppress the generation of excited modes and to have a small (about 0.9 μm) depth of the active region from the surface of the laser crystal. A high-temperature stability of the angular emission divergence (34.0° ± 1.5°) in the temperature range 20-80°C is demonstrated. The largest value of the output power is limited to 12.2 W in the continuous-wave mode by the catastrophic mirror damage. [ABSTRACT FROM AUTHOR]

We study the current-controlled lasing switching from the ground state (GS) to the excited state (ES) transition in broad-area (stripe width 100 µm) InGaAs/GaAs quantum well-dot (QWD) and quantum well (QW) lasers. In the lasers with one QWD layer and a 0.45 µm-thick GaAs waveguide, pure GS lasing takes place up to an injection current as high as 8 A (40 kA/cm 2 ). In contrast, in QW lasers with a similar design, ES lasing emerges already at 3 A (15 kA/cm 2 ). The ES lasing in the QWD lasers is observed only in the devices with a waveguide thickness of 0.78 µm that supports a 2nd order transverse mode at the wavelength of the ES transition. Increasing the modal gain in the lasers with 0.78 µm-thick waveguide by using two QWD layers in the active region suppresses the ES lasing.