Showing papers on "Quantum well published in 2004"
TL;DR: The results indicate that the use of SPs would lead to a new class of very bright LEDs, and highly efficient solid-state light sources.
Abstract: Since 1993, InGaN light-emitting diodes (LEDs) have been improved and commercialized, but these devices have not fulfilled their original promise as solid-state replacements for light bulbs as their light-emission efficiencies have been limited. Here we describe a method to enhance this efficiency through the energy transfer between quantum wells (QWs) and surface plasmons (SPs). SPs can increase the density of states and the spontaneous emission rate in the semiconductor, and lead to the enhancement of light emission by SP–QW coupling. Large enhancements of the internal quantum efficiencies (etaint) were measured when silver or aluminium layers were deposited 10 nm above an InGaN light-emitting layer, whereas no such enhancements were obtained from gold-coated samples. Our results indicate that the use of SPs would lead to a new class of very bright LEDs, and highly efficient solid-state light sources.
1,349 citations
TL;DR: The theoretical and experimental results indicate that this transfer is fast enough to compete with electron–hole recombination in the quantum well, and results in greater than 50 per cent energy-transfer efficiencies in the tested structures.
Abstract: As a result of quantum-confinement effects, the emission colour of semiconductor nanocrystals can be modified dramatically by simply changing their size1,2. Such spectral tunability, together with large photoluminescence quantum yields and high photostability, make nanocrystals attractive for use in a variety of light-emitting technologies—for example, displays, fluorescence tagging3, solid-state lighting and lasers4. An important limitation for such applications, however, is the difficulty of achieving electrical pumping, largely due to the presence of an insulating organic capping layer on the nanocrystals. Here, we describe an approach for indirect injection of electron–hole pairs (the electron–hole radiative recombination gives rise to light emission) into nanocrystals by non-contact, non-radiative energy transfer from a proximal quantum well that can in principle be pumped either electrically or optically. Our theoretical and experimental results indicate that this transfer is fast enough to compete with electron–hole recombination in the quantum well, and results in greater than 50 per cent energy-transfer efficiencies in the tested structures. Furthermore, the measured energy-transfer rates are sufficiently large to provide pumping in the stimulated emission regime, indicating the feasibility of nanocrystal-based optical amplifiers and lasers based on this approach.
544 citations
TL;DR: In this article, a triangular lattice photonic crystal is formed by dry etching into the top GaN layer, and the chosen lattice spacing causes Bragg scattering of guided modes out of the LED, increasing the extraction efficiency.
Abstract: Electrical operation of InGaN/GaN quantum-well heterostructure photonic crystal light-emitting diodes (PXLEDs) is demonstrated. A triangular lattice photonic crystal is formed by dry etching into the top GaN layer. Light absorption from the metal contact is minimized because the top GaN layers are engineered to provide lateral current spreading, allowing carrier recombination proximal to the photonic crystal yet displaced from the metal contact. The chosen lattice spacing for the photonic crystal causes Bragg scattering of guided modes out of the LED, increasing the extraction efficiency. The far-field radiation patterns of the PXLEDs are heavily modified and display increased radiance, up to ∼1.5 times brighter compared to similar LEDs without the photonic crystal.
395 citations
TL;DR: In this article, a review of InAs/AlSb quantum wells is presented, which is an ideal medium to study the low-temperature transport properties in InAs itself, with gate-induced electron sheet concentrations on the order 10 12 cm −2, they exhibit a pronounced conductivity quantization.
Abstract: The three semiconductors InAs, GaSb, and AlSb form an approximately lattice-matched set around 6.1 A , covering a wide range of energy gaps and other properties. Of particular interest are heterostructures combining InAs with one or both of the antimonides, and they are emphasized in this review. In addition to their use in conventional device types (FETs, RTDs, etc.), several heterostructure configurations with unique properties have been explored, especially InAs/AlSb quantum wells and InAs/GaSb superlattices. InAs/AlSb quantum wells are an ideal medium to study the low-temperature transport properties in InAs itself. With gate-induced electron sheet concentrations on the order 10 12 cm −2 , they exhibit a pronounced conductivity quantization. The very deep wells (1.35 eV ) provide excellent electron confinement, and also permit modulation doping up to at least 10 13 electrons cm −2 . Because of the very low effective mass in InAs, heavily doped wells are essentially metals, with Fermi energies around 200 meV , and Fermi velocities exceeding 10 8 cm s −1 . Contacted with superconducting electrodes, such structures can act as superconductive weak links. InAs/GaSb-related superlattices with their broken-gap lineup behave like semimetals at large lattice periods, but if the lattice period is shortened, increasing quantization effects cause a transition to a narrow-gap semiconductor, making such structures of interest for infrared detectors, often combined with the deliberate addition of strain.
302 citations
TL;DR: In this article, the relative strengths of Rashba and Dresselhaus terms describing spin-orbit coupling in semiconductor quantum well (QW) structures are extracted from photocurrent measurements on n-type InAs QWs containing a two-dimensional electron gas (2DEG).
Abstract: The relative strengths of Rashba and Dresselhaus terms describing the spin-orbit coupling in semiconductor quantum well (QW) structures are extracted from photocurrent measurements on n-type InAs QWs containing a two-dimensional electron gas (2DEG). This novel technique makes use of the angular distribution of the spin-galvanic effect at certain directions of spin orientation in the plane of a QW. The ratio of the relevant Rashba and Dresselhaus coefficients can be deduced directly from experiment and does not relay on theoretically obtained quantities. Thus our experiments open a new way to determine the different contributions to spin-orbit coupling.
270 citations
TL;DR: In this paper, the effect of quantum confinement in PbSe quantum wells and dots was studied using tight binding calculations, and unusual physical properties were predicted for rock salt PbS nanostructures.
Abstract: The effect of quantum confinement in PbSe quantum wells and dots is studied using tight binding calculations. Compared to zinc-blende semiconductors, unusual physical properties are predicted for rock salt PbSe nanostructures. The energy gap increases as the inverse of the size both for wells and dots. For PbSe nanocrystals, the luminescence lifetime, the confinement energy, and the intraband optical properties are in good agreement with experiments. The high quantum yield observed experimentally can be explained by the absence of surface dangling bonds in these systems. The origin of the second peak measured in the absorption spectra is discussed, whereas S-P interband transitions exhibit very small oscillator strength. The full frequency-dependent dielectric function $ϵ(\ensuremath{\omega})$ is calculated for PbSe quantum wells. Its imaginary part ${ϵ}_{2}(\ensuremath{\omega})$ is strongly anisotropic and shows large variations with respect to its bulk value even far from the gap region.
258 citations
TL;DR: In this paper, a self-consistent model has been employed to calculate the various radiative and nonradiative current components in p-doped and undoped laser and to analyze the measured data.
Abstract: Temperature invariant output slope efficiency and threshold current (T0=∞) in the temperature range of 5–75 °C have been measured for 1.3 μm p-doped self-organized quantum dot lasers. Similar undoped quantum dot lasers exhibit T0=69K in the same temperature range. A self-consistent model has been employed to calculate the various radiative and nonradiative current components in p-doped and undoped lasers and to analyze the measured data. It is observed that Auger recombination in the dots plays an important role in determining the threshold current of the p-doped lasers.
255 citations
TL;DR: In this paper, the properties of ZnMgO epilayers and ZnO-ZnmgO quantum well structures grown by metalorganic vapor phase epitaxy were investigated.
Abstract: We have investigated the properties of ZnMgO epilayers and ZnO–ZnMgO quantum well structures grown by metalorganic vapor-phase epitaxy. A well-controlled incorporation of magnesium, x⩽0.10, could be confirmed resulting in a blueshift of the photoluminescence emission wavelength of the Zn1−xMgxO layers up to 200meV. Using ZnMgO as barrier material, ZnO–ZnMgO quantum well structures with different well widths have then been fabricated. The confinement effect in the ZnO quantum wells leads to the expected increase of the corresponding quantum well emission energy with decreasing well width. A comparison to calculations also suggests a further enhancement of the exciton binding energy in the quantum wells of up to 90meV.
252 citations
TL;DR: In this article, a blue-purple pn-junction light-emitting diodes (LEDs) with a-plane GaN-InGaN multiple quantum well active region were reported.
Abstract: We report blue-purple pn-junction light-emitting diodes (LEDs) with a-plane GaN–InGaN multiple quantum well active region. The LEDs were grown over r-plane sapphire substrates. Our study has shown the low pump intensity photoluminencence and electroluminescence to be dominated by emission from the band-tail states which then saturates rapidly giving rise to band-edge emission.
228 citations
TL;DR: In this article, the first experimental demonstration of an end-pumped Cs laser using a Ti:sapphire laser for pump excitation is presented, and a discussion is given on power scaling diodepumped alkali lasers, indicating a potential efficiency advantage over power-scaled diode-pump solid-state lasers.
Abstract: End-pumped alkali vapor lasers excited on their D2 transition and lased on their D1 transition offer a pathway to high average power that potentially competes with diode-pumped solid-state lasers in many applications that require cw or quasi-cw laser operation. We report on the first experimental demonstration of an end-pumped Cs laser using a Ti:sapphire laser for pump excitation. Detailed experimental and model results are presented that indicate our understanding of the underlying physics involved in such systems is complete. Using an extrapolation of our developed model, a discussion is given on power scaling diode-pumped alkali lasers, indicating a potential efficiency advantage over power-scaled diode-pumped solid-state lasers.
221 citations
TL;DR: In this paper, the design and projected performance of quantum-well infrared photodetectors (QWIP) for the terahertz (1-10 THz) or the very-far-infrared region are presented together with the initial demonstration of a GaAs/AlGaAs QWIP working at photon energies below the optical phonons.
Abstract: The design and projected performance of quantum-well infrared photodetectors (QWIP) for the terahertz (1–10 THz) or the very-far-infrared region are presented together with our initial demonstration of a GaAs/AlGaAs QWIP working at photon energies below the optical phonons. We point out the problem with this initial device, discuss possible causes, and suggest areas of improvement.
TL;DR: In this paper, a quantum cascade detector (QCD) was proposed for photovoltaic inter-subband detector based on electron transfer on a cascade of quantum levels, and the highest photoresponse of inter-band transition-based photovellaic detectors is demonstrated: 35mA∕W at null bias.
Abstract: A photovoltaic intersubband detector based on electron transfer on a cascade of quantum levels is presented: A quantum cascade detector (QCD). The highest photoresponse of intersubband transition-based photovoltaic detectors is demonstrated: 35mA∕W at null bias. The deduced absorption is of the same order of magnitude as that of a classical quantum-well infrared photodetector, i.e., 20%. Because they work with no dark current, QCDs are very promising for small-pixel large focal plane array applications.
TL;DR: Optically pumped, external-cavity, surface emitting semiconductor lasers (also known as optically pumped semiconductor, OPS lasers, and vertical external cavity surface emitting lasers, VECSELs) generate near-diffraction limited beams from low brightness diode-array pumps as mentioned in this paper.
Abstract: Optically pumped, external-cavity, surface emitting semiconductor lasers (also known as optically pumped semiconductor lasers, OPS lasers, and vertical external cavity surface emitting lasers, VECSELs) generate near-diffraction limited beams from low brightness diode-array pumps. We have demonstrated 30 W cw at 980 nm and 15 W cw at 488 nm in a single spatial mode from these emitters and believe they can be scaled to > 100 W. Potential applications we have explored for such devices include wavelength conversion, spectral and spatial brightness conversion.
TL;DR: In this article, the photoluminescence intensity of the {112¯2} QW is the strongest among the three QWs, and the internal quantum efficiency was estimated to be as large as about 40% at room temperature.
Abstract: InxGa1−xN multiple quantum wells (QWs) with [0001], ⟨112¯2⟩, and ⟨112¯0⟩ orientations have been fabricated by means of the regrowth technique on patterned GaN template with striped geometry, normal planes of which are (0001) and {112¯0}, on sapphire substrates. It was found that photoluminescence intensity of the {112¯2} QW is the strongest among the three QWs, and the internal quantum efficiency of the {112¯2} QW was estimated to be as large as about 40% at room temperature. The radiative recombination lifetime of the {112¯2} QW was about 0.38ns at low temperature, which was 3.8 times shorter than that of conventional [0001]-oriented InxGa1−xN QWs emitting at a similar wavelength of about 400nm. These findings strongly suggest the achievement of stronger oscillator strength owing to the suppression of piezoelectric fields.
TL;DR: In this article, temperature-insensitive eye-opening under 10-Gb/s direct modulation of 1.3-µm p-doped quantum-dot lasers without using any current adjustments was demonstrated.
Abstract: We demonstrate temperature-insensitive eye-opening under 10-Gb/s direct modulation of 1.3-µm p-doped quantum-dot lasers without using any current adjustments. The lasers show a 6.5-dB extinction ratio between 20°C and 70°C. An active region consisting of ten quantum-dot layers with p-type doping enabled this highly temperature-stable dynamic performance, which was much superior to conventional 1.3-µm quantum-well lasers. These results make it possible to use uncooled 1.3-µm quantum-dot lasers without any current adjustments.
TL;DR: In this paper, a quantum cascade structure based on a bound-to-continuum design exhibiting a broad gain curve was presented, where the full width at half maximum of the measured luminescence spectrum is 297 cm−1 at room temperature.
Abstract: A quantum-cascade structure based on a bound-to-continuum design exhibiting a broad gain curve is presented. The full width at half maximum of the measured luminescence spectrum is 297 cm−1 at room temperature. Grating-coupled external cavity lasers using this active region could be tuned over 150 cm−1 (1.45 μm), which is equal to 15% of the free running wavelength (λ≅10 μm), in pulsed mode at room temperature. Time resolved spectra showed a single-mode operation with a 30 dB side mode suppression ratio after the first 12 ns of the pulse.
TL;DR: In this article, a theory based on localized-orbital approaches is developed to describe the valley splitting observed in silicon quantum wells, which is appropriate in the limit of low electron density and relevant for quantum computing architectures.
Abstract: A theory based on localized-orbital approaches is developed to describe the valley splitting observed in silicon quantum wells. The theory is appropriate in the limit of low electron density and relevant for quantum computing architectures. The valley splitting is computed for realistic devices using the quantitative nanoelectronic modeling tool NEMO. A simple, analytically solvable tight-binding model reproduces the behavior of the splitting in the NEMO results and yields much physical insight. The splitting is in general nonzero even in the absence of electric field in contrast to previous works. The splitting in a square well oscillates as a function of S, the number of layers in the quantum well, with a period that is determined by the location of the valley minimum in the Brillouin zone. The envelope of the splitting decays as S−3. The feasibility of observing such oscillations experimentally in Si/SiGe heterostructures is discussed.
TL;DR: In this article, the experimental aspects of the optical properties of excitons in ZnO-based MQW heterostructures are discussed. But the authors focus mainly on the optical spectra of dense excitonic systems are determined mainly by the interaction process between exciton and biexcitons.
Abstract: Recently the developments in the field of II-VI-oxides have been spectacular. Various epitaxial methods has been used to grow epitaxial ZnO layers. Not only epilayers but also sufficiently good-quality multiple quantum wells (MQWs) have also been grown by laser molecular-beam epitaxy (laser-MBE). We discuss mainly the experimental aspect of the optical properties of excitons in ZnO-based MQW heterostructures. Systematic temperature-dependent studies of optical absorption and photoluminescence in these MQWs were used to evaluate the well-width dependence and the composition dependence of the major excitonic properties. Based on these data, the localization of excitons, the influence of exciton-phonon interaction, and quantum-confined Stark effects are discussed.
The optical spectra of dense excitonic systems are shown to be determined mainly by the interaction process between excitons and biexcitons. The high-density excitonic effects play a role for the observation of room-temperature stimulated emission in the ZnO MQWs. The binding energies of exciton and biexciton are enhanced from the bulk values, as a result of quantum-confinement effects.
TL;DR: In this paper, the active region is composed of three Al0.36Ga0.64N quantum wells with Al 0.48 Ga0.52N barriers for emission at 290 nm.
Abstract: Ultraviolet light-emitting diodes (LEDs) have been grown by metalorganic vapor phase epitaxy using AlN nucleation layers and thick n-type Al0.48Ga0.52N current spreading layers. The active region is composed of three Al0.36Ga0.64N quantum wells with Al0.48Ga0.52N barriers for emission at 290 nm. Devices were designed as bottom emitters and flip-chip bonded to thermally conductive submounts using an interdigitated contact geometry. The ratio of quantum well emission to 330 nm sub-band gap emission is as high as 125:1 for these LEDs. Output power as high as 1.34 mW at 300 mA under direct current operation has been demonstrated with a forward voltage of 9.4 V. A peak external quantum efficiency of 0.18% has been measured at an operating current of 55 mA.
TL;DR: In this paper, the authors demonstrate high-power AlGaN-based ultraviolet light-emitting diodes grown on sapphire with an emission wavelength of 280 nm using an asymmetric singlequantum-well active layer configuration on top of a high-quality ALGaN/AlN template layer.
Abstract: We demonstrate high-power AlGaN-based ultraviolet light-emitting diodes grown on sapphire with an emission wavelength of 280 nm using an asymmetric single-quantum-well active layer configuration on top of a high-quality AlGaN/AlN template layer. An output power of 1.8 mW at a pulsed current of 400 mA was achieved for a single 300 μm×300 μm diode. This device reached a high peak external quantum efficiency of 0.24% at 40 mA. An array of four diodes produced 6.5 mW at 880 mA of pulsed current.
TL;DR: Theoretical overview of quantum dot detectors and detectors can be found in this paper, where the authors discuss the growth of Semiconductor Nanostructures and the development of high speed Quantum Dot Detectors.
Abstract: Introduction. Growth of Semiconductor Nanostructures. Characterization of Semiconductor Nanostructures. Quantum Dot Lasers: Theoretical Overview. High-Speed Quantum Dot Lasers. Quantum Dot Detectors. InGaAs Quantum Dots. III-Nitride Quantum Dots. Self Assembled Ge Quantum Dots on Si for Optoelectronics. ZnO Nanostructures. Carbon Nanotubes.
TL;DR: In this paper, a three-level ladder-type system with similar transition energies has been studied and the system interacts with a strong driving field which is in two-photon resonance with the intersubband transition and thus simultaneously drives all three levels into phase-locked quantum coherence.
Abstract: Optical bistable behavior in a unidirectional ring cavity (or a Fabry–Perot cavity) containing a semiconductor quantum well, described as a three-level ladder-type system with similar transition energies, has been studied The system interacts with a strong driving field which is in two-photon resonance with the intersubband transition and thus simultaneously drives all three levels into phase-locked quantum coherence The threshold for switching to upper branch of the bistable curve is found to be reduced due to the presence of quantum interference Such system can be used for making efficient and fast all-optical switching devices
TL;DR: In this article, a detailed theory of nonisothermal electron transport perpendicular to multilayer superlattice structures is presented, and the currentvoltage and cooling power density are calculated using Fermi-Dirac statistics, density-of-states for a finite quantum well and the quantum mechanical reflection coefficient.
Abstract: A detailed theory of nonisothermal electron transport perpendicular to multilayer superlattice structures is presented. The current–voltage (I–V) characteristics and the cooling power density are calculated using Fermi–Dirac statistics, density-of-states for a finite quantum well and the quantum mechanical reflection coefficient. The resulting equations are valid in a wide range of temperatures and electric fields. It is shown that conservation of lateral momentum plays an important role in the device characteristics. If the lateral momentum of the hot electrons is conserved in the thermionic emission process, only carriers with sufficiently large kinetic energy perpendicular to the barrier can pass over it and cool the emitter junction. However, if there is no conservation of lateral momentum, the number of electrons participating in a thermionic emission will increase. This has a significant effect on the I–V measurements as well as the cooling characteristics. Theoretical calculations are compared with...
TL;DR: In this article, a threshold current density of 343 A/cm2 was recorded from a laser with 2 mm cavity length and 30 μm ridge width in pulsed-mode operation.
Abstract: 3.04 μm emission has been achieved in GaInAsSb/AlGaAsSb double-quantum-well ridge waveguide diode lasers in continuous-wave mode up to 20 °C. A threshold current density of 343 A/cm2 was recorded from a laser with 2 mm cavity length and 30 μm ridge width in pulsed-mode operation. A characteristic temperature of 30 K was measured from a 1.2 mm long device. Threshold current densities and characteristic temperatures of GaInAsSb/AlGaAsSb laser diodes with wavelengths from 2.24 to 3.04 μm are summarized. The threshold current density per quantum well increases strongly with wavelength; at 3.04 μm, it is three times that value of a 2.24 μm device.
TL;DR: Surprisingly, the individual emission lines show a pronounced blueshift when raising the temperature, while virtually no energy shift occurs for increasing excitation density, which gives a fundamental new insight into the recombination process in semiconductor nanostructures in the presence of localization and strong internal electric fields.
Abstract: Photoluminescence (PL) spectroscopy with subwavelength lateral resolution has been employed to probe individual localization centers in a thin InGaN/GaN quantum well. Spectrally narrow emission lines with a linewidth as small as 0.8 meV can be resolved, originating from the recombination of an electron-hole pair occupying a single localized state. Surprisingly, the individual emission lines show a pronounced blueshift when raising the temperature, while virtually no energy shift occurs for increasing excitation density. These findings are in remarkable contrast to the behavior usually found in macro-PL measurements and give a fundamental new insight into the recombination process in semiconductor nanostructures in the presence of localization and strong internal electric fields. We find clear indications for a biexciton state with a negative binding energy of about -5+/-0.7 meV.
TL;DR: In this paper, it is shown that amplified spontaneous emission acts to decrease the inversion of the wetting layer states, thus helping to quench the gain of these states, which might otherwise dominate.
Abstract: Based on extensive numerical calculations, quantum-dot (QD) amplifiers are predicted to offer higher output power and lower noise figure compared to bulk as well as quantum well amplifiers. The underlying physical mechanisms are analyzed in detail, leading to the identification of a few key requirements that QD amplifiers should meet in order to achieve such superior linear characteristics. The existence of a highly inverted wetting layer or barrier region, acting as a carrier reservoir, is central to this performance enhancement. It is shown that amplified spontaneous emission acts to decrease the inversion of the wetting layer states, thus helping to quench the gain of these states, which might otherwise dominate.
TL;DR: In this article, the effects of compressive stress on the binding energy and the density of shallow-donor impurity states in symmetrical GaAs/Al x Ga 1 - x As double quantum wells are calculated using a variational procedure within the effective-mass approximation.
Abstract: The effects of the compressive stress on the binding energy and the density of shallow-donor impurity states in symmetrical GaAs/Al x Ga 1 - x As double quantum wells are calculated using a variational procedure within the effective-mass approximation. Results are for different well and barrier widths, shallow-donor impurity position, and compressive stress along the growth direction of the structure. We have found that independently of the well and barrier widths, for stress values up to 13.5 kbar (in the direct-gap regime) the binding energy increases linearly with the stress. For stress values greater than 13.5 kbar (indirect gap regime) and for impurities at the center of the wells, the binding energy increases up to a maximum and then decreases. For all impurity positions the binding energy shows a nonlinear behavior in the indirect gap regime due to the I'-X crossing effect. The density of impurity states is calculated for a homogeneous distribution of donor impurities within the barriers and the wells of the low-dimensional heterostructures. We have found that there are three special structures in the density of impurity states: one associated with on-center-barrier-, the second one associated with on-center-well-, and the third one corresponding to on-external-edge-well-impurity positions. The three structures in the density of impurity states must be observed in valence-to-donor-related absorption and conduction-to-donor-related photoluminescence spectra, and consequently these peaks can be tuned at specific energies and convert the system in a stress detector.
TL;DR: In this paper, a model of cold excitons was proposed for studying collective states and many-body phenomena in a system of cold bosons, including pattern formation and macroscopically ordered exciton states.
Abstract: Bound electron?hole pairs?excitons?are light Bose particles with a mass comparable to or smaller than that of the free electron. Since the quantum degeneracy temperature scales inversely with the mass, it is anticipated that Bose?Einstein condensation of an exciton gas can be achieved at temperatures of about 1?K, orders of magnitude larger than the micro-Kelvin temperatures employed in atomic condensation. High quantum degeneracy temperatures and the possibility to control exciton density by laser photoexcitation make cold excitons a model system for studies of collective states and many-body phenomena in a system of cold bosons. Experimentally, an exciton temperature well below 1?K is achieved in a gas of indirect excitons in coupled quantum-well semiconductor heterostructures. Here, we overview phenomena in the cold exciton gases: condensation, pattern formation, and macroscopically ordered exciton states.
TL;DR: In this article, the spectral linewidth of three continuous-wave quantum cascade lasers operating at terahertz frequencies was measured by heterodyning the free-running quantum cascade laser with two far-infrared gas lasers.
Abstract: We have measured the spectral linewidths of three continuous-wave quantum cascade lasers operating at terahertz frequencies by heterodyning the free-running quantum cascade laser with two far-infrared gas lasers. Beat notes are detected with a GaAs diode mixer and a microwave spectrum analyzer, permitting very precise frequency measurements and giving instantaneous linewidths of less than ∼30 kHz. Characteristics are also reported for frequency tuning as the injection current is varied.
TL;DR: In this article, multiple quantum wells were grown on InGaN underlying layers 50 nm thick by metalorganic vapor phase epitaxy and photoluminescence measurements were performed by selective excitation of the quantum wells under a weak excitation condition.
Abstract: InGaN multiple quantum wells were grown on InGaN underlying layers 50 nm thick by metalorganic vapor phase epitaxy. Photoluminescence (PL) measurements were performed by selective excitation of the quantum wells under a weak excitation condition. The PL intensity was almost constant at temperatures ranging from 17 to 150 K. Assuming that the internal quantum efficiency (ηint) equals unity at 17 K, we obtained ηint as high as 0.71 even at room temperature. The reason for the high ηint is the reduction of nonradiative recombination centers by the incorporation of indium atoms into the underlying layer.