QW Structures Research Articles

Effect of cap layer and post growth on-site hydride passivation on the surface and interface quality of InAsP/InP hetero and QW structures

The performance of devices made from III-V compound semiconductors relies heavily on their surface and interface properties. The InAsP/InP material system is recently gaining interest due to its suitability for the next generation of long-haul classical and quantum communication applications. Researchers are studying how surface and interface properties affect the efficiency of the device and concludes that the epitaxial growth conditions responsible for creating surface and interface states require further improvement. To address this, we have studied the effect of the top (cap) layer and post-growth on-site hydride passivation on the properties of InAsP/InP hetero-structures grown using metal-organic vapor phase epitaxy technique. The flow rate and flux ratios of the hydrides significantly affect the surface reaction rates and gas-phase diffusion coefficients, which in turn impact the As↔P exchange mechanisms. Our findings suggest that post-growth on-site arsine passivation encourages the As↔P substitutions at the vicinity of the desorption sites of phosphorus, leading to the arsenic-rich surface of InAsP with the diffused hetero-interfaces. The activation energy for such As↔P exchange reaction mechanism is evaluated as ∼ (1.4 ± 0.3) eV. On the other hand, it has been observed that the thin cap layer of InP protects the surface of the InAsP epilayer and thereby preserving the sharp interface. Further, surface photovoltage and photoluminescence spectroscopy is employed to examine the role of the diffused and sharp interface of InAsP/InP hetero-structures in charge carrier transport, their redistribution and recombination process. Our analysis of the energy transitions occurring in the surface photovoltage and photoluminescence spectrum reveal that the energy band alignment and the subsequent charge carrier redistribution processes is influenced by the surface and interface states. These changes in the surface photovoltage phase spectra of InAsP/InP system also support the role of surface and interface states in the generation and separation of the charge carriers. The study provides insights into the effects of As↔P exchange on surface and interfacial quality, highlighting the implications for optoelectronic device development using InAsP/InP material system.

High-responsivity InAs quantum well photo-FET integrated on Si substrates for extended-range short-wave infrared photodetector applications

Low-intensity light detection necessitates high-responsivity photodetectors. To achieve this, we report In0.53Ga0.47As/InAs/In0.53Ga0.47As quantum well (InAs QW) photo-field-effect-transistors (photo-FETs) integrated on a Si substrate using direct wafer bonding. Structure of the InAs QW channel was carefully designed to achieve higher effective mobility and a narrower bandgap compared with a bulk In0.53Ga0.47As, while suppressing the generation of defects due to lattice relaxations. High-performance 2.6 nm InAs QW photo-FETs were successfully demonstrated with a high on/off ratio of 105 and a high effective mobility of 2370 cm2/(V·s). The outstanding transport characteristics in the InAs QW channel result in an optical responsivity 1.8 times greater than InGaAs photo-FETs and the fast rising/falling times. Further, we experimentally confirmed that the InAs QW photo-FET can detect light in the short-wavelength infrared (SWIR; 1.0–2.5 μm) near 2 μm thanks to bandgap engineering through InAs QW structures. Our result suggests that the InAs QW photo-FET is promising for high-responsivity and extended-range SWIR photodetector applications.

Performance of Improvement of AlGaN‐Based Deep UV Light‐Emitting Diode with Two Parts Linearly Graded Barriers

Herein, a novel AlGaN‐based multiple quantum well (MQW) deep UV light‐emitting diode (DUV‐LED) structure with two parts linearly graded barriers is presented. The simulation result shows that at a current of 50 mA, the light output power of the DUV‐LED with two parts linearly graded barrier MQWs has significant improvement as compared to stationary barriers. The electroluminescence spectrum and radiative recombination rate of novel DUV‐LEDs are also larger more than twice that of the conventional QW structure. The reason is that the injection efficiency of holes is increased which helps improve the hole and electron concentration in the active area. Meanwhile, the electric field is also decreased by using two parts linearly graded quantum barriers, and according to reduce the electric field the quantum‐confined Stark effect and the bend of the energy band get relieved.

Determinants Affecting the Performance of CZTSSe: Antisite Defects and Multiple Quantum Confinement for Photon-Sensitive Devices

For its earth availability and non-toxicity, kesterite (CZTS, CZTSe and CZTSSe) material has gained much importance in photon-sensitive(PS) applications. Additionally, effect of multiple carrier confinement adds the performance of the devices.The high <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\textit {oc}} $ </tex-math></inline-formula> deficit in chalcogenide materials is caused by structural antisite defects. The use of carrier confinement using Quantum Wells with CZTSSe and CZTS as well and barrier material has been investigated in this study. The defect distribution on the CZTS material and the effects of creating more potential wells with variations in the (S,Se) composition of CZTSSe is explored. The analsysis has a substantial influence on the electrical and optical properties of the absorber layer. The quantum efficiency is also calculated in order to observe sensitivity of device w.r.t solar spectrum. A comparative analysis is performed between four major aspects: first, the performance of with and without defect structures, second, the compositional change of S,Se in CZTSSe material, third, the growth in the number of QWs, and finally, the variation in defect density. According to the findings of the study, recombination in the barrier region has a significant impact in the performance of QW structures, particularly higher QW structures. According to the acquired results, at a defect density on the order of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sup> , a range of nearly 16 to 18% efficiency has been achieved for the 70QW structure for various CZTSSe compositions.

Performance enhancement of nitrogen-polar GaN-based light-emitting diodes prepared by metalorganic chemical vapor deposition.

Nitrogen-polar (N-polar) III-nitride materials have great potential for application in long-wavelength light-emitting diodes (LEDs). However, the poor quality of N-polar nitride materials hinders the development of N-polar devices. In this work, we report the enhanced performance of N-polar GaN-based LEDs with an optimized InGaN/GaN double quantum well (DQW) structure grown by metalorganic chemical vapor deposition. We improved the quality of the N-polar InGaN/GaN DQWs by elevating the growth temperature and introducing hydrogen as the carrier gas during the growth of the quantum barrier layers. N-polar LEDs prepared based on the optimized InGaN/GaN DQWs show significantly enhanced (by over 90%) external quantum efficiency and a weakened droop effect compared with a reference LED. More importantly, the optimized N-polar DQWs show a significantly longer emission wavelength than Ga-polar DQWs grown at the same QW growth temperature. This work provides a feasible approach to improving the quality of the N-polar InGaN/GaN QW structure, and it will promote the development of N-polar GaN-based long-wavelength light-emitting devices for micro-LED displays.

Investigation of Quantum Size Effects on the Optical Absorption in Ultrathin Single Quantum Well Solar Cell Embedded as a Nanophotonic Resonator

Subwavelength optical nanocavity using semiconductor nanostructures is a key nanophotonic approach for various optoelectronic devices. In such low-dimensional systems, size-dependent changes can arise due to quantum confinement (QC). In this article, the implications of quantum-size effects on the light harvesting in ultrathin single quantum well solar cell (SQWSC) are analyzed. This device is based on silicon (barrier)/germanium (QW) nanostructures integrated as a deep-subwavelength nanophotonic resonator. Compared with the state-of-the-art, the novelty of this article consists of the investigation of the synergy between photonic and electronic confinements at both functional materials and device levels. It is shown that QC effects enhance the optical absorption efficiency in both low-dimensional germanium single layers and QW structures. However, this is affected by the barrier heights and the interface states. In the SQWSC devices, the changes of the photocurrent output, the resonance condition and the absorption edge as a function of QW thickness are explained based on the optical field and the local absorption distributions. Shorter nanocavity lengths with thinner QW nanoabsorbers result in blue-shifted resonance wavelength, suitable maximum optical field intensity in the visible wavelengths range as well as promoted photonic confinement. This enables an enhancement of the optical absorption efficiency relative to thick counterparts. The nonlinearity in the thickness-related photocurrent implies a drastic reduction in QW thickness while preserving a high photocurrent level. The presented considerations in SQWC could be extended as design rules for the optimization of the photocurrent in derived multiple quantum well systems and for relevant color-neutral semitransparent devices.

Photoluminescence properties of GaAsBi single quantum wells with 10% of Bi

A set of single quantum well (SQW) samples of GaAs1-xBix with x ~ 0.1 and p-doped GaAs barriers grown by molecular beam epitaxy was investigated by the temperature-dependent photoluminescence (PL) spectroscopy. Those GaAsBi SQW structures showed a high crystalline quality, a smooth surface and sharp interfaces between the layers and exhibited a high PL intensity and a lower than 100 meV PL linewidth of QW structures. Temperature dependence of the optical transition energy was S-shape-free for all investigated structures and it was weaker than that of GaAs. An analysis of the carrier recombination mechanism was also carried out indicating that the radiative recombination is dominant even at room temperature. Moreover, numerical calculations revealed that a higher Be doping concentration leads to an increased overlap of the electron and heavy hole wave functions and determines a higher PL intensity.

Optimized design of strain-compensated InxGa1-xN/GaN and InxGa1-xN/InYGa1-YN multiple-quantum-well laser diodes

We carried out a study of the strain-compensated InxGa1−xN/GaN and InxGa1-xN/InyGa1-yN multiple quantum wells, In order to carry out this analysis, we choose a set of three different types of samples. The optimization of this laser structure allowed us to determine the optimal values of the functional parameters, in order to adjust their performance and interest. We also studied the electronic and structural properties of compound semiconductor alloys used in wurtzite phase and we have presented a comparative theoretical study of both structures. Our studies show the improvement of the spontaneous emission spectra and better carrier confinement from the use of InxGa1-xN/InyGa1-yN MQW with higher In-content in barrier as active regions for diode lasers and this structure is useful for the design of new high performance Laser diodes emitting in the Blue/Violet range, and it’s also shows that the process of the electron-holes transition is strongly affected by the quantum well width and the Indium composition, and the InGaN lattice mismatch that increases with In-content causing the strain accumulation inside the QW structure. However, strain is undesirable as it can cause defects such as cracking at the interface.We can optimize the InGaN/GaN strained quantum well structures to achieve a reliable optoelectronic component. It suffices to incorporate small amounts of indium in the barrier enhances the annihilation of the defect and strain, thereby improving their structural properties.

A general design guideline for strain-balanced quantum-wells toward high-efficiency photovoltaics

Due to the tunable optical absorption threshold and several intriguing physical properties, multiple-quantum-well (MQW) structures have been playing a crucial role in achieving ultra-high efficiency in tandem photovoltaic cells and various optoelectronic technologies. However, devices incorporating such nano-structures suffer from poor perpendicular carrier transport, which hinders device performance. On the other hand, designing MQWs is challenging. Simultaneously optimizing the structural parameters and constituent materials suggests a high design complexity with a large parameter space. In this report, on the basis of the quantitative analysis on the degradation of carrier transport, we propose a general design guideline for MQWs by which the structures and constituent materials can both be optimized targeting at a particular absorption threshold. We firstly demonstrate our design flow by optimizing an InGaP/InGaP strain-balanced (SB) MQW at 1.91 eV to replace In0.49Ga0.51P bulk serving as the top cell of dual-MQW triple-junction solar cells. Secondly, we apply the design concept to a conventional InGaAs/GaAsP SBMQW targeting at 1.23 eV, which is significant for not only high-efficiency single-junction photovoltaics but also current-matched tandem cells. The results illustrate the possibility of further improving current devices in terms of their constituent materials for QWs. Our design optimization method is considered to be applicable to any device based on QW structures.

Advantage of heteroepitaxial GaSb thin-film buffer and GaSb dot nucleation layer for GaSb/AlGaSb multiple quantum well structure grown on Si(1 0 0) substrate by molecular beam epitaxy

We grew a GaSb/Al0.3Ga0.7Sb multiple-quantum-well (MQW) structure on a two-inch Si(1 0 0) substrate using a 100-nm-thick heteroepitaxial GaSb thin-film buffer with a nucleation layer of GaSb dots by molecular beam epitaxy (MBE) and evaluated the surface morphology and the photoluminescence (PL) and X-ray diffraction spectra of the MQW structure. The full width at half maximum of the PL spectrum of the GaSb/Al0.3Ga0.7Sb MQW structure was very narrow, although the buffer thickness was much lower than those for previously reported GaSb-based QW structures on Si(1 0 0) substrates. This indicated that the surface of the 100-nm-thick GaSb thin-film buffer was sufficiently flat to form heterostructures and MQWs. The surface roughness and crystalline quality of the GaSb buffer and MQW structure were strongly dependent on the growth temperature; high-performance devices were realized by optimizing the growth temperature. These results showed the advantage and potential applicability of the GaSb/Al0.3Ga0.7Sb MQW structure and the GaSb thin-film buffer with GaSb dots as a nucleation layer grown on Si(1 0 0) substrates.

MBE-Grown SixGe1-x- ySny Diode and Quantum Well Diode Structures with High Sn Content for Optical Applications

Recent years have seen an increasing interest in Group IV photonics approach for monolithic integration of optoelectronic devices on the Si platform. While passive and active devices such as photodetectors [1,2], modulators [3–5], waveguides and splitters have been successfully realized on-chip, light sources are the last missing key component. Ever since the optically pumped Ge1-zSnz laser was demonstrated experimentally [6], this binary alloy presented itself as a direct Group IV semiconductor at high Sn concentrations. However, the growth of Ge1-zSnz is challenging due to the lattice mismatch to Si and Ge, which limits the layer thickness as well as the crystal quality. Furthermore, solid solubility of Sn in Ge is limited, making it difficult to achieve high Sn concentrations. The ternary alloy SixGe1-x-ySny is particularly interesting in this context because it allows to decouple its bandgap from its lattice constant, which enables e.g. the lattice matched growth on Ge at a given Si to Sn ratio. Moreover, SixGe1-x-ySny can have a larger bandgap than Ge, which makes it interesting as cladding material. The ternary alloy, therefore, is interesting for the growth e.g. of double hetero (DHS) as well as quantum well structures (QW) with Ge1-zSnz as the well material. We have recently investigated the molecular beam epitaxy (MBE) based growth of SixGe1-x-ySny bulk alloys lattice matched to Ge with very high Sn content up to 12,5 % [7,8] Here, we will highlight the opportunities and difficulties of lattice matched growth of Sn-rich SixGe1-x-ySny layers by MBE for SixGe1-x-ySny pin diodes. We doped SixGe1-x-ySny with B as well as Sb, achieving a total layer thickness of up to d = 900nm on a Ge virtual substrate (VS). Furthermore, we developed a growth strategy for SixGe1-x-ySny QW structures, where doped SixGe1-x-ySny layers work as cladding for a Sn-rich Ge1-zSnz quantum well, with the aim of combining the advantages of lattice matched growth on Ge with the direct semiconductor behaviour of Ge1-zSnz. We discuss material and device characterization results of a series of three SixGe1-x-ySny pin diodes with variable intrinsic zone and a total layer thickness of 900 nm (Fig. 1 (a)). The growth process takes place in a 6” MBE system, where Si, Ge and Sn are used as matrix materials and B and Sb as dopants respectively. The growth rate of the SixGe1-x-ySny layers is calibrated and kept at R = 1 Å/s. The condition of lattice matched growth of SixGe1-x-ySny (i.e. x/y = 3.67) requires highly precise calibration of the alloy compound fluxes, which is done in a complex multi-step method. The most critical growth parameter is the growth temperature, which is therefore measured and controlled in-situ by a thermocouple as well as two pyrometers. While a lower temperature allows better suppression of the Sn segregation, it can also result in a reduced crystal quality. For our samples, we chose to keep the substrate temperature at TSub = 200 °C for the growth of the ternary alloy, which is mainly based on our experience from previous SixGe1-x-ySny growth studies. In our pin diode device layers, the intrinsic zone is sandwiched between p- and n-doped SixGe1-x-ySny layers. While simple co-evaporation of B was used for p-type doping, the n-doped top contact layer was grown as follows: after the growth of the intrinsic zone with a thickness of 300 nm the growth was interrupted to deposit a pre-built up of Sb (≈ 1012 cm-2) for the following n-SixGe1-x-ySny contact in order to counterbalance the segregation of Sb [9,10]. In order to obtain detailed information of the composition as well as the crystal quality, the samples were analysed by X-Ray diffraction (XRD) and Raman spectroscopy. The reciprocal space map (RSM) of sample A (Fig. 1 (b)) shows that very good lattice matching was achieved for the SixGe1-x-ySny layers. After MBE growth the samples were processed to devices in a CMOS compatible single mesa process. Our samples clearly show diode behaviour with dark current densities as low as jD = 0.1 A/cm2 for sample A (Fig. 1 (c)). We present detailed results on the electrical and optical characterization of our devices. Our results show that MBE based growth not only enables the fabrication of SixGe1-x-ySny bulk alloys with high Sn content, it can also be used to dope the ternary alloy as a prerequisite for the fabrication of SixGe1-x-ySny diodes that contain single or multiple quantum well structures with high-Sn content Ge1-zSnz. We discuss possible improvements on growth strategies as well as future steps for the investigation of MBE-grown Sn-based light emitters on Si. Figure 1

Stacking of ZnSe/ZnCdSe Multi-Quantum Wells on GaAs (100) by Epitaxial Lift-Off

Here we present stacking of GaAs/ZnSe/ZnCdSe single-quantum well (QW) structures using epitaxial lift-off (ELO). Molecular beam epitaxy (MBE)-grown II–VI QW structure was lifted using our standard ELO technique. The QW structures were transferred onto glass plates and then subsequent layers stacked on top of each other to form a triple-QW structure. This was compared to an MBE-grown multiple-QW (MQW) structure of similar design. Low-temperature (77 K) photoluminescence (PL) spectroscopy was used to compare the two structures and showed no obvious degradation of the ELO stacked layer. It was observed that by stacking the single QW layer on itself we could increase the PL emission intensity beyond that of the grown MQW structure while maintaining narrow line width.

Investigation on interface-related defects by photoluminescence of cubic (Al)GaN/AlN multi-quantum wells structures

Cubic (Al)GaN/AlN multiple quantum wells were grown by plasma assisted molecular beam epitaxy with three different configurations at interfaces. We employ temperature-dependent photoluminescence to characterize interface imperfections. Our results show shallow localization states responsible to photocarrier localization at low temperatures. The potential fluctuation model estimates localization energies in the order of few meV. We investigated a single GaN/AlN, double GaN/AlN quantum wells, and a double quantum well with an additional AlGaN spacer layer as a step between the wells. The introduction of AlN and AlGaN interlayer reduces the effect of localization and indicates better interfaces for the QW structures based on cubic GaN.

Highly mismatched III–V semiconductor alloys applied in multiple quantum well photovoltaics

Adding dilute concentrations of nitrogen (N) or bismuth (Bi) into conventional III–V semiconductor alloys causes a large bowing of the bandgap energy due to the modification of the electronic band structure. This behaviour has attracted significant interest due to the resulting optical and electronic properties. Firstly, the authors present theoretical band structure models for GaAs-based dilute nitride, dilute bismide and dilute bismide-nitride alloys and then use them within current continuity equations to show the photovoltaic behaviour. To describe the band structures of these highly mismatched III–V semiconductor alloys, the authors introduce a 10-, 12- and 14-band k ⋅ p Hamiltonian for dilute nitride, dilute bismide and dilute bismide-nitride semiconductors, respectively. The authors then use this approach to analyse GaBiAs multi-quantum well p-i-n structures for photovoltaic performance. Through theoretical analysis the authors can: (i) elucidate important trends in the properties and photovoltaic performance of GaBiAs QW structures and (ii) comment generally on the suitability of GaBiAs alloys and heterostructures for applications in multi-junction solar cells. In particular, the authors identify and quantify the limitations associated with current GaBiAs solar cells, and describe the improvements in performance that can be expected pending further development of this emerging class of devices.

Design and properties of planar-type tunnel FETs using In0.53Ga0.47As/InxGa1-xAs/In0.53Ga0.47As quantum well

Tunnel Field Effect Transistors (tunnel FETs) have been proposed using In0.53Ga0.47As/InxGa1-xAs/In0.53Ga0.47As Quantum Well (InxGa1-xAs QW) channels which improve their performance. It is expected in this structure that the high-In-content InxGa1-xAs QW layer with the lower bandgap can increase the tunneling current and resulting on-current (Ion), while the low-In-content In0.53Ga0.47As layer, where the source junction edge is mainly formed, can suppress the increase in the junction leakage current because of the higher bandgap. Considering the strain effect and the quantum confinement effect of the InxGa1-xAs QW layers, the In content and the QW thickness are designed carefully in terms of the reduction in the effective bandgap. The proposed tunnel FETs using the QW layers grown by Metal-organic Vapor Phase Epitaxy are fabricated, and the electrical and physical properties are systematically evaluated. It is found that the InxGa1-xAs QW can significantly enhance the performance of tunnel FETs. As expected in the calculation of the effective bandgap, the higher In content and thicker QW thickness lead to higher Ion, while the thinner QW thickness makes the sub-threshold swing (S.S.) steeper through the reduction in off-current (Ioff) and enhancement of carrier confinement. The minimum sub-threshold swing (S.S.min) of 62 mV/dec is obtained at VD = 150 mV for a tunnel FET with an In0.53Ga0.47As (2.6 nm)/In0.67Ga0.33 As (3.2 nm)/In0.53Ga0.47As (96.3 nm) QW structure. Also, the highest Ion of 11 μA/μm at VD = 150 mV and VG = 1 V, which is 8.5 times higher than 1.3 μA/μm of a control In0.53Ga0.47As tunnel FET, is obtained for a tunnel FET with an In0.53Ga0.47As (2.2 nm)/InAs (6.3 nm)/In0.53Ga0.47As (94.4 nm) QW structure. It is found that the InAs QW tunnel FETs with the InAs QW thicker than 5 nm significantly degrade by high junction leakage current attributed to the lattice relaxation.

Enhancing the spontaneous emission rate by modulating carrier distribution in GaN-based surface plasmon light-emitting diodes.

Based on the nanorod structure, we have fabricated GaN-based surface plasmon light-emitting diodes with Ag nanoparticles deposited laterally proximity to the multiple quantum wells (MQWs) region, which allows us to investigate the quantum well - surface plasmon (QW-SP) coupling effect. Our results show that the QW-SP coupling effect increases significantly when the SP resonant wavelength of Ag nanoparticles is close to the QW emission wavelength, especially by using a shorter wavelength light source, which will further enhance the spontaneous emission rate. Combined with the simulations, we find that the enhancement is due to the decreased excitation light penetration depth into the active region, which can modulate the carrier distribution and increase the proportion of SP-coupled carriers in the MQWs of LEDs. To increase the spontaneous emission rate for the electrical QW-SP coupled LEDs, we can use single QW or MQW structure to confine the carriers in the topmost QW, which will effectively increase the proportion of SP-coupled carriers. Our findings pave a way to design the ultrafast LED light source for the application of visible light communication (VLC).

Temperature shift of intraband absorption peak in tunnel-coupled QW structure

An experimental study of the intersubband light absorption by the 100-period GaAs/Al0.25Ga0.75As double quantum well heterostructure doped with silicon is reported and interpreted. Small temperature redshift of the 1–3 intersubband absorption peak is detected. Numerical calculations of the absorption coefficient including self-consistent Hartree calculations of the bottom of the conduction band show good agreement with the observed phenomena. The temperature dependence of energy gap of the material and the depolarization shift should be accounted for to explain the shift.

An origin behind Rashba spin splitting within inverted doped sGe heterostructures

In this paper, we demonstrate why cubic Rashba spin splitting is observed within inverted doped strained germanium (sGe) hetrostructures. Magnetotransport measurements showed beating within the SdH oscillation, with fast Fourier analysis revealing cubic Rashba spin splitting to be present. A cubic Rashba coefficient of β=7.97×10−29 eVm3 and a spin-splitting energy of Δ=1.17 meV were determined. The source of the cubic Rashba spin splitting was identified from a combination of ultra low energy secondary ion mass spectrometry analysis and subsequent band structure modelling using Nextnano3. Ultra-low energy secondary ion mass spectrometry revealed an unintentional, highly B doped near surface region accounted for structure inversion asymmetry, whereas subsequent band structure modelling using Nextnano3 demonstrates how this asymmetric B doping generates structural inversion asymmetry within the sGe QW structure and cubic Rashba spin splitting realized.

Effect of QW growth temperature on the optical properties of blue and green InGaN/GaN QW structures

In this paper we report on the impact that the quantum well growth temperature has on the internal quantum efficiency and carrier recombination dynamics of two sets of InGaN/GaN multiple quantum well samples, designed to emit at 460 and 530 nm, in which the indium content of the quantum wells within each sample set was maintained. Measurements of the internal quantum efficiency of each sample set showed a systematic variation, with quantum wells grown at a higher temperature exhibiting higher internal quantum efficiency and this variation was preserved at all excitation power densities. By investigating the carrier dynamics at both 10 K and 300 K we were able to attribute this change in internal quantum efficiency to a decrease in the non-radiative recombination rate as the QW growth temperature was increased which we attribute to a decrease in incorporation of the point defects. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Simulation investigation of dual-wavelength tuning of light emitting diodes with single QW structure

In the present study, spectral tuning of dual-wavelength emission in monolithic InGaN/GaN multiple-quantum well light-emitting diodes was investigated based on an experiment. The reference InGaN/GaN QWs are composed of GaN barriers and “three layers” wells containing a “wetting layer”, a grading layer and a relatively low indium content InGaN layer, which has been grown in the laboratory. The simulation results show that the short wavelength light-emitting peak rises with the increasing of the grading layer thickness. In the meantime, when the thickness of the low indium content InGaN layer decreases, the long wavelength light-emitting peak falls. Dual-wavelength emissions can be achieved by tuning the grading layer thickness and the low indium content InGaN layer thickness. In addition, as the ratios of grading layer to the low indium content InGaN layer increase, the emission peaks show redshift because the interband transitions energy became smaller.