Multi-quantum Well Research Articles

480 nm InGaN-based cyan laser diode grown on Si by interface engineering of active region

InGaN-based long wavelength laser diodes (LDs) grown on Si are highly desirable for expanding the applications in laser display and lighting. Proper interface engineering of high In-content InGaN multi-quantum wells (MQWs) is urgently required for the epitaxial growth of InGaN-based long wavelength LD on Si, because the deteriorated interfaces and crystalline quality of InGaN MQWs can severely increase the photon scattering and further exacerbate the internal absorption loss of LDs, which prevents the lasing wavelength of InGaN-based LDs from extending. In this work, a significantly improved morphology and sharp interface of the InGaN active region are obtained by using a graded-compositional InGaN lower waveguide (LWG) capped with a 10-nm-thick Al0.1Ga0.9N layer. The V-pits density of the InGaN LWG was one order of magnitude reduction from 4.8 × 108 to 3.6 × 107 cm-2 along with the root-mean-square surface roughness decreasing from 0.3 to 0.1 nm. Therefore, a room-temperature electrically injected 480 nm InGaN-based cyan LD grown on Si under pulsed current operation was successfully achieved with a threshold current density of 18.3 kA/cm2.

Demystifying metal-assisted chemical etching of GaN and related heterojunctions

GaN and related semiconductors have become an increasingly prominent material for a wide range of active and passive devices from optoelectronics to high frequency and power electronics as well as photocatalysis. Regardless of the application, anisotropic etching is required for micro and nano structuring, currently performed by reactive ion etching (RIE). Alternately, metal-assisted chemical etching (MacEtch) is an open-circuit plasma-free anisotropic etching method that has demonstrated high aspect ratio device structures devoid of plasma-induced damage found in RIE. This paper presents an in-depth study of the ensemble electrochemical mechanisms that govern the photo-enhanced MacEtch process of GaN and related heterojunctions. Through in-depth experimental investigations, modeling and simulations, the effects of local cathode and anode design, energy-band alignments, and solution chemistry on MacEtch are correlated with the underlying electronic mechanisms of carrier generation, annihilation, transport, and extraction, establishing a fundamental framework for parametrized prediction of system behavior. These findings carry profound implications for tailored design of photoelectrochemical processes employed not just for uniformly etching wide/ultrawide bandgap materials but more broadly for semiconductor-based photocatalytic reactions in general. One-pot photo-enhanced MacEtching of AlInGaN multi-heterojunction device structures including superlattices and multi-quantum wells are demonstrated.

Correlation of quantum well periods on the 3rd order nonlinear optical responses of InGaN/GaN heterostructures

Semiconductor multi quantum well (MQW) design allows for the compression of electron-interaction dimensions, offering advantages for various applications, particularly in nonlinear optics. Despite the potential improvements in nonlinear optical responses, the influence of quantum well periods remains unexplored. In this study, we report the correlation of quantum well periods on the 3rd order nonlinear optical properties in In0.15 Ga0.85 N/GaN MQW using z-scan technique under femtosecond and continous wave laser regime. In0.15 Ga0.85 N well/GaN barrier with x1, x5, x10, x15 periods were grown by MOCVD technique. Good structural quality of grown MQWs were confirmed via HRTEM imaging, EDS, AFM and XRD. Absorption coefficient from UV-Vis coupled with PL emission spectrum shows systematic response of optical linear properties which provide an insight on the overall band gap structure. Positive nonlinear refraction, n2 and nonlinear absoprtion, β trends is observed under femtosecond an CW laser albeit differences of one order magnitude in χ3 value. The increase in χ3 value is shown to be monotonous with the increasing number of quantum well suggesting that compounding effect took place. This findings indicate the possibility of manipulating and tuning nonlinear reponses of MQW structures leading to improvement in semiconductor design in various areas such as optoelectronics, photonics, solar cell research, as well as quantum information processing.

Conduction-band engineering of polar nitride semiconductors with wurtzite ScAlN for near-infrared photonic devices

Wurtzite ScxAl1−xN/GaN (x = 0.13–0.18) multi-quantum wells grown by molecular beam epitaxy on c-plane GaN are found to exhibit remarkably strong and narrow near-infrared intersubband absorption in the technologically important 1.8–2.4 μm range. Band structure simulations reveal that, for GaN wells wider than 3 nm, the quantized energies are set by the steep triangular profile of the conduction band caused by intrinsic polarization fields. As a result, the intersubband transition energies provide unique and direct access to essential ScAlN polarization parameters. Measured infrared absorption indicates that the spontaneous polarization difference of the presumed lattice-matched Sc0.18Al0.82N/GaN heterostructure is smaller than the theoretically calculated value. The intersubband transition energies are relatively insensitive to the barrier alloy composition indicating negligible variation of the net polarization field in the probed 0.13–0.18 Sc composition range.

Machine learning-based method for predicting C–V-T characteristics and electrical parameters of GaAs/AlGaAs multi-quantum wells Schottky diodes

In this work, two models of artificial neural networks are developed to predict the electrical parameters and capacitance-voltage characteristics of GaAs/AlGaAs multi-quantum wells Schottky diodes at different temperatures. Capacitance-Voltage-Temperature (C–V-T) characteristics for voltages and temperatures in the ranges (-4 V–0 V) and (20 K–400 K), respectively, were used to assess the effectiveness of the proposed approach. The first model (Model 1) is used to evaluate how well the neural network predicts the C–V-T characteristics. The second simulation, known as Model 2, was constructed to simultaneously overcome the problems of determining the electrical parameters and predicting C–V-T characteristics. Model 2 allows the calculation of the built-in voltage, effective density, and capacitance. Three-fold cross-validation and mean square error are used to assess the effectiveness of the developed models. The results clearly demonstrate the high prediction accuracy of the electrical parameters and C–V characteristics at all temperatures. After training, Model 1 Mean Square Error performance is 1.5033×10−6 at 1450 epochs, whereas Model 2 MSE is 4.9951×10−6 at 642 epochs. According to the error distribution frequency histogram, about 95 % of errors for Model 1 and Model 2 lie between [0.00535 and 0.005608] and [0.00328 and 0.00333], respectively. The R-values that correspond to the training and validation datasets for both models are close to one (0.9999). Parameters determination results have been compared against those obtained using ant lion optimizer based method. It was found that the results obtained from the neural networks models strongly agree with the experimental data.

Spatially correlated stress-photoluminescence evolution in GaN/AlN multi-quantum wells

In the manufacture of semiconductor devices, cracking of heterostructures has been recognized as a major obstacle for their post-growth processing. In this work, we explore cracked GaN/AlN multi-quantum wells (MQWs) to study the influence of pressure on the recombination energy of the photoluminescence (PL) from the polar GaN QWs. We grow GaN/AlN MQWs on a GaN(0001)/sapphire template, which provides 2.4% tensile strain for epitaxial AlN. This strain relaxes through the generation and propagation of cracks, resulting in a final inhomogeneous distribution of stress throughout the film. The crack-induced strain variation investigated by micro-Raman spectroscopy and X-ray diffraction mapping revealed a correlation between the spacing of the cracks and the amount of strain between them. We have developed a 2D model that allows us to calculate the spatial variation of the in-plane strain in the GaN and AlN layers. The measured values of compressive in-plane strain in the GaN QWs vary from -0.4 % away from cracks, to -0.7 % near cracks. PL from the GaN QWs exhibits a clear correlation to the varying strain resulting in an energy shift of ∼ 140 meV. As a result, we can experimentally calculate a pressure coefficient of PL energy of ∼ -60.4 meV/GPa for the ∼ 7 nm thick polar GaN QWs. This agrees well with the previously predicted theoretical results by Kaminska et al. in 2016 [DOI: 10.1063/1.4962282], which were demonstrated to break down for such wide QWs. We will discuss this difference with respect to the reduction in both the expected point defects and extended defects resulting from not doping and growth on a GaN template, respectively. As a result, our work indicates that cracks can be utilized for investigating some fundamental material properties related to strain effects.

Composition-Dependent Phonon and Thermodynamic Characteristics of C-Based XxY1−xC (X, Y ≡ Si, Ge, Sn) Alloys

Novel zinc-blende (zb) group-IV binary XC and ternary XxY1−xC alloys (X, Y ≡ Si, Ge, and Sn) have recently gained scientific and technological interest as promising alternatives to silicon for high-temperature, high-power optoelectronics, gas sensing and photovoltaic applications. Despite numerous efforts made to simulate the structural, electronic, and dynamical properties of binary materials, no vibrational and/or thermodynamic studies exist for the ternary alloys. By adopting a realistic rigid-ion-model (RIM), we have reported methodical calculations to comprehend the lattice dynamics and thermodynamic traits of both binary and ternary compounds. With appropriate interatomic force constants (IFCs) of XC at ambient pressure, the study of phonon dispersions ωjq→ offered positive values of acoustic modes in the entire Brillouin zone (BZ)—implying their structural stability. For XxY1−xC, we have used Green’s function (GF) theory in the virtual crystal approximation to calculate composition x, dependent ωjq→ and one phonon density of states gω. With no additional IFCs, the RIM GF approach has provided complete ωjq→ in the crystallographic directions for both optical and acoustical phonon branches. In quasi-harmonic approximation, the theory predicted thermodynamic characteristics (e.g., Debye temperature ΘD(T) and specific heat Cv(T)) for XxY1−xC alloys. Unlike SiC, the GeC, SnC and GexSn1−xC materials have exhibited weak IFCs with low [high] values of ΘD(T) [Cv(T)]. We feel that the latter materials may not be suitable as fuel-cladding layers in nuclear reactors and high-temperature applications. However, the XC and XxY1−xC can still be used to design multi-quantum well or superlattice-based micro-/nano devices for different strategic and civilian application needs.

Inorganic-Organic Hybrid Layered Semiconductor AgSePh: Quasi-Solution Synthesis, Optical Properties, and Thermolysis Behavior.

Two-dimensional inorganic-organic hybrid layered semiconductors are actively studied because of their naturally formed multiquantum well (MQW) structures and associated optical, photoelectric, and quantum optics characteristics. Silver benzeneselenolate (AgSePh, Ph = C6H5) is a new member of such hybrid layered materials, but has not fully been exploited. Herein, we present a quasi-solution method to prepare high quality free-standing AgSePh flake-like microcrystals by reacting diphenyl diselenide (Ph2Se2) with silver nanoparticles. The resultant AgSePh microflakes exhibit room-temperature (RT) resolvable MQW-induced quasi-particle quantization and interesting optical properties, such as three distinct excitonic resonance absorptions X1 (2.67 eV), X2 (2.71 eV), and X3 (2.83 eV) in the visible region, strong narrow-line width blue photoluminescence at ∼2.64 eV (470 nm) from the radiative recombination of the X1 exciton state, and a large exciton binding energy (∼0.35 eV). Furthermore, AgSePh microcrystals show high stability under water, oxygen, and heat environments, while above 220 °C, they will thermally decompose to silver and Ph2Se2 as evidenced by a combination of thermogravimetry and differential scanning calorimetry and pyrolysis-coupled gas chromatography-mass spectrometry studies. Finally, a comparison is extended between AgSePh and other metal benzeneselenolates, benzenethiolates, and alkanethiolates to clarify differences in their solubility, decomposition/melting temperature, and pyrolytic products.

Thermally stable radiative recombination centers within trench structures of red multi-quantum wells

High-Indium (In)-content multi-quantum wells (MQWs) are generally thermally unstable due to poor crystal quality resulting from low-temperature growth. In this study, red emission was achieved by modulating trench structures using dual-colour MQW structures. Impressively, the red MQWs inside deep trenches showed excellent thermal stability despite being grown at low temperatures. After high-temperature annealing at 950 °C for 30 min, the photoluminescence (PL) intensity of red MQWs exhibited a significant reduction of 91.9% outside trenches, while it dropped by only 9.3% inside trenches, as confirmed by confocal PL mapping. Transmission electron microscopy results show that massive In-rich phases and stacking faults appeared in the MQWs outside trenches after annealing. By contrast, the red MQWs inside deep trenches remained intact in lattice arrangement without being significantly damaged. The superior thermal stability of red MQWs inside deep trenches was mainly attributed to the low-defect-density epitaxy of InGaN layers in strain-relaxed states.

Photoreflectance Analysis of InAsPSb/InGaAs Multi-Quantum Well LED Structures with Different Well/Barrier Numbers

InAsPSb is an emerging material used as an efficient barrier in quantum well structures, and the resulting devices can be employed in the mid-infrared region of the electromagnetic spectrum. This study investigates the photoreflectance spectra of two InAsPSb/InGaAs multi-quantum well light-emitting diodes with 6 and 15 quantum well periods. The photoreflectance of the samples was analyzed at various temperatures and excitation powers. By examining the Franz-Keldysh oscillations in the spectra, we explored the influence of the number of well layers on the electric field strength in the junction. The results showed that the number of quantum wells can influence the electric field at the junction, potentially impacting the overall performance of the devices. The simulation of the electric field strength aligns with the results of the photoreflectance analysis. This suggests that the field extracted from Franz-Keldysh oscillations characterizes the field inside the multi-quantum wells, offering potential reasons for the observed effects on the number of multi-quantum wells in the field.

Watt-level continuous-wave antimonide laser diodes with high carrier-confined active region above 2.5 µm

Thanks to high performance above room temperature, antimonide laser diodes have shown great potential for broad application in the mid-infrared spectral region. However, the laser`s performance noticeably deteriorates due to the reduction of carrier confinement with increased emission wavelength. In this paper, a novel active region with higher carrier confinements both of electron and hole, by the usage of an indirect bandgap material of Al0.5GaAs0.04Sb as the quantum barrier, was put up to address the poor carrier confinement of GaSb-based type-I multi-quantum-well (MQW) diode lasers emission wavelength above 2.5 µm. The carrier confinement and the differential gain in the designed active region are enhanced as a result of the first proposed usage of an indirect-gap semiconductor as the quantum barrier with larger band offsets in conduction and valence bands, leading to high internal quantum efficiency and low threshold current density of our lasers. More importantly, the watt-level output optical power is obtained at a low injection current compared to the state of the art. Our work demonstrates a direct and cost-effective solution to address the poor carrier confinement of the GaSb-based MQW lasers, thereby achieving high-power mid-infrared lasers.

High-power, electrically-driven continuous-wave 1.55-μm Si-based multi-quantum well lasers with a wide operating temperature range grown on wafer-scale InP-on-Si (100) heterogeneous substrate

A reliable, efficient and electrically-pumped Si-based laser is considered as the main challenge to achieve the integration of all key building blocks with silicon photonics. Despite the impressive advances that have been made in developing 1.3-μm Si-based quantum dot (QD) lasers, extending the wavelength window to the widely used 1.55-μm telecommunication region remains difficult. In this study, we develop a novel photonic integration method of epitaxial growth of III-V on a wafer-scale InP-on-Si (100) (InPOS) heterogeneous substrate fabricated by the ion-cutting technique to realize integrated lasers on Si substrate. This ion-cutting plus epitaxial growth approach decouples the correlated root causes of many detrimental dislocations during heteroepitaxial growth, namely lattice and domain mismatches. Using this approach, we achieved state-of-the-art performance of the electrically-pumped, continuous-wave (CW) 1.55-µm Si-based laser with a room-temperature threshold current density of 0.65 kA/cm−2, and output power exceeding 155 mW per facet without facet coating in CW mode. CW lasing at 120 °C and pulsed lasing at over 130 °C were achieved. This generic approach is also applied to other material systems to provide better performance and more functionalities for photonics and microelectronics.

Inhibited Inelastic Scattering of Incoherent Excitons for Near-Band Edge Excitations.

A multiple pump-terahertz probe experiment enables the clear distinction between elastic and inelastic scattering of excitons with a free electron-hole plasma in (Ga,In)As multiquantum wells. Low plasma energies dictate the prevalence of elastic scattering by inhibiting inelastic processes due to the absence of final states for quasiparticles. Yet, an increased plasma energy results in a progressive destruction of excitons. Notably, despite plasma energy variations, the interaction strength between excitons and the electron-hole plasma remains unaltered.

Buried InGaAs/InP quantum wells selectively grown on SOI for lateral membrane laser diodes

The monolithic integration of energy-efficient and high-speed III–V lasers on silicon-on-insulator (SOI) platform in a cost-effective and scalable manner is the crux for the ubiquitous application of Si photonics in various applications. Here, aiming for lateral p-i-n membrane laser diodes, we report the growth of InGaAs/InP multi-quantum wells (MQWs) buried inside InP membranes on (001) SOI wafers using the lateral aspect ratio trapping method. We first obtain uniform InP membranes through careful tuning of a low-temperature nucleation layer, effectively trapping crystalline defects at the InP/Si heterogeneous interface and obtaining dislocation-free InP crystals away from the interface. We then construct buried (110)-oriented InGaAs/InP MQWs emitting in the telecom wavelengths by engineering the faceting of the InP membrane to enable the epitaxy of InGaAs alloy on (110) planes. These as-grown InGaAs/InP MQWs are fully embedded inside the InP membrane and provide effective confinement of both light and charged carriers. Our results demonstrate an elegant solution for future lateral membrane laser diodes directly grown on SOI wafers.

Startified thermal degradation in blue InGaN quantum well structures: P-GaN growth temperature and its influence on quantum well optical properties

Thermal degradation in blue InGaN multi-quantum well (MQW) structures induced by varying high p-GaN growth temperature and the subsequent influence on the optical properties of MQW are investigated. The results indicate that higher p-GaN growth temperatures improve p-GaN layer contact quality, but may lead to an optical property degradation of InGaN MQWs. A stratified thermal degradation mechanism is observed. The degradation primarily affects the upper quantum barrier layers and results in indium desorption and re-evaporation, where elevated p-GaN growth temperatures may induce more indium segregation and decomposition than in lower layers of MQW. In extreme conditions, such as 1060℃, indium atoms in lower layers escape, causing partial lattice structure corruption and severe degradation in MQW structure, which is also more distinctive in the upper layers.

Low-Temperature Growth of InGaAs Quantum Wells Using Migration-Enhanced Epitaxy.

The growth of InGaAs quantum wells (QWs) epitaxially on InP substrates is of great interest due to their wide application in optoelectronic devices. However, conventional molecular beam epitaxy requires substrate temperatures between 400 and 500 °C, which can lead to disorder scattering, dopant diffusion, and interface roughening, adversely affecting device performance. Lower growth temperatures enable the fabrication of high-speed optoelectronic devices by increasing arsenic antisite defects and reducing carrier lifetimes. This work investigates the low-temperature epitaxial growth of InAs/GaAs short-period superlattices as an ordered replacement for InGaAs quantum wells, using migration-enhanced epitaxy (MEE) with low growth temperatures down to 200-250 °C. The InAs/GaAs multi-quantum wells with InAlAs barriers using MEE grown at 230 °C show good single crystals with sharp interfaces, without mismatch dislocations found. The Raman results reveal that the MEE mode enables the growth of (InAs)4(GaAs)3/InAlAs QWs with excellent periodicity, effectively reducing alloy scattering. The room temperature (RT) photoluminescence (PL) measurement shows the strong PL responses with narrow peaks, revealing the good quality of the MEE-grown QWs. The RT electron mobility of the sample grown in low-temperature MEE mode is as high as 2100 cm2/V∗s. In addition, the photoexcited band-edge carrier lifetime was about 3.3 ps at RT. The high-quality superlattices obtained confirm MEE's effectiveness for enabling advanced III-V device structures at reduced temperatures. This promises improved performance for applications in areas such as high-speed transistors, terahertz imaging, and optical communications.

Series-Biased Micro-LED Array for Lighting, Detection, and Optical Communication

Micro-LED arrays exhibit high brightness, a long lifespan, low power consumption, and a fast response speed. In this paper, we have proposed a series-biased micro-LED array by using a nitride layer with multi-quantum wells epitaxial on sapphire substrate. The III-nitride multiple quantum wells serving as the micro-LED active material enable both luminescence and detection functionalities. The micro-LED array combines lighting, detection, and communication capabilities. We have conducted a thorough analysis of the micro-LED array’s optoelectronic features in both lighting and detection modes. We also explore visible light communication performance across different arrangements of single micro-LED devices within the series-biased array. Our research achieves 720p video transmission via visible light communication using the micro-LED array, supporting a communication rate of up to 10 Mbps. Our contributions encompass the successful integration of lighting and detection functions and a comprehensive assessment of optoelectronic and communication performance. This study highlights the multifunctional micro-LED array’s potential as a transceiver terminal in visible light communication systems, expanding its applications from smart lighting to visible light communication and photonic integrated chips. These innovations enhance our understanding of micro-LED technology and its versatile applications.

Observation of structural defects in GaN/InGaN multi-quantum wells grown on semipolar (112¯2) substrate using cathodoluminescence in transmission electron microscopy

Defect structures of semipolar GaN thin film, grown on the m-plane of sapphire, were investigated using the home-built cathodoluminescence (CL) stage in TEM. The CL maps with high spatial resolution identify the type of basal plane stacking faults (BSFs) and visualize their distribution. I1-BSF type defects had the highest population and the I2-BSF type defect was revealed in the form of thin strips with less population. Partial dislocations and basal stacking fault-related defects existed in the form of segmented lines but with strong luminescence characteristics. TEM-CL was able to identify the distribution and the characteristic luminescence from the defects, which were difficult to discern in the typical defect analysis.

Progress and Outlook of 10% Efficient AlGaN‐Based (290–310 nm) Band UVB LEDs

Eco‐friendly and low‐cost aluminum gallium nitride (AlGaN) for the epitaxial growth of ultraviolet‐B (UVB) light‐emitting diodes (LEDs) on c‐Sapphire has the possibility of high external‐quantum efficiency (EQE). In this review paper a special growth techniques for 50% relaxed and 4 μm thick AlGaN buffer layer underneath the multi‐quantum wells (MQWs) are challenged to achieve a maximum internal‐quantum efficiency of 50–57% in 310–290 nm band UVB LEDs. The influence of a thin “Valley” layer in p‐type multi‐quantum barrier electron‐blocking layer on 2D hole generation and injection via intraband tunneling was attempted. Finally, the influence of soft polarized Mg‐doped p‐type Al‐graded AlGaN hole injection layer assisted by excimer laser annealing for better hole injection toward the MQWs was investigated and quite high hole concentration of 2 × 1016 cm−3 and resistivity of 24 Ω‐cm at room temperature was achieved. Consequently, the EQE of transparent 310 and 304 nm UVB LEDs, respectively, reached to a confirmed world record values of ≈5% and ≈10% with light powers of 29 and 40 mW on wafer. This EQE value can surpass 21% if flip‐chip, nanoPSS, photonic crystal, and lens with highly reflective p‐electrodes are incorporated in LED.

Efficient InGaN‐Based Red Light‐Emitting Diodes by Modulating Trench Defects

AbstractTrench defects in multi‐quantum wells (MQWs) have been considered as flawed structures that severely degraded the internal quantum efficiency (IQE) of light‐emitting diodes (LEDs) in the past. In this research, trench defects are innovatively utilized to enhance the efficiency of red InGaN LEDs. Specifically, dual‐color MQWs structures are applied to modulate trench defects. The upper red MQWs, grown on top of green MQWs with a high density of trench defects, exhibit a significant wavelength redshift of 68 nm and ≈ 6‐fold luminescence enhancement compared to those without intentionally introduced trench defects. Red InGaN LEDs with an IQE of 16.4% are achieved with this epitaxy growth strategy. Such wavelength redshift is attributed to the more indium incorporation due to the strain relaxation effect of trench defects. Moreover, the luminescence enhancement originates from the strong emission of the red MQWs inside trench defects, mainly attributed to strain relaxation and defect shielding by the wide and deep trenches. Achieving red emission by modulating trench defects is simple and reproducible without requiring additional substrate designs, which provides a novel way toward high‐efficiency red InGaN LEDs.