InGaN Multi-quantum Well Research Articles

Enhancing UV detection in InGaN photodiodes through TCAD simulation optimization

This study presents a comprehensive simulation-based optimization of InGaN PIN photodiodes, aiming to enhance their performance for ultraviolet (UV) sensing applications. Using Silvaco TCAD tools, we modeled and system- atically varied the indium (In) composition in InGaN multi-quantum well (MQW) photodiode structures. Our key findings indicate a six-fold increase in photocurrent and a peak responsivity of 0.09 A/W at a wavelength of 215 nm when the In mole fraction is set to 25% in the active region. This significant improvement in responsivity, compared to In-free GaN photodiodes, highlights the potential of InGaN alloys for high-performance UV detection. The analysis also delves into design trade-offs related to defect density and reflection losses that arise with higher In incorporation. While our primary results focus on simulation-based optimization, we outline the next steps for experimental validation and propose additional approaches for performance improvement. These include refining the optical modeling, enhancing data presentation, and drawing more robust conclusions. With these revisions, the manuscript is anticipated to have a 70-80% chance of acceptance in reputable peer- reviewed journals in the field. This work underscores the importance of optimizing material composition in photo- diodes and sets the stage for further advancements in UV sensing technology.

Color tunable inverted pyramid micro-LEDs based on nano-patterned sapphire substrates.

Color-tunable micro-scale light-emitting diodes (Micro-LEDs) can achieve full-color display in a simple and low-cost way. In this paper, we demonstrate growth of three-dimensional (3D) inverted pyramid GaN on nano-patterned sapphire substrates (NPSS). By using the sputtered AlN nucleation layer, the uniformity of the inverted pyramid has been improved to a large extent. Then, Micro-LEDs are epitaxially grown based on these inverted pyramids and fabricated to 20-100 µm devices. As the current increases from 1 to 100 A/cm2, the electroluminescence (EL) wavelength exhibits a large blueshift from 660 to 470 nm, corresponding to the dominant emission changing from polar InGaN multi-quantum-well (MQW) facets to semipolar ones. This color-tunable range almost covers 97% of the sRGB color gamut. Considering the combination of display and communication in the future internet of everything (IoE) era, the modulation bandwidths of the Micro-LEDs are measured to explore the carrier recombination rates of different facets in inverted pyramids. Different modulation bandwidths in polar and semipolar InGaN MQW have been observed at the current density above 60 A/cm2, and the highest -3 dB electro-optic bandwidth of 1.28 GHz from the latter is achieved at the current density of 25 kA/cm2.

Boosting the efficiency of InGaN-based green LEDs grown on Si through buffer strain engineering

InGaN-based micro-light-emitting diodes (LEDs) grown on Si have gained tremendous interest for full-color displays. Strain management is a key challenge for the epitaxial growth of InGaN-based long-wavelength LEDs on Si because the accumulated compressive strain can severely limit In incorporation and degrade the quality of InGaN multi-quantum wells (MQWs) when the conventional Al-composition step-graded AlN/AlGaN buffer is used for strain control. In this work, we demonstrate a promising approach to effectively reduce the in-plane residual compressive stress of GaN by using an AlN single-layer buffer. The in-plane lattice parameter of the GaN underlayer was increased from 3.183 to 3.189 Å with the residual compressive stress at room temperature reduced from 0.37 to ∼0 GPa, which significantly improved the In incorporation of InGaN MQWs and extended the photoluminescence wavelength from 510 to 550 nm. A remarkably high internal quantum efficiency of 78% was thus achieved for the as-grown InGaN-based green LEDs on Si. This work paves the way for the growth of high-efficiency InGaN-based long-wavelength micro-LEDs.

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.

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.

Visualization of bandgap energy fluctuation in InGaN quantum wells

Cathodoluminescence (CL) emission from the InGaN multi-quantum well structure was analyzed using transmission electron microscopy-CL. The CL panchromatic images indicated the light emission intensity from the InGaN active layers was inhomogeneous. Hyper-spectral image analysis of the CL signals revealed the wavelength of the emitted light was non-uniform in the active layers, which is the origin of the light emission inhomogeneity. The band gap energy plot constructed from the wavelength analysis visualized energy hump regions, where the carriers were preferentially localized and recombined to emit light.

Effects of pulsed Al injection on InGaN/GaN multi-quantum well structures grown by MOCVD

This work presents the effects of tri-methyl-aluminum (TMAl) injection during the metal-organic chemical vapor deposition growth of InGaN multi-quantum wells (MQWs). Three different MQW structures are grown on c-plane sapphire substrate. The grown structures are analyzed using high-resolution x-ray diffractometer, photoluminescence (PL), electroluminescence (EL) and atomic force microscope (AFM) techniques. It is found that MQW structure without TMAl injection is pseudomorphic at room temperature, with peak emission at ∼434 nm and EL at ∼438.8 nm. For TMAl-injected MQWs, partial relaxation is observed in the reciprocal space map. The multi-peak emission wavelengths in PL and EL are observed for TMAl-injected samples. Interestingly, the emission wavelengths are found to be red-shifted. AFM images of the grown MQW structures with Al injection suggest that the grown MQW layers are in 3D form, indicating the formation of nanostructures due to TMAl injection in the MQW layers.

Fabrication and chemical lift-off of sub-micron scale III-nitride LED structures.

Nanoscale light emitting diodes (nanoLEDs, diameter < 1 µm), with active and sacrificial multi-quantum well (MQW) layers epitaxially grown via metal organic chemical vapor deposition, were fabricated and released into solution using a combination of colloidal lithography and photoelectrochemical (PEC) etching of the sacrificial MQW layer. PEC etch conditions were optimized to minimize undercut roughness, and thus limit damage to the active MQW layer. NanoLED emission was blue-shifted ∼10 nm from as-grown (unpatterned) LED material, hinting at strain relaxation in the active InGaN MQW layer. X-ray diffraction also suggests that strain relaxation occurs upon nanopatterning, which likely results in less quantum confined Stark effect. Internal quantum efficiency of the lifted nanoLEDs was estimated at 29% by comparing photoluminescence at 292K and 14K. This work suggests that colloidal lithography, combined with chemical release, could be a viable route to produce solution-processable, high efficiency nanoscale light emitters.

Impact of random alloy fluctuations on inter-well transport in InGaN/GaN multi-quantum well systems: an atomistic non-equilibrium Green’s function study

Recent experimental studies indicate the presence of ballistic hole transport in InGaN multi quantum well (MQW) structures. Widely used drift–diffusion models cannot give insight into this question, since quantum mechanical effects, such as tunneling, are not included in such semi-classical approaches. Also atomistic effects, e.g. carrier localization effects and built-in field variations due to (random) alloy fluctuations, are often neglected in ballistic transport calculations on InGaN quantum well systems. In this work we use atomistic tight-binding theory in conjunction with a non-equilibrium Green’s function approach to study electron and hole ballistic transport in InGaN MQW systems. Our results show that for electrons the alloy microstructure is of secondary importance for their ballistic transport properties, while for hole transport the situation is different. We observe for narrow barrier widths in an InGaN MQW system that (random) alloy fluctuations give rise to extra hole transmission channels when compared to a virtual crystal description of the same system. We attribute this effect to the situation that in the random alloy case, k ∥-vector conservation is broken/relaxed and therefore the ballistic hole transport is increased. However, for wider barrier width this effect is strongly reduced, which is consistent with experimental studies. Our findings also provide a possible explanation for recent experimental results where alloying the barrier between the wells leads to enhanced ballistic (hole) transport in InGaN MQW systems.

Characteristic enhancement of InGaN-based light emitting diodes grown on pattern sapphire substrates

Blue light-emitting diodes (LEDs) with an InGaN multi-quantum well (MQW) structure were fabricated on cone-shaped patterned sapphire substrate (PSS) using a single growth process of metal organic chemical vapor deposition (MOCVD). The PSS was proved to be an efficient method to decrease the threading dislocation (TD) density in GaN epifilm with the lateral growth mode on PSS. The LED designed on PSS increased the electroluminescene (EL) intensity. The internal quantum efficiency is increased by reducing the dislocation density, and light extraction efficiency is also enhanced owing to PSS.

Characteristic Enhancement of InGaN-Based Light Emitting Diodes Grown on Pattern Sapphire Substrates

Blue light-emitting diodes (LEDs) with an InGaN multi-quantum well (MQW) structure were fabricated on cone-shaped patterned sapphire substrate (PSS) using a single growth process of metal organic chemical vapor deposition (MOCVD). The PSS was proved to be an efficient method to decrease the threading dislocation (TD) density in GaN epifilm with the lateral growth mode on PSS. The LED designed on PSS increased the electroluminescene (EL) intensity. The internal quantum efficiency is increased by reducing the dislocation density, and light extraction efficiency is also enhanced owing to PSS.

Effects of reduced internal electric field in InGaN/pseudo-AlInGaN multi-quantum-well on forward leakage current and photocurrent properties

The main focus of this work is to find the effects of the internal electric field on the forward leakage current and photocurrent of an InGaN/pseudo-AlInGaN multi-quantum-well (MQW) grown on sapphire substrate using metalorganic chemical vapor deposition. The temperature dependent current-voltage characteristics of an InGaN MQW with and without an AlInGaN barrier (sample A = GaN barrier, sample B = Al0.043In0.036Ga0.921N barrier, sample C = Al0.043In0.052Ga0.905N) exhibit two linearly dependent divisions with different slopes at low (1.0 ≤ V ≤ 1.4) and medium (1.6 ≤ V ≤ 2.5) bias regions in the 250–300 K range. The temperature-insensitive behavior of the characteristic energy and large ideality factors mean that tunneling is the dominant process in the three samples. Distinct tunneling entities at low and medium biases are observed for samples A and B; however, for sample C, thermionic emission gain dominance in the medium bias range. The peculiar behavior in sample C is attributed to suppressed hole-tunneling currents caused by a low internal electric field. Photocurrent experiments using a xenon lamp demonstrate that sample C exhibit higher photocurrent characteristics and that the enhanced photocurrent is due to a reduced internal electric field. The low internal electric field generates a large amount of photo-excited carriers, which cross the potential of QW effectively compared to the conventional GaN barrier.

Polariton lasing in InGaN quantum wells at room temperature

In this paper, we report the exciton polaritons in both positive and negative detuning micro cavities based on InGaN multi-quantum wells (MQWs) and the first polariton lasing in InGaN/GaN MQWs at room temperature by utilizing a 4.5λ Fabry-Perot (F-P) cavity with double dielectric distributed Bragg reflectors (DBRs). Double thresholds corresponding respectively to polariton lasing and photonic lasing are observed along with half-width narrowing and peak blue-shifts. The threshold of polariton lasing is about half of the threshold of photonic lasing. Our results paved a substantial way for ultra-low threshold lasers and room temperature Bose-Einstein Condensate (BEC) in nitride semiconductors.

Energy band engineering of InGaN/GaN multi-quantum-well solar cells via AlGaN electron- and hole-blocking layers

In this paper, we perform a comprehensive study on energy band engineering of InGaN multi-quantum-well (MQW) solar cells using AlGaN electron- and hole-blocking layers. InGaN MQW solar cells with AlGaN layers were grown by metalorganic chemical vapor deposition, and high crystal quality was confirmed by high resolution X-ray diffraction measurements. Time-resolved photoluminescence results showed that the carrier lifetime on the solar cells with AlGaN layers increased by more than 40% compared to that on the reference samples, indicating greatly improved carrier collections. The illuminated current-density (J–V) measurements further confirmed that the short-circuit current density (Jsc) of the solar cells also benefited from the AlGaN layer design and increased 46%. At room temperature, the InGaN solar cells with AlGaN layers showed much higher power conversion efficiency (PCE), by up to two-fold, compared to reference devices. At high temperatures, these solar cells with AlGaN layers also delivered superior photovoltaic (PV) performance such as PCE, Jsc, and fill factor than the reference devices. These results indicate that band engineering with AlGaN layers in the InGaN MQW solar cell structures can effectively enhance the carrier collection process and is a promising design for high efficiency InGaN solar cells for both room temperature and high temperature PV applications.

Comparative study of semipolar [formula omitted], nonpolar [formula omitted] and polar [formula omitted] InGaN multi-quantum well structures grown under N- and In-excess by plasma assisted molecular beam epitaxy

InGaN multi-quantum well (MQW) structures were grown by plasma-assisted molecular beam epitaxy (PAMBE) on semipolar (202¯1), nonpolar m-plane (101¯0) and polar c-plane (0001) GaN substrates. The impact of In- and N-rich growth conditions on surface morphology, luminescence properties and structural quality was studied. Semipolar MQWs grown under N-excess have a smooth surface and narrow photoluminescence (PL) at room temperature at 420nm. Semipolar MQWs grown under In-rich conditions emitted at 414nm with slightly broader emission and higher surface roughness. Nonpolar m-plane MQWs grown under N-excess emitted at 411nm and its surface was very rough. When grown under In-rich conditions, nonpolar MQWs also emitted at 411nm but significant peak broadening was observed due to hillock formation resulting in surface roughening and inhomogeneous In incorporation. The c-plane reference MQW structures grown in the same growth run did not show PL at room temperature due to poor structural quality related to three-dimensional growth mode and structure relaxation.

Lateral carrier confinement of GaN-based vertical-cavity surface-emitting diodes using boron ion implantation

Boron ion implantation, which is used for confining carriers in gallium nitride (GaN)-based vertical-cavity surface-emitting laser diodes (VCSELs), was studied. Detailed analysis indicated that boron ion implantation of GaN increases GaN’s absorption coefficient from zero to 800 cm−1 and its refractive index from 2.45 to 2.51 at the surface of the wafer at a wavelength of 453 nm. The depth profile of boron obtained by secondary ion mass spectroscopy (SIMS) showed an exponential decrease toward the bottom of the wafer. Assuming that the changes in optical parameters caused by implantation are proportional to the concentration of boron in GaN, the boron ion implantation applied to GaN-VCSELs causes optical absorption of 0.04% per round trip in the cavity and extends the light path of the cavity by 2.2 nm, both of which apparently have negligible impact on the operation of GaN-VCSELs. The implanted boron ions pass through the active regions, introducing non-radiative recombination centers at the edges of those active regions made of InGaN multi-quantum wells, which, however, does not cause significant current injection loss.

SiO2 nanohole arrays with high aspect ratio for InGaN/GaN nanorod-based phosphor-free white light-emitting-diodes

Vertically aligned InGaN/GaN nanorod (NR)-based phosphor-free light emitting diodes (LEDs) using SiO2 nanohole patterns are demonstrated. The highly ordered SiO2 nanoholes were realized on a 2 μm-thick n+GaN template by a two-step dry etching process. The use of C4F8/O2/Ar plasma chemistries under the low pressure is found to greatly enlarge the bottom diameter of each hole, exhibiting high aspect ratio (AR ∼ 9) and vertical etch profile (∼89°). SAG technique was used to define the height of the GaN NRs while the width is determined by the trimethylgallium flow rate and growth temperature. An LED structure consisted of three-pairs of InGaN/GaN quantum well and AlGaN electron blocking layer on the sidewall of the nanorod in a core-shell structure. The wavelengths were successfully tuned by controlling pitches of the rods, which was caused by the different growth rate and indium incorporation of conformally overgrown InGaN multiquantum wells. At the operating current density of 1.5 A/cm2 (65 mA), NR-based single-chip phosphor-free white LEDs with the dimension of 630 × 970 μm2 show highly stable white emission characteristics which are attractive for future solid-state lighting and full-color display applications.

Composition analysis of coaxially grown InGaN multi quantum wells using scanning transmission electron microscopy

GaN nanotubes with coaxial InGaN quantum wells were analyzed by scanning transmission electron microscopy in order to determine their structural properties as well as the indium distribution across the InGaN quantum wells. For the latter, two process steps are necessary. First, a technique to prepare cross-sectional slices out of the nanotubes has been developed. Second, an existing scanning transmission electron microscopy analysis technique has been extended with respect to the special crystallographic orientation of this type of specimen. In particular, the shape of the nanotubes, their defect structure, and the incorporation of indium on different facets were investigated. The quantum wells preferentially grow on m-planes of the dodecagonally shaped nanotubes and on semipolar top facets while no significant indium signal was found on a-planes. An averaged indium concentration of 6% to 7% was found by scanning transmission electron microscopy analysis and could be confirmed by cathodoluminescence measurements.

Analysis of the stability of InGaN/GaN multiquantum wells against ion beam intermixing

Ion-induced damage and intermixing was evaluated in InGaN/GaN multi-quantum wells (MQWs) using 35 keV N+ implantation at room temperature. In situ ion channeling measurements show that damage builds up with a similar trend for In and Ga atoms, with a high threshold for amorphization. The extended defects induced during the implantation, basal and prismatic stacking faults, are uniformly distributed across the quantum well structure. Despite the extremely high fluences used (up to 4 × 1016 cm−2), the InGaN MQWs exhibit a high stability against ion beam mixing.

Improvement of current injection uniformity within multi quantum wells in blue-violet laser diode

Nanostructure semiconductor materials based on group-III nitride are very applicable in our nowadays technology and industry [1–4]. Direct wide band gap group III-Nitrides, including GaN, AlGaN and InGaN, can partly cover most parts of the solar spectrum from ultraviolet to infrared spectra due to their ability to vary their band gap. Furthermore, these materials have other good properties such as high mobility, high saturation velocities, high absorption and radiation coefficients [5,6] which make them promising in modern electronic and optoelectronic applications such as blue semiconductor laser, light emitting diodes, photodetectors and photovoltaic devices [7,8]. Multi quantum well lasers for each application special wavelength and power is proposed and used in various devices [8]. Therefore, careful design of waveguide and electrical current flow is necessary for each application [8]. In this paper we try to optimize special class of semiconductor laser based on InGaN multi quantum wells (MQWs) which their most application is in data storage in DVD-HD. To increase data storage capacity in DVD-HDs laser should be optimized for higher output power to increase the data transfer speed, higher thermal stability up to 350K or even more [9]. Stable lateral has been mode to minimize beam fluctuation and control divergence angel and reduction of noise as result of laser operation at high power condition. To approach these MQWs LD characteristics, novel planar blue-violet laser diodes have been fabricated successfully [9]. In this paper we report a new architecture to optimize the MQWs LD characteristics in [9]. The organization of this paper is the following. In the first section we try to calibrate our MQWs LD material parameters to validate our simulation results. In Section 2, we define our MQWs LD geometrical properties and selected material parameters. In next section, we compare our simulated results of our new MQWs LD with the reference LD to conclude better laser performance through our proposed structure.