Relaxed InGaN Research Articles

Influence of GaN substrate miscut on the XRD quantification of plastic relaxation in InGaN

In the epitaxy of semiconducting materials, substrate miscut is introduced to improve the morphology of deposited layers. However, in the mismatched epitaxial system, the substrate miscut also changes the stress geometry in the deposited layer, thus influencing the relaxation processes. In this paper, we show that InGaN layers grown on misoriented (0001)-GaN substrates relax by preferential activation of certain glide planes for misfit dislocation formation. Substrate misorientation changes resolved shear stresses, affecting the distribution of misfit dislocations within each dislocation set. We demonstrate that this mechanism leads to an anisotropic strain as well as a tilt of the InGaN layer with respect to the GaN substrate. It appears that these phenomena are more pronounced in structures grown on substrates misoriented toward 〈112¯0〉 direction than corresponding structures with 〈1¯100〉 misorientation. We reveal that the lattice of partially relaxed InGaN has a triclinic deformation, thus requiring advanced XRD analysis. The presentation of just a single asymmetric reciprocal space map commonly practiced in the literature can lead to misleading information regarding the relaxation state of partially relaxed wurtzite structures.

Electrochemistry in Photonic Devices Processing: a Disruptive Approach in GaN Technology

Electrochemistry, except the electrodeposition of metal for making contacts, is rarely represented in microelectronics, despite the many possibilities it may offer like “soft” surface treatments (no surface bombardment, low damage), very sensitive methods (femtoampers sensitivity) and its large compatibility with high aspect ratio structures (TSV Cu filling). Nowadays, the More than Moore law compels researchers to look for other solutions than standard microelectronic processes to reach disruptive solutions: electrochemical processes may provide this new pathway. In that context, our study focuses on III-N material, specifically on GaN porosification through electrochemical anodization for photonic applications. After a study to understand GaN electrochemistry, we will see how new photonic device architectures may arise from the controlled porosification of GaN.Before going towards photonic applications, the understanding of the GaN electrochemical system is required. First we show that the variation of the main electrochemical and material parameters like GaN doping level, anodization potential, and electrolyte composition enables the fine-tuning of the porosity level, pore density, pore size and pore morphology. Then nano-indentation, ellipsometry and reflectometry measurements give us access to a good knowledge of the variation of the Young modulus and refractive index versus porosity level and pore morphology. The measured physico-chemical properties, mechanical as well as optical, of porous GaN eventually paves the way for new device developments.In our talk, we will show how electrochemistry requirements have an impact on the design of the final structure. We will focus on two porous GaN structures built from the previous electrochemical systemic study on GaN thin layers: i) a LED on porous GaN Bragg mirror (DBR) and ii) a relaxed InGaN pseudo-substrate for RGB micro-display applications. LED on DBR: Specifically designed epitaxial stack and technology allow the fabrication of a blue GaN/InGaN based LED structure on a DBR made of alternating porous and dense GaN layers. The optimized one-step electrochemical process results in a very efficient DBR with 99,99% reflectance and a large stop band centered on 460-520 nm. The presence of the porous GaN DBR below the LED stack exalts the photoluminescence and the cathodoluminescence signals compared with standard LEDs grown on bulk substrates. These results open a new field of research regarding the capability of tuning GaN refractive index. Fully relaxed InGaN structure for red light emission: Results on partially or totally relaxed InGaN pseudo-substrate will be presented. The InGaN pseudo-substrate relaxation helps indium incorporation in the overgrown quantum wells and enables light emission in long wavelength towards red. The control of the electrochemical and semi-conductor parameters shows that the relaxation of the III-N structure measured by HR-DRX clearly depends on the porosity level and pore morphology. This means that relaxation can be fine-tuned: that will allow an epitaxial regrowth of micro-LED structures compatible with high indium concentration in the quantum wells and possibly RGB micro-LED fabrication for micro-display applications. In that part, we will demonstrate how electrochemistry associated with microelectronic technology brings a new way of controlling relaxation of InGaN on GaN and how the obtained experimental results are promising for the fabrication of high indium content relaxed structure. Through these two examples, we put in evidence how electrochemistry allows inventing solutions unimaginable with the standard microelectronics processes.

The dissociation of (a+c) misfit dislocations at the InGaN/GaN interface.

In hexagonal materials, (a+c) dislocations are typically observed to dissociate into partial dislocations. Edge (a+c) dislocations are introduced into (0001) nitride semiconductor layers by the process of plastic relaxation. As there is an increasing interest in obtaining relaxed InGaN buffer layers for the deposition of high In content structures, the study of the dissociation mechanism of misfit (a+c) dislocations laying at the InGaN/GaN interface is then crucial for understanding their nucleation and glide mechanisms. In the case of the presented plastically relaxed InGaN layers deposited on GaN substrates, we observe a trigonal network of (a+c) dislocations extending at the interface with a rotation of 3° from <1 00> directions. High-resolution microscopy studies show that these dislocations are dissociated into two Frank-Shockley 1/6<2 03> partial dislocations with the I1 BSF spreading between them. Atomistic simulations of a dissociated edge (a+c) dislocation revealed a 3/5-atom ring structure for the cores of both partial dislocations. The observed separation between two partial dislocations must result from the climb of at least one of the dislocations during the dissociation process, possibly induced by the mismatch stress in the InGaN layer.

Porous pseudo-substrates for InGaN quantum well growth: Morphology, structure, and strain relaxation

Strain-related piezoelectric polarization is detrimental to the radiative recombination efficiency for InGaN-based long wavelength micro-LEDs. In this paper, partial strain relaxation of InGaN multiple quantum wells (MQWs) on the wafer scale has been demonstrated by adopting a partially relaxed InGaN superlattice (SL) as the pseudo-substrate. Such a pseudo-substrate was obtained through an electro-chemical etching method, in which a sub-surface InGaN/InGaN superlattice was etched via threading dislocations acting as etching channels. The degree of strain relaxation in MQWs was studied by x-ray reciprocal space mapping, which shows an increase of the in-plane lattice constant with the increase of etching voltage used in fabricating the pseudo-substrate. The reduced strain in the InGaN SL pseudo-substrate was demonstrated to be transferable to InGaN MQWs grown on top of it, and the engineering of the degree of strain relaxation via porosification was achieved. The highest relaxation degree of 44.7% was achieved in the sample with the porous InGaN SL template etched under the highest etching voltage. Morphological and structural properties of partially relaxed InGaN MQWs samples were investigated with the combination of atomic force and transmission electron microscopy. The increased porosity of the InGaN SL template and the newly formed small V-pits during QW growth are suggested as possible origins for the increased strain relaxation of InGaN MQWs.

Biaxial, Hybrid Plastic-Elastic Relaxation in Micropatterned Semipolar InGaN Buffer Layers Improves Quality of Templated Quantum Well Emitters

Despite significant progress and multiple creative approaches taken toward the realization of long-wavelength III-nitride based light emitters over the past decade, high double-digit external quantum efficiencies remain elusive for GaN/InGaN based devices for wavelengths longer than 525 nm. This stems from the large mismatch between the GaN and InGaN lattice that manifests in deleterious crystal strain gradients, degrades surface growth morphology, and introduces diverse and potent nonradiative defects.A promising route to mitigation of strain-based effects is templating epitaxial growth on relaxed InGaN epilayers; in particular, a known and controllable platform for uniaxial strain relaxation is the creation of 1-D misfit dislocation arrays at semipolar GaN/InGaN heterointerfaces. Leveraging work by Hardy et al. on achieving >200 nm thick, partially relaxed semipolar InGaN layers [1] and precise determination of InGaN epilayer strain state and composition by Young et al. [2], we explore the potential for 2-D buffer layer relaxation in (11-22) InGaN layers via micron- and sub-micron patterning. Cathodoluminescence microscopy and x-ray diffraction indicated significant increases in biaxial epilayer relaxation with increased pillar aspect ratio; quantum wells deposited atop these relaxed InGaN buffers showed dramatic threading dislocation reduction, luminescence and morphology improvements, and evidence of improved indium incorporation relative to planar samples at nominally identical growth conditions.[1] Hardy, M.T., Young, E.C., Hsu, P.S., Haeger, D.A., Koslow, I.L., Nakamura, S., DenBaars, S.P., Speck, J.S. Suppression of m-plane and c-plane slip through Si and Mg doping in partially relaxed (20-21) InGaN/GaN heterostructures. Appl. Phys. Lett. 101, 132102 (2012).[2] Young, E. C., Romanov, A.E., Speck, J.S., Determination of composition and lattice relaxation in semipolar ternary (In,Al,Ga)N strained layers from symmetric x-ray diffraction measurements. Appl. Phys. Express. 4, 061001 (2011).

N-Polar Indium Nitride Quantum Dashes and Quantum Wire-like Structures: MOCVD Growth and Characterization

The electrical properties of InN give it potential for applications in III-nitride electronic devices, and the use of lower-dimensional epitaxial structures could mitigate issues with the high lattice mismatch of InN to GaN (10%). N-polar MOCVD growth of InN was performed to explore the growth parameter space of the horizontal one-dimensional InN quantum wire-like structures on miscut substrates. The InN growth temperature, InN thickness, and NH3 flow during growth were varied to determine optimal quantum wire segment growth conditions. Quantum wire segment formation was observed through AFM images for N-polar InN samples with a low growth temperature of 540 °C and 1–2 nm of InN. Below 1 nm of InN, quantum dashes formed, and 2-D layers were formed above 2 nm of InN. One-dimensional anisotropy of the electrical conduction of N-polar InN wire-like samples was observed through TLM measurements. The sheet resistances of wire-like samples varied from 10–26 kΩ/□ in the longitudinal direction of the wire segments. The high sheet resistances were attributed to the close proximity of the treading dislocations at the InN/GaN interface and might be lowered by reducing the lattice mismatch of InN wire-like structures with the substrate using high lattice constant base layers such as relaxed InGaN.

Structural, Optical, and Electrical Characterization of 643 nm Red InGaN Multiquantum Wells Grown on Strain‐Relaxed InGaN Templates

Red‐emitting (≈643 nm) InGaN multiquantum well active device layers and micro‐LEDs are grown by metal organic chemical vapor deposition (MOCVD) on relaxed InGaN templates, the latter created via thermal decomposition of an InGaN underlayer, and examined via power‐ and temperature‐dependent photoluminescence and electrical measurements. Maximum internal quantum efficiencies are determined to be 7.5% at an excitation power density of 13 W cm−2, radiative recombination occurs through monomolecular recombination, and the fabricated micro‐LEDs do not show any efficiency degradation with decreasing size. Peak on‐wafer external quantum efficiency (EQE) of a 5 × 5 μm2device is 0.44%, demonstrating that thermally decomposed InGaN “strain‐relaxing” underlayers may be useful for long wavelength micro‐LED applications.

Long wavelength red to green emissions from {112} semipolar multi-quantum wells on fully relaxed InGaN underlayer

In this study, we present {112} InGaN underlayers of high In composition and multi-quantum wells (MQWs) grown using the m-plane sapphire substrate. Fully relaxed InGaN templates with high In composition (In: ∼18%) were investigated. We used an InGaN template with an In composition of 16.5%. The photoluminescence (PL) spectrum of MQWs on the InGaN template exhibited higher emission intensity and longer emission wavelength than that on a GaN template. Moreover, an InGaN barrier was found to be more suitable than a GaN barrier for the long-wavelength (red) region in the InGaN underlayer. The intensity of the PL spectrum of InGaN/InGaN MQWs was twice as high as that of InGaN/GaN MQWs in the red emission region. Finally, we analyzed the optical polarization of the MQWs on {112} InGaN underlayers and its characteristics were discussed using theoretical equations.

Vertical profiling of ultrafast carrier dynamics in partially strain relaxed and strained InGaN grown on GaN/sapphire template of different In composition

InGaN is one of the important ternary alloys which enables the nitrides to have bandgap energy in a wide range of 0.77–3.44 eV corresponding to the photon wavelength of 360–1610 nm by simply adjusting In content. However, the research on the InGaN has primarily focused on low-dimensional structures though knowledge of the physical properties of bulk InGaN thin-film is important in designing optoelectronic applications that utilize thick InGaN layers. In this study, we revisited partially strain relaxed bulk InGaN thin-films of different In compositions. We found that fast carrier decay was caused by hot carrier cooling due to the presence of oxygen impurity, and the slow carrier decay was governed by the carrier localization initiated by V-shape defects which concentrated at the bottom of the InGaN layer starting at InGaN/GaN interface. We also observed that the V-shape defects became severe, and the slow decay carrier lifetime decreased as In composition of the InGaN layer increased. Our observation gives guidance in designing optoelectronic applications using partially relaxed thick InGaN layers, such as buffer layers for long-wavelength InGaN light emitting diodes as well as solar absorber layer for InGaN photovoltaic cells.

Reduction of V-pit density and depth in InGaN semibulk templates and improved LED performance with insertion of high temperature semibulk layers

Highly relaxed InGaN templates with an effective In-content of ∼10% that exhibit reduced V-pit density and an improved surface roughness are reported using the semibulk (SB) growth approach. This was achieved by the insertion of five period high temperature SB (HTSB) InGaN SB regions. This report demonstrates that better quality InGaN templates can be achieved by the insertion of HTSB within the templates, rather than by ending the templates with a superlattice structure or by refilling the pits with GaN interlayers. Three SB samples were grown with and without the HTSB layers. Using secondary-ion mass spectrometry, photoluminescence, and x-ray diffraction, the effective In-content of the templates was determined to be 9.6%, 5.8%, and 8.7%. Using atomic force microscopy, the surface roughness was found to improve from 4.4 to 1.7 nm by using the two HTSB regions, and the average V-pit density and depth improved from 7.6 × 10−7 to 4.5 × 10−7 cm−2 and 8.2 to 2.8 nm, respectively. Also, the maximum V-pit depth was reduced from about 30.5 nm to about 9.6 nm in the sample with the HTSB regions. Two LEDs were studied, one with both HTSB regions, and one with only the topmost HTSB. The optical power density of the LED with both HTSB regions was 1.4 times higher at the peak injection current, displayed a ∼1.3 times higher external quantum efficiency peak, and a delay of the EQE droop onset. These results show that higher In-content SB templates can be improved with the implementation of a modified growth approach.

Demonstration of device-quality 60% relaxed In0.2Ga0.8N on porous GaN pseudo-substrates grown by PAMBE

Achieving high-quality, relaxed InGaN substrates for longer-wavelength light emitting diodes (LEDs) is of great interest for the development of micro-LED based display technology. This work demonstrates molecular beam epitaxy (MBE)-grown In0.2Ga0.8N with a strain relaxation of 60% corresponding to an equivalently fully relaxed In composition of 12%. This was done by growing on a GaN-on-porous GaN pseudo-substrate (PS). The surface morphology of this film was found to be free of V-defects on the surface and with a threading dislocation density comparable to that of the GaN layers beneath. While InGaN grown on planar GaN-on-sapphire substrates remained nearly strained to the GaN underlayer, InGaN grown under identical conditions on PS displayed elastic-like relaxation. Furthermore, an increase in indium (In) composition was observed for the InGaN grown on PS. Where past work of InGaN grown on porous GaN PS by metalorganic chemical vapor deposition also resulted in relaxed InGaN templates suitable for device application, the surfaces of these relaxed films exhibited V-defects for thicker layers. Employing MBE, thicker films with higher In composition can be achieved with smooth surface morphology, thus enabling pseudo-substrates with a wide range of lattice constants. These pseudo-substrates of varying in-plane lattice constant are attractive for III-nitride based optoelectronics, particularly for green, amber, and red micro-LEDs.

Shifting LED emission from blue to the green gap spectral range using In0.12Ga0.88N relaxed templates

In y Ga 1-y N templates are grown with y ≤ 13.5% and a few nm surface roughness . These templates are used successfully to address two of the main issues facing long wavelength emitting LEDs, mainly the low growth temperature and high values of strain in the quantum wells (QWs). In this work, three LED structures are investigated: the first is a blue LED grown on GaN, the second and third are green LEDs grown on relaxed In y Ga 1-y N templates with y of about 10% and 12%, respectively. The same multiple quantum wells (MQWs) were used in the three LED structures, with the same well width, barrier width, and growth temperature. The reduced strain in the QWs due to the use of InGaN templates enhances the indium incorporation rate in the QWs. Red shift in emission wavelength of about 100 nm, from 470 nm to 570 nm, was achieved, at low injection current. Optical output power and external quantum efficiency (EQE) measurements showed that at high level of current injection, performance of the blue LED is about twice of the green emitting LEDs on InGaN templates. The current results indicate the potential of the InGaN template approach, with high values of y , in addressing problems facing long wavelength InGaN LEDs. • Relaxed InGaN templates are used to shift blue LED emission from blue to the green gap spectral range. • Indium content>10% shows surface roughness of few nanometers and pit density in the 10 7 cm −2 to the mid 10 8 cm −2 range. • Performance of the blue the blue LED on GaN is about twice that of green LED on InGaN templates.

Growth of highly relaxed InGaN pseudo-substrates over full 2-in. wafers

A highly relaxed InGaN buffer layer was demonstrated over a full two-inch c-plane sapphire substrate by metalorganic chemical vapor deposition. The InGaN buffer layer was grown on a 100 nm GaN decomposition stop layer with a 3 nm thick high indium composition InGaN underlayer. After thermal decomposition of the underlayer at 1000 °C, a 200 nm thick In0.04Ga0.96N buffer showed 85% biaxial relaxation measured by a high resolution x-ray diffraction reciprocal space map. When used as a pseudo-substrate for the regrowth of InGaN/InGaN multi-quantum wells, the sample showed a 75 nm red-shift in room temperature photoluminescence when compared to a co-loaded GaN template reference. The longer emission wavelength is associated with higher indium incorporation in the InGaN layers from the lessening of the compositional pulling effect caused by compressive strain. Using this technique, a simple red light emitting diode was demonstrated with an active layer growth temperature of 825 °C and a peak wavelength of 622 nm at a current density of 20 A cm−2. This work represents a unique method to relax a III-nitride based layer over a full substrate.

Realization of III-Nitride c-Plane microLEDs Emitting from 470 to 645 nm on Semi-Relaxed Substrates Enabled by V-Defect-Free Base Layers

We examine full InGaN-based microLEDs on c-plane semi-relaxed InGaN substrates grown by metal organic chemical vapor deposition (MOCVD) that operate across a wide range of emission wavelengths covering nearly the entire visible spectrum. By employing a periodic InGaN base layer structure with high temperature (HT) GaN interlayers on these semi-relaxed substrates, we demonstrate robust μLED devices. A broad range of emission wavelengths ranging from cyan to deep red are realized, leveraging the indium incorporation benefit of the relaxed InGaN substrate with an enlarged lattice parameter. Since a broad range of emission wavelengths can be realized, this base layer scheme allows the tailoring of the emission wavelength to a particular application, including the possibility for nitride LEDs to emit over the entire visible light spectrum. The range of emission possibilities from blue to red makes the relaxed substrate and periodic base layer scheme an attractive platform to unify the visible emission spectra under one singular material system using III-Nitride MOCVD.

Patterned III‐Nitrides on Porous GaN: Extending Elastic Relaxation from the Nano‐ to the Micrometer Scale

Investigations of the use of patterned porous GaN underlayers to achieve elastic relaxation of lattice‐mismatched top layers such as InGaN and AlGaN are reviewed. Thereby, the degree of relaxation of the top layers increases with the porosity and associated decrease in mechanical hardness of the porous GaN underlayers as well as with decreasing pattern size and increase in thickness of the lattice‐mismatched top layers, following the trends observed for nanostructures. Micrometer‐sized, high‐fill‐factor GaN‐on‐porous‐GaN tile arrays are used as universal substrate for the deposition of InGaN and AlGaN. Due to the elastic nature of the relaxation process, the threading dislocation density in the epitaxial material grown on top of the GaN‐on‐porous‐GaN tiles is equivalent to that in the GaN base material. InGaN and AlGaN layers grown on top of relaxed or partially relaxed InGaN or AlGaN underlayers by metal–organic chemical vapor deposition display a higher indium or aluminum content compared to their counterparts deposited on coloaded planar GaN reference wafers due to the decreased lattice mismatch. First applications of the patterned porous GaN‐based technology for optoelectronic and electronic devices are presented and serve as a pathway toward future implementations.

Origins of nanoscale emission inhomogeneities of high content red emitting InGaN/InGaN quantum wells

The origin of the nanoscale emission inhomogeneities of red emitting InGaN/InGaN quantum wells (QWs) grown directly on a GaN template and on an InGaN on sapphire (InGaNOS) substrate is investigated. InGaNOS is a partly relaxed InGaN pseudo-substrate fabricated by Soitec. As the latter approach provides an interesting optical internal quantum efficiency of 6.5% at 624 nm at 290 K, a deeper study, at the microstructure level, was conducted. The emission inhomogeneities on InGaNOS were highlighted by cathodoluminescence wavelength mappings where three areas were chosen: one emitting at a shorter wavelength, i.e., 588 nm, and two at a longer wavelength, i.e., 607 and 611 nm. Specimens from these zones were extracted by focused ion beam milling to perform cross-sectional characterization techniques. High-angle annular dark field scanning transmission electron microscopy images demonstrated that, while red emitting areas present homogeneous QWs, shorter wavelength areas exhibit non-uniform QWs, in terms of thickness and In composition. Complementary deformation mappings in the growth direction obtained by geometrical phase analysis show that longer emission wavelengths are originating from homogeneous QWs with an InN mole fraction evaluated at 39.0 ± 1.5%. This result demonstrates the possibility of achieving red emission with a coherent (In,Ga)N alloy when using an adapted substrate. A comparison of identical QWs grown on a GaN template is also given.

Full InGaN red light emitting diodes

The full InGaN structure is used to achieve red light emitting diodes (LEDs). This LED structure is composed of a partly relaxed InGaN pseudo-substrate fabricated by Soitec, namely, InGaNOS, a n-doped buffer layer formed by a set of InxGa1−xN/GaN superlattices, thin InyGa1−yN/InxGa1−xN multiple quantum wells, and a p doped InxGa1−xN area. p-doped InGaN layers are first studied to determine the optimal Mg concentration. In the case of an In content of 2%, an acceptor concentration of 1 × 1019/cm3 was measured for a Mg concentration of 2 × 1019/cm3. Red electroluminescence was then demonstrated for two generations of LEDs, including chip sizes of 300 × 300 μm2 and 50 × 50 μm2. The differences between these two LED generations are detailed. For both devices, red emission with a peak wavelength at 620 nm was observed for a pumping current density of 12 A/cm2. Red light-emission is maintained over the entire tested current range. From the first to the second LED generation, the maximum external quantum efficiency, obtained in the range of 17–40 A/cm2, was increased by almost one order of magnitude (a factor of 9), thanks to the different optimizations.

Determination of the internal piezoelectric potentials and indium concentration in InGaN based quantum wells grown on relaxed InGaN pseudo-substrates by off-axis electron holography

Micro light emitting diodes have been grown by metal organic vapor phase epitaxy on standard GaN and partly relaxed InGaNOS substrates with the purpose of incorporating higher concentrations of indium for identical growth conditions. Green emission has been demonstrated at wavelengths of 500 nm for the GaN template and 525 and 549 nm for the InGaNOS substrates, respectively. The structure, deformation, indium concentration and piezoelectric potentials have been measured with nm-scale spatial resolution in the same specimens by transmission electron microscopy. We show by off-axis electron holography that the piezoelectric potential and information about the indium concentration from the mean inner potential are obtained simultaneously. By separating the components using a model, we show that for higher concentrations of indium in the quantum wells (QWs) grown on InGaNOS substrates, the piezoelectric potentials are reduced. The measurements of the indium concentrations by electron holography have been verified by combining energy dispersive x-ray spectrometry, x-ray diffraction and from the tensile deformation made by precession electron diffraction. A discussion of the limitations of these advanced aberration-corrected transmission electron microscopy techniques when applied to nm-scale QW structures is given.

First experimental demonstration and analysis of electrical transport characteristics of a GaN-based HEMT with a relaxed InGaN channel

In this paper, we demonstrate the first GaN/InGaN high electron mobility transistor with a partially relaxed InGaN channel, realized by utilizing a porous GaN buffer obtained by the selective and controlled electrochemical etch of GaN. According to reciprocal space map analysis, ∼70% of InGaN relaxation relative to GaN was achieved by this process. With the transfer length method and extracted charge profile, the relaxed InGaN channel demonstrates ∼9.6% two-dimensional electron gas mobility enhancement with respect to the strained InGaN channel which is consistent with a reduced effective mass predicted by theoretical analysis based on Vegard’s law. On comparing the output characteristics of devices with relaxed and strained InGaN channel, the relaxed channel devices show a 10% improvement of on-resistance while maintaining similar saturation current. A non-uniform charge distribution was found in the relaxed InGaN channel, which can be attributed to the strain relaxation fabrication process.

Realization of Ultrahigh Quality InGaN Platelets to be Used as Relaxed Templates for Red Micro-LEDs.

In this work, arrays of predominantly relaxed InGaN platelets with indium contents of up to 18%, free from dislocations and offering a smooth top c-plane, are presented. The InGaN platelets are grown by metal–organic vapor phase epitaxy on a dome-like InGaN surface formed by chemical mechanical polishing of InGaN pyramids defined by 6 equivalent {101̅1} planes. The dome-like surface is flattened during growth, through the formation of bunched steps, which are terminated when reaching the inclined {101̅1} planes. The continued growth takes place on the flattened top c-plane with single bilayer surface steps initiated at the six corners between the c-plane and the inclined {101̅1} planes, leading to the formation of high-quality InGaN layers. The top c-plane of the as-formed InGaN platelets can be used as a high-quality template for red micro light-emitting diodes.