Crystals

Research

22 pages, 1322 KiB

Open AccessEditor’s ChoiceArticle

Numerical Analysis of Gas Flow Instabilities in Simplified Vertical HVPE GaN Reactors

by Markus Zenk, Gleb Lukin, Dirk Bastin, Roman Doradziński, Franziska C. Beyer, Elke Meissner and Jochen Friedrich

Crystals 2022, 12(9), 1248; https://doi.org/10.3390/cryst12091248 - 2 Sep 2022

Cited by 1 | Viewed by 2342

Abstract

This paper investigates the gas flow and the mass transport in simplified axial-symmetric vertical HVPE reactors for the growth of GaN bulk crystals through numerical simulations. We evaluate the relative significance of different flow and transport phenomena in dependence on the direction of [...] Read more.

This paper investigates the gas flow and the mass transport in simplified axial-symmetric vertical HVPE reactors for the growth of GaN bulk crystals through numerical simulations. We evaluate the relative significance of different flow and transport phenomena in dependence on the direction of gravity. The performed simulations show that buoyancy effects due to density differences between neighboring gas lines are the main factor causing the deformation of laminar flow patterns and the formation of recirculation cells within the growth zone. Baroclinic instabilities have been identified as the source for these phenomena. In contrast, typical vertical temperature gradients show only a minor impact on the stability of the gas flow within the growth zone in the vicinity of the growing crystal. Based on these results, major differences of the species transport in vertical HVPE reactors, where the flow is parallel or anti-parallel to the direction of gravity, referred to as down-flow and up-flow, respectively, are summarized. The performed analysis of the interplay and relative significance of different flow effects in the HVPE environment allows a general recommendation for reactor design and scaling with respect to stable gas flow conditions within the growth zone. Full article

(This article belongs to the Special Issue GaN-Based Materials and Devices)

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8 pages, 1896 KiB

Open AccessArticle

InGaN Based C-Plane Blue Laser Diodes on Strain Relaxed Template with Reduced Absorption Loss

by Hsun-Ming Chang, Philip Chan, Norleakvisoth Lim, Vincent Rienzi, Haojun Zhang, Daniel A. Cohen, Michael J. Gordon, Steven P. DenBaars and Shuji Nakamura

Crystals 2022, 12(9), 1230; https://doi.org/10.3390/cryst12091230 - 1 Sep 2022

Cited by 1 | Viewed by 1587

Abstract

InGaN based c-plane blue LDs on strain relaxed template (SRT) with a reduced absorption loss was demonstrated. The loss is reduced from 27 cm⁻¹ to 20 cm⁻¹. Due to the lower loss, threshold current density is improved from 51.1 kA/cm [...] Read more.

InGaN based c-plane blue LDs on strain relaxed template (SRT) with a reduced absorption loss was demonstrated. The loss is reduced from 27 cm⁻¹ to 20 cm⁻¹. Due to the lower loss, threshold current density is improved from 51.1 kA/cm² to 43.7 kA/cm², and slope efficiency is also increased by a factor of 1.22. The absorption loss from decomposition layer (DL) in SRT is confirmed to be a major extra loss source by both experimental and simulation results. With a higher indium content in buffer and waveguide layers, optical leakage into DL can be suppressed. Full article

(This article belongs to the Special Issue GaN-Based Materials and Devices)

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10 pages, 2344 KiB

Open AccessArticle

Influence of Superlattice Structure on V-Defect Distribution, External Quantum Efficiency and Electroluminescence for Red InGaN Based µLEDs on Silicon

by Jacob Ewing, Cheyenne Lynsky, Jiaao Zhang, Pavel Shapturenka, Matthew Wong, Jordan Smith, Michael Iza, James S. Speck and Stephen P. DenBaars

Crystals 2022, 12(9), 1216; https://doi.org/10.3390/cryst12091216 - 28 Aug 2022

Cited by 15 | Viewed by 2976

Abstract

Achieving high quantum efficiency in long-wavelength LEDs has posed a significant challenge to the solid-state lighting and display industries. In this article, we use V-defect engineering as a technique to achieve higher efficiencies in red InGaN LEDs on (111) Si through lateral injection. [...] Read more.

Achieving high quantum efficiency in long-wavelength LEDs has posed a significant challenge to the solid-state lighting and display industries. In this article, we use V-defect engineering as a technique to achieve higher efficiencies in red InGaN LEDs on (111) Si through lateral injection. We investigate the effects of superlattice structure on the V-defect distribution, the electroluminescence properties, and the external quantum efficiency. Increasing the relative thickness of In in the InGaN/GaN superlattice and the total superlattice thickness correlate with a reduction of active region defects and increased external quantum efficiencies. The highest measured on-chip EQE was 0.15% and based on Monte-Carlo ray tracing simulations for light extraction we project this would correspond to a flip-chip EQE of ~2.5%. Full article

(This article belongs to the Special Issue GaN-Based Materials and Devices)

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8 pages, 1819 KiB

Open AccessArticle

Demonstration of C-Plane InGaN-Based Blue Laser Diodes Grown on a Strain-Relaxed Template

by Hsun-Ming Chang, Philip Chan, Norleakvisoth Lim, Vincent Rienzi, Michael J. Gordon, Steven P. DenBaars and Shuji Nakamura

Crystals 2022, 12(9), 1208; https://doi.org/10.3390/cryst12091208 - 27 Aug 2022

Cited by 6 | Viewed by 2049

Abstract

Electrically driven c-plane InGaN-based blue edge emitting laser diodes on a strain-relaxed template (SRT) are successfully demonstrated. The relaxation degree of the InGaN buffer was 26.6%, and the root mean square (RMS) roughness of the surface morphology was 0.65 nm. The laser diodes [...] Read more.

Electrically driven c-plane InGaN-based blue edge emitting laser diodes on a strain-relaxed template (SRT) are successfully demonstrated. The relaxation degree of the InGaN buffer was 26.6%, and the root mean square (RMS) roughness of the surface morphology was 0.65 nm. The laser diodes (LDs) on the SRT laser at 459 nm had a threshold current density of 52 kA/cm² under the room temperature pulsed operation. The internal loss of the LDs on the SRT was 30–35 cm⁻¹. Regardless of the high threshold current density, this is the first demonstrated laser diode using the strain-relaxed method on c-plane GaN. Full article

(This article belongs to the Special Issue GaN-Based Materials and Devices)

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10 pages, 2175 KiB

Open AccessArticle

Demonstration of III-Nitride Red LEDs on Si Substrates via Strain-Relaxed Template by InGaN Decomposition Layer

by Vincent Rienzi, Jordan Smith, Norleakvisoth Lim, Hsun-Ming Chang, Philip Chan, Matthew S. Wong, Michael J. Gordon, Steven P. DenBaars and Shuji Nakamura

Crystals 2022, 12(8), 1144; https://doi.org/10.3390/cryst12081144 - 15 Aug 2022

Cited by 10 | Viewed by 3394

Abstract

A III-nitride red LED with an active region temperature of 835 °C on a Si substrate utilizing a strain-relaxed template (SRT) is demonstrated. The peak wavelength blueshifts from 670 nm at 1 A/cm² to 636 nm at 150 A/cm². The [...] Read more.

A III-nitride red LED with an active region temperature of 835 °C on a Si substrate utilizing a strain-relaxed template (SRT) is demonstrated. The peak wavelength blueshifts from 670 nm at 1 A/cm² to 636 nm at 150 A/cm². The on-wafer external quantum efficiency was 0.021% at 7 A/cm² with an emission wavelength of 655 nm. The LED grown on a Si substrate exhibited a 116 nm redshift when compared to a co-loaded LED grown on sapphire. This is attributed to the difference in strain state for the III-nitride layers grown on Si compared to sapphire, allowing for more indium to be incorporated in the LED grown on Si. This suggests efficient III-nitride red LEDs and µLEDs on Si with a SRT can be realized with further material, device structure, and processing optimizations. Full article

(This article belongs to the Special Issue GaN-Based Materials and Devices)

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6 pages, 1583 KiB

Open AccessArticle

Low Forward Voltage III-Nitride Red Micro-Light-Emitting Diodes on a Strain Relaxed Template with an InGaN Decomposition Layer

by Matthew S. Wong, Philip Chan, Norleakvisoth Lim, Haojun Zhang, Ryan C. White, James S. Speck, Steven P. Denbaars and Shuji Nakamura

Crystals 2022, 12(5), 721; https://doi.org/10.3390/cryst12050721 - 19 May 2022

Cited by 9 | Viewed by 2633

Abstract

In this study, III-nitride red micro-light-emitting diodes (µLEDs) with ultralow forward voltage are demonstrated on a strain relaxed template. The forward voltage ranges between 2.00 V and 2.05 V at 20 A/cm² for device dimensions from 5 × 5 to 100 × [...] Read more.

In this study, III-nitride red micro-light-emitting diodes (µLEDs) with ultralow forward voltage are demonstrated on a strain relaxed template. The forward voltage ranges between 2.00 V and 2.05 V at 20 A/cm² for device dimensions from 5 × 5 to 100 × 100 µm². The µLEDs emit at 692 nm at 5 A/cm² and 637 nm at 100 A/cm², corresponding to a blueshift of 55 nm due to the screening of the internal electric field in the quantum wells. The maximum external quantum efficiency and wall-plug efficiency of µLEDs are 0.31% and 0.21%, respectively. This suggests that efficient III-nitride red µLEDs can be realized with further material optimizations. Full article

(This article belongs to the Special Issue GaN-Based Materials and Devices)

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10 pages, 9354 KiB

Open AccessArticle

Effect of Flux Rate Variation at Fixed V/III Ratio on Semi-Polar (11

\bar{2}

2) GaN: Crystal Quality and Surface Morphology Study

by Chong Seng Ooi, Ahmad Shuhaimi, Gary Tan, Omar Al-Zuhairi and Wan Haliza Abd Majid

Crystals 2022, 12(2), 247; https://doi.org/10.3390/cryst12020247 - 11 Feb 2022

Cited by 2 | Viewed by 2086

Abstract

We report on the crystal improvement of semi-polar (11

\bar{2}

2) gallium nitride epitaxy layer on m-plane (10

\bar{1}

0) sapphire substrate by changing the flux rate at a fixed V/III ratio. The high-resolution X-ray diffraction (HR-XRD) analysis showed that lower [...] Read more.

We report on the crystal improvement of semi-polar (11

\bar{2}

2) gallium nitride epitaxy layer on m-plane (10

\bar{1}

0) sapphire substrate by changing the flux rate at a fixed V/III ratio. The high-resolution X-ray diffraction (HR-XRD) analysis showed that lower flux rate enhanced the crystal quality of GaN epitaxy with the lowest FWHM values of 394 and 1173 arc seconds at [

\bar{11}

23] and [1

\bar{1}

00] planes, respectively. In addition, Raman spectroscopy showed that flux rate did not affect the stress state of the GaN crystal. However, atomic force microscopy (AFM) micrograph depicted an anomalous trend where the lowest flux rate produces roughest surface with RMS roughness of 40.41 nm. Further analysis of AFM results on the undulation period length along [

\bar{11}

23] and [1

\bar{1}

00] directions is carried out. It shows that as the growth rate decreases, the average undulation period along [

\bar{11}

23] and [1

\bar{1}

00] directions increases from 2.59 µm and 1.90 µm to 3.52 µm and 3.52 µm, respectively. The mechanism for the surface roughening at the lower flux rate is then explained by using the adatom surface diffusion relation

L ~ \sqrt{D τ}

. Full article

(This article belongs to the Special Issue GaN-Based Materials and Devices)

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9 pages, 1717 KiB

Open AccessArticle

Passivation of Surface States in GaN by NiO Particles

by Martin Velazquez-Rizo, Pavel Kirilenko, Daisuke Iida, Zhe Zhuang and Kazuhiro Ohkawa

Crystals 2022, 12(2), 211; https://doi.org/10.3390/cryst12020211 - 30 Jan 2022

Cited by 2 | Viewed by 2764

Abstract

GaN and NiO/GaN electrodes were characterized by impedance spectroscopy measurements in 0.1 M NaOH. We observed the suppression of the surface states capacitance due to the modification of the chemical state of superficial Ga atoms by NiO. This result suggests that the carriers [...] Read more.

GaN and NiO/GaN electrodes were characterized by impedance spectroscopy measurements in 0.1 M NaOH. We observed the suppression of the surface states capacitance due to the modification of the chemical state of superficial Ga atoms by NiO. This result suggests that the carriers involved in the photocorrosion of GaN in alkaline conditions originate in its surface states. In addition, we characterized the epitaxial relationship between the NiO particles deposited on GaN by transmission electron microscopy, finding the NiO

{111}

||GaN

{0002}

and NiO

[220]

||GaN

[11 \bar{2} 0]

symmetry constraints. Full article

(This article belongs to the Special Issue GaN-Based Materials and Devices)

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9 pages, 763 KiB

Open AccessArticle

InGaN-Based microLED Devices Approaching 1% EQE with Red 609 nm Electroluminescence on Semi-Relaxed Substrates

by Ryan C. White, Hongjian Li, Michel Khoury, Cheyenne Lynsky, Michael Iza, Stacia Keller, David Sotta, Shuji Nakamura and Steven P. DenBaars

Crystals 2021, 11(11), 1364; https://doi.org/10.3390/cryst11111364 - 8 Nov 2021

Cited by 34 | Viewed by 4854

Abstract

In this paper, we report the successful demonstration of bright InGaN-based microLED devices emitting in the red spectral regime grown by metal organic chemical vapor deposition (MOCVD) on c-plane semi-relaxed InGaN substrates on sapphire. Through application of an InGaN/GaN base layer scheme to [...] Read more.

In this paper, we report the successful demonstration of bright InGaN-based microLED devices emitting in the red spectral regime grown by metal organic chemical vapor deposition (MOCVD) on c-plane semi-relaxed InGaN substrates on sapphire. Through application of an InGaN/GaN base layer scheme to ameliorate high defect density and maintain appropriate lattice constant throughout the growth, high-In quantum wells (QWs) can be grown with improved crystal quality. Improvement to the design of the growth scheme also yields higher power output resulting in an increase to the external quantum efficiency (EQE). Combined, these two improvements allow for an 80 × 80

μ

m

^{2}

microLED device emitting at 609 nm to achieve 0.83% EQE. Furthermore, the true In content of the QW is measured using atomic probe tomography (APT) to confirm the improved In incorporation during high temperature active region growth. These developments represent advancement toward the realization of bright, highly efficient red III-nitride LEDs to be used in RGB applications under one material system. Full article

(This article belongs to the Special Issue GaN-Based Materials and Devices)

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11 pages, 1033 KiB

Open AccessArticle

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

by Ryan C. White, Michel Khoury, Matthew S. Wong, Hongjian Li, Cheyenne Lynsky, Michael Iza, Stacia Keller, David Sotta, Shuji Nakamura and Steven P. DenBaars

Crystals 2021, 11(10), 1168; https://doi.org/10.3390/cryst11101168 - 26 Sep 2021

Cited by 7 | Viewed by 3360

Abstract

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 [...] Read more.

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

μ

LED 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. Full article

(This article belongs to the Special Issue GaN-Based Materials and Devices)

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