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Recent Advances in III-Nitride Semiconductors and Correlated Wide Bandgap Semiconductors,...
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Recent Advances in III-Nitride Semiconductors and Correlated Wide Bandgap Semiconductors, 2nd Edition

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Materials for Energy Applications".

Deadline for manuscript submissions: 20 November 2025 | Viewed by 6846

Special Issue Editors

Prof. Dr. Peng Chen

E-Mail Website
Guest Editor
1. Jiangsu Provincial Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing 210023, China
2. Nanjing National Laboratory of Microstructures, Nanjing University, Nanjing 210093, China
Interests: semiconductor optoelectronics; plasmon photonics; semiconductor micro/nano structure; solid-state electronics and power electronic devices; III-nitrides on Si substrates
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Zhizhong Chen

E-Mail Website
Guest Editor
State Key Laboratory for Artificial Microstructure and Mesoscopic Physics, School of Physics, Peking University, Beijing 100871, China
Interests: III-nitride device physics; LED; GaN-based micro-nano light-emitting structure; GaN-based micro-nano device; LED light source for regulating the biological rhythm
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Following the remarkable success of the first edition of the Special Issue titled “Recent Advances in III-Nitride Semiconductors” (https://www.mdpi.com/journal/crystals/special_issues/nitride_semiconductors_2 ), we are pleased to announce the second edition of this Special Issue, titled “Recent Advances in III-Nitride Semiconductors and Correlated Wide Bandgap Semiconductors”.

The group-III nitrides are typical wide-bandgap semiconductors. The interest in group-III nitrides lies in their irreplaceable and efficient blue-UV luminescence capability. Recently, more correlated wide-bandgap semiconductor materials, including Ga2O3, NiO, diamond, LiNbO3, and AlScN , have been at the forefront of research. Nitrides, along with those wide bandgap materials, have become key materials for the next generation of novel optoelectronic and electronic technologies. Recent progress in III-nitride semiconductors and the correlated wide bandgap semiconductor material quality and device design relies on well-mastered techniques of material growth and the formation of desired structures with their combinations. This process offers a high possibility of creating high-performance and diverse functional devices. III-nitride semiconductors and related wide-bandgap semiconductors are also promising candidates for next-generation power electronic applications because of their outstanding material properties, but their potential is far from being realized, and many material properties and device mechanisms still require investigation.

Therefore, we invite researchers to contribute to this Special Issue titled “Recent Advances in III-Nitride Semiconductors and Correlated Wide Bandgap Semiconductors”, which covers a broad spectrum of topics, extending from the study of wide-bandgap semiconductor materials, micro/nano structures, and novel functional devices to new applications in frontier fields.

The topics include, but are not limited to, the following subjects:

  • Growth of III-nitride semiconductors and correlated wide-bandgap semiconductor materials and micro/nanostructures;
  • Characterization of these materials and the heterostructures;
  • Novel devices, including emission, detection, and power devices;
  • Application and integration of these materials and novel devices in novel electronics and photonics.

Prof. Dr. Peng Chen
Prof. Dr. Zhizhong Chen
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2100 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • nitrides
  • GaN
  • Ga2O3
  • NiO
  • diamond
  • AlScN
  • heterostructures
  • epitaxy
  • electro-optics devices
  • micro-electronics devices
  • power devices
  • integrated circuits and modules
  • photonic crystal enhanced light-matter interaction
  • photonic crystal and plasmonics

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Related Special Issue

Published Papers (7 papers)

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Research

16 pages, 7712 KiB  
Article
Impact of KOH Wet Treatment on the Electrical and Optical Characteristics of GaN-Based Red μLEDs
by Shuhan Zhang, Yun Zhang, Hongyu Qin, Qian Fan, Xianfeng Ni, Li Tao and Xing Gu
Crystals 2025, 15(4), 288; https://doi.org/10.3390/cryst15040288 - 22 Mar 2025
Viewed by 226
Abstract
Micro-size light-emitting diodes (μLEDs) are high-brightness, low-power optoelectronic devices with significant potential in display technology, lighting, and biomedical applications. AlGaInP-based red LEDs experience severe size-dependent effects when scaled to the micron level, and addressing the fabrication challenges of GaN-based red μLED arrays is [...] Read more.
Micro-size light-emitting diodes (μLEDs) are high-brightness, low-power optoelectronic devices with significant potential in display technology, lighting, and biomedical applications. AlGaInP-based red LEDs experience severe size-dependent effects when scaled to the micron level, and addressing the fabrication challenges of GaN-based red μLED arrays is crucial for achieving homogeneous integration. This study investigates the employment of KOH wet treatments to alleviate efficiency degradation caused by sidewall leakage currents. GaN-based red μLED arrays with pixel sizes ranging from 5 × 5 µm2 to 20 × 20 µm2 were grown using metal-organic chemical vapor deposition (MOCVD), and then fabricated via rapid thermal annealing, mesa etching, sidewall wet treatment, electrode deposition, sidewall passivation, chemical-mechanical polishing, and via processes. The arrays, with pixel densities ranging from 668 PPI (Pixel Per Inch) to 1336 PPI, consist of 10,000 to 40,000 emitting pixels, and their optoelectronic properties were systematically evaluated. The arrays with varying pixel sizes fabricated in this study were subjected to three distinct processing conditions: without KOH treatment, 3 min of KOH treatment, and 5 min of KOH treatment. Electrical characterization reveals that the 5-min KOH treatment significantly reduces leakage current, enhancing the electrical performance, as compared to the samples without KOH treatment or 3-min treatment. In terms of optical properties, while the arrays without any KOH treatment failed to emit light, the ones with 3- and 5-min KOH treatment exhibit excellent optical uniformity and negligible blue shift. Most arrays treated for 5 min demonstrate superior light output power (LOP) and optoelectronic efficiency, with the 5 µm pixel arrays exhibiting unexpectedly high performance. The results suggest that extending the KOH wet treatment time effectively mitigates sidewall defects, reduces non-radiative recombination, and enhances surface roughness, thereby minimizing optical losses. These findings provide valuable insights for optimizing the fabrication of high-performance GaN-based red μLEDs and contribute to the development of stable, high-quality small-pixel μLEDs for advanced display and lighting applications. Full article
(This article belongs to the Special Issue Recent Advances in III-Nitride Semiconductors and Correlated Wide Bandgap Semiconductors, 2nd Edition)
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15 pages, 8753 KiB  
Article
Dielectric Passivation Treatment of InGaN MESA on Si Substrates for Red Micro-LED Application
by Hongyu Qin, Shuhan Zhang, Qian Fan, Xianfeng Ni, Li Tao and Xing Gu
Crystals 2025, 15(3), 267; https://doi.org/10.3390/cryst15030267 - 13 Mar 2025
Viewed by 604
Abstract
The emergence of GaN-based micro-LEDs has revolutionized display technologies due to their superior brightness, energy efficiency, and thermal stability compared to traditional counterparts. However, the development of red-emitting micro-LEDs on silicon substrates (GaN-on-Si) faces significant challenges, among them including hydrogen-induced deactivation of p-GaN [...] Read more.
The emergence of GaN-based micro-LEDs has revolutionized display technologies due to their superior brightness, energy efficiency, and thermal stability compared to traditional counterparts. However, the development of red-emitting micro-LEDs on silicon substrates (GaN-on-Si) faces significant challenges, among them including hydrogen-induced deactivation of p-GaN caused by hydrogen species generated from SiH4 decomposition during SiO2 passivation layer growth, which degrades device performance. This study systematically investigates the use of high-density metal-oxide dielectric passivation layers deposited by atomic layer deposition (ALD), specifically Al2O3 and HfO2, to mitigate these effects and enhance device reliability. The passivation layers effectively suppress hydrogen diffusion and preserve p-GaN activation, ensuring improved ohmic contact formation and reduced forward voltage, which is measured by the probe station. The properties of the epitaxial layer and the cross-section morphology of the dielectric layer were characterized by photoluminescence (PL) and scanning electron microscopy (SEM), respectively. Experimental results reveal that Al2O3 exhibits superior thermal stability and lower current leakage under high-temperature annealing, while HfO2 achieves higher light-output power (LOP) and efficiency under increased current densities. Electroluminescence (EL) measurements confirm that the passivation strategy maintains the intrinsic optical properties of the epitaxial wafer with minimal impact on Wp and FWHM across varying process conditions. The findings demonstrate the efficacy of metal-oxide dielectric passivation in addressing critical challenges in InGaN red micro-LED on silicon substrate fabrication, contributing to accelerating scalable and efficient next-generation display technologies. Full article
(This article belongs to the Special Issue Recent Advances in III-Nitride Semiconductors and Correlated Wide Bandgap Semiconductors, 2nd Edition)
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13 pages, 6224 KiB  
Article
The Impact of GaN Crystal Growth on Ammonia Flow Dynamics in Ammonothermal Processes
by Marek Zak, Pawel Kempisty, Boleslaw Lucznik, Robert Kucharski and Michal Bockowski
Crystals 2025, 15(3), 261; https://doi.org/10.3390/cryst15030261 - 11 Mar 2025
Viewed by 450
Abstract
A computational fluid dynamics simulation was developed for the growth zone of gallium nitride crystallized using the alkaline ammonothermal method, considering the geometry of the seed crystals and the installation setup. The model focuses on temperature and velocity distributions, revealing turbulent and transient [...] Read more.
A computational fluid dynamics simulation was developed for the growth zone of gallium nitride crystallized using the alkaline ammonothermal method, considering the geometry of the seed crystals and the installation setup. The model focuses on temperature and velocity distributions, revealing turbulent and transient flow characteristics. Significant findings include the effect of crystal thickness on temperature and velocity changes, as well as the relationship between temperature distribution and growth rate. The results indicate that transient variations in flow and thermal fields affect the uniformity of growth and structural quality of the crystals. The paper contributes to optimizing ammonothermal crystallization processes by addressing critical parameters such as turbulence, thermal mixing, and crystal geometry. Full article
(This article belongs to the Special Issue Recent Advances in III-Nitride Semiconductors and Correlated Wide Bandgap Semiconductors, 2nd Edition)
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14 pages, 2436 KiB  
Article
Dependence of GaN Exciton Energy on Temperature
by Xiancheng Liu, Peng Chen, Zili Xie, Xiangqian Xiu, Dunjun Chen, Hong Zhao, Yi Shi, Rong Zhang and Youdou Zheng
Crystals 2025, 15(2), 137; https://doi.org/10.3390/cryst15020137 - 26 Jan 2025
Viewed by 538
Abstract
In this paper, we investigate the relationship between GaN exciton energy and temperature by using high-quality, strain-free GaN epilayers. Traditional models, such as Varshni’s model and the Bose–Einstein model, are primarily based on empirical fitting and give little or no consideration to electron–phonon [...] Read more.
In this paper, we investigate the relationship between GaN exciton energy and temperature by using high-quality, strain-free GaN epilayers. Traditional models, such as Varshni’s model and the Bose–Einstein model, are primarily based on empirical fitting and give little or no consideration to electron–phonon interactions, which prevents them from accurately calculating GaN exciton energy over a wide temperature range. Considering the interaction of electrons and phonons, we use singular functions, linear functions and power functions to express the phonon density of GaN, and then 2BE, singular-linear, power-law-delta, and power-law-v models are proposed. All of them provide results that are more consistent with actual measurements compared to traditional models. Among them, the singular-linear model summarizes the contributions of acoustic and optical phonons. The error associated with the singular-linear model is smaller than that of the 1BE and Varshni models across nearly the entire temperature range. Therefore, the singular-linear model is a better choice. Full article
(This article belongs to the Special Issue Recent Advances in III-Nitride Semiconductors and Correlated Wide Bandgap Semiconductors, 2nd Edition)
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12 pages, 3122 KiB  
Article
Effect of p-InGaN Cap Layer on Low-Resistance Contact to p-GaN: Carrier Transport Mechanism and Barrier Height Characteristics
by Mohit Kumar, Laurent Xu, Timothée Labau, Jérôme Biscarrat, Simona Torrengo, Matthew Charles, Christophe Lecouvey, Aurélien Olivier, Joelle Zgheib, René Escoffier and Julien Buckley
Crystals 2025, 15(1), 56; https://doi.org/10.3390/cryst15010056 - 8 Jan 2025
Viewed by 1219
Abstract
This study investigated the low contact resistivity and Schottky barrier characteristics in p-GaN by modifying the thickness and doping levels of a p-InGaN cap layer. A comparative analysis with highly doped p-InGaN revealed the key mechanisms contributing to low-resistance contacts. Atomic force microscopy [...] Read more.
This study investigated the low contact resistivity and Schottky barrier characteristics in p-GaN by modifying the thickness and doping levels of a p-InGaN cap layer. A comparative analysis with highly doped p-InGaN revealed the key mechanisms contributing to low-resistance contacts. Atomic force microscopy inspections showed that the surface roughness depends on the doping levels and cap layer thickness, with higher doping improving the surface quality. Notably, increasing the doping concentration in the p++-InGaN cap layer significantly reduced the specific contact resistivity to 6.4 ± 0.8 × 10−6 Ω·cm2, primarily through enhanced tunneling. Current–voltage (I–V) characteristics indicated that the cap layer’s surface properties and strain-induced polarization effects influenced the Schottky barrier height and reverse current. The reduction in barrier height by approximately 0.42 eV in the p++-InGaN layer enhanced hole tunneling, further lowering the contact resistivity. Additionally, polarization-induced free charges at the metal–semiconductor interface reduced band bending, thereby enhancing carrier transport. A transition in current conduction mechanisms was also observed, shifting from recombination tunneling to space-charge-limited conduction across different voltage ranges. This research underscores the importance of doping, cap layer thickness, and polarization effects in achieving ultra-low contact resistivity, offering valuable insights for improving the performance of p-GaN-based power devices. Full article
(This article belongs to the Special Issue Recent Advances in III-Nitride Semiconductors and Correlated Wide Bandgap Semiconductors, 2nd Edition)
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11 pages, 858 KiB  
Article
Two-Dimensional Electron Gas in Thin N-Polar GaN Channels on AlN on Sapphire Templates
by Markus Pristovsek, Itsuki Furuhashi, Xu Yang, Chengzhi Zhang and Matthew D. Smith
Crystals 2024, 14(9), 822; https://doi.org/10.3390/cryst14090822 - 20 Sep 2024
Viewed by 1398
Abstract
We report on 2-dimensional electron gases realized in binary N-polar GaN channels on AlN on sapphire templates grown by metal–organic vapor phase epitaxy. The measured sheet carrier density of 3.8×1013 cm−2 is very close to the theoretical value of [...] Read more.
We report on 2-dimensional electron gases realized in binary N-polar GaN channels on AlN on sapphire templates grown by metal–organic vapor phase epitaxy. The measured sheet carrier density of 3.8×1013 cm−2 is very close to the theoretical value of 3.95×1013 cm−2 due to the low carbon and oxygen background doping in the N-polar GaN if grown with triethyl-gallium. By inserting an intermediate AlN transition layer, room temperature mobilities in 5 nm channels up to 100 cm2/Vs were realized, probably limited by dislocations and oxygen background in N-polar AlN. Thicker channels of 8 nm or more showed relaxation and thus much lower mobilities. Full article
(This article belongs to the Special Issue Recent Advances in III-Nitride Semiconductors and Correlated Wide Bandgap Semiconductors, 2nd Edition)
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11 pages, 46096 KiB  
Article
Demonstration of HCl-Based Selective Wet Etching for N-Polar GaN with 42:1 Selectivity to Al0.24Ga0.76N
by Emmanuel Kayede, Emre Akso, Brian Romanczyk, Nirupam Hatui, Islam Sayed, Kamruzzaman Khan, Henry Collins, Stacia Keller and Umesh K. Mishra
Crystals 2024, 14(6), 485; https://doi.org/10.3390/cryst14060485 - 22 May 2024
Viewed by 1728
Abstract
A wet-etching technique based on a mixture of hydrochloric (HCl) and nitric (HNO3) acids is introduced, demonstrating exceptional 42:1 selectivity for etching N-polar GaN over Al0.24Ga0.76N. In the absence of an AlGaN etch stop layer, the etchant [...] Read more.
A wet-etching technique based on a mixture of hydrochloric (HCl) and nitric (HNO3) acids is introduced, demonstrating exceptional 42:1 selectivity for etching N-polar GaN over Al0.24Ga0.76N. In the absence of an AlGaN etch stop layer, the etchant primarily targets N-polar unintentionally doped (UID) GaN, indicating its potential as a suitable replacement for selective dry etches in the fabrication of GaN high-electron-mobility transistors (HEMTs). The efficacy and selectivity of this etchant were confirmed through its application to a gate recess module of a deep-recess HEMT, where, despite a 228% over-etch, the 2.6 nm AlGaN etch stop layer remained intact. We also evaluated the proposed method for the selective etching of the GaN cap in the n+ regrowth process, achieving a contact resistance matching that of a BCl3/SF6 ICP process. These findings underscore the applicability and versatility of the etchant in both the electronic and photonic domains and are particularly applicable to the development of N-polar deep-recess HEMTs. Full article
(This article belongs to the Special Issue Recent Advances in III-Nitride Semiconductors and Correlated Wide Bandgap Semiconductors, 2nd Edition)
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