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Wide Bandgap Semiconductor Materials and Devices

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A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Inorganic Crystalline Materials".

Deadline for manuscript submissions: closed (1 December 2021) | Viewed by 44009

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Special Issue Editors

Prof. Dr. Haiding Sun

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Guest Editor

School of Microelectronics, University of Science and Technology of China, Hefei 230026, China
Interests: molecular beam epitaxy; semiconductor device physics; epitaxial growth; optoelectronics; thin films and nanotechnology; gallium nitride (GaN) epilayers and LEDs; III–V semiconductors; MOCVD; semiconductor lasers; power electronics
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Bharat Jalan

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Materials Science and Engineering, University of Minnesota, Minneapolis, MN 55455, USA
Interests: electronic; magnetic and photonic materials; energy materials; processing nanomaterials and nanotechnology

Prof. Dr. Shibing Long

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Guest Editor

School of Microelectronics, University of Science and Technology of China, Hefei 230026, China
Interests: wide bandgap semiconductors includes gallium oxides and gallium nitrides based power electronics including MOSFET, SBD as well as solar-blind/x-ray detectors, device fabrication and test

Prof. Dr. Yuhao Zhang

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Guest Editor

Department of Electrical and Computer Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
Interests: The physics, design, simulation, fabrication, characterization, reliability, robustess, packaging, and circuit applications of WBG and UWBG devices for electronic as well as photonic applications

Prof. Dr. Rajendra Singh

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Department of Physics, Indian Institute of Technology, New Delhi 110016, India
Interests: wide bandgap semiconductor-based materials and devices; 2D materials and devices

Dr. Xuelin Yang

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Guest Editor

School of Physics, Peking University, Beijing 100871, China
Interests: MOCVD epitaxial growth of GaN based semiconductors; explore new physics of impurity/defects in III-nitrides; new physics and new functionality of electronic materials and devices for III-nitrides

Prof. Dr. Yuji Zhao

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Guest Editor

Electrical & Computer Engineering, Rice University, Houston, TX 77005, USA
Interests: wide bandgap semiconductor III-nitride materials and devices for both power electronics and optoelectronics

Prof. Dr. Bin Liu

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Guest Editor

School of Electronic Science and Engineering, Nanjing University, Nanjing 210023, China
Interests: group III-nitride wide bandgap semiconductor materials and devices, including LEDs/microLED etc

Special Issue Information

Dear Colleagues,

Wide bandgap semiconductors (WBGS) comprise those materials with bandgaps greater than 3.0 eV and exhibit many attractive properties far beyond the capabilities of Si and GaAs, including gallium nitride (GaN), aluminum gallium nitride (AlGaN), silicon carbide (SiC), gallium oxide (Ga₂O₃), aluminum gallium oxide (AlGaO), diamond, boron nitride and perovskite oxides (alkaline earth stannates) etc. The WBGS’s extraordinary physical and electrical properties make the materials a natural for meeting the performance demands of optoelectronic and power electronic device applications, thus the material- and device-related research based on these WBGSs is one of the hottest topics in the semiconductor community.

We invite researchers to contribute to the Special Issue titled “Wide Bandgap Semiconductor Materials and Devices”; potential topics include but are not limited to:

WBGS thin film growth, doping and defects, processing, and theory;
WBGS low dimensional and nanostructure (quantum dot, quantum well, and quantum wire) synthesis, processing, and theory;
WBGS electronic and optoelectronic properties and characterization;
WBGS optoelectronic devices (LED, lasers, and detectors) and characterizations;
WBGS power electronic devices and characterizations.

Prof. Dr. Haiding Sun
Prof. Dr. Bharat Jalan
Prof. Dr. Yuhao Zhang
Prof. Dr. Shibing Long
Prof. Dr. Rajendra Singh
Dr. Xuelin Yang
Prof. Dr. Yuji Zhao
Prof. Dr. Bin Liu
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

wide bandgap semiconductors
crystal growth
optoelectronic devices
power electronic devices
nanostructures
doping
defects
MBE
CVD/MOCVD
HVPE

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Published Papers (13 papers)

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Research

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10 pages, 4078 KiB

Open AccessArticle

The Sign of Exciton-Photon Coupling in GaN-Based Triangular-like Ridge Cavity

by Jing Zhou, Peng Chen, Zili Xie, Xiangqian Xiu, Dunjun Chen, Ping Han, Yi Shi, Rong Zhang and Youdou Zheng

Crystals 2022, 12(3), 348; https://doi.org/10.3390/cryst12030348 - 4 Mar 2022

Viewed by 1831

Abstract

In this paper, the behavior of exciton radiative recombination in a GaN-based triangular-like ridge cavity is studied at room-temperature. The triangular-like ridge cavity is fabricated on a standard-blue-LED epitaxial wafer grown on a sapphire substrate. Through the photoluminescence (PL) and time-resolved photoluminescence (TR-PL) measurements, a clear modulation of the original spontaneous emission is found in the microcavity, a new transition channel is observed, and the effect is angle-dependent. Furthermore, by changing the tilt angle during angle-resolution photoluminescence (AR-PL), it is found that the coupling between excitons and photons in the cavity is the strongest when tilted at 10°. By simulation, the strong localization of photons in the top of the cavity can be confirmed. The PL, TR-PL, and AR-PL results showed the sign of the exciton-photon coupling in the triangular-like ridge cavity. Full article

(This article belongs to the Special Issue Wide Bandgap Semiconductor Materials and Devices)

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9 pages, 5932 KiB

Open AccessArticle

Characterization of the Micro-Structural Properties of InAlN/GaN Epilayer Grown by MOCVD

by Youhua Zhu, Tao Hu, Meiyu Wang, Yi Li, Mei Ge, Xinglong Guo, Honghai Deng and Zhitao Chen

Crystals 2022, 12(2), 203; https://doi.org/10.3390/cryst12020203 - 29 Jan 2022

Cited by 1 | Viewed by 2366

Abstract

An InAlN/GaN heterostructure has been successfully grown on GaN/sapphire and AlN/sapphire substrate by metal organic chemical vapor deposition. The whole epitaxial quality has been confirmed through X-ray diffraction, while some corresponding micro-structural propagation defects have been characterized by means of transmission electron microscopy. It can be concluded that these defects have been originating from the extended threading dislocation in GaN layer. In addition, with the increasing of acceleration voltage, a series of the cathodoluminescence peak shifting can be clearly observed, and the interesting phenomenon has been attributed to the several complex factors, such as inhomogeneous composition, internal absorption, and so on. Nevertheless, with further optimization of the structural parameters of the epilayers, it can be expected that these experimental results would promote a better epitaxy quality and the optoelectronic device design. Full article

(This article belongs to the Special Issue Wide Bandgap Semiconductor Materials and Devices)

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9 pages, 2899 KiB

Open AccessArticle

Numerical Simulation of a Novel Method for PVT Growth of SiC by Adding a Graphite Block

by Hao Luo, Xuefeng Han, Yuanchao Huang, Deren Yang and Xiaodong Pi

Crystals 2021, 11(12), 1581; https://doi.org/10.3390/cryst11121581 - 18 Dec 2021

Cited by 16 | Viewed by 4918

Abstract

SiC crystal is an excellent substrate material for high power electronic devices and high-frequency electronic devices. Being cost-effective and defect-free are the two biggest challenges at present. For the physical vapor transport (PVT) growth of a SiC single crystal, SiC powder is used as the source material, which determines the cost and the quality of the crystal. In this paper, we propose a new design in which graphite blocks are substituted for the non-sublimated SiC powder. Temperature distribution in the SiC powder, the evolution of the SiC powder, and the vapor transport are investigated by using finite element calculations. With the addition of graphite blocks, the utilization and sublimation rate of SiC powder is higher. In addition, the reverse vapor transport above the SiC powder is eliminated. This design provides a new idea to reduce the cost of SiC crystals in industrialization. Full article

(This article belongs to the Special Issue Wide Bandgap Semiconductor Materials and Devices)

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10 pages, 2356 KiB

Open AccessArticle

Semipolar {

20 \bar{2} 1

} GaN Edge-Emitting Laser Diode on Epitaxial Lateral Overgrown Wing

by Srinivas Gandrothula, Haojun Zhang, Pavel Shapturenka, Ryan Anderson, Matthew S. Wong, Hongjian Li, Takeshi Kamikawa, Shuji Nakamura and Steven P. DenBaars

Crystals 2021, 11(12), 1563; https://doi.org/10.3390/cryst11121563 - 14 Dec 2021

Cited by 1 | Viewed by 2747

Abstract

Edge-emitting laser diodes (LDs) were fabricated on a reduced dislocation density epitaxial lateral overgrown (ELO) wing of a semipolar {

20 \bar{2} 1

} GaN substrate, termed an ELO wing LD. Two types of facet feasibility studies were conducted: (1) “handmade” facets, [...] Read more.

Edge-emitting laser diodes (LDs) were fabricated on a reduced dislocation density epitaxial lateral overgrown (ELO) wing of a semipolar {

20 \bar{2} 1

} GaN substrate, termed an ELO wing LD. Two types of facet feasibility studies were conducted: (1) “handmade” facets, wherein lifted-off ELO wing LDs were cleaved manually, and (2) facets formed on wafers through reactive ion etching (RIE). Pulsed operation electrical and optical measurements confirmed the laser action in the RIE facet LDs with a threshold current of ~19 kAcm⁻² and maximum light output power of 20 mW from a single uncoated facet. Handmade facet devices showed spontaneous, LED-like emission, confirming device layers remain intact after mechanical liftoff. Full article

(This article belongs to the Special Issue Wide Bandgap Semiconductor Materials and Devices)

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10 pages, 34625 KiB

Open AccessArticle

Influences of Powder Source Porosity on Mass Transport during AlN Crystal Growth Using Physical Vapor Transport Method

by Danyang Fu, Qikun Wang, Gang Zhang, Zhe Li, Jiali Huang, Jiang Wang and Liang Wu

Crystals 2021, 11(11), 1436; https://doi.org/10.3390/cryst11111436 - 22 Nov 2021

Cited by 4 | Viewed by 2013

Abstract

We developed a two-dimensional (2D) transport model to investigate mass transport during bulk AlN crystal growth via the physical vapor transport (PVT) process using the finite element method (FEM), taking the powder source porosity, buoyancy, and vapor diffusion into account. The porosity effects of the powder source on mass transport under various growth conditions were investigated in detail. The simulation results show that the porosity of the powder source significantly affects the mass transport process during AlN sublimation growth. When the porosity of the powder source decreases, the growth rate becomes more uniform along the seed deposition surface, although the sublimation rate and crystal growth rate decrease, which can be attributed to the reduced specific surface area of the powder source and the reduced flow rate of Al vapor in the powder source. A flat growth interface can be achieved at a porosity of 0.2 under our specific growth conditions, which in turn facilitate the growth of high-quality AlN crystals and better yield. The decomposition of the powder source and the transport of Al vapor in the growth chamber can be suppressed by increasing the pressure. In addition, the AlN growth rate variation along the deposition surface can be attributed to the Al vapor pressure gradient caused by the temperature difference in the growth chamber. Full article

(This article belongs to the Special Issue Wide Bandgap Semiconductor Materials and Devices)

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8 pages, 2301 KiB

Open AccessArticle

Low-Threshold and Wavelength-Tunable InGaN Tubular WGM Laser Embedded in a Flexible Substrate

by Peng Hu, Yufeng Li, Shengnan Zhang, Ye Zhang, Zhenhuan Tian and Feng Yun

Crystals 2021, 11(10), 1251; https://doi.org/10.3390/cryst11101251 - 15 Oct 2021

Cited by 4 | Viewed by 1801

Abstract

We have fabricated a tubular whispering gallery mode laser based on InGaN/GaN quantum wells and transferred it onto a flexible substrate. Compared with those without the transferring processes, the threshold energy density was reduced by 60%, at about 25.55 µJ/cm², while a high-quality factor of >15,000 was obtained. Finite-difference time-domain simulation demonstrated that such a low threshold energy density can be attributed to the decreased mode volume, from 1.32 × 10⁻³ μm³ to 6.92 × 10⁻⁴ μm³. The wavelength dependences on strain were found to be 5.83 nm, 1.38 nm, and 2.39 nm per stretching unit ε in the X, Y, and Z directions, respectively. Such strain sensitivity was attributed to the deformation of the GaN microtube and the change in the refractive index of the PDMS. Full article

(This article belongs to the Special Issue Wide Bandgap Semiconductor Materials and Devices)

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11 pages, 19345 KiB

Open AccessArticle

Performance Improvement of Amorphous Ga₂O₃/P-Si Deep Ultraviolet Photodetector by Oxygen Plasma Treatment

by Jin Cao, Liang Chen, Xin Chen, Yu Zhu, Jianqi Dong, Baoyu Wang, Miao He and Xingfu Wang

Crystals 2021, 11(10), 1248; https://doi.org/10.3390/cryst11101248 - 15 Oct 2021

Cited by 10 | Viewed by 3401

Abstract

Gallium oxide (Ga₂O₃) is an attractive semiconductor that is very suitable for deep ultraviolet (DUV) inspection. However, due to the existence of many types of oxygen vacancies in the amorphous Ga₂O₃ (a-Ga₂O₃) film, it greatly limits the performance of the a-Ga₂O₃-based photodetector. Here, we perform oxygen plasma treatment on the a-Ga₂O₃/p-Si photodetector to reduce the concentration of oxygen vacancies in the a-Ga₂O₃ film, so that the dark current is reduced by an order of magnitude (from 1.01 × 10⁻³ A to 1.04 × 10⁻⁴ A), and the responsivity is increased from 3.7 mA/W to 9.97 mA/W. In addition, oxygen plasma processing makes the photodetector operate well at 0 V bias. The response speed is that the rise time is 2.45 ms and the decay time is 1.83 ms, while it does not respond to the DUV illumination without oxygen plasma treating at a zero bias. These results are attributed to the fact that oxygen plasma treatment can reduce the Schottky barrier between a-Ga₂O₃ and the electrode indium tin oxide (ITO), which promotes the separation and collection efficiency of photo-generated carriers. Therefore, this work proposes a low-cost method to improve the performance of Ga₂O₃ film-based DUV photodetectors. Full article

(This article belongs to the Special Issue Wide Bandgap Semiconductor Materials and Devices)

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7 pages, 2303 KiB

Open AccessArticle

Improved Performance of GaN-Based Ultraviolet LEDs with the Stair-like Si-Doping n-GaN Structure

by Xiaomeng Fan, Shengrui Xu, Hongchang Tao, Ruoshi Peng, Jinjuan Du, Ying Zhao, Jinfeng Zhang, Jincheng Zhang and Yue Hao

Crystals 2021, 11(10), 1203; https://doi.org/10.3390/cryst11101203 - 6 Oct 2021

Cited by 1 | Viewed by 2288

Abstract

A method to improve the performance of ultraviolet light-emitting diodes (UV-LEDs) with stair-like Si-doping GaN layer is investigated. The high-resolution X-ray diffraction shows that the UV-LED with stair-like Si-doping GaN layer possesses better quality and a lower dislocation density. In addition, the experimental results demonstrate that light output power and wall plug efficiency of UV-LED with stair-like Si-doping GaN are significantly improved. Through the analysis of the experimental and simulation results, we can infer that there are two reasons for the improvement of photoelectric characteristics: reduction of dislocation density and alleviating of current crowding of UV-LEDs by introduced stair-like Si-doping GaN. Full article

(This article belongs to the Special Issue Wide Bandgap Semiconductor Materials and Devices)

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14 pages, 4825 KiB

Open AccessArticle

Comprehensive Study and Optimization of Implementing p-NiO in β-Ga₂O₃ Based Diodes via TCAD Simulation

by Hong Zhou, Shifan Zeng, Jincheng Zhang, Zhihong Liu, Qian Feng, Shengrui Xu, Jinfeng Zhang and Yue Hao

Crystals 2021, 11(10), 1186; https://doi.org/10.3390/cryst11101186 - 29 Sep 2021

Cited by 26 | Viewed by 4899

Abstract

In this paper, we carried out a comprehensive study and optimization of implementing p-NiO in the β-Ga₂O₃ based diodes, including Schottky barrier diode (SBD) with p-NiO guard ring (GR), p-NiO/β-Ga₂O₃ heterojunction (HJ) barrier Schottky (HJBS) diode, and HJ-PN diode through the TCAD simulation. In particular, we provide design guidelines for future p-NiO-related Ga₂O₃ diodes with material doping concentrations and dimensions to be taken into account. Although HJ-PN has a ~1 V higher turn-on voltage (V_on), its breakdown voltage (BV) is the highest among all diodes. We found that for SBD with p-NiO GRs and HJBS, their forward electrical characteristics and reverse leakage current are related to the total width and the doping concentration of p-NiO, the BV is only related to the doping concentration of p-NiO_, and the optimal doping concentration of p-NiO is found to be 4 × 10¹⁷ cm⁻³. Compared with the SBD without p-NiO, the BV of the SBD with p-NiO and HJBS diode can be essentially improved by 3 times. As a result, HJ-PN diode, SBD with p-NiO GRs, and HJ-BS diode achieve a BV/specific on-resistance (R_on,sp) of 5705 V/4.3 mΩ·cm², 3006 V/3.07 mΩ·cm², and 3004 V/3.06 mΩ·cm², respectively. Based on different application requirements, this work provides a useful insight about the diode selection with various structures. Full article

(This article belongs to the Special Issue Wide Bandgap Semiconductor Materials and Devices)

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8 pages, 2053 KiB

Open AccessArticle

Investigation of a Separated Short-Wavelength Peak in InGaN Red Light-Emitting Diodes

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

Crystals 2021, 11(9), 1123; https://doi.org/10.3390/cryst11091123 - 15 Sep 2021

Cited by 10 | Viewed by 3823

Abstract

We fabricated indium gallium nitride (InGaN) red light-emitting diodes (LEDs) with a peak emission wavelength of 649 nm and investigated their electroluminescence (EL) properties. An additional separated peak in the EL spectrum of the red LEDs at 20 mA was observed at 465 nm. This additional peak also exhibits a blue-shift with increasing currents as does the main emission peak. Using high-resolution microscopy, we observed many point-like emission spots in the EL emission images at the currents below 1 mA. However, these emission spots cannot be identified at currents above 5 mA because the red emission from quantum wells (QWs) is much stronger than that emitted by these spots. Finally, we demonstrate that these emission spots are related to the defects generated in red QWs. The measured In content was lower at the vicinity of the defects, which was regarded as the reason for separated short-wavelength emission in red InGaN LEDs. Full article

(This article belongs to the Special Issue Wide Bandgap Semiconductor Materials and Devices)

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17 pages, 3534 KiB

Open AccessArticle

Transport Mechanism of Enhanced Performance in an Amorphous/Monoclinic Mixed-Phase Ga₂O₃ Solar-Blind Deep Ultraviolet Photodetector

by Haowen Liu, Honglin Li, Shuren Zhou, Hong Zhang, Shiqiang Fan, Yuting Cui, Chunyang Kong, Lijuan Ye, Yuanqiang Xiong and Wanjun Li

Crystals 2021, 11(9), 1111; https://doi.org/10.3390/cryst11091111 - 12 Sep 2021

Cited by 6 | Viewed by 2936

Abstract

Recently, as an emerging material, ultrawide bandgap Ga₂O₃ has been investigated extensively in solar-blind deep-ultraviolet (DUV) photodetectors (PDs). High sensitivity and signal-to-noise ratio of PDs are essential for the detection of solar-blind DUV signals; however, such factors are often not mutually compatible. In the present study, an amorphous/monoclinic homogeneous mixed-phase structure was demonstrated to be significantly beneficial in enhancing the comprehensive performance of Ga₂O₃ solar-blind DUV PDs, especially with respect to sensitivity and the signal-to-noise ratio. Further experimental and theoretical findings provide insights on the transport mechanism of enhanced performance in the mixed-phase Ga₂O₃ solar-blind DUV PD. For effectively separating the photogenerated carriers, a type-II band alignment between amorphous and crystalline Ga₂O₃ can be exploited. Furthermore, the change of the barrier height of the mixed-phase interface also has a significant impact on the transport properties of the mixed-phase Ga₂O₃ PD. Additionally, the potential applications of mixed-phase Ga₂O₃ PD in high-voltage corona discharge were explored, and clear and stable corona discharge signals were obtained. The results of the present study may promote understanding of DUV photoelectronic devices with various mixed-phase Ga₂O₃ materials and provide an efficient approach for promoting comprehensive performance in future solar-blind detection applications. Full article

(This article belongs to the Special Issue Wide Bandgap Semiconductor Materials and Devices)

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8 pages, 2523 KiB

Open AccessArticle

Deep-Level Traps Responsible for Persistent Photocurrent in Pulsed-Laser-Deposited β-Ga₂O₃ Thin Films

by Bhera Ram Tak, Ming-Min Yang, Marin Alexe and Rajendra Singh

Crystals 2021, 11(9), 1046; https://doi.org/10.3390/cryst11091046 - 30 Aug 2021

Cited by 12 | Viewed by 2761

Abstract

Gallium oxide (β-Ga₂O₃) is emerging as a promising wide-bandgap semiconductor for optoelectronic and high-power electronic devices. In this study, deep-level defects were investigated in pulsed-laser-deposited epitaxial films of β-Ga₂O₃. A deep ultraviolet photodetector (DUV) fabricated on β-Ga₂O₃ film showed a slow decay time of 1.58 s after switching off 250 nm wavelength illumination. Generally, β-Ga₂O₃ possesses various intentional and unintentional trap levels. Herein, these traps were investigated using the fractional emptying thermally stimulated current (TSC) method in the temperature range of 85 to 473 K. Broad peaks in the net TSC curve were observed and further resolved to identify the characteristic peak temperature of individual traps using the fractional emptying method. Several deep-level traps having activation energies in the range of 0.16 to 1.03 eV were identified. Among them, the trap with activation energy of 1.03 eV was found to be the most dominant trap level and it was possibly responsible for the persistent photocurrent in PLD-grown β-Ga₂O₃ thin films. The findings of this current work could pave the way for fabrication of high-performance DUV photodetectors. Full article

(This article belongs to the Special Issue Wide Bandgap Semiconductor Materials and Devices)

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Review

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30 pages, 95132 KiB

Open AccessReview

Recent Advances in Fabricating Wurtzite AlN Film on (0001)-Plane Sapphire Substrate

by Hualong Wu, Kang Zhang, Chenguang He, Longfei He, Qiao Wang, Wei Zhao and Zhitao Chen

Crystals 2022, 12(1), 38; https://doi.org/10.3390/cryst12010038 - 27 Dec 2021

Cited by 26 | Viewed by 6005

Abstract

Ultrawide bandgap (UWBG) semiconductor materials, with bandgaps far wider than the 3.4 eV of GaN, have attracted great attention recently. As a typical representative, wurtzite aluminum nitride (AlN) material has many advantages including high electron mobility, high breakdown voltage, high piezoelectric coefficient, high thermal conductivity, high hardness, high corrosion resistance, high chemical and thermal stability, high bulk acoustic wave velocity, prominent second-order optical nonlinearity, as well as excellent UV transparency. Therefore, it has wide application prospects in next-generation power electronic devices, energy-harvesting devices, acoustic devices, optical frequency comb, light-emitting diodes, photodetectors, and laser diodes. Due to the lack of low-cost, large-size, and high-ultraviolet-transparency native AlN substrate, however, heteroepitaxial AlN film grown on sapphire substrate is usually adopted to fabricate various devices. To realize high-performance AlN-based devices, we must first know how to obtain high-crystalline-quality and controllable AlN/sapphire templates. This review systematically summarizes the recent advances in fabricating wurtzite AlN film on (0001)-plane sapphire substrate. First, we discuss the control principles of AlN polarity, which greatly affects the surface morphology and crystalline quality of AlN, as well as the electronic and optoelectronic properties of AlN-based devices. Then, we introduce how to control threading dislocations and strain. The physical thoughts of some inspirational growth techniques are discussed in detail, and the threading dislocation density (TDD) values of AlN/sapphire grown by various growth techniques are compiled. We also introduce how to achieve high thermal conductivities in AlN films, which are comparable with those in bulk AlN. Finally, we summarize the future challenge of AlN films acting as templates and semiconductors. Due to the fast development of growth techniques and equipment, as well as the superior material properties, AlN will have wider industrial applications in the future. Full article

(This article belongs to the Special Issue Wide Bandgap Semiconductor Materials and Devices)

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