The development of new kinds of semiconductor material is a very attractive topic of scientific research and applications. Graphene is considered as one of the most impressive 2D materials for many applications, like graphene-reinforced metal matrix nanocomposites.1 Wide-bandgap (WBG) semiconductors have received widespread attention in recent years because of their superior physical properties such as large band gap, high carrier mobility, and high thermal conductivity. Represented by silicon carbide (SiC) and gallium nitride (GaN), WBG semiconductor materials, therefore, can be operated in extreme working environments or conditions such as high temperature, high frequency, and high power. 4H-SiC is the most prominent wide-bandgap semiconductor material concerning commercially available power semiconductor devices. Very recently, 4H-SiC has also become very attractive for quantum devices. Among the versatile applications of WBG devices, defects play a significant role – either being detrimental to power device performance (e.g., compensation of p-type doping, reduction of charge carrier mobility, or lifetime) or being essential for quantum effects (e.g., color centers).

This special issue includes contributed papers in different areas of wide-bandgap semiconductors. Some fundamental studies on SiC defects are included in the subjects. Carbon vacancy (Vc) is one kind of vital defect in 4H-SiC. The understanding of the properties of Vc is critical for the application of SiC devices. Calculations of the density functional theory of carbon vacancy defects in SiC were conducted.2 The zero-phonon line energies, hyperfine tensors, and formation energies of carbon vacancies with different charge states in different supercells were calculated. Silicon vacancy (VSi) color centers in SiC are expected to serve as solid qubits used in quantum computing and sensing. VSi color centers were fabricated in SiC by femtosecond (fs) laser writing.3 The influence of fs laser machining parameters on the VSi formation was analyzed, and the three-dimensional distribution of VSi defects was also determined by using confocal photoluminescence spectroscopy.

Apart from fundamental research on silicon carbide, topics related to the direct relevance of the processing or application of 4H-SiC devices are also included in this special issue. High-quality fabrication of SiC homoepitaxial layers is critical for the fabrication of today's and future 4H-SiC devices. Analyzed by optical microscopy and KOH-defect selective etching analysis, several kinds of surface defects of the 4H-SiC homoepitaxial layer are systemically investigated4 triangles, carrots, surface pits, basal plane dislocations, and step bunching. Compared with silicon-insulated gate bipolar transistors (IGBTs), SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) have higher current density and smaller chip size. However, they exhibit less short circuit withstand time that requires proper gate drive design during short circuit tests, which are relevant to investigate MOSFET robustness. Evaluation of a suggested test setup and resulting benefits for device characterization are presented for 1.2 kV SiC MOSFETs using different test voltages and setups.5 

Also, this WBG special issue includes a topic related to GaN-based devices. The damage due to energetic particle irradiation is one key concern in the field of GaN-based devices. The effect of X-ray irradiation on the threshold voltage of AlGaN/GaN high-electron-mobility transistors (HEMTs) was studied.6 Furthermore, it was found that enhancement-mode GaN HEMT fabricated using p-GaN gate owns a stable threshold voltage.

In the end, the special issue also include one contribution on silicon, which is used as a high quality and relatively cheap substrate for epitaxial growth of WBG materials (e.g., 3C-SiC and GaN). As the final removal of this substrate might be beneficial, new Si removal techniques could boost such activities. A paper about atmospheric-pressure plasma etching for Si wafer thinning7 is presented in this context.

Therefore, this special issue might trigger new ideas and approaches in the research field on wide-bandgap semiconductors. We strongly believe that intensive and collaborative research on all aspects of WBG semiconductor device processing, including fundamental research, is critical to increase and broaden their application, which is mandatory for realizing human society's sustainable growth.

We would like to sincerely thank all the authors for their brilliant contribution and firm support; the reviewers for their constructive feedbacks; and Ms. Yuanyuan Sun, Ms. Wenge Liu, and Prof. Xuexin Duan of Nanotechnology and Precision Engineering for their kind help and support.

1.
Chen
W
,
Yang
T
,
Dong
L
, et al 
Advances in graphene reinforced metal matrix nanocomposites: mechanisms, processing, modelling, properties and applications
.
Nanotechnol Precis Eng
2020
;
3
(
4
):
189
210
.
2.
Wang
X
,
Zhao
J
,
Zongwei
X
, et al 
Density functional theory calculation of the properties of carbon vacancy defects in silicon carbide
.
Nanotechnol Precis Eng
2020
;
3
(
4
):
211
217
.
3.
Liu
J
,
Xu
Z
,
Mathias
R
, et al 
Confocal photoluminescence characterization of silicon-vacancy color centers in 4H-SiC fabricated by a femtosecond laser
.
Nanotechnol Precis Eng
2020
;
3
(
4
):
218
228
.
4.
Zhao
L
.
Surface defects in 4H-SiC homoepitaxial layers
.
Nanotechnol Precis Eng
2020
;
3
(
4
):
229
234
.
5.
Diao
S
.
Determination of failure degree of 1.2 kV SiC MOSFETs after short-circuit test using an improved test setup
.
Nanotechnol Precis Eng
2020
;
3
(
4
):
235
240
.
6.
Qi
Y
,
Wang
D
,
Zhou
J
, et al 
Effect of X-ray irradiation on threshold voltage of AlGaN/GaN HEMTs with p-GaN and MIS gates
.
Nanotechnol Precis Eng
2020
;
3
(
4
):
241
243
.
7.
Guo
W
,
Senthil Kumar
A
,
Peng
X
.
Investigation of material removal characteristics of Si (100) wafer during linear field atmospheric-pressure plasma etching
.
Nanotechnol Precis Eng
2020
;
3
(
4
):
244
259
.

Zongwei Xu is Associate Professor (Tenure track) from College of Precision Instrument & Opto-electronics Engineering, Tianjin University, China. His principle research interests include micro/nano optical devices’ fabrication by Focused ion Beam (FIB), fabrication of wide band gap semiconductor devices, mechanism of ion beam micromachining by atomistic simulation methods, ultrafast laser processing, and Raman and fluorescence spectroscopy characterization. As Principal Investigator (PI), Four National Natural Science Foundation of China (NSFC) projects have been granted, including one International Cooperation and Exchange project (Newton fund). He is the Committee Member of Chinese Focused Ion Beam (FIB) Committee (2012-), Chinese Society of Micro- Nano Technology (2016-). He was the Associate Editor of Journal of Mechanical Engineering Science, and the Editorial Board Member of Nanotechnology and Precision Engineering. He was selected as a representative by Chinese Academy of Engineering (CAE) in 2015 and participated the “4th China-America Frontiers of Engineering Symposium” organized by US National Academy of Engineering (NAE). He is the conference Chairman of the 4th National Conference on FIB Technology and Applications of China in 2013, 1st Sino-German Summer School “Material-Oriented MicroNano Manufacturing” (GZ 1471), 1st Sino-German Symposium “Defect Engineering in SiC Device Manufacturing - Atomistic Simulations, Characterization and Processing” (GZ 1615). As Chinese PI, one Mobility Programme of the Sino-German Center for Research Promotion (M-0396) has been granted in 2020.

Yidan Tang, PhD in Microelectronics and Solid State Electronics, assistant researcher of Institute of Microelectronics of Chinese Academy of Sciences (IMECAS). Major in the research and industrialization work ofwide bandgap semiconductor silicon carbide (SiC) power devices. Recent research areas include the design and development of high temperature high-current SiC power electronic devices, development of ohmic contact, implant and active annealing key device processing, investigation in the formation and evolution mechanism of ion implantation defects, research on high temperature reliability of SiC devices. Hosted and participated in the National Science and Technology Major Project (02), National Key Research and Development Program of China under Grant, National Natural Science Foundation, Enterprise and other projects, which are more than 10 projects. More than 20 articles have been published in J. Appl. Phys., Micro electron. Reliab., Chin. Phys. B, Materials Science Forum, Semiconductor Technology etc. 15 Chinese invention patents and 1 US patent have been granted.

Mathias Rommel received a diploma degree in Electrical Engineering in 1993 from the University of Erlangen and a Master of Science in 1994 from the University of Oldenburg (both in Germany). He obtained his PhD in Electrical Engineering on carrier lifetime spectroscopy and oxide characterization in 2007 from the University of Erlangen. From 1995 to 2001 he was teaching and research assistant at the Chair of Electron Devices at the University of Erlangen focusing on contamination control and electrical device characterization. In 2002 he joined the Fraunhofer Institute for Integrated Systems and Device Technology (IISB) in Erlangen and is responsible for the nanotechniques group since 2006 with additional research focus on nanopatterning by focused ion beam (FIB), nanoimprint lithography (UV-NIL and UV-SCIL) aswell as electrical scanning probemicroscopy (SPM) techniques for the characterization of high-k layers and semiconductor materials. Since several years, he also focused on the in-depth characterization of defects in 4H-SiC bymeans of carrier lifetime measurements and deep level transient spectroscopy (DLTS). He was involved in several German national BMBF and DFG projects as well as in several European research projects including OMMCOS, NANOCMOS, PullNANO, CHARPAN, TASNANO, UTTERMOST, STEEP, and IONS4SET, and published or co-published more than 100 Scopus-indexed papers. He is the conference Chairman of 1st Sino-German Symposium “Defect Engineering in SiC Device Manufacturing - Atomistic Simulations, Characterization and Processing” (GZ 1615). As German PI, one Mobility Programme of the Sino-German Center for Research Promotion (M-0396) has been granted in 2020.