We've all been brainwashed by the phrase "charge in 5 minutes, talk in 2 hours". Who doesn't love a fast and small charging head? Since fast charging became standard, gallium nitride (GaN) has been widely used in the fast charging wars of mobile phone brands. When you start using a charging head made of gallium nitride, the industry is already targeting a fourth-generation semiconductor material, gallium oxide (Ga2O3), to make a stronger charging head.
What is fourth generation semiconductor? It refers to the semiconductor materials represented by gallium oxide (Ga2O3) and antimonides. Compared with other semiconductor materials, the fourth-generation semiconductor materials have the advantages of smaller volume, lower energy consumption and stronger function, which can be better used in optoelectronic devices and power electronic devices under harsh environmental conditions.
01 Why is it "HOT"?
The first generation of semiconductor materials mainly refers to silicon (Si), germanium (Ge) elemental semiconductor materials; The second generation of semiconductor materials mainly refers to gallium arsenide (GaAs), indium phosphide (InP) and other compound semiconductor materials; The third generation semiconductor materials refer to the wide band gap semiconductor materials represented by silicon carbide (SiC), gallium nitride (GaN) and zinc oxide (ZnO).
The fourth-generation semiconductor materials are mainly ultra-wide band gap (UWBG) semiconductor materials represented by diamond (C), gallium oxide (GaO) and aluminum nitride (AlN), with band gap widths exceeding 4eV, and ultra-narrow band gap (UNBG) semiconductor materials represented by antimonides (GaSb, InSb). In application, the ultra-wide band gap material overlaps with the third generation material, which has more prominent characteristic advantages in the field of power devices. Ultra-narrow band gap materials are mainly used in detectors, lasers and other devices because of their easy excitation and high mobility.
Gallium oxide is an oxide of gallium and a semiconductor compound. Up to now, five crystal morphisms have been confirmed, α, β, γ, δ and ε, of which β phase is the most stable.
Figure: β-phase gallium oxide crystal structure (network)
The following chart shows the different areas of application of Si, SiC, GaN and gallium oxide power electronic devices in terms of current and voltage requirements.
Cost is also an important factor that has made gallium oxide attractive to the industry
Based on SiC substrate, high quality epitaxial layer is obtained by chemical vapor deposition (CVD), and then the power device is manufactured on the epitaxial layer. Due to the higher defect density of SiC substrate wafers compared with Si, epitaxial layer growth will be further interfered, epitaxial layer itself will also produce crystallization defects, affecting the performance of subsequent devices.
Like sapphire, GaO can be transformed from solution state to Bulk single crystal state. For gallium oxide, high quality and large size natural substrates offer unique and significant cost advantages over currently used wide band gap SiC and GaN technologies.
Figure: Cost comparison between GaO and SiC (EEPOWER)
The industry characteristics of power semiconductors suit the growth of gallium oxide devices. In addition, new applications such as new energy vehicles continue to promote the rise of new semiconductor materials. Our market space is huge and it is expected to shorten the gap with overseas enterprises quickly in this field.
02 Fourth generation, who's the fastest?
Fujifilm forecasts that the gallium oxide power component market will reach 154.2 billion yen (about 9.276 billion yuan) in 2030, which is larger than the gallium nitride power component market (108.5 billion yen (about 6.51 billion yuan).
In terms of gallium oxide, Japan leads the world in the research and development of substrate - epitaxy - devices. Japan's Ministry of Economy, Trade and Industry (METI) is preparing to provide financial support to private companies and universities working to develop a new generation of low-energy semiconductor material, "gallium oxide," Japanese media reported in September 2020. METI will set aside about $20.3 million for 2021 and expects to invest more than $85.6 million over the next five years. METI believes Japanese companies will be able to start supplying gallium-based semiconductors for data centres, home appliances and cars by the late 2020s. Once gallium oxide replaces silicon, which is widely used today, it will reduce carbon dioxide emissions by 14.4 million tons per year.
NICT's success was noted by the U.S. Air Force Research Office in 2012, when a team led by researcher Gregg Jessen explored the properties of the GaO material and showed that the GaO material's speed and high critical field strength had the potential to be disruptive in fast power switching and RF power applications. Inspired by this achievement, Jessen set up the GaO research foundation in the United States and obtained the first samples.
"We were able to be a leader in the field because we were able to get the material early," said the team leader.
03 Gallium oxide from China
In China, gallium oxide research has been carried out for ten years, and breakthroughs have been made in recent years. Hao Yue, an academician at the Chinese Academy of Sciences, said in an interview that gallium oxide is one of the most likely materials to shine in the future. In the next 10 years or so, gallium oxide devices could become competitive power electronics, directly competing with silicon carbide devices.
In May 2022, Zhejiang University Hangzhou Science and Technology Innovation Center announced that the Advanced Semiconductor Research Institute of the Center invented a new melt method to develop gallium oxide bulk single crystals and wafers, and has successfully prepared gallium oxide wafers with a diameter of 2 inches (50.8mm). Domestic research institutions and universities on gallium oxide include Xidian University, Shanghai Institute of Optics and Machinery, Shanghai Institute of Microsystems, Fudan University, Nanjing University, Shandong University, etc. The 46 Institute of China Electronics Science and Technology Corporation successfully produced the first 100mm single crystal gallium oxide wafer in China. The development of a material industry requires materials, devices, modules, applications and other links to form a complete cycle. At present, the third generation of semiconductor materials has a complete industry chain, and the cost is constantly down direction; Gallium oxide is still in a stage of further research and industrialization.
The coordinated development of all links of the industrial chain is very important. If we want to really bring up the whole industrial chain from the application and demand side, we need to have good devices and demonstrative applications. For example, Tesla used silicon carbide in the Model 3, and Xiaomi used gallium nitride in the fast charge. If gallium oxide is made to good specifications one day, you may find a field in which it is cheaper, performs better, and has no safety concerns, and the era of fourth-generation semiconductors has arrived.