Member News
【Member News】World's First! 6-inch β type Gallium Oxide single crystal was successfully prepared by Vertical Bridgman method (VB)
日期：2023-12-25阅读：190
For the first time in the world, 6-inch β type Gallium Oxide single crystal was successfully prepared by Vertical Bridgman method (VB)
-Contributes to the large size and high quality of β-type Gallium Oxide substrates -
Novel Crystal Technology, Inc. has successfully prepared 6-inch β-type Gallium Oxide (β-Ga2O3) single crystal by Vertical Bridgman (VB) method for the first time in the world. With this result, we can look forward to a big step towards achieving a larger diameter and higher quality β-Ga2O3 substrate. If β-Ga2O3 power devices are widely used, power regulators, general-purpose industrial inverters, power supplies and other power electronics for solar power generation will become more efficient and compact. Eventually, the electrification of automobiles and industry will help to make efficient use of electric energy in things like EVs and flying cars.
Overview
In recent years, Silicon Carbide (SiC) *1 and Gallium Nitride (GaN) *2 have attracted attention as materials that surpass the performance of Silicon (Si) power devices. β-type Gallium Oxide (β-Ga2O3) *3 has a greater bandgap energy *4 than these two materials, so it has the potential to achieve higher performance power devices and, like Silicon (Si), is a low-cost fabrication of high-quality single crystal substrates using the "melt growth method". Based on these characteristics, if the β-Ga2O3 power device *5 is put into practical application, it will help home appliances, electric vehicles, railway vehicles, industrial equipment, solar power generation, wind power generation and other power electronic equipment with lower loss. Because it can reduce costs, enterprises and research institutions at domestic and international are constantly developing it. In addition, in order to reduce the cost of β-Ga2O3 power devices and make them widely used in society, it is necessary to increase the diameter of β-Ga2O3 substrates, and there is a strong desire for larger single crystal.
Novel Crystal Technology, Inc. develops single crystal manufacturing technologies using the EFG (Edge-defined Film-fed Growth) method and is currently manufacturing and selling 2-inch and 100-mm substrates for R&D. To achieve larger diameters and higher quality substrates, we have been working on the development of 6-inch β-Ga2O3 substrates using the VB method under the JST Research Results Optimized Deployment Support Program (A-STEP)*6. The VB method for growing β-Ga2O3 single crystal was invented and developed by Shinshu University and has successfully produced 2 inch and 4 inch single crystal. Novel Crystal Technology Co., Ltd. has inherited this cultivation technology from Shinshu University and continues to develop larger diameters. Therefore, we recently launched the VB 6-inch crystal growth unit and successfully produced the world's first VB 6-inch single crystal. In addition, National Institute of Advanced Industrial Science and Technology (AIST), which is responsible for crystal evaluation and analysis, evaluated and compared the substrates obtained from single crystal manufactured by EFG method and VB method using X-ray topography. As a result, they found that the high density linear defect observed in the EFG method were significantly suppressed in the crystals produced by VB, and that the crystals produced by VB were superior in terms of quality.
The results of this time
[1] 6 inch single crystal prepared by VB method
Figure 1(a) shows an overview of the EFG method currently used for crystal production by Novel Crystal Technology, Inc. The EFG method is one of the growth methods and is a growth method that can easily achieve a high growth rate. However, the obtained crystal is plate, circular substrate is not good processing, unnecessary waste in the processing process, increase the cost, and because the β-Ga2O3 crystal has a strong anisotropy, there are great restrictions on its processing. At the same time, the lifting direction limits the surface orientation of the substrate that can be obtained. Figure 1 (b) shows an overview of the VB method currently under development. The VB method is a growth method in which a crucible containing raw materials is stored in a furnace with a temperature gradient, and after the raw materials are melted, the crucible is pulled down to solidify it. In this way, the crystal with the same shape as the crucible can be obtained, so if the cylindrical crucible is used, the cylindrical crystal can be obtained, which greatly reduces the unnecessary waste in the processing of the substrate, so that the cost can be reduced. In addition, unlike the growth method using the lifting method, this growth method solidifies the melt in the crucible, so it is not easily constrained by the crystal anisotropy on the growth plane, and can produce a variety of substrate plane orientations, which is expected to solve the problems of the EFG method. In addition, compared with the lifting method, it can be grown in an environment with a smaller temperature gradient, which allows higher quality crystals to be obtained, and because a substrate perpendicular to the direction of crystal growth can be obtained, another feature is that crystals can be grown in an environment with a smaller temperature gradient, which is expected to improve the in-plane concentration uniformity.
Figure 1. (a) Outline of EFG method (b) outline of VB method
Figure 2 shows the appearance of a crystal obtained using a newly constructed 6-inch crystal growth device for the VB method. From the seed to the final solidification part are transparent, indicating that they are single crystal. In addition, the equal diameter part (the widest part) is more than 6 inches in diameter, resulting in crystals that can be used to form a 6-inch substrate. In addition, we found that we were able to grow single crystal that inherited the seed orientation.
FIG. 2. 6-inch single crystal prepared by VB method
(a) Overall appearance (b) seed crystal side appearance (c) final cured portion side appearance
[2] The substrate quality of EFG method and VB method was evaluated using X-ray topography
In order to compare the quality of crystals grown by EFG method and VB method, we evaluated the crystal quality using X-ray morphology method, one of the methods for evaluating defect of crystals. Figure 3 shows the images observed by the X-ray topography method for substrates manufactured using the EFG method and the VB method. As shown in Figure 3(a), it can be seen that high density linear defect appear on the substrate manufactured using the EFG method. On the other hand, it can be seen that the substrate manufactured by the VB method shown in Figure 3(b) has almost no linear defect. However, the reticulated appearance on the surface of the substrate manufactured using the VB method is considered to be a dislocation network. Although mesh contrast is not observed on the surface of substrates manufactured using the EFG method, it is difficult to see due to the large strain field caused by linear defect. From the above observations, it is found that the crystal quality of the substrate manufactured using the VB method is improved compared to the substrate manufactured using the EFG method.
Figure 3. Images viewed by X-ray photography
(a) Substrate prepared by EFG method (b) substrate prepared by VB method
Future plans
In the future, we will continue to develop high-quality single crystal growth technology using the VB method and strive to develop a substrate that takes advantage of the flexibility of the growth plane orientation of the VB method.
Novel Crystal Technology, Inc. will continue to be committed to the popularization of β-Ga2O3 power devices through the development of β-Ga2O3 massive single crystal growth technology using the melt growth method to achieve a sustainable energy saving society.
Acknowledgements
This research was supported by the A-STEP Enterprise-Led (matching fund type) program that supports the optimized deployment of research results under the Japan Science and Technology Agency's Research Results Deployment Program.
[Note]
*1 Silicon Carbide (SiC)
It is a compound of silicon and carbon and is one of wide band gap semiconductors.
*2 Gallium Nitride (GaN)
It is a compound of gallium and nitrogen and is a wide-band gap semiconductor.
*3 β type Gallium Oxide (β-Ga2O3)
It is a compound of gallium and oxygen and is one of the wide band gap semiconductors.
*4 bandgap energy
In the band structure of a crystal, the energy state between the lowest energy level of the conduction band and the highest energy level of the valence band, in which no electrons can exist.
*5 Power supply device
Semiconductor components that can control high voltage and current, used in power conversion devices such as inverters.
*6 JST Research Results Optimal Deployment Support Program (A-STEP)
