2024 MRS Fall Meeting & Exhibit
SF04.09.01

Recent Progress in Crystal Growth and Defect Evaluation of Gallium Oxide

When and Where

Dec 4, 2024
10:30am - 11:00am
Hynes, Level 3, Room 311

Presenter(s)

Co-Author(s)

Kohei Sasaki1,Akito Kuramata1

Novel Crystal Technology, Inc.1

Abstract

Kohei Sasaki1,Akito Kuramata1

Novel Crystal Technology, Inc.1
Although the band gap of β-gallium oxide (β-Ga<sub>2</sub>O<sub>3</sub>) is about 4.5 eV, <sup>1)</sup> a shallow donor level can be formed by doping with donor impurities, and the carrier concentration can be controlled over a wide range (10<sup>15</sup>-10<sup>20</sup> cm<sup>-3</sup>) at room temperature. In addition, as in the case of Si and GaAs, large-diameter bulk single crystals with high quality can be obtained by using the standard melt growth method. Although the impact ionization rate of β-Ga<sub>2</sub>O<sub>3</sub> has not been measured yet, the breakdown electric field strength is estimated to be about 6-8 MV/cm from the breakdown characteristics. <sup>2, 3)</sup> Because of these attractive features, the development of β-Ga<sub>2</sub>O<sub>3</sub> power devices has been vigorously pursued over the past ten years.<br/> Because of its large band gap, β-Ga<sub>2</sub>O<sub>3</sub> can normally operate as a semiconductor even in high-temperature environments where Si devices cannot operate. The material is also expected to have high radiation hardness, and various evaluations have been conducted to this end.<sup>4)</sup> For device application, it is important to establish a technique for producing crystals with low defect densities and to understand the distribution of defects in a wafer; these requirements are not limited to devices meant to operate in severe environments, but also apply to general power devices. In this talk, I will explain recent progress in crystal growth technology of β-Ga<sub>2</sub>O<sub>3</sub> and the latest trend in crystal defect evaluation.<br/> Various methods, such as the Czochralski method, edge-defined film-fed growth (EFG) method, <sup>5)</sup> and vertical Bridgman method, have been investigated for β-Ga<sub>2</sub>O<sub>3</sub> bulk crystal growth. For power-device applications, it is essential to increase the diameter of the wafer to 6 inches or more. At present, the EFG method has the largest diameter, with 6-inch wafers having been demonstrated. One of the future problems with β-Ga<sub>2</sub>O<sub>3</sub> bulk crystal growth is its high cost. Each of the above-mentioned growth methods uses an expensive metal crucible, which greatly affects the fabrication cost. Recently, a new method that does not use a metal crucible has been studied.<br/> Epitaxial methods, including molecular beam epitaxy (MBE), <sup>6)</sup> halide vapor phase epitaxy (HVPE), <sup>7)</sup> and metalorganic vapor phase epitaxy (MOCVD), have been studied as ways of growing β-Ga<sub>2</sub>O<sub>3</sub>. These methods have advantages and disadvantages, and it is expected that their development will advance in parallel for the time being. At present, HVPE is widely used to grow thick films with low-donor concentrations for vertical devices, and MBE or MOCVD is widely used to grown thin films for horizontal devices.<br/> X-ray diffraction, the etch pit method, X-ray topography, and transmission electron microscopy, i.e., methods that have been used on other semiconductors, have been used to evaluate the crystal defects of β-Ga<sub>2</sub>O<sub>3</sub>. In particular, emission microscopy is useful for studying the relationship between device characteristics and defects.<sup>8)</sup> The quality of wafers has been improved by utilizing these technologies. On the other hand, there is a problem that a nondestructive defect inspection method has not been established. In particular, the widely used photoluminescence and cathodoluminescence methods that work on GaN and SiC cannot be used to inspect β-Ga<sub>2</sub>O<sub>3</sub>wafers. Here, I would like to summarize the progress made so far on a defect evaluation technique and its prospects.<br/><br/>1) T. Onuma, et al., Jpn. J. Appl. Phys. <b>54</b>, 112601 (2015).<br/>2) J. Zhang, et al., Nature Communications. <b>13</b>, 3900 (2022).<br/>3) J.-S. Li, et al., ECS Journal of Solid State Science and Technology. <b>13</b>, 035003 (2024).<br/>4) J. Kim, et al., Journal of Materials Chemistry C. <b>7</b>, 10 (2019).<br/>5) A. Kuramata, et al., Jpn. J. Appl. Phys. <b>55</b>, 1202a2 (2016).<br/>6) K. Sasaki, et al., Appl. Phys. Express. <b>5</b>, 035502 (2012).<br/>7) H. Murakami, et al., Appl. Phys. Express. <b>8</b>, 015503 (2015).<br/>8) S. Sdoeung, et al., Jpn. J. Appl. Phys. <b>62</b>, Sf1001 (2023).

Keywords

crystalline | defects | Ga

Symposium Organizers

Jianlin Liu, University of California, Riverside
Farida Selim, Arizona State University
Chih-Chung Yang, National Taiwan Univ
Houlong Zhuang, Arizona State University

Session Chairs

Farida Selim
Joel Varley

In this Session