Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2018)
    Thin Films Wednesday Sessions
       Session TF-WeP

Paper TF-WeP3
Effect of α-(AlxGa1-x)2O3 Overgrowth on MSM-Type α-Ga2O3 Ultraviolet Photodetectors Grown by Mist CVD

Wednesday, December 5, 2018, 4:00 pm, Room Naupaka Salon 1-3

Session: Thin Films Poster Session II
Presenter: Kenichiro Rikitake, Kogakuin University, Japan
Authors: K. Rikitake, Kogakuin University, Japan
T. Yamaguchi, Kogakuin University, Japan
T. Onuma, Kogakuin University, Japan
T. Honda, Kogakuin University, Japan
Correspondent: Click to Email
Ultraviolet (UV) photodetectors using high Al content AlGaN have been studying towards applications such as flame detection, sterilization and so on [1]. However, the growth of high-quality AlGaN with increased Al content required for UV photodetector has difficulty in epitaxy. Therefore, we have been focusing on corundum-structured gallium oxide (α-Ga2O3) as an alternative material. a-Ga2O3 has a wide bandgap of 5.3 eV, and the bandgap engineering is possible in whole composition range of (Al, Ga, In)2O3 alloys [2, 3]. A β-Ga2O3 based UV photodetector has been shown to have high responsivity [4], and Al2O3 deposition on β-Ga2O3 for surface passivation has been reported [5]. In contrast, α-Ga2O3 detector has so far not yet been reported.

In this study, a metal-semiconductor-metal (MSM)-type UV photodetector using α-(AlxGa1-x)2O3 on α-Ga2O3 is fabricated by mist CVD.

1-μm-thick unintentionally doped α-Ga2O3 film was grown on c-plane sapphire substrate by mist CVD. Ga acetylacetonate was used as a source material for this mist CVD growth, and it was solved in deionized water with a small amount of hydrochloric acid. The concentration of Ga was 0.05 mol/L. It was followed by 20-50-nm-thick (AlxGa1-x)2O3 growth using Al and Ga acetylacetonate as source materials. Then, α-Ga2O3-based MSM-type photodetector was fabricated by employing Ni (50 nm)/Au (100 nm) pads as Schottky electrodes.

Figure 1 shows XRD 2θ-ω scan profile. (0006)α-Al2O3 and (0006)α-Ga2O3 diffraction peaks were observed. 2θ-ω and phi scan profiles indicate growth of single crystalline epitaxial film. As shown in Fig. 2, the full-width at half maximum of the X-ray rocking curve for (0006)α-Ga2O3 diffraction peak is 39.8 arcsec. The absorption coefficient a was determined by optical transmittance measurements. Then, (αhν)2-hν plots give bandgap energy of 5.3 eV. Figure 3 shows photo-responsivity of the MSM-type photodetector. Increase in responsivity above the bandgap energy of 5.3 eV was successfully observed. Maximum photo-responsivity was estimated to be 1.0 A/W. However, the photo-responsivity decreased in the energy range between 5.6 and 5.8 eV due to surface effect of the α-Ga2O3 film. Surface effect on MSM-type UV photodetectors using α-(AlxGa1-x)2O3 on α-Ga2O3 structure will be shown at the cofference.

[1] A. Yoshikawa et al., Jpn. J. Appl. Phys. 55, 05FJ04 (2016).

[2] N. Suzuki et al., J. Cryst. Growth 401, 670 (2014).

[3] S. Fujita and K. Kaneko, J. Cryst. Growth 401, 588 (2014).

[4] T. Oshima, T. Okuno and S. Fujita, Jpn. J. Appl. Phys. 46, 7217 (2007).

[5] S. Pratiyush et al., Appl. Phys. Lett. 110, 221107 (2017).