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Houqiang Fu1 Hong Chen1 Xuanqi Huang1 Izak Baranowski1 Jossue Montes1 Tsung-Han Yang1 Yuji Zhao1

1, Arizona State University, Tempe, Arizona, United States

Due to its material properties such as the large bandgap of ~ 4.8 eV and breakdown electric field of ~ 8 MV/cm, wide bandgap semiconductor β-Ga2O3 has garnered tremendous interest for efficient power conversion applications in smart grids, renewable energy, data center, automotive electronics, and so on. β-Ga2O3 exhibits a much larger Baliga’s figure of merit (FOM) than SiC and GaN, indicating β-Ga2O3 power electronics have the potential to outperform SiC and GaN devices. In addition, the cost-effective single-crystal β-Ga2O3 substrates are also commercially available, which will enable high performance vertical electronics devices. β-Ga2O3 based field-effect transistors (FETs) and Schottky barrier diodes (SBDs) have been demonstrated on single-crystal substrates with various orientations including (-201), (010), (001), and (100). Studies have shown that the material properties of β-Ga2O3 are different along different crystal orientations (i.e., anisotropic) because of the highly asymmetric monoclinic crystal structure of β-Ga2O3. However, systematic study on the effect of crystalline anisotropy on the electrical properties of β-Ga2O3 electronic devices is still lacking. In this work, we fabricated vertical (-201) and (010) β-Ga2O3 SBDs on single-crystal substrates grown by the edge-defined film-fed growth (EFG) method. Their electrical properties such as temperature-dependent I-V and C-V characteristics were comprehensively measured and compared. The (-201) and (010) SBDs exhibited on-resistances of 0.56 and 0.77 mΩcm2, turn-on voltages of 1.0 and 1.3 V, Schottky barrier heights (SBH) of 1.05 and 1.20 eV, electron mobilities of 125 and 65 cm2/(Vs), respectively, with a high on-current of ~ 1.3 kA/cm2 and an on/off ratio of ~109. At the forward bias, the (010) SBD had a larger turn-on voltage and SBH than the (-201) device due to different surface Fermi level pinning and band bending, as confirmed by X-ray photoelectron spectroscopy measurements. The difference in the electron mobilities results from the anisotropic electronic transport properties of β-Ga2O3. According to the temperature-dependent I-V, both devices had inhomogeneous SBHs, where (-201) SBD showed a more uniform SBH distribution. The homogeneous SBH was also extracted: 1.33 eV for the (-201) SBD and 1.53 eV for the (010) SBD. At the reverse bias, the leakage current of the devices could be simulated by either the two-step trap-assisted tunneling model or the one-dimensional variable range hopping conduction (1D-VRH) model. Further investigations are needed to determine the dominant mechanism. The (010) SBD showed a smaller leakage current and larger breakdown voltage due to its higher SBH. These results indicate the crystalline anisotropy of β-Ga2O3 can significantly affect the electrical properties of vertical SBDs and should be taken into consideration when designing β-Ga2O3 electronics.

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