【Domestic Papers】8.7 A/700 V β-Ga₂O₃ Schottky barrier diode demonstrated by oxygen annealing combined with self-aligned mesa termination

      Researchers from the University of Science and Technology of China have published a dissertation titled "8.7 A/700 V β-Ga₂O₃ Schottky barrier diode demonstrated by oxygen annealing combined with self-aligned mesa termination" in Applied Physics Express.

Abstract

      β-Ga₂O₃ Schottky barrier diodes (SBDs) with low-defect epitaxial surface and effective termination are essential for realizing excellent blocking characteristics. This work systematically studied oxygen annealing at various temperatures, optimizing the epitaxial surface by reducing the surface roughness and dislocation density. Combined with mesa termination, the results showed that the breakdown voltage (V_br) significantly increased from 845 V to 1532 V. The device with a 3 × 3 mm² anode size was fabricated simultaneously, and the high forward currents of 8.7 A@2 V and V_br > 700 V were achieved. This work shows a possible solution for the commercialization of β-Ga₂O₃ SBDs.

      Figure 1 (a) shows the cross-section schematic of the β-Ga₂O₃ SBDs, including the control SBD (left), the SBD with OA (middle) and the SBD with mesa termination after OA (right). The devices were fabricated on a 10 μm thick lightly Si doped β-Ga₂O₃ drift layer, which was grown by HVPE on a Sn-doped β-Ga₂O₃ substrate with a carrier concentration of 5 × 10¹⁸ cm⁻³ by Novel Crystal Technology, Inc., Japan. The wafer preparation started with organic and piranha solution cleaning. After cleaning in de-ionized water, different thermal oxidation temperatures of 200 °C, 400 °C, 600 °C and 800 °C for 30 min were taken, separately. Then, dry etching Inductively Coupled Plasma (ICP) was performed on the above samples (including the control sample) to eliminate the increase in ohmic contact resistance caused by thermal oxidation annealing. The Ti (100 nm)/Au (150 nm) metals were then deposited on the sample backside by electron-beam evaporation. After that, the patterned circular Schottky anode with a radius of 100 μm consisting of a Ni (100 nm)/Au (150 nm) metal stack were fabricated by evaporation and lift-off, which was also used as the hard mask for the self-aligned etching. Finally, the devices were etched in ICP 180 system to form the mesa termination, and the ICP parameters were the same as our previous work.  Large area SBDs (3 × 3 mm²) were also fabricated in the process. The difference is that the anode was finally thickened to 1.5 μm through a shadow mask to facilitate the packaging process.

Fig. 1. (a) Schematic cross-sectional view of control β-Ga₂O₃ SBD (left) and SBD with OA (middle) and SBD with 350 nm mesa termination after annealing (right). (b) The AFM images of the β-Ga₂O₃ (001) surface with and without surface pre-treatment by OA at 400 °C for 30 min. (c) Cross-sectional SEM of device structure.

      The Atomic Force Microscope (AFM) images of the epitaxial layer before and after OA at 400 °C for 30 min are presented in Fig. 1(b). The RMS decreases from 0.435 nm to 0.245 nm in a 2 × 2 μm² area after annealing and has clear atomic step. Figure 1(c) displays the scanning electron microscopy (SEM) cross-section imaging of the SAMT device with OA, which has an etching depth of approximately 350 nm and an etching angle of 90°.

      Figure 2(a) displays the carrier concentration (N_d-N_a) extracted by capacitance-voltage (C-V) measurements of devices before and after annealing with different temperatures at 100 kHz. Equation (1) expresses the relationship between the measured capacitance and the N_d-N_a of the epitaxial layer.

Fig. 2. (a) N_d-N_a profile extracted from the C-V characteristics and (b) linear plot of forward I-V characteristics and (c) the reverse leakage density profiles of devices without and with annealing of different OA temperatures at 200 °C, 400 °C, 600 °C and 800 °C (radius of 100 μm).

Paper Link：https://doi.org/10.35848/1882-0786/ad2d73