【Member Papers】Xi’an Jiaotong University---Mechanism of Improving Al₂O₃/β-Ga₂O₃ Interface After Supercritical Fluid Process at a Low Temperature

      Researchers from the Xi’an Jiaotong University have published a dissertation titled "Mechanism of Improving Al₂O₃/β-Ga₂O₃ Interface After Supercritical Fluid Process at a Low Temperature" in IEEE Transactions on Electron Devices.

Project support

      This work was supported in part by the National Natural Science Foundation of China under Grant 62204198 and in part by the Joint Funds of the National Natural Science Foundation of China under Grant U23A20367.

Background

      The wide bandgap semiconductor devices have become more attractive in power electronics systems. The performances of wide bandgap semiconductor devices, such as the stabilities, reliabilities, and applications, are heavily influenced by the properties of interface states between semiconductor and dielectric layers. As an ultrawide bandgap semiconductor (4.9 eV), gallium oxide (β-Ga₂O₃) has recently attracted much more attention. Exceptional performances of the β-Ga₂O₃ devices, including high breakdown voltage and fast switching characteristics, have been reported in specific technologies. However, unlike the GaN high electron mobility transistor (HEMT) and metal–oxide–semiconductor HEMT (MOSHEMT) with buried channels, β-Ga₂O₃ can only form a depletion-mode metal–oxide–semiconductor field-effect transistor (MOSFET). Therefore, a high-quality dielectric/β-Ga₂O₃ interface plays an essential role in forming high-performance MOSFETs. In general, high-k dielectric, high conduction band offset, and high dielectric/β-Ga₂O₃ interface quality are significant concerns in obtaining high-performance devices.

Abstract

      β-Ga₂O₃, a wide bandgap semiconductor, has gained attention for its high breakdown voltage and fast switching properties. However, challenges exist because of high interface densities at the Al₂O₃/β-Ga₂O₃ interface, which greatly impacts the performance and reliability of metal-oxide–semiconductor field-effect transistor (MOSFET) devices. As a low-temperature solution, the supercritical fluid process (SCFP) is introduced to the fabrication process of Al₂O₃/β-Ga₂O₃ metal-oxide–semiconductor capacitor (MOSCAP), which effectively reduces the oxygen vacancies and interface defects, in particular avoiding the damage to the materials caused by high temperature. The near-interface traps are decreased by two times, and the interface states are reduced by five times. As a result, the breakdown electric field is improved from 6.01 to 8.47 MV cm⁻¹. The mechanism of the SCFP is explored and explained by using different measurement and analysis methods. Deep-level transient spectroscopy (DLTS) results indicate that the defect concentration of SCFP devices decreases and the electron capture interface increases. Supercritical fluid treatment can passivate the traps by reducing O vacancies in the Al₂O₃. The study concludes that the proposed SCFP significantly improves the dielectric/semiconductor interface, which can greatly enhance the performance of transistors.

Conclusion

      In conclusion, the Al₂O₃/β-Ga₂O₃ MOSCAPs were fabricated. The SCFP treatment was first developed to improve the interface quality of the Al₂O₃/β-Ga₂O₃ interface. The near-interface traps N_bt decreased from 5.6 × 10¹¹ to 3.6 × 10¹¹ cm⁻², and the interface states D_it at 0.2 eV below E_C reduced from 1.29 × 10¹² to 2.54 × 10¹¹ eV⁻¹ cm⁻² for the SCF samples. The DLTS results indicate that the trap energy-level position of SCF devices is deeper, the defect concentration decreases, and with a deeper trap emission energy, which further supports the improvement of the interface quality of the devices. In addition, the breakdown electric field was improved from 6.01 to 8.47 MV cm⁻¹ after the SCFP treatment. Moreover, XPS analysis revealed that the SCFP treatment can passivate the traps by reducing O vacancies in the Al₂O₃. This work demonstrated the novel SCFP treatment’s effectiveness in improving the interface quality of the β-Ga₂O₃ MOS structure at low temperatures. It is the first to systematically study the SCFP action and effect on Al₂O₃/β-Ga₂O₃ MOS devices, which provides a detailed method description, testing characterization, and mechanism analysis. Other oxide interfaces used in β-Ga₂O₃ are also very worthwhile to study. SCFP’s high efficiency, low-cost process consumption, and simple process flow make it promising for application in the manufacturing process. This work provides a systematic research methodology and lays a solid foundation for the subsequent related works.