| AVS 63rd International Symposium & Exhibition | |
| Electronic Materials and Photonics | Monday Sessions |
| Session EM-MoA |
| Session: | Surface and Interface Challenges in Wide Bandgap Materials |
| Presenter: | Steven Ringel, The Ohio State University |
| Authors: | S.A. Ringel, The Ohio State University A. Arehart, The Ohio State University E. Farzana, The Ohio State University Z. Zhang, The Ohio State University E. Ahmadi, University of California at Santa Barbara Y. Oshima, University of California at Santa Barbara J. Speck, University of California at Santa Barbara |
| Correspondent: | Click to Email |
Deep level defects are pervasive in wide bandgap (WBG) semiconductors such as GaN. Over the years deep levels in GaN have been extensively studied. Several states have been directly linked with device degradation mechanisms in high electron mobility transistors and there is continued exploration of defect mitigation strategies to improve reliability. At the same time, there has been intense interest on the so-called ultra-wide bandgap (UWBG) semiconductors, whose bandgaps are > 3.4 eV, driven by the desire to develop devices that can sustain even higher fields, operate at higher temperatures, while maintaining good high frequency performance. Of these UWBG materials, beta-phase gallium oxide (β-Ga2O3) is attracting particular interest due to its large, direct bandgap of ~ 4.8 eV, the availability of n doping, the ability to create heterostructures, and the availability of native substrates to support homoepitaxial growth. This latter point is unique amongst WBG and UWGB materials.
However, compared with incumbent technologies, β-Ga2O3 is in its infancy, with transistors recently announced that have created excitement regarding the future of this material.[1] This presentation will build from our work on GaN and focus on basic aspects of β-Ga2O3: (a) the application of deep level optical and transient spectroscopy (DLOS/DLTS) to reveal traps throughout the entire material bandgap, (b) comparative DLOS/DLTS studies made on substrates and epitaxial layers grown by molecular beam epitaxy, and (c) the influence of wafer orientation on the properties of β-Ga2O3 Schottky diodes using various metals. DLTS and DLOS measurements revealed a spectrum of distinct bandgap states at Ec – 0.62 eV, 0.82 eV, 1 eV, 2.4 eV and 4.42 eV, with a total trap concentration of ~ mid 1016 cm-3 range, dominated by the traps at Ec –0.82 eV and Ec – 4.42 eV.[2] Several traps show strong lattice-coupling effects. Regarding Schottky contacts, Ni Schottky contacts were fabricated on (010) and (-201) surfaces, revealing a change in barrier height of almost 0.5 V, as measured by both internal photoemission and C-V methods, suggesting a surface orientation dependence of Schottky barrier formation. Comparing Ni, Au, Pt and Pd contacts on (010) β-Ga2O3, barrier heights appear partially unpinned with barriers ranging from ~ 1.2 eV for Pd, to ~ 1.55 eV for both Ni and Pt and as high as ~ 1.8 eV for Au. In all cases, nearly ideal Schottky barrier transport characteristics were observed. This presentation will focus on the extension of trap studies from GaN to β-Ga2O3.
[1] M. Higashiwaki, et al., Appl. Phys. Lett. 100, 013504 (2012)
[2] Z. Zhang, et al., Appl. Phys. Lett. 108, 052105 (2016)