Ultrawide Bandgap Semiconductors Modeling, Epitaxy, Processing, and Applications for Deep Ultraviolet Emission and Detection

  • Yi Lu

Student thesis: Doctoral Thesis


Wide bandgap semiconductor visible light-emitting diodes (LED) development has spawned the prestigious Nobel Prize in Physics in 2014. Building upon this success, the scope of research has expanded to ultrawide bandgap semiconductors, which possess immense potential in the realm of deep ultraviolet (DUV) photonics. These materials have gained attention for their applicability in various areas, including public sterilization, solar-blind DUV communication, and real-time monitoring. Leveraging on the unique ultrawide tunable bandgap property, highly crystalline capability, and robust behavior, group III-Oxide and III-Nitride semiconductors were employed for sensitive DUV photodetector (PD) and efficient DUV emission, respectively. The primary research are as follows: •III-Oxide heteroepitaxial growth optimization: The influences of substrate temperature, laser energy, and oxygen pressure for the Ga2O3 growth are systematically investigated. Furthermore, the doping capability, multi-phase availability, and bandgap tunability are demonstrated. •Flexible Ga2O3 film growth and electronic devices: Flexible Mica substrate is employed to epitaxially grow κ-phase Ga2O3 thin film. The fabricated flexible PD has an Iphoton/Idark ratio of over 107 under DUV luminescence. The fatigue test performed with 1-3 cm bending radii and 10,000 bending cycles exhibits the robust flexibility of the demonstrated DUV PD. •Transferable Ga2O3 membrane for vertical electronics: Mica as a Ga2O3 growth platform enables the large-scale transfer of ultra-thin Ga2O3 membrane from mica to arbitrary tape due to the weak interfacial bond energy. A vertical and self-powered PD is demonstrated with a responsivity of 17 mA/W under DUV illumination and 0 V bias. •Interfacial mismatch engineering for freestanding Ga2O3 membrane: Looking beyond the hetero-mismatch and engineering the interfacial thermal strain between Si-doped Ga2O3 and AlN could result in the exfoliation of freestanding ultrathin Ga2O3 membrane, allowing vertical device configuration and preferable thermal management. The exfoliation mechanism has been clarified and vertical DUV PD with high on/off ratio is demonstrated. •Efficient III-Nitride LEDs: Buried polarization-induced tunneling junction is employed to suppress electron overflow and simultaneously enhance hole injection. Furthermore, monolithic integration of DUV and visible LEDs is proposed and demonstrated by deliberately cascading DUV and visible active regions, which could replace the current integration technique in the sterilization system.
Date of AwardJun 2023
Original languageEnglish (US)
Awarding Institution
  • Computer, Electrical and Mathematical Sciences and Engineering
SupervisorXiaohang Li (Supervisor)


  • ultrawide bandgap semiconductor
  • Ga2O3
  • photodetector
  • LED
  • flexible electronics
  • membrane exfoliation

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