Objective of the project is the development of high-efficiency solar-blind UV-C photodetectors based on κ (orthorhombic) and α (hexagonal) GaO, two relatively unexplored polymorphs that exhibit potential advantages over the well-studied monoclinic β GaO, in particular more symmetric crystal lattice and easier deposition conditions, while maintaining wide bandgap and thermodynamic stability up to 700 °C. Photoresistors and self-powered photodiodes (heterojunctions) with performance beyond the state of the art will be prepared. To tune the UV optical absorption to specific applications, InGaO ternary alloys may also be developed.
The project develops along two main guidelines:
1) Material improvement through deeper understanding of kinetic and thermodynamics of the chosen GaO phases. Improvement of MOVPE epitaxial growth to achieve a material quality that allows for fabrication of photodetectors with performance beyond the state-of-the-art.
In case of κ-GaO, efforts will be directed to eliminate the typical rotational domains and related columnar structures that limit the in-plane electron mobility. Suppression of domains is a major goal to enhance photocarrier collection and increase detection efficiency. In the case of α-GaO research will aim at testing non-conventional substrates of hexagonal materials. To understand the physical nature of deep intragap states in both polymorphs, and find ways to reduce their density, is a second major goal of the material development. Their presence causes absorption in the UV-A and visible range, thus is detrimental to solar-blind operation. The third goal is to get a full control over phase nucleation and growth of the desired GaO UV-C absorber on different templates in view of optimized p-n heterojunction fabrication.
2) Design and fabrication of novel solar-blind UV-C sensors based on epitaxial films of κ (orthorhombic) and α (hexagonal) GaO polymorphs. A major effort is directed to develop efficient self-powered diodes that make the photodetector suitable for use in remote places (for example for fire detection). The heterostructures basically include n-type Ga2O3 and different p-type materials as substrates or overgrown films. Suitable photolitographic processes are employed for the device preparation. The experimental activity is supported by device modelling and simulations.