Development of Avalanche Photo Detector for UV-C Using Gallium Oxide Material System

This work describes the metal-organic chemical vapor deposition (MOCVD) optimization process for epitaxially grown gallium oxide (Ga2O3) layers, electrical field distribution, and the design for Avalanche Photo Detector (APD). MOCVD is a well-accepted process in the semiconductor industry, as it is well-known for its precise deposition of ultra-thin, high-quality semiconductor layers with extraordinary control over composition and thickness. The choice of Ga2O3 is due to r its distinctive properties of ultra-wide bandgap and low turn-on resistance. Thus, Ga2O3-based materials can withstand high voltage and current with the least energy loss, making them an attractive choice for future applications in power electronics and short wavelength detection in a hostile environment. An APD is a semiconductor-based photodetector that can detect a small amount of light. Besides, APDs are small and compact devices that can operate at lower bias voltages and have a reduced aging effect; thus, less maintenance and less frequent calibration are required. The use of a gallium-oxide (Ga2O3) based material system for APD applications results in a high signal-to-noise ratio, fast response, and low dark current. The Ga2O3-based APDs have applications in particle physics, fiber optic telecommunication, and optical receivers. In this project, the thin film of Ga2O3 was grown on c-plane sapphire substrates by the Metal MOCVD process to optimize initial growth conditions first and later grown on Ga2O3-bulk substrates. The APD designs for filed electric field distribution were simulated using an Ansys Electrical Module; the final design of APD is composed of 3 ´ 3 array elements, and each APD is connected and separately addressed, increasing the detector response time. The electrical simulation shows that specific APD can be addressed without stimulating the adjacent APD. The responsivity of the detector was calculated from the resulting electrical field strength. The simulations were performed up to the maximum electric field strength close to almost 10 (MV/cm), the limit of Ga2O3 material breakdown. To realize APD arrays, we optimized the growth conditions for Ga2O3-related materials on bulk-Ga2O3 using the MOCVD process, which included the continuous and sequential flow of precursors. It was observed that the sequential flow of precursors to grow Ga2O3 films produces smoother layers than the continuous growth process as measured by Atomic Force Microscopy (AFM). The films grown using both processes were also compared using x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The growth technique, characterization methods, and design of the APD will be discussed in this MS thesis.