| Summary: | 碩士 === 國立成功大學 === 微電子工程研究所碩博士班 === 96 === The main goal of this research is the fabrication and characterization of GaN-based ultraviolet (UV) photodetectors (PDs) and metal-oxide-semiconductor heterostructure field effect transistors (MOSHFETs) with a low temperature (LT) GaN interlayer. AlGaN/GaN heterostructures used in this experiment were prepared by metal-organic chemical vapor deposition system (MOCVD). Due to the lack of suitable lattice-matched substrates, most of the GaN-based materials and devices were grown on sapphire substrate. However, a large lattice mismatch between GaN and sapphire substrate causes a large amount of threading dislocations (TDs) embedded in the GaN epilayer, leading to extremely high leakage currents. It is known that the LT GaN layer as nucleation layer is necessary to grow high quality GaN epilayer. It is also known that LT GaN interlayer can suppress TDs extending to the subsequently grown high-temperature (HT) GaN epilayers. Therefore, a LT GaN layer was applied as an interlayer in the HT GaN channel layer of the AlGaN/GaN heterostructure.
First, material analyses of AlGaN/GaN heterostructure with a LT GaN interlayer were investigated by X-ray diffractometer (XRD), secondary ion mass spectrometer (SIMS), atomic force microscopy (AFM), etching pit density (EPD) and transmission spectra. It was found that high crystalline quality AlGaN/GaN heterostructure could be achieved with insertion of a LT GaN interlayer.
Based on the aforementioned results, we apply a LT GaN interlayer to the fabrication of GaN-based UV PDs and MOSHFETs. In the part of PDs, we demonstrate metal-semiconductor-metal (MSM) and Schottky barrier PDs by using a LT GaN interlayer with good characteristics, including low dark leakage current, high photo-to-dark current ratio, high UV-to-visible rejection ratio, suppressed internal gain, low noise level and high detectivity. In the part of HFETs, we demonstrate MOSHFETs by using a LT GaN interlayer with high performance, including low gate leakage current, low noise level, good pinch-off and transfer characteristics. Integration of GaN-based UV PDs and MOSHFETs with a LT GaN interlayer will be realized in application to monolithic receiver optoelectronic integrated circuits (receiver OEIC) in the near future.
|
|---|
