In this work, we investigate the thermal stability and surface morphology of Ti metal contact on unintentionally doped n-type aluminum gallium nitride (AlGaN). Different annealing temperatures (400°C - 800°C) and durations (1 - 30 minutes) are investigated, as thermally stable metal-semiconductor contacts are essential for high quality devices. Cryogenic quenching after heat treatment is also performed to determine the effects of this treatment on the characteristics of the contacts. Specific contact resistivity, ρ<sub>c</sub> (SCR) determined using transmission line method (TLM) and scanning electron microscopy (SEM) measurements are carried out to the as-deposited, annealed (<i>A</i>), and annealed-and-cryogenically (<i>A</i>+<i>C</i>) treated contacts where the electrical behavior and the surface morphology of each of these conditions are compared. The result shows that cryogenic treatment is able to reduce the SCRs after annealing as most of the <i>A</i>+<i>C</i> samples exhibited lower SCR as compared to <i>A</i> samples. For relatively low annealing temperatures, i.e. 500°C and below, the difference of SCR values between <i>A</i> and <i>A</i>+<i>C</i> treated samples is insignificant, however, when the samples are thermally treated at higher temperatures, i.e. 600°C and above, substantial difference of the SCR values is observed between <i>A</i> and <i>A</i>+<i>C</i> treated samples. SEM images indicate that little difference of surface morphology is observed for all the samples regardless of the annealing temperatures, durations and treatments. The <i>A</i>+<i>C</i> sample annealed at 600°C for 2 minutes is found to be able to yield the lowest SCR in this study.
The III-V nitrides (GaN and AlGaN) wide band gap semiconductors have been recognized recently as a very important technological material system for fabricating optoelectronic devices operating in the blue/ultraviolet (UV) spectral region and electronic devices capable of operating under high-power and high-temperature conditions. These materials are remarkably tolerant to aggressive environments, due to its thermal stability and radiation hardness and are excellent photodetector materials to cover the 240-360 nm range. A key advantage of III-nitrides detectors over competing devices based on semiconductors with smaller bandgaps is the long wavelength response cut-off, which is directly related to the bandgap of the material in the active region and thus does not require external filters.
Metal-semiconductor-metal (MSM) photodiodes are of interest for many applications because of their relatively simple fabrication process, low dark currents, low noise, and fast response time. In this work, AlGaN-based MSM photodetectors with nickel (Ni) Schottky contacts were fabricated and characterized. A comparative study of the photodiodes characteristics were carried out. The thermal stability of the contacts at various annealing temperatures (300°C-700°C) was investigated. Cryogenic cooling after heat treatment was also performed to determine the effects of this treatment on the electrical characteristics of the devices. Electrical characterization was performed by current-voltage (I-V) measurement to investigate the Schottky contact properties of the photodetectors.