A thin aluminum gallium nitride (AlGaN) electron blocking layer (EBL), above the active region, is used to improve the performance and reduce threshold current of indium gallium nitride (InGaN) quantum well (QW) lasers. A new structure, with delta barrier close to EBL (AlGaN/0.3 nm GaN/InGaN), was devised to prevent deleterious polarization effects and confer other advantages. The effect of a 0.3 nm-thick GaN delta barrier on the performance of a deep violet InGaN double QW laser was investigated using ISE TCAD software. The results indicate that the delta barrier significantly enhances the output power, slope efficiency and external differential quantum efficiency while decreasing the threshold current.
The performance of quantum well GaN/AlGaN light emitting diode (LED) is reviewed for three different barrier compositions; symmetric barrier composition with low Al content, asymmetric barrier composition with higher Al content on p-type cladding layer and lower Al content on n-type cladding layer, and symmetric barrier composition with higher Al content. The study was conducted using ATLAS/BLAZE & LUMINOUS software developed by Silvaco International Inc. Integrated radiative recombination rate was studied on applied voltages up to 5V. Results showed three phases of LED performance with different applied voltages and these were explained using bandgap theory. I-V characteristic for each design agrees with the total additional voltage drop equation for a quantum well structure. The dominant radiative recombination rate regions in LED at low and high supplied voltages are also presented for the best performance LED design.
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, ρc (SCR) determined using transmission line method (TLM) and scanning electron microscopy (SEM) measurements are carried out to the as-deposited, annealed (A), and annealed-and-cryogenically (A+C) 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 A+C samples exhibited lower SCR as compared to A samples. For relatively low annealing temperatures, i.e. 500°C and below, the difference of SCR values between A and A+C 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 A and A+C 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 A+C 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.