Narrow Results

The application of thermal annealing at various annealing temperatures (473–1073 K) has been shown to significantly modify surface morphology of platinum (Pt) metal contacts on AlGaN/GaN/AlN heterostructure grown on silicon by plasma-assisted molecular beam epitaxy (PA-MBE). Structural analysis of the AlGaN/GaN samples used for the Pt Schottky contacts fabrication were performed by using high resolution X-ray diffraction (HR-XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The Pt metal contacts were then deposited on the samples followed by current–voltage (I–V) characterization. Thermally-treated samples showed significant decrease in current compared with untreated samples. From the I–V measurements, the Schottky barrier height (SBH) and ideality factor (n) were calculated. We found that the lowest value of SBH obtained was 0.526 eV at 873 K annealing temperature. Unfortunately, there are no values for the SBH and ideality factor at 1073 K annealing temperature. The SEM analysis has shown some island formation at high annealing temperature due to the difference of surface energies between thin metal films and AlGaN that causes dewetting. We suggest that the reason for the barrier height reduction is due to the metal island formation on the samples.

In this paper, the growth and characterization of epitaxial Al_0.29Ga_0.71N grown on Si(111) by RF-plasma assisted molecular beam epitaxy (MBE) are described. The Al mole fraction was derived from the HR-XRD symmetric rocking curve (RC) ω/2θ scans of (0002) plane as x = 0.29. PL spectrum of sample has shown sharp and intense band edge emission of GaN without the existence of yellow emission band, showing that it is comparable in crystal quality of the sample when compared with previous reports. From the Raman measurement of as-grown Al_0.29Ga_0.71N layer on GaN/AlN/Si sample. We found that the dominant E₂ (high) phonon mode of GaN appears at 572.7 cm^-1. The E₂ (high) mode of AlN appears at 656.7 cm^-1 and deviates from the standard value of 655 cm^-1 for unstrained AlN. Finally, AlGaN Schottky photodiode have been fabricated and analyzed by mean of electrical characterization, using current–voltage (I–V) measurement to evaluate the performance of this device.

An experimental investigation was conducted to explore the effect of inserting a single AlGaN interlayer between AlN epilayer and GaN/AlN heterostructures on Si (111) grown by molecular beam epitaxy (MBE). It is confirmed from the scanning electron microscopy (SEM) that the AlGaN interlayer has a remarkable effect on reducing the tensile stress and dislocation density in AlN top layer. Capacitance–voltage (C–V) measurements were conducted to study the electrical properties of AlN/GaN heterostructures. While deriving the findings through the calculation it is suggested that the AlGaN interlayer can significantly reduce the value of effective oxide charge density and total effective number of charges per unit area which are $1.37\times 10^{-6}{\mathrm{\text{C/cm}}}^2$ and $8.55\times 10^{12}{\mathrm{\text{cm}}}^{-2}$, respectively.