Impurity diffusion in ion implanted AlN layers on sapphire substrates by thermal annealing

We report on impurity diffusion in ion implanted AlN layers after thermal annealing. Silicon, tin, germanium, and magnesium ions were implanted into single-crystal AlN layers grown on sapphire substrates. By annealing at 1600oC, silicon and magnesium atoms were diffused in the AlN layer, while less change was observed in the distribution of germanium atoms. Silicon implantation introduced vacancy-related defects. By annealing at temperatures over 1300oC, the vacancy-related defects were reduced, while oxygen atoms were diffused from the substrate due to sapphire decomposition. We reproducibly achieved silicon-implanted AlN layers with electrical conductance by controlling the annealing temperature and distribution of silicon and oxygen concentrations.

Chemical vapor deposition of sp2-boron nitride films on Al2O3 (0001), (11𝟐0), (1𝟏02) and (10𝟏0) substrates

Thin films of boron nitride in its sp2-hybridized form (sp2-BN) have potential use in UV-devices and dielectrics. Here, we explore chemical vapor deposition (CVD) of sp2-BN on various cuts of sapphire; Al2O3(112̅0), Al2O3(11̅02), Al2O3(11̅00) and Al2O3 (0001) using two CVD processes with different boron precursors; triethylborane (TEB) and trimethylborane (TMB). Fourier transform infrared spectroscopy (FTIR) showed that sp2-BN grows on all the sapphire substrates, using X-ray diffraction (XRD), 2θ/ω diffractograms showed that only Al2O3(112̅0) and Al2O3(0001) renders crystalline films and using phi(ɸ)-scans the growth of rhombohedral polytype (r-BN) films on these substrates is confirmed. These films are found to be epitaxially grown on an AlN interlayer with a higher crystalline quality for the films grown on the Al2O3(112̅0) substrate which is determined using omega(ω)-scans. Our study suggests that Al2O3(112̅0) is the most favorable sapphire substrate to realize the envisioned applications of r-BN films.

Characterization of the N-polar GaN film grown on C-plane sapphire and misoriented C-plane sapphire substrates by MOCVD

Gallium nitride (GaN) thin film of the nitrogen polarity (N-polar) was grown on C-plane sapphire and misoriented C-plane sapphire substrates respectively by metal-organic chemical vapor deposition (MOCVD). The misorientation angle is off-axis from C-plane toward M-plane of the substrates, and the angle is 2° and 4° respectively. The nitrogen polarity was confirmed by examining the images of the scanning electron microscope before and after the wet etching in potassium hydroxide (KOH) solution. The morphology was studied by the optical microscope and atomic force microscope. The crystalline quality was characterized by the X-ray diffraction. The lateral coherence length, the tilt angle, the vertical coherence length, and the vertical lattice-strain were acquired using the pseudo-Voigt function to fit the X-ray diffraction curves and then calculating with four empirical formulae. The lateral coherence length increases with the misorientation angle, because higher step density and shorter distance between adjacent steps can lead to larger lateral coherence length. The tilt angle increases with the misorientation angle, which means that the misoriented substrate can degrade the identity of crystal orientation of the N-polar GaN film. The vertical lattice-strain decreases with the misorientation angle. The vertical coherence length does not change a lot as the misorientation angle increases and this value of all samples is near to the nominal thickness of the N-polar GaN layer. This study helps to understand the influence of the misorientation angle of misoriented C-plane sapphire on the morphology, the crystalline quality, and the microstructure of N-polar GaN films.

Influence of the Iron as a Dopant on the Refractive Index of WO3

Results on studies of pure tungsten oxide WO3 and 2, 3 and 4% Fe-doped WO3 grown on the sapphire substrates by reactive pulsed laser deposition technique are reported. From X-ray diffraction it results that the crystalline structures changed with the substrate temperature and the peaks diffraction having a small shift by the amount of Fe content in WO3 lattice was noticed. Scanning electron microscopy presented a random behavior of WO3 nanocrystallites size with substrate temperatures. In the presence of 2% Fe-doped WO3, the nanocrystallites size varied gradually from 60 nm to 190 nm as substrate temperature increased. The transmission spectra of the pure and 2, 3 and 4% Fe-doped WO3 films were obtained within the 300–1200 nm spectral range. The refractive index of WO3 and Fe-doped WO3 layers were calculated by the Swanepoel method. The refractive index of pure WO3 shows a variation from 2.35–1.90 and for 2% Fe-doped WO3 from 2.30–2.00, as the substrate temperature increased. The contents of 3 and 4% Fe-doped WO3 presented nearly identical values of the refractive index with pure and 2% Fe-doped WO3, in error limits, at 600 °C. The optical band gap changes with substrate temperature from 3.2 eV to 2.9 eV for pure WO3 and has a small variation with the Fe.