The band gap energies AlxGa1-xN epilayers prepared on two different substrates were assessed using Fourier Transform Infrared (FTIR) reflectance spectroscopy, photoluminescence (PL) and scanning electron microscopy electron dispersive spectroscopy (SEM-EDS). The results were compared to various theoretical formulae to calculate the band gap, and deviations elucidated.

AlxGa1-xN epilayers, grown on c-plane oriented sapphire substrates by metal organic chemical vapour deposition (MOCVD), were evaluated using FTIR infrared reflectance spectroscopy. A peak at similar to 850 cm(-1) in the reflectance spectra, not reported before, was observed. Possible origins for this peak are considered and discussed. (C) 2016 Elsevier B.V. All rights reserved.

A study of the nucleation and crystal structure evolution at the early stages of the growth of sp(2)-BN thin films on 6H-SiC and alpha-Al2O3 substrates is presented. The growth is performed at low pressure and high temperature in a hot wall CVD reactor, using ammonia and triethylboron as precursors, and H-2 as carrier gas. From high-resolution transmission electron microscopy and X-ray thin film diffraction measurements we observe that polytype pure rhombohedral BN (r-BN) is obtained on 6H-SiC substrates. On alpha-Al2O3 an AlN buffer obtained by nitridation is needed to promote the growth of hexagonal BN (h-BN) to a thickness of around 4 nm followed by a transition to r-BN growth. In addition, when r-BN is obtained, triangular features show up in plan-view scanning electron microscopy which are not seen on thin h-BN layers. The formation of BN after already one minute of growth is confirmed by X-ray photoelectron spectroscopy. (C) 2016 The Japan Society of Applied Physics

Low-temperature photoluminescence of a nitrogen-doped 8H-SiC epilayer homoepitaxially grown by a chemical vapor deposition method is reported. The polytype and stacking sequence of the epilayers were confirmed by transmission electron microscopy analyses. The identification of emission lines is discussed in terms of the temperature dependence of the luminescence spectra. Luminescence related to the free excitons and the nitrogen-bound excitons is observed, which allows the determination of the excitonic bandgap of the 8H-SiC polytype. In addition, the low binding energies found for the nitrogen-bound excitons imply shallow levels for the nitrogen donors. (C) 2016 The Japan Society of Applied Physics

Knowledge of the structural evolution of thin films, starting by the initial stages of growth, is important to control the quality and properties of the film. The authors present a study on the initial stages of growth and the temperature influence on the structural evolution of sp(2) hybridized boron nitride (BN) thin films during chemical vapor deposition (CVD) with triethyl boron and ammonia as precursors. Nucleation of hexagonal BN (h-BN) occurs at 1200 degrees C on alpha-Al2O3 with an AlN buffer layer (AlN/alpha-Al2O3). At 1500 degrees C, h-BN grows with a layer-by-layer growth mode on AlN/alpha-Al2O3 up to similar to 4 nm after which the film structure changes to rhombohedral BN (r-BN). Then, r-BN growth proceeds with a mixed layer-by-layer and island growth mode. h-BN does not grow on 6H-SiC substrates; instead, r-BN nucleates and grows directly with a mixed layer-by-layer and island growth mode. These differences may be caused by differences in substrate surface temperature due to different thermal conductivities of the substrate materials. These results add to the understanding of the growth process of sp(2)-BN employing CVD. (C) 2015 American Vacuum Society.

The doping level of a semiconductor material can be determined using the plasma resonance frequency to obtain the carrier concentration associated with doping. This paper provides an overview of the procedure for the three most common polytypes of SiC. Results for 3C-SiC are presented and discussed. In phosphorus doped samples analysed, it is submitted that the 2nd plasma resonance cannot be detected due to high values of the free carrier damping constant gamma. (C) 2015 Elsevier B.V. All rights reserved.

Boron nitride (BN) is a promising semiconductor material, but its current exploration is hampered by difficulties in growth of single crystalline phase-pure thin films. We compare the growth of sp²-BN by chemical vapor deposition on (0001) 6H-SiC and on (0001) α-Al₂O₃ substrates with an AlN buffer layer. Polytype-pure rhombohedral BN (r-BN) with a thickness of 200 nm is observed on SiC whereas hexagonal BN (h-BN) nucleates and grows on the AlN buffer layer. For the latter case after a thickness of 4 nm, the h-BN growth is followed by r-BN growth to a total thickness of 200 nm. We find that the polytype of the sp²-BN films is determined by the ordering of Si-C or Al-N atomic pairs in the underlying crystalline structure (SiC or AlN). In the latter case the change from h-BN to r-BN is triggered by stress relaxation. This is important for the development of BN semiconductor device technology.

This work deals with two applications of the Selective Epitaxial Growth of highly p-type doped buried 4H-SiC in Vapor-Liquid-Solid configuration (SEG-VLS). The first application is the improvement of the Specific Contact Resistance (SCR) of contacts made on such p-type material. As a result of the extremely high doping level, SCR values as low as 1.3x10-6 Ω.cm2 have been demonstrated. Additionally, the high Al concentration of the SEG-VLS 4H-SiC material induces a lowering of the Al acceptor ionization energy down to 40 meV. The second application is the fabrication of PiN diodes with SEG-VLS emitter and guard-rings peripheral protection. Influence of some process parameters and crystal orientation on the forward and reverse characteristics of the PiN diodes is discussed. © (2014) Trans Tech Publications, Switzerland.

Rhombohedral boron nitride (r-BN) layers were grown on sapphire substrate in a hot-wall chemical vapor deposition reactor. Characterization of these layers is reported in details. X-ray diffraction (XRD) is used as a routine characterization tool to investigate the crystalline quality of the films and the identification of the phases is revealed using detailed pole figure measurements. Transmission electron microscopy reveals stacking of more than 40 atomic layers. Results from Fourier Transform InfraRed (FTIR) spectroscopy measurements are compared with XRD data showing that FTIR is not phase sensitive when various phases of sp(2)-BN are investigated. XRD measurements show a significant improvement of the crystalline quality when adding silicon to the gas mixture during the growth; this is further confirmed by cathodoluminescence which shows a decrease of the defects related luminescence intensity.

Epitaxial growth of rhombohedral boron nitride (r-BN) on different polytypes of silicon carbide (SiC) is demonstrated using thermally activated hot-wall chemical vapour deposition and triethyl boron and ammonia as precursors. With respect to the crystalline quality of the r-BN films, we investigate the influence of the deposition temperature, the precursor ratio (N/B) and the addition of a minute amount of silicon to the gas mixture. From X-ray diffraction and transmission electron microscopy, we find that the optimal growth temperature for epitaxial r-BN on the Si-face of the SiC substrates is 1500 degrees C at a N/B ratio of 642 and silicon needs to be present not only in the gas mixture during deposition but also on the substrate surface. Such conditions result in the growth of films with a c-axis identical to that of the bulk material and a thickness of 200 nm, which is promising for the development of BN films for electronic applications.