Search

GaN thin films have been grown on Si(001) substrate with specially designed composite intermediate layers (CIL) consisting of an ultrathin amorphous silicon layer and a GaN/AlxGa1—xN multilayered buffer by low pressure metal-organic chemical vapor deposition (MOCVD). The improved film quality has been obtained from adjusting the parameters and redesigning the buffer layer structures. These were verified from different materials characterization measurements. XRD patterns showed strong and narrow (0002) and (0004) peaks of wurtzite phase GaN, and no cubic or other phase features. Room temperature photoluminescence showed strong GaN near band edge emission at 3.42 eV with almost no deep defect emission features to be detected from the improved quality films. Raman scattering and infrared spectroscopy exhibited phonon and lattice vibration modes characteristic of wurtzite GaN with no modes related to cubic or other structural phase. Scanning electron microscopy reveals the polycrystalline structure with large grain sizes near 2 μm in these films.

Undoped and Si-doped GaN films grown on sapphire were investigated by infrared reflectance spectroscopy. The carrier concentrations were determined from theoretical simulation fitting to the reststrahlen band, which are in agreement with Hall measurements. A damping behavior of the interference fringe contrast was observed, which can be well explained by the effect of an interface layer. Such interface layer was proposed to be due to the high density of defects near the GaN–substrate interface. As the doping level increases, this contrast damping is weakened, accompanying with the lowering of reflectivity in the higher frequency region. Combined with the atomic force microscopy analysis, an improvement of the interface quality, due to the Si-doping, is demonstrated.

Wear behavior of Al–Si alloys reinforced with SiC particulate has been investigated under dry and lubricated reciprocating sliding conditions using a ball-on-block wear test method. It was shown that in the dry sliding wear of the composite/steel ball system, the wear mechanism of the composite was predominantly adhesive. With further sliding motion, delamination and abrasive wear occurred as a result of fracture and debonding of the SiC particles. Under lubricated conditions, the wear rate of the composite was drastically reduced due to the presence of the lubricant, and a boundary lubrication condition existed and dominated the normal wear process. The debonding of the SiC particles from the matrix of the composite was a predominant factor in determining the wear loss of the composite in the boundary lubrication sliding process.

Laser chemical vapour deposition (LCVD) of TiN and TiC films has been achieved by scanning linear deposition in a dynamic atmosphere on AISI 52100 bearing steel using TiCl4, NH3, C2H4and H2as reactant gases induced by CO2laser. It has been found in our experiment that hydrogen played an important role in the LCVD TiN process. LCVD TiN film is golden in colour, single phase, stoichiometric in composition and homogeneously distributed. Preferential orientation of LCVD TiN film is correlated with deposition pressure. The microstructure of LCVD TiN film comprises about 2 μm equiaxial particles, each particle consisting of about 15 nm nanocrystalline grains. The average Knoop microhardness of LCVD TiN films is HK 1400 and the highest is HK 1602.3. The wear resistance of LCVD TiN film is four times that of the substrate. LCVD TiC film, with no preferential orientation, comprises homogeneous stoichiometric single-phase equiaxial particles.

The design, fabrication and characterisation results are reported of junction barrier Schottky (JBS) diodes of 1500 4;V-9 4;A and 1000 4;V-50 4;A based on 10.5 4;µm 4H-SiC blocking layers doped to 6.4×1015 4;cm−3 and 1.3×1016 4;cm−3, respectively. The clear advantages of JBS diodes over conventional Schottky diodes can be achieved without extra fabrication penalty.