ABSTRACT
This paper concerns research on magnesium oxide layers in terms of their potential use as a gate material for SiC MOSFET structures. The two basic systems of MgO/SiC(0001) and MgO/graphite/SiC(0001) were deeply investigated in situ under ultrahigh vacuum (UHV). In both cases, the MgO layers were obtained by a reactive evaporation method. Graphite layers terminating the SiC(0001) surface were formed by thermal annealing in UHV. The physicochemical properties of the deposited MgO layers and the systems formed with their participation were determined using X-ray and UV photoelectron spectroscopy (XPS, UPS). The results confirmed the formation of MgO compounds. Energy level diagrams were constructed for both systems. The valence band maximum of MgO layers was embedded deeper on the graphitized surface than on the SiC(0001).
ABSTRACT
We describe a new technique for random surface texturing of a gallium nitride (GaN) light-emitting diode wafer through a mask-less dry etch process. This involves depositing a sub-monolayer film of silica nanospheres (typical diameter of 200 nm) and then subjecting the coated wafer to a dry etch process with enhanced physical bombardment. The silica spheres acting as nanotargets get sputtered and silica fragments are randomly deposited on the GaN epi-layer. Subsequently, the reactive component of the dry etch plasma etches through the exposed GaN surface. Silica fragments act as nanoparticles, locally masking the underlying GaN. The etch rate is much reduced at these sites and consequently a rough topography develops. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) inspections show that random topographic features at the scale of a few tens of nanometres are formed. Optical measurements using angle-resolved photoluminescence show that GaN light-emitting diode material thus roughened has the capability to extract more light from within the epilayers.
