Radoslaw Wasielewski

Nanotexturing of GaN light-emitting diode material through mask-less dry etching

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.

Preparation technique of 6H-SiC(0001) wafers

We investigated 6H-SiC(0001) crystal Si face-oriented, prepared by ex situ hydrogen etching in a home made cold-wall tubular reactor. The atomic structure and topography were characterized by atomic force microscopy (AFM) and scanning tunneling microscopy (STM). Surface reconstructions were monitored by low energy electron diffraction (LEED). Chemical composition was determined using X-ray photoelectron spectroscopy under ultrahigh vacuum. Specific preparation conditions have been found for removing all scratches arising from the polishing process. We report the procedure how to achieve an atomically smooth, oxygen-free surface of SiC(0001).

Preparation of TiO 2 thin films by reactive evaporation method

Thin films of TiO2 were prepared on glass substrates by reactive evaporation of TiO. Properties of the thin films were investigated under ultrahigh vacuum conditions by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). AFM topography exhibits a uniformity structure of the thin films and shows a high quality nanocrystalline structure of TiO2 with grain size ranging from 28 nm to 35nm. The XPS Ti-2p spectra confirmed the occurrence of the 4+oxidation state of Ti and the O-1s spectra revealed the presence of an O−2 photoelectron peak. The calculated O/Ti ratio in TiO2 thin films was in the range 1.85–2.15 depending on the samples. Additional analysis of the thin films was carried out by X-ray powder diffraction (XRD).