We report on blue and green light-emitting-diodes (LEDs) grown on (11-22)-GaN templates. The templates were created
by overgrowth on structured r-plane sapphire substrates. Low defect density, 100 mm diameter GaN templates were
obtained by metal organic vapour phase epitaxy (VPE) and hydride VPE techniques. Chemical-mechanical polishing
was used to obtain smooth surfaces for the subsequent growth of LED structures. Ohmic contacts to the p-type GaN
were obtained despite the lower activated acceptor levels. The LEDs show excellent output power and fast carrier
dynamics. Freestanding LEDs have been obtained by use of laser-lift-off. The work is the result of collaboration under
the European Union funded ALIGHT project.
Confinement of light at submicron wavelengths is of great importance for highly specific sensing of bio-molecules and
for compact photonic circuits based on waveguiding. Currently this confinement can be achieved through the well
established high index contrast silicon on insulator (SOI) platform. However this material combination requires light at
wavelengths beyond 1 micron where the component cost of the InP based lasers and photodetectors are very expensive.
It is thus of great interest to develop a similar platform that could operate in the range of 850 nm where low cost lasers
(e.g. Vertical Cavity Surface Emitting Lasers as used in optical mice) and detectors (e.g., as used in camera phones) are
readily available. A possible high index material suited to this application is Gallium Phosphide which has a bandgap of
2.26 eV and refractive index of ~ 3.2 at this wavelength. For the highest index contrast, GaP should be grown on a
substrate with low index of refraction such as quartz (n=1.5) or sapphire (1.7). We report on the design and
characteristics of GaP waveguides grown on c-plane (0001) sapphire substrates using metalorganic vapour phase
epitaxy. Growth parameters such as substrate temperature and, in particular, the V:III ratio are reviewed with respect to
their effect on the nucleation, surface roughness and uniformity of the films. Modal analysis and the design of a grating
coupler at wavelengths around 850 nm have been designed for GaP on sapphire using vectorial finite element method in
order to validate the feasibility of GaP waveguides.
Thin films of wurtzite Ga1-xMnxN have been grown by pulsed laser deposition from a range of Mn-doped-ceramic targets (x = 0.005-0.10). The effect of varying the substrate temperature, background nitrogen pressure and deposition time on the Mn concentration in the deposited films has been studied. Film thickness and surface roughness were monitored during deposition by in situ optical reflectometry. X-ray diffraction measurements showed that under optimal deposition conditions, the films were single phase and epitaxial. Room temperature ferromagnetism was observed over the whole range of Mn concentration, though it was observed that the moment per Mn ion increases as the concentration is reduced.
Thin films of ZnO and GaN have been deposited by pulsed laser deposition in atmospheres of oxygen and nitrgoen respectively. A time-of-flight ion probe and optical spectroscopy were used to study the interaction of the ablation plasma with the background gas. The deposition rate was measured using in situ optical reflectivity, and the thin film quality was assessed using x-ray diffraction and photoluminescence. By correlating the plasma measurements and the thin film characterization it was possible to identify the plasma regime required for the deposition of good quality films.