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III-nitride semiconductors are the leading material for use in solid state lighting (SSL), with highly efficient blue and white nitride-based light emitting diodes (LEDs) commercially available. However challenges still remain to improve their efficiency. The work in this thesis focuses on the optical and compositional characterisation of InGaN and InAlN alloys, which are widely used as active regions in such light emitters. Composition and luminescence properties of InGaN epilayers with varying growth temperature and hydrogen flow rates are investigated. The measurements revealed that the samples grown with small amounts of hydrogen improved in surface quality, compositional and luminescence homogeneity when compared with samples grown at equivalent temperature. The additional hydrogen did reduce the InN fraction slightly. Investigations of the optical, compositional and structural properties of Ga auto-incorporated InAl(Ga)N epilayers are made. Composition measurements revealed 1 2-28 % of Ga incorporated. The growth parameters and resultant Ga indicated the likely cause is residual Ga coming from the reactor walls and delivery pipes, as by increasing the total flow rate from 8000 sccm to 24000 sccm was seen to suppress the GaN from 28 to 12 %. A broad spectral emission peak was seen, whose energy varied with InN content and not GaN. A large set of InAlN epilayers grown on AlN buffers are studied. Composition measurements revealed a wide range of InN contents from 0.1 % to 25.6 %. The analysis revealed no presence of Ga within the samples. Optical measurements produced broad InAlN luminescence spectra which varied with InN content. The peak energy was found to be 3.46-3.93 eV for InN compositions of 0.7-6.6 %. Analysis suggests this is not bandedge emission due to the low peak energy and very wide FWHMs. Finally, a home built PL mapping system is demonstrated, along with the design and operation challenges. Utilising this mapping system, investigations of InGa N/GaN MQW LED samples grown under different barrier growth methods are made. |
