Defect investigation in In(Ga,Al)N-related alloy by SPM methodology

Nitride based alloys such as InGaN, AlInN, AlN, InN alloys and their heterostructures have attracted a lot of attention for different applications as photovoltaic solar cells, high mobility transistors (HEMT) and light emitting devices. The strong polarization fields and good free carrier confinement at the interface, the flexibility in tuning the energy gap form the basis of achieving high quality device properties in HEMTs, LEDs, LASERs, etc. The achievement of this target is hindered by the difficulty in growing high quality epitaxial layer, due to high lattice mismatch and high thermal expansion coefficients indifferences between InN and GaN or AlN. As a result, these epilayers are highly strained and are prone to relaxation by elastic or non-elastic process, leading to the formation of structural defects. Here we will investigate the electronic and optical properties of structural defects such as threading dislocations, trenches and slip planes in indium-rich InGaN and AlInN epilayers. The electronic properties have been investigated by various Scanning probe microscopy such as Scanning Capacitance Microscopy (SCM), Kelvin Probe Force Microscopy (KPFM) and Conductive Atomic Force Microscopy (CAFM). These defects have been found to be related with leakage current paths, carrier localization and change in surface potential. The effect of these structural defects on optical properties has been investigated by Cathodo-Luminescence (CL), while their recombination strength has been studied by Electron Beam Induced Current (EBIC) measurements. The presence of a high density of threading dislocations has a detrimental effect on the emission in indium-rich InGaN. The present results on the optical and electronic properties of threading dislocations are correlated to the emission efficiency of these heterostructures investigated by photoluminescence (PL). Apart from the electronic and optical properties, their impact on the electrical devices has also been investigate