Research On The Growth And Characteristics Of Inalgan Quaternary Alloys Films

In recent years, light-emitting diode(LED) associated solid lighting sources have been widely used。AlInGaN quaternary alloys have attracted considerable attention as a promising material for making ultraviolet (UV) LED。 As the energy band gap and the lattice constants of AlInGaN quaternaryalloys can be adjusted independently by changing In and Al compositions, it is possible to produce lattice-matched AlInGaN with desirable energy band gap-The main research contents of this dissertation are as follows:(1) An novel p-InAlGaN super lattice structure used in InGaN-based blue light-emitting diodes (LEDs) as electron blocking layers(EBLs) was proposed. The possibility of separate adjustment of the lattice constant and the band gap of these alloys allows the lattice-matched growth on GaN.This in turn can reduce the dislocation density and the piezoelectric field at the GaN/AlxInyGa1-x-yN interface. Therefore, the quaternary AlInGaN film is a promising candidate toward enhancing electrical/optical confinement and minimizing mismatch-induced strain simultaneously to reduce the current leakage between MQW and p-GaN.(2) A p-InAlGaN/GaN superlattice (SL) was designed and inserted into the InGaN-based blue LEDs as EBL. The electrical and optical characteristics of GaN-based LEDs with various kinds of EBLs are analyzed numerically by APSYS. These results indicate that an enhanced hole injection efficiency and a reduced electron leakage could be achieved.Moreover, it was found that the efficiency droop could be significantly improved at high injection current density for GaN-based LEDs with p-InAlGaN/GaN SL EBL, as compared with the conventional GaN-based LEDs using rectangular p-AlGaN EBL.(3) AlInGaN quaternary epitaxial layers with high Al/In mole ratio were grown on GaN/sapphire templates by Metal Organic Vapour Phase Epitaxy (MOVPE). The optical and structural properties were characterized by various kinds of technical tools. The full width at halfmaximum of the (0002) X-ray diffraction rocking curves was found to decrease as the Al/In mole ratio was increased. The density and size of V-shaped defect pits observed on the surface of AlInGaN epitaxial layers with energy-dispersive X-ray spectroscopy could be reduced by lowering the MOVPE growth pressure.It was also discovered with the variable temperature photoluminescence spectra that the emission peak energy for the AlInGaN epitaxial layers demonstrated an S-shaped shift (red shift-blue shift-red shift) behavior with increasing the measurement temperature. This feature was more significant for those AlInGaN epitaxial layers with lower Al/In mole ratio, This phenomenon can be explained by taking into account the localized excitonic states influenced by the size fluctuation and the inhomogeneous distribution of In-rich or InGaN-like clusters within the AlInGaN epitaxial layers.