Effective localization of quantum well excitons in InGaN quantum well structures with high InN mole fraction

InxGa1-xN quantum well (QW) structures having high InN mole fractions, x, o f both hexagonal and cubic phases were investigated to verify the importanc e of localized QW excitons in their spontaneous emission mechanisms. The in ternal piezoelectric field (F-PZ) across the QWs in the hexagonal phase nat urally increases with increasing x since the in-plain strain increases. The field was confirmed to point from the surface to the substrate. Absorption spectra of both hexagonal and cubic InGaN QWs exhibited a broad band-tail regardless of the presence of F-PZ normal to the QW plane. The emission lif etime of the InGaN single-quantum-well amber light emitting diode increased with increasing detection wavelength. Its electroluminescence (EL) did not show a remarkable energy shift between 20 and 300 K, and the higher energy portion of the spectra increased more rapidly than that of the lower energ y one. This may reflect thermal distribution of the Fermi level within the tail states. Since the well thickness is only 2.5 nm, the device exhibited a reasonably efficient emission in spite of the presence of F-PZ and large number of threading dislocations.