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

In_xGa_1-xN quantum well (QW) structures having high InN mole fractions, x, of both hexagonal and cubic phases were investigated to verify the importance of localized QW excitons in their spontaneous emission mechanisms. The internal piezoelectric field (F_PZ) across the QWs in the hexagonal phase naturally 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 lifetime 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 energy 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.