Luminescence and electrical properties of InGaN/AlGaN/GaN light emitting diodes with multiple quantum wells

Luminescence spectra of light-emitting diodes based on InGaN/AlGaN/GaN heterostructures with multiple quantum wells are studied for currents in the range J=0.15 µA-150 mA. The comparatively high quantum efficiency for low J(Jmax=0.5–1 mA) is a consequence of a low probability for the nonradiative tunnel current. The current-voltage characteristics J(V) are studied for J=10−12–10−1 A; they are approximated by the function V=ϕk+mkT· [1n(J/J0)+(J/J1)0.5] + J · Rs. The portion of V∞(J/J1)0.5 and measurements of the dynamic capacitance indicate that i-layers adjacent to the active layer play an important role. The spectra are described by a model with a two-dimensional density of states with exponential tails in multiple quantum wells. The rise in T with increasing J is determined from the short-wavelength decay of the spectrum of the blue diodes: T=360–370 K for J=80–100 mA. An emission band is observed at 2.7–2.8 eV from green diodes at high J; this band may be explained by phase separation with different amounts of In in the InGaN.