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 ( J max =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 =ϕ k + mkT · [1n( J/J 0 )+( J/J 1 ) 0.5 ] + J · R s . The portion of V ∞( J/J 1 ) 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.