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 mu A-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 = phi(k) + mkT . [ln(J/J(0)) + (J/J(1))(0.5)] + J . R-s. The portion of V proportional to(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. (C) 1999 American Institute of Physics. [S1063-7826(99)01404-0].