Spectra of superbright blue and green InGaN/AlGaN/GaN light-emitting diodes

Electroluminescence spectra of blue and green light-emitting diodes (LEDs) based on InxGa1-xN/ AlyGa1-yN/GaN heterostructures with a thin quantum well active layers were studied at currents J = 0.01-20 mA. Spectral maxima of blue LEDs are (h) over bar omega(max) = 2.58-2.75 eV, of green are (h) over bar omega(max) = 2.3-2.45 eV, depending on the In content in the active layer. The low and high energy tails of the spectra are exponential with the parameters E-0 = 42-50 meV and E-1 approximate to 1-1.3 kT, respectively. The spectra can be described taking into account quantum-size effects, impurities and fluctuations in active layers. An interference structure in spectra was detected. Light intensity depended on J linearly in the interval 1-20 mA. Efficiency of blue LEDs dropped at J <0.7 mA as I similar to J(4-5) (300 K). The green LEDs had no such dependence. Tunnel radiation spectra with maxima moving with the voltage were detected at low J. (C) 1997 Elsevier Science Limited.