Spectra and Quantum Efficiency of Light-Emitting Diodes Based on GaN Heterostructures with Quantum Wells

Spectra and quantum efficiency ηe of green LEDs based on heterostructures InGaN/AlGaN/GaN with multiple quantum wells were studied at currents J = 10—6 to 10—1 A. Minor differences in ηe (of ±10% at J ≈ 10 mA) are caused by sufficiently different distributions of effective charges in the space charge regions and the different role of tunnel component of J at low voltages. The main peak in the spectra at low J (ħωmax = 2.35 to 2.36 eV) does not depend on the voltage. At J > 0.2 mA the spectral band is shifted with J (ħωmax = 2.36 to 2.52 eV). The origin of the “standing” and “moving” bands is discussed. The model of 2D structures with band tails describes the spectral form with four fitting parameters rather well. A tunnel radiation band is revealed in the long wavelength range (1.93 to 2.03 eV) in the LEDs with a thin space charge region (w ≤ 120 nm). The dependence of ηe on J has a maximum which correlates with the fitting parameters and J(V) and NA(w) curves. Possible microscopic and macroscopic inhomogeneities in the structures are discussed.