Characteristics of InGaN-Based UV/Blue/Green/Amber/Red Light-Emitting Diodes

Abstract

Highly efficient light-emitting diodes (LEDs) emitting ultraviolet (UV), blue, green, amber and red light have been obtained through the use of InGaN active layers instead of GaN active layers. Red LEDs with an emission wavelength of 675 nm, whose emission energy was almost equal to the band-gap energy of InN, were fabricated. The dependence of the emission wavelength of the red LED on the current (blue shift) is dominated by both the band-filling effect of the localized energy states and the screening effect of the piezoelectric field. In the red LEDs, a phase separation of the InGaN layer was clearly observed in the emission spectra, in which blue and red emission peaks appeared. In terms of the temperature dependence of the LEDs, InGaN LEDs are superior to the conventional red and amber LEDs due to a large band offset between the active and cladding layers. The localized energy states caused by In composition fluctuation in the InGaN active layer contribute to the high efficiency of the InGaN-based emitting devices, in spite of the large number of threading dislocations and a large effect of the piezoelectric field. The blue and green InGaN-based LEDs had the highest external quantum efficiencies of 18% and 20% at low currents of 0.6 mA and 0.1 mA, respectively.

Identification of nnp and npp Auger recombination as significant contributor to the efficiency droop in (GaIn)N quantum wells by visualization of hot carriers in photoluminescence

“…Despite great progress in recent years, resulting in peak power conversion efficiencies of up to 81%, 1 one obstacle still to overcome is the decrease in efficiency towards high operating current densities, a phenomenon commonly known as droop. 2,3 The current dependency of the internal quantum efficiency (IQE) can be modeled in good quantitative agreement with experimental data using an ABC rate equation model [4][5][6] IQE ¼ Bn 2 An þ Bn 2 þ Cn 3 ;…”

“…Since electrons and holes in all green QWs are generated in pairs by absorption of laser photons, we can assume n g ffi p g , where n g is the electron and p g is the hole density in the green wells, respectively. The generation rates G n;uv and G p;uv of electrons (n uv ) and holes (p uv ) in the UV wells by Auger processes in the green QWs can be expressed as function of n g G n;uv ¼ a n  C nnp  n g  n g  p g ffi a n  C nnp  n g 3 (2) and…”

Improved performance of GaN based light emitting diodes with ex-situ sputtered AlN nucleation layers

“…1,2 Crystal quality is always one of the most important factors which affect quantum efficiency in GaN based light-emitting diodes (LEDs). Due to the lack of natural GaN substrates, GaN-based LED structures are made typically on the (0001) c-plane sapphire substrates.…”

Well-arranged novel InGaN hexagonal nanoplates at the tops of nitrogen-polarity GaN nanocolumn arrays

“…6,21 The PL FWHM of the nanoplate sample was evaluated to be 103 nm, which is double the electroluminescence FWHM of well developed amber (594 nm) InGaN LEDs. 22 The spatial fluctuation in the In composition of InGaN increases with increased In composition; therefore, one of the reasons for the broad PL spectrum was the compositional fluctuation of In inside each nanoplate. Energy-dispersive X-ray spectroscopy (EDX) line scan analysis provided the elemental distribution of In, Ga, and N along the radial direction of an InGaN hexagonal nanoplate, as shown in Fig.…”