The impact of gross well width fluctuations on the efficiency of GaN-based light emitting diodes

Abstract

Photoluminescence and electroluminescence measurements on InGaN/GaN quantum well (QW) structures and light emitting diodes suggest that QWs with gross fluctuations in width (formed when, during growth, the InGaN is exposed unprotected to high temperatures) give higher room temperature quantum efficiencies than continuous QWs. The efficiency does not depend on the growth temperature of the GaN barriers. Temperature-dependent electroluminescence measurements suggest that the higher efficiency results from higher activation energies for defect-related non-radiative recombination in QW samples with gaps. At high currents the maximum quantum efficiency is similar for all samples, indicating the droop term is not dependent on QW morphology.

Effects of quantum well growth temperature on the recombination efficiency of InGaN/GaN multiple quantum wells that emit in the green and blue spectral regions

“…Thomas Swan close-coupled showerhead reactor on GaN pseudo-substrates which consisted of about 4 lm of GaN on (0001) sapphire substrates. 23 The dislocation density for all the pseudo-substrates is ca. 4 Â 10 8 cm À2 .…”

“…In order to ensure that the three blue and the three green MQW samples grown at the different temperatures had a constant peak emission wavelength, the TMI flux for the InGaN growth was varied (see Table I), while the TMG flux remained constant at 4.4 lmol/min, to compensate for the changes in indium incorporation rate. The GaN barriers were grown at a more optimal (higher) temperature using a two-temperature growth method, 23 which leads to gross well-width fluctuations (GWWFs). To characterize the thickness and composition of the QW stacks, X-ray diffraction (XRD) was employed, by performing an x-2h scan along the symmetric (002) reflection.…”

Room temperature PL efficiency of InGaN/GaN quantum well structures with prelayers as a function of number of quantum wells

“…On top of the prelayer was then grown a 3 nm layer of unintentionally (< 10 17 cm -3 ) doped GaN followed by the InGaN QW(s) and GaN barrier(s). The QWs and barriers had nominal thicknesses of 2.3 nm and 7 nm, respectively, and were grown using the twotemperature (2T) growth method [14]. X-ray diffraction (XRD) measurements performed on each sample found all of the QWs and barriers in all of the structures to have thicknesses of 2.3 ± 0.1 nm and 7.0 ± 0.1 nm, respectively.…”

Effect of the barrier growth mode on the luminescence and conductivity micron scale uniformity of InGaN light emitting diodes

“…A set of four otherwise identical samples was grown with the 1 T, 2 T, Q2T, and T-B methods. The full growth details of the samples are described by Oliver et al 10 These were mapped by CL hyperspectral imaging using an electron beam acceleration voltage of 9 kV and beam current of 10 nA. A subsequent pair of devices grown with the Q2T and the 2 T methods was studied by EL mapping and simultaneous CL and EBIC imaging to investigate both the luminescence and the conductivity variations on a micron scale.…”

“…In this work, a fourth method was used where the temperature is ramped to around 800 C after growth of the QWs before bringing it back down to grow the barriers at the low temperature. We refer to this as T-bounce (T-B), 10 and use it to investigate the importance of annealing the InGaN layer and of the barrier quality on the LED performance.…”