Investigation of Efficiency-Droop Mechanisms in Multi-Quantum-Well InGaN/GaN Blue Light-Emitting Diodes

Abstract

Efficiency-droop mechanisms and related technologicalremedies are critically analyzed in multi-quantum-well (QW) InGaN/GaN blue light-emitting diodes by means of numerical device simulations and their comparison with experimental data. Auger recombination, electron leakage, and incomplete QW carrier capture can separately produce droop effects in quantitative agreement with experimental data, but “extreme” values, at the limit of or outside their generally accepted range, must be imposed for related droop-controlling parameters. Less stringent conditions are needed if combinations of the aforementioned mechanisms are assumed to act jointly. Applying technological/structural modifications like QW thickness or number increase and barrier p-type doping leads to distinctive effects on droop characteristics depending on the assumed droop mechanism. Increasing the QW number appears, in particular, to be the most effective droop remedyin case the phenomenon is induced by Auger recombination. Possible technology-dependent variation of droop-controlling parameters and/or multiple droop mechanisms can, however, makediscrimination of droop origin on the basis of the effects of applied technological remedies very difficult

On the mechanisms of InGaN electron cooler in InGaN/GaN light-emitting diodes

“…According to Figs. 3(a) and 3(b), the incoming electrons are scattered and fall into the quantum wells (i.e., process ) with τ cap being the electron capture time, and a value of 4 × 10 −12 s is used for electrons in the following simulations [18]. Those fallen electrons thereafter on one hand are trapped onto the quantum energy levels and become bound electrons.…”

Influence of electron distribution on efficiency droop for GaN-based light emitting diodes

“…The screening effect factor was 0.5. The other parameter details can be found in the previous article [29]. 2 ).…”

Correlating electroluminescence characterization and physics-based models of InGaN/GaN LEDs: Pitfalls and open issues

“…In the previous analysis, a standard DD model for carrier transport across the active region has been adopted, not including carrier flyover (ballistic transport) [13][14][15]24 or Auger-induced leakage. 17 The dependence of carrier velocity on the electric field has been approximated with a Canali-like description 93 using state-of-the-art model parameters.…”

“…99 This split-state description, separating the 3D and 2D quasi-Fermi levels in the active region, requires the definition of an appropriate recombinationlike coupling term, in turn involving a set of time constants τ QW associated with the capture/escape processes. 100,101 A recent body of work using split-state models in InGaN-based LEDs 16,24,102,103 suggests that capture time constants τ QW ≈ 10 −6 s are required in order to obtain realistic IQE values if other loss mechanisms (Auger recombination in particular) are assumed to be negligible. The need of such long τ QW has led the authors of Ref.…”

“…The need of such long τ QW has led the authors of Ref. 24 to rule out incomplete QW capture (at least, in its present formulation) as a possible droop mechanism. A similar conclusion seems appropriate also in the case of the present LED structures, since not only low capture rates have to be assumed (τ QW ≈ 10 −7 s), but also the IQE dependence on current density and temperature cannot be satisfactorily reproduced when long τ QW are used in the simulations (see Fig.…”