Optimization of Current Injection in AlGaInP Core-Shell Nanowire Light-Emitting Diodes
Pyry Kivisaari1, Alexander Berg1, Mohammad Karimi1,2
1Solid State Physics and NanoLund, Lund University , P.O. Box 118, SE-221 00 Lund, Sweden.
Nano Letters
|May 24, 2017
Summary
Small core-shell nanowire dimensions, crucial for efficient light extraction in LEDs, unexpectedly cause significant current losses. This study identifies hole leakage as the main cause and proposes structural modifications to boost nanowire LED efficiency.
Area of Science:
- Materials Science
- Optoelectronics
- Nanotechnology
Background:
- Core-shell nanowires (NWs) show promise for enhancing light-emitting diode (LED) efficiency and expanding wavelength coverage.
- Optimizing NW diameter to half the emission wavelength (λ/2) improves light extraction and emission, but AlGaInP NW LEDs lag behind planar technologies in efficiency.
- The specific parameters limiting AlGaInP NW LED efficiency remain largely unidentified.
Purpose of the Study:
- To investigate the efficiency limitations in core-shell AlGaInP nanowire LEDs, particularly those with diameters around λ/2.
- To identify the underlying causes of low efficiency, focusing on loss currents and contact resistance.
- To propose structural modifications for enhancing the efficiency of NW LEDs.
Main Methods:
- Fabrication of AlGaInP core-shell nanowire LEDs with diameters near λ/2.
- Experimental characterization including loss current and contact resistance measurements.
- 3D device simulations to analyze current leakage mechanisms and validate proposed structural changes.
- Development of an optical output measurement technique to estimate the ideality factor.
Main Results:
- Fabricated NW LEDs exhibited significant loss currents and high contact resistance.
- Device simulations revealed substantial hole leakage to the outer barrier layer as the primary cause of low efficiency in radial NW LEDs.
- Proposed modifications to the epitaxial structure are predicted to eliminate leakage currents and achieve near-unity efficiency.
- The new optical measurement technique accurately estimated ideality factors (1-2) even with large voltage losses, proving useful for early-stage device development.
Conclusions:
- Small nanowire dimensions, while beneficial for optical properties, introduce significant electrical loss currents, primarily due to hole leakage.
- Structural optimization of the epitaxial layer is crucial for overcoming these limitations and achieving high-efficiency NW LEDs.
- The developed characterization technique offers a valuable tool for optimizing both electrical and optical performance in NW LEDs, facilitating advancements in light emitter technology.
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