| About this Abstract |
| Meeting |
2011 Electronic Materials Conference
|
| Symposium
|
2011 Electronic Materials Conference
|
| Presentation Title |
M3, Effect of InxAl1-xN Electron Blocking Layer on Quantum Efficiency in Visible Light-Emitting Diodes Grown by Metalorganic Chemical Vapor Deposition |
| Author(s) |
Suk Choi, Mi-Hee Ji, Jeomoh Kim, Hee Jin Kim, Jae-Hyun Ryou, P. Douglas Yoder, Russell Dupuis, Kewei Sun, Alec M. Fischer, Fernando A. Ponce |
| On-Site Speaker (Planned) |
Suk Choi |
| Abstract Scope |
In this study, we have investigated the effect of In<sub>x</sub>Al<sub>1-x</sub>N layers nearly lattice-matched to GaN as active-layer-friendly electron-blocking layers (EBLs) on the quantum efficiency and efficiency droop at high current densities in visible III-nitride-based light-emitting diodes (LEDs). The lower growth temperature, larger conduction-band offset, and flexibility in lattice-matching and strain engineering offered by InAlN EBLs are expected to enhance the quantum efficiency of visible blue and green LEDs, compared to conventional AlGaN EBLs, by reducing the thermal budget during the EBL growth, and providing a larger electron confinement effect. However, the wide bandgap of InAlN may act as a large hole blocking barrier in the valence band, resulting in reduced hole injection efficiency. A thinner EBL can reduce the hole barrier height, but this also will lower the electron blocking efficiency. The strain-engineered InAlN EBL with higher indium (In) composition is another technique for enhancing hole injection. Higher In composition will reduce the bandgap of InAlN, thus decreasing height of both electron blocking barrier and hole blocking barrier. However, the compressive strain of the layer will induce piezoelectric field and reduce band bending of InAlN EBL inserted between the <i>p</i>-layer and InGaN/GaN the active region. This helps to maintain the effective height of the electron barrier maintaining under forward bias conditions. The band structure calculation at the zero bias indicates that the height of electron barrier at the multi-quantum-well (MQW) side remains almost unchanged while that of hole barrier at the p-type layer side is greatly reduced with increased In composition and layer strain. Therefore, the effect of various EBL structures on the luminescence performance of LED should be closely examined. All epitaxial layer structures were grown by low-pressure metalorganic chemical deposition on <i>c</i>-plane sapphire substrates. InAlN EBLs with different thicknesses from 5 nm to 20 nm, with different In composition from 19% to 27%, and conventional Al<sub>0.2</sub>Ga<sub>0.8</sub>N are inserted between the GaN:Mg <i>p</i>-type layer and the InGaN/GaN MQW active region of a blue LED structure. Electroluminescence (EL) measurements of LEDs were performed using pulse-mode currents with a duty cycle of 10% up to 360 A/cm<sup>2</sup>. In the quantum efficiency comparison, LEDs with a 20 nm In<sub>0.19</sub>Al<sub>0.81</sub>N EBL show only an 18% efficiency droop in contrast to the LEDs with an Al<sub>0.2</sub>Ga<sub>0.8</sub>N EBL which show a droop of ~32%. LEDs without an EBL which suffer from a high efficiency droop of over 50%. These results indicate that the In<sub>0.19</sub>Al<sub>0.81</sub>N EBL is confining electrons within the active region more effectively than an Al<sub>0.2</sub>Ga<sub>0.8</sub>N EBL. A detailed comparison and analysis of the EL intensity and quantum efficiency of LEDs including InAlN EBLs with different thickness will be also reported. |
| Proceedings Inclusion? |
Undecided |