Improvement in the Light Extraction of Blue InGaN/GaN-Based LEDs Using Patterned Metal Contacts

We demonstrate a method to improve the light extraction from an LED using photonic crystal (PhC)-like structures in metal contacts. A patterned metal contact with an array of Silicon Oxide (SiOx) pillars (440 nm in size) on an InGaN/GaN-based MQW LED has shown to increase output illumination uniformity through experimental characterization. Structural methods of improving light extraction using transparent contacts or dielectric photonic crystals typically require a tradeoff between improving light extraction and optimal electrical characteristics. The method presented here provides an alternate solution to provide a 15% directional improvement (surface normal) in the radiation profile and ~ 30% increase in the respective intensity profile without affecting the electrical characteristics of the device. Electron beam patterning of hydrogen silesquioxane (HSQ), a novel electron beam resist is used in patterning these metal contacts. After patterning, thermal curing of the patterned resist is done to form SiOx pillars. These SiOx pillars aid as a mask for transferring the pattern to the p-metal contact. Electrical and optical characterization results of LEDs fabricated with and without patterned contacts are presented. We present the radiation and intensity profiles of the planar and patterned devices extracted using Matlab-based image analysis technique from 200 μm (diameter) circular unpackaged LEDs.

[1]  L. Hornak,et al.  Accelerated Publication: Direct fabrication of two-dimensional photonic crystal structures in silicon using positive and negative Hydrogen Silsesquioxane (HSQ) patterns , 2012 .

[2]  S. Denbaars,et al.  High efficiency LEDs by photonic crystal-assisted extraction , 2006, 2006 IEEE Nanotechnology Materials and Devices Conference.

[3]  Yik-Khoon Ee,et al.  Light Extraction Efficiency and Radiation Patterns of III-Nitride Light-Emitting Diodes With Colloidal Microlens Arrays With Various Aspect Ratios , 2011, IEEE Photonics Journal.

[4]  Dennis W. Prather,et al.  Photonic Crystals: Theory, Applications and Fabrication , 2009 .

[5]  Yong-Hee Lee,et al.  Enhancement of light extraction from two-dimensional photonic crystal slab structures , 2002 .

[6]  L. E. Rodak,et al.  Aluminum Gallium Nitride Alloys Grown via Metalorganic Vapor-Phase Epitaxy Using a Digital Growth Technique , 2011 .

[7]  Khan Mohammad Moniruzzaman Development of a single-step fabrication process for nanoimprint stamps , 2011 .

[8]  Seon-Ho Jang,et al.  High-performance and current crowding-free InGaN-GaN-based LEDs integrated by an electrically-reverse-connected Schottky diode and a Mg-delta doped p-GaN , 2012 .

[9]  A. I. Zhmakin Enhancement of light extraction from light emitting diodes , 2011 .

[10]  E. F. Schubert,et al.  Light‐Extraction Enhancement of GaInN Light‐Emitting Diodes by Graded‐Refractive‐Index Indium Tin Oxide Anti‐Reflection Contact , 2008 .

[11]  Meng-Chyi Wu,et al.  Enhanced Light Extraction Efficiency of GaN-Based LEDs With 3-D Colloidal-Photonic-Crystal Bottom Reflector , 2012, IEEE Photonics Technology Letters.

[12]  Hongxing Jiang,et al.  Effects of plasma treatment on the Ohmic characteristics of Ti∕Al∕Ti∕Au contacts to n-AlGaN , 2006 .

[13]  J. Ha,et al.  Reduction of leakage current in InGaN-based LEDs with V-pit embedded structures , 2012 .

[14]  Joonmo Park,et al.  Improved Light Output of Photonic Crystal Light-Emitting Diode Fabricated by Anodized Aluminum Oxide Nano-Patterns , 2008, IEEE Photonics Technology Letters.

[15]  L. E. Rodak,et al.  Surfactant effects of indium on cracking in AlN/GaN distributed Bragg reflectors grown via metal organic vapor phase epitaxy , 2011 .

[16]  John Peck,et al.  Solid state led lighting technology for hazardous environments; lowering total cost of ownership while improving safety, quality of light and reliability , 2011, Petroleum and Chemical Industry Conference Europe Electrical and Instrumentation Applications.

[17]  Kurt Busch,et al.  Diffraction properties of two-dimensional photonic crystals , 2003 .

[18]  Xu Zhou,et al.  Influence of Dry Etching Damage on the Internal Quantum Efficiency of Nanorod InGaN/GaN Multiple Quantum Wells , 2012 .

[19]  Yik-Khoon Ee,et al.  Light Extraction Efficiency Enhancement of III-Nitride Light-Emitting Diodes by Using 2-D Close-Packed ${\hbox{TiO}}_{2}$ Microsphere Arrays , 2013, Journal of Display Technology.

[20]  R. Dupuis,et al.  History, Development, and Applications of High-Brightness Visible Light-Emitting Diodes , 2008, Journal of Lightwave Technology.

[21]  S. An Transparent conducting ZnO nanorods for nanoelectrodes as a reverse tunnel junction of GaN light emitting diode applications , 2012 .

[22]  Comparison of various surface textured layer in InGaN LEDs for high light extraction efficiency. , 2011, Optics express.

[23]  Hadis Morkoç,et al.  InGaN based light emitting diodes utilizing Ga doped ZnO as a highly transparent contact to p-GaN , 2011 .

[24]  S. Nakamura,et al.  Thermal Annealing Effects on P-Type Mg-Doped GaN Films , 1992 .

[25]  James S. Speck,et al.  Directional emission control and increased light extraction in GaN photonic crystal light emitting diodes , 2008 .

[26]  Yiping Zeng,et al.  Improvement of the performance of GaN-based LEDs grown on sapphire substrates patterned by wet and ICP etching , 2008 .

[27]  F. Lai,et al.  Enhancement in the extraction efficiency and resisting electrostatic discharge ability of GaN-based light emitting diode by naturally grown textured surface , 2011 .

[28]  Steven G. Johnson,et al.  Photonic Crystals: Molding the Flow of Light , 1995 .

[29]  Jung-Hee Lee,et al.  Stress Reduction and Enhanced Extraction Efficiency of GaN-Based LED Grown on Cone-Shape-Patterned Sapphire , 2008, IEEE Photonics Technology Letters.

[30]  C. Eddy,et al.  Gallium nitride light emitter on a patterned sapphire substrate for improved defectivity and light extraction efficiency , 2011 .

[31]  Hussain Shareef,et al.  LEDs as energy efficient lighting systems: A detail review , 2011, 2011 IEEE Student Conference on Research and Development.

[32]  J. Yu,et al.  Characteristics and simulation analysis of GaN‐based vertical light emitting diodes via wafer‐level additional surface roughening process , 2012 .

[33]  Yongzhong Wu,et al.  Growth of single-crystalline rutileTiO2 nanorod arrays on GaN light-emitting diodes with enhanced light extraction , 2012 .

[34]  A. Fiore,et al.  Enhanced spontaneous emission in a photonic-crystal light-emitting diode , 2008, 0805.2750.

[35]  Double embedded photonic crystals for extraction of guided light in light-emitting diodes , 2012 .

[36]  Q. Zhan,et al.  Diffraction inhibition in two-dimensional photonic crystals. , 2011, Optics letters.

[37]  Tae Geun Kim,et al.  High Efficiency GaN Light-Emitting Diodes With Two Dimensional Photonic Crystal Structures of Deep-Hole Square Lattices , 2010, IEEE Journal of Quantum Electronics.

[38]  N. Bochkareva,et al.  Nonuniformity of carrier injection and the degradation of blue LEDs , 2006 .