Light extraction improvement of GaN-based light-emitting diodes using patterned undoped GaN bottom reflection gratings

Abstract

The Gallium Nitride (GaN) Light-Emitting-Diode (LED) bottom refection grating simulation and results are presented. A microstructure GaN bottom grating, either conical holes or cylindrical holes, was calculated and compared with the non-grating (flat) case. A time monitor was also placed just above the top of the LED to measure both time and power output from the top of the LED. Many different scenarios were simulated by sweeping three parameters that affected the structure of the micro-structure grating: unit cell period (Α) from 1 to 6 microns, unit cell width (w) from 1 to 6 microns, and unit cell grating height (d) from 50 to 200nm. The simulation results show that the cylindrical grating case has a 98% light extraction improvement, and the conical grating case has a 109% light extraction improvement compared to the flat plate case.

Enhanced Light Extraction Efficiency from GaN Light Emitting Diodes using Photonic Crystal Grating Structures

“…We produce the optimized structure and list the results in the Table 5.1. The best cases for single gratings from each grating type were taken from our previous studies [16,31], which also compare to and agree with experimental data provided by Peking University [9] [18]. Ref.…”

“…A variety of methods, including wet etching with an amorphous sacrificial layer [6][7][8][9] or by laser etching to obtain a more periodic spacing [10][11][12][13][14], can etch a transmission grating on a semiconductor surface. In previous literature, the same patterning can also apply, with a similar effect, to an Ag reflector plate in either pillar or hole grating shapes to form a reflection grating [15][16]. Finally, if one could exchange the semiconductor for a polymer, such as polyphenylene vinylene (PPV), polyfluorene, or poly(N-vinylcarbazole) (PVK), the critical angle could be reduced, due to a polymer's lower index of refraction.…”

“…Our simulation gives a light extraction improvement of about 150% for the 120nm-depth grating and 65% for the 75nm-depth grating. Reference [16] gives a more detailed comparison of experimental data and simulation. Our simulation also shows that the single grating can achieve about 80 to 165% light extraction efficiency improvement.…”

Virtual International Research/Education Center: Energy Saving LEDs

“…2) With the virtual center, we are able to further expand our research topic from GaN LEDs [3]- [5] to OLEDs (Organic LEDs) and collaborate with both Prof. Zhang from PKU and Prof. Dong from Tsinghua University who are experts in those fields. Cal Poly EE department also has a Polymer LED teaching Lab and photonic research/teaching lab; we invited Prof. Dong to visit us to improve our Polymer lab and will send our students to work in her lab in summer 2013.…”

Enhancement of Blue Light Emission Using Surface Plasmons Coupling With Quantum Wells

“…The light emission can be strongly improved when the quantum wells (QWs) of LED is surrounded by the materials of different compositions and shapes, as it was predicted by Purcell and later corroborated experimentally [9][10][11]. Theoretical proposals along this direction have been made, and some of them consist in surrounding the QWs by different kinds of dielectrics and metals, such as photonic crystals [12][13][14][15], optical cavity [16], left-handed materials [17], mirrors [18][19][20], etc. Since 1990, surface plasmon (SP) has also received great interests when used in LED [21][22][23][24][25][26].…”