NUSOD 2006 Optical Performance of InGaN/AlGaN Double Heterostucture Light Emitting Diodes S. M. Thahab, H. Abu Hassan, Z. Hassan Nano-Optoelectronics Research and Technology Laboratory School of Physics, Universiti Sains Malaysia, 11800 Penang, Malaysia E-mail address: sabahmr@yahoo.com, haslan@usm.my, zai@usm.my Abstract- A simulation study of the output power characteristics of In0.13Ga0.87N/Al0.1Ga0.9N double heterostucture light emitting diodes (DH LEDs) at room temperature was performed using ISETCAD software. We have selected Ino.13Gao.87N as the active layer with thickness of 40nm sandwiched between 30 nm n-type Alo.1 Gao.9 N and 60nm p-type Al0.15 Gao.85N cladding layers. The output power with value of 0.2 mW was obtained at forward current of 60 mA and with peak emission wavelength at 426 nm. We investigated the effect of doping concentration on the output power and peak emission wavelength. No change in the output power was observed for light doping. We also investigated the effect of varying the thickness of the active layer on the output power. Index Terms-InGaN, light emitting diode, AlGaN I. INTRODUCTION GaN and related materials such as AlGaInN are Ill-V nitride semiconductors with the wurtzite crystal structure and a direct energy band structure which is suitable for light emitting devices. Major developments in wide-gap Ill-V nitride semiconductors have recently led to the commercial production of high-brightness blue/green light emitting diodes (LEDs) and to the demonstration of room temperature (RT) violet laser light emission in InGaN/GaN/AlGaN-based heterostructures under pulsed and continuous-wave (CW) operations [1]. Heterostructure is a structure where two different semicon- ductors (that have the same structure) are brought in a junction (a so-called heterojunction). Thus, double heterostucture (DH) is when three semiconductors are brought together to from two herterojunctions. High brightness blue InGaN /AlGaN DH LEDs with a luminous intensity of 2 cd was commercialized in 1993 for the first time [2], the active layer was InGaN co- doped with Si and Zn to enhance the blue emission. The need for Co-doping suggests that the high efficiency of this InGaN/AlGaN DH LED is the result of impurity assisted recombination, such as donor - acceptor pair recombination. We simulated Ino 13Ga0 87N /Al0 1Ga0 9N DH LED [3] by using Integrated Systems Engineering software (ISE TCAD). Output power of 0.2 mW and peak emission wavelength of 426 nm were obtained using In0 13 Ga0 87N active layer. We also tested the effect of active layer thickness and doping concentration on the output power, wavelength and forward current. II. InGaN/AlGaN DH LED STRUCTURE AND PARAMERETRS USED IN NUMERICAL SIMULATION A schematic diagram of In0 13Ga0O87N /Al0 1Ga0 9N DH LED under study is shown in Fig. 1. The band gap energy (Eg) of the In,Gal-N and Al,Gaj- N is governed by (1) and (2) respectively at room temperature (300 K) [4, 5]. Eg (In§Gal-N) =XEJnN + (1 -X)EGaN -bx(1 -x), Eg (Al,Gal- N) = xEA/N + (1- X)EGaN -bx(1- x), (1) (2) Where EIfN EA1N and EGaN are band gap energy of InN, AlN and GaN respectively, with corresponding values of 0.77 eV, 6.28 eV and 3.42 eV, b is the bowing parameter of In,Gal-N and Al,Gal -N and has value of 1.4 eV and 1.3 eV respectively. Our simulation was conducted by choosing the following models; carrier concentration, mobility with high field satu- ration, effective intrinsic density (with no band gap narrowing), Fermi model, recombination (Shockley Read Hall) and quantum transport equation. The doping levels are 5*1018 cm-3 for p-type and 1*1018 cm-3 for n-type. All other parameters like hole electron mobility, nonradiative lifetime, and refractive index for all materials used were involved in the simulation parameters. p-electrode 120nm p-GaN 60nm p-Al0.15 Ga0.85 N 40nm In0.13 Ga0.87N 30nm n-Al1o. Ga0.gN 4,um n-GaN 30nm GaN Buffer layer Sapphire substrate n-electrode Fig. 1. The In0.13Ga0.87N /Al0.Ga0 9N double heterostructure light emitting diode (DH LED) 0-7803-9755-X/06/$20.00 ©2006 IEEE 1 3