InGaN MQW LED structures using AlN/GaN DBR and Ag-based p-contact
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InGaN MQW LED structures using AlN/GaN DBR and Ag-based p-contact K. Lee1 , L. E. Rodak1 , V. Kumbham1 , V. Narang2 , J. S. Dudding1 , R. Rahimi1 , S. Kuchibhatla1, L. Hornak1 , and D. Korakakis1 1
Lane Department of Computer Science and Electrical Engineering, West Virginia University, Morgantown, WV 26506, USA 2 Department of Physics, West Virginia University, Morgantown, WV 26506, USA ABSTRACT Resonant cavity light emitting diode (RCLED) structure was grown using digital AlGaN/GaN Distributed Bragg Reflector (DBR) and Ag-based p-contact. A five period of InGaN/GaN multi-quantum well (MQW) layers are placed between these two high reflectance mirrors. Digital AlGaN/GaN DBR have a maximum reflectivity of about 60 % at 445 nm and 90 % at 439 nm for 6 period and 12 period, respectively. Ag-based p-contact exhibits an average reflectance of around 85-90 % for a wavelength of 400-600 nm. The light output intensity of the RCLEDs with 12 period digital AlGaN/GaN DBR is higher by a factor of 3 as compared to that of the similar structure without digital AlGaN/GaN DBR at an injection current of 50 mA. INTRODUCTION InGaN based light emitting diodes (LEDs) have drawn attraction due to their capability to emit from ultraviolet (UV) to infrared spectrum and their application in the area of signal, display, and illumination devices.1 LEDs with high external efficiency are highly in demand for their applications so that technology developments have been made accordingly. In order to improve the light external efficiency, it is essential to enhance the extraction efficiency as well as the internal efficiency in LED structures.2 A resonant cavity LED is a viable solution because the use of a resonant cavity guides the preferential propagation of generated photons into the light extraction cone. RCLED has advantages compared to conventional LEDs, such as a narrow spectral linewidth, better emission directionality, higher spontaneous emission efficiency, higher output efficiency, and enhanced light extraction efficiency.3,4,5,6 The RCLED structure requires high reflective DBRs. In the III-Nitride materials, allumium nitride (AlN) and gallium nitride (GaN) are commonly used to fabricate DBRs because of a large contrast in refractive index. However, large lattice mismatch between AlN and GaN and difference in thermal expansion coefficient significantly increase the dislocation density or introduce crack formation.7,8 In order to avoid crack formation and increase the reflectivity, a digital alloy structure of AlGaN/GaN has been used to fabricate the DBRs in this study and we have successfully fabricated crack-free DBRs with high reflectivity. Ag-based p-contact has been used as top mirror because the growth temperature for digital AlGaN/GaN DBR structure is between 980 °C and 1000 °C and this high growth temperature is expected to affect the InGaN MQWs and thus the performance of the LEDs. In this report, we have fabricated RCLED structure using digital AlGaN/GaN DBR as a bottom mirror and Agbased p-contact as top mirror and the chara
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