Effect of Undoped GaN Layer Thickness on The Wavelength Uniformity of GaN Based Blue LEDs
LI Tian-bao;ZHAO Guang-zhou;LU Tai-ping;ZHU Ya-dan;ZHOU Xiao-run;DONG Hai-liang;SHANG Lin;JIA Wei;YU Chun-yan;XU Bing-she;Key Laboratory of Interface Science and Engineering in Advanced Materials,Ministry of Education,Taiyuan University of Technology;Research Center of Advanced Materials Science and Technology,Taiyuan University of Technology;Shanxi Fei Hong Micro-Nano Photoelectron Science and Technology Co.Ltd.;
InGaN based blue light emitting diodes( LED) with different thickness of undoped GaN( u-GaN) layer were grown on c-plane pattern sapphire substrates by metal-organic chemical vapor deposition( MOCVD). The structure and photoelectric properties were characterized by in-situ wafer bowing measurements,high-resolution X-ray diffraction( HRXRD) and photoluminescence( PL).Due to the different thermal expansion coefficients between the sapphire and the epitaxial film,the curvature of wafer varies constantly in the progress of temperature changing. It is found that the wafer presents concave bowing at the end of n-GaN growth directly affects the wafer status of bowing during the MQWs growth. The wafer with 3. 63 μm u-GaN layer is under the biggest bowing status indicating that the stress value of n-GaN is the maximum. In the subsequent lower temperatureMQWs deposition stage,the concave deformation constantly decreases,and even transforms into the convex deformation. The in-situ wafer bowing measurements results are in accordance with the PLmapping tests. The wafer with better uniformity and consistency can be obtained by adjusting the thickness of u-GaN layer which can change the status of stress in the epitaxial structures,and finally be beneficial to reduce the processing time and the cost of the LED chips.