Effect of Graded AlxGa1-xN Interlayer Buffer on the Strain of GaN Grown on Si (111) Using MOCVD Method
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1068-C03-07
Effect of Graded AlxGa1-xN Interlayer Buffer on the Strain of GaN Grown on Si (111) Using MOCVD Method KungLiang Lin1, Edward-Yi Chang1, Tingkai Li2, Wei-Ching Huang1, Yu-Lin Hsiao1, Douglas Tweet2, Jer-shen Maa2, and Sheng-Teng Hsu2 1
Department of Materials Science and Engineering, National Chiao Tung University, 1001 University Road, Hsinchu, 300, Taiwan 2
Sharp Laboratories of America, Inc., Camas, WA, 5700
ABSTRACT GaN film grown on Si substrate with AlN/AlxGa1-xN buffer is studied by low pressure metal organic chemical vapor deposition (MOCVD) method. The AlxGa1-xN film with Al composition varying from 0~ 0.66 was used. The correlation of the Al composition in the AlxGa1-xN film with the stress of the GaN film grown was studied using high resolution X-ray diffraction including symmetrical and asymmetrical ω/2θscans and reciprocal space maps. It is found that with proper design of the Al composition in the AlxGa1-xN buffer layer, crack-free GaN films can be successfully grown on Si (111) substrates using AlN and AlxGa1-xN buffer layers. INTRODUCTION Growth of GaN on Si (111) is of particular interest to the industry because of it large area in comparison with other substrates and the possibility of integrating conventional Si-based devices with group III-nitride devices on a single wafer. Due to the considerable differences in lattice parameters and thermal expansion coefficients (CTE) between GaN and Si substrates, the growth of high quality crack-free GaN films on Si substrate poses serious difficulties. Thus, strain is an important issue of group-III-nitride growth on Si to achieve devices as GaN-based light emitting diodes and field effect transistor on Si substrates. Therefore, reduction of the stress and crack density in the GaN film was required for the growth of GaN on the Si (111) substrate. To obtain high quality GaN film on Si substrates, the design of the interlayer structure between the GaN and the Si substrate is crucial. Using a low temperature AlN (LT-AlN) interlayer contributes to a reduction in the growth stress.1-6 However, the AlN film grown at low temperature is of inferior quality to the AlN grown at high temperature, the LT-AlN layer cannot stop the edge threading dislocations and may introduce new dislocations, which influences the quality of the GaN film grown. Due to a significant lattice mismatch between AlN and Si, cracks and higher defect density were formed on the high temperature (1100ºC) grown AlN epi-layer. However, compressive stress (about 9 GPa) were generated on GaN epitaxially grown on high quality AlN due to the lattice mismatch between AlN and GaN which compensates the tensile stress caused by the CTE mismatch.7 AlxGa1-xN intermediate buffer was used to reduced the lattice mismatch between GaN and AlN to relax the tensile stress induced by the thermal mismatch between GaN an Si.8 In this letter, we report the properties of the GaN layer grown on a multilayer buffer including AlxGa1-xN interlayer with fixed Al composition (x was set at a fixed value between
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