Amorphous silicon Bragg reflectors fabricated by oblique angle deposition
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Amorphous silicon Bragg reflectors fabricated by oblique angle deposition S. J. Jang1*, C. I. Yeo1, and Y. T. Lee1, 2, 3 1 School of Information & Mechatronics, Gwangju Institute of Science & Technology, Gwangju, 500-712 Korea 2 Graduate Program of Photonic and Applied Physics, Gwangju Institute of Science & Technology, Gwangju, 500-712 Korea 3 Department of Nanobio Materials & Electronics, Gwangju Institute of Science & Technology, Gwangju, 500-712 Korea ABSTRACT We demonstrate the highly reflective broadband a-Si distributed Bragg reflector fabricated by oblique angle deposition. By tuning the refractive index of a-Si film, the high index contrast material system was achieved. The broadband reflective characteristics of a-Si distributed Bragg reflector were investigated by calculation and fabrication. The broad stop band (Δλ/λ=33.7%, R>99%) with only a five-pair a-Si distributed Bragg reflector was achieved experimentally at center wavelength of 650, 980, and 1550 nm. The size-, feature- and substrateindependent method for highly reflective Bragg reflectors was realized by simple oblique angle evaporation. INTRODUCTION Broadband high reflective distributed Bragg reflectors (DBRs) are essential for various applications, including telecommunications, solar cells, optical sensors, and photodetectors. The surface reflection and stop bandwidth of high reflective spectral width directly depend on the refractive index contrast between high-and low-index material, i.e., the higher the refractive index contrast contribute the higher the reflectivity with the wider stop bandwidth. Up to now, various material systems or novel techniques have been used to realize broadband high reflective mirror, however they still have their own limitations which are substrate dependency, expensive equipment, complicate and long process, low index contrast and poor thermal properties [1-4]. In this work, we report homogeneous amorphous silicon (a-Si) Bragg reflector fabricated by oblique angle deposition (OAD). The DBR structure was made of same material for both the high-and low-index layers. Because the oblique angle deposition is the one of the superior method to engineer the refractive index of materials by controlling a porosity of it, the index contrast of the a-Si Bragg reflector fabricated by oblique angle deposition was about 1.5-2.0 and this index contrast is comparable with any other material systems [1-4]. EXPERIMENT We reported that the refractive index and extinction coefficient of materials can be engineered by oblique angle of deposition [5]. The silicon especially has higher refractive index
than that of the other materials used for the OAD [6,7]. Therefore the large index contrast can be demonstrated by silicon OAD. The oblique angle deposition by e-beam evaporation was used to realize a low-index a-Si film. The refractive index of oblique angle deposited films was decreased as the oblique angle was increased. However, a tilted angle over 70˚ makes too porous to deposit next layer on the low-index layer. Because the atoms
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