عنوان پایان‌نامه
تحلیل و مدلسازی آشکار سازهای نوری مبتنی بر گرافن
- رشته تحصیلی
- نانوفناوری-مهندسی الکترونیک
- مقطع تحصیلی
- دکتری تخصصی PhD
- محل دفاع
- کتابخانه مرکزی پردیس 2 فنی شماره ثبت: E 2829;کتابخانه مرکزی -تالار اطلاع رسانی شماره ثبت: 71468
- تاریخ دفاع
- ۲۹ شهریور ۱۳۹۴
- دانشجو
- مهدی مرادی نسب
- استاد راهنما
- مرتضی فتحی پور
- چکیده
- ساختارهای نانویی ساخته شده از گرافن ومواد دوبعدی نوظهور افق جدیدی را درمنابع نوری و آشکارسازهای طیف نوری باز کرده اند. قابلیت تنظیم دقیق شکاف انرژی در نانو نوارها وابر شبکه های گرافنی کاربردهای نوری متعددی را فرامم می آورد. دراین پایان نامه خواص نوری چنین ساختارهایی مطالعه و بررسی شده است.
- Abstract
- Abstract Nanostructures made from graphene and two dimensional materials are promising building blocks for light sources and detectors. One dimensional graphene nanoribbons and superlattices provide precisely tunable energy gaps for optical applications. The optical properties of such nanostructures are investigated. The nearest neighbor tight-binding model is employed to describe the electronic bandstructure. An analytical solution for the dispersion relation and the wave functions are introduced in this study. Based on developed models, selection rules for optical transitions of each structure are obtained. The results are verified against first principles calculations. Single-layer hexagonal boron nitride patterned into nanoribbons exhibit large enough band gaps which make more suitable photodetectors for infrared applications from 0 to 3eV energy range. In these structures the optical transitions from subbands with odd (even) index number to odd (even) index number are allowed which exhibit more transitions in compare to conventional graphene nanoribbons and provide larger optical current which results in higher quantum efficiency and responsivity. In addition, the transition rules in hexagonal boron nitride structures are completely different from that in zigzag graphene nanoribbons. The flexibility of bandgap engineering for optical transitions provides desirable selectivity in these structures. The optical properties of such embedded graphene nanoribbons and superlattices are investigated. The optical spectrum, the quantum efficiency, and the photoresponsivity are evaluated by recalculating the tight-binding parameters regarding the first principle calculations. Photodetectors based on graphene/graphene boron-nitride superlattices exhibit high quantum efficiency in a wide frequency range. Investigating the structural parameters indicates that wider structures exhibit more peaks in optical spectrum and higher quantum efficiency at higher energies. This effect increases with increasing the well/barrier width. The role of line-edge roughness on the optical properties of such devices is carefully studied. The results indicate that the quantum efficiency and responsivity decrease at the presence of line-edge roughness. Additional peaks are appeared in photocurrent spectrum due to the induced states in hydrogen-passivated superlattice structures.
