Performance enhancement of armchair graphene nanoribbon resonant tunneling diode using V-shaped potential well

We study the electron transport in armchair graphene nanoribbon (AGNR) resonant tunneling diode (RTD) using square and V-shaped potential well profiles. We use non-equilibrium Green’s function formalism to analyze the transmission and I-V characteristics. Results show that an enhancement in the peak current (Ip ) can be obtained by reducing the well width (Ww ) or barrier width (Wb ). As Ww decreases, Ip shifts to a higher peak voltage (Vp ), while there is almost no change in Vp with decreasing Wb . It is gratifying to note that there is an enhancement in Ip by about 1.6 times for a V-shaped well over a square well. Furthermore, in the case of a V-shaped well, the negative differential resistance occurs in a shorter voltage range, which may beneficial for ultra-fast switching and high-frequency signal generation. Our work anticipates the suitability of graphene, having better design flexibility, to develop ideally 2D RTDs for use in ultra-dense nano-electronic circuits and systems.

Passive mode-locking and terahertz frequency comb generation in resonant-tunneling-diode oscillator

Optical frequency combs in the terahertz frequency range are long-awaited frequency standards for spectroscopy of molecules and high-speed communications. However, a terahertz frequency comb based on a compact, efficient and room-temperature-operating device remains unavailable especially in the frequency range of 0.1 to 3 THz. In this paper, we show that the resonant-tunneling-diode oscillator can be passively mode-locked by optical feedback and generate a terahertz frequency comb. The standard deviation of the spacing between the comb lines, i.e., the repetition frequency, is reduced to less than 420 mHz by applying external bias modulation. A simulation model successfully reproduces the mode-locking behavior by including the nonlinear capacitance of RTD and multiple optical feedback. Since the mode-locked RTD oscillator is a simple semiconductor device that operates at room temperature and covers the frequency range of 0.1 to 3 THz, it can be used as a frequency standard for future terahertz sensing and communications.