Role of Phonon Scattering on the Transport and Performance of an N-Channel Monolayer Black Phosphorus Transistor

Abstract

We investigate the influence of phonon scattering on the transport properties and performance metrics of a monolayer n-channel black phosphorus transistor within a four-band tight binding Hamiltonian, employing a recursive Green's function algorithm and Buttiker probe scattering model. Our analysis reveals that electron-phonon scattering significantly degrades the on-state current, while its effects in the subthreshold region are found to be negligible. Further examination identifies optical phonons as the primary contributors to the degradation of on-state current, with acoustic phonons playing a less prominent role. The ballisticity of the device declines from 42% to 24% when transitioning from solely acoustic phonon scattering to the combined influence of acoustic and optical phonons. Expanding the placement of Buttiker probes from beneath the gate region to cover the entire path from source to drain results in a further 48% reduction in on-state current. The on-state current exhibits a parabolic relationship with the inverse Kelvin temperature. To quantify the effects of phonon scattering on device performance, we assess the key parameters, transconductance and unity current gain frequency. Phonon scattering is observed to severely impact both the parameters. The on-state transconductance declines from its ballistic value of 24.9 mS/µm to 3.99 mS/µm when both acoustic and optical phonons are concurrently active. Similarly, the unity current gain frequency decreases from 1.18 to 0.2 THz due to phonon scattering. Additionally, our analysis reveals that approximately 7–9% of the total power dissipated within the device is attributed to phonon scattering effects, while the remainder is released through thermalization in the device's contacts. Phonon scattering is shown to induce both lattice cooling and heating, depending on the presence or absence of potential barriers. When a potential barrier exists in the channel, electrons injected from the source experience lattice cooling before the barrier region and lattice heating after crossing the barrier. Including the source and drain contact resistances in our model unveils that achieving a contact resistance value of approximately 100 Ω-µm is crucial for the effective functioning of black phosphorus devices.