Exploring transport mechanisms in atomic precision advanced manufacturing enabled pn junctions

TL;DR

This paper investigates transport mechanisms in atomic precision pn junctions across temperatures, revealing band-gap narrowing effects and the interplay of tunneling processes, with implications for device behavior at cryogenic and room temperatures.

Contribution

It provides a detailed analysis of transport phenomena in APAM pn junctions, identifying band quantization, band-gap narrowing, and trap-assisted tunneling as key factors affecting device behavior.

Findings

Band-to-band tunneling parameters can approximate low-bias current shapes.

Band-gap narrowing explains lower-than-expected valley voltages.

Trap-assisted tunneling may dominate at room temperature.

Abstract

We investigate the different transport mechanisms that can occur in pn junction devices made using atomic precision advanced manufacturing (APAM) at temperatures ranging from cryogenic to room temperature. We first elucidate the potential cause of the anomalous behavior observed in the forward-bias response of these devices in recent cryogenic temperature measurements, which deviates from the theoretical response of a silicon Esaki diode. These anomalous behaviors include current suppression at low voltages in the forward-bias response and a much lower valley voltage at cryogenic temperatures than theoretically expected for a silicon diode. To investigate the potential causes of these anomalies, we studied the effects of a few possible transport mechanisms, including band-to-band tunneling, band gap narrowing, potential impact of non-Ohmic contacts, band quantization, impact of leakage, and inelastic trap-assisted tunneling, through semi-classical simulations. We find that a combination of two sets of band-to-band tunneling (BTBT) parameters can qualitatively approximate the shape of the tunneling current at low bias. This can arise from band quantization and realignment due to the strong potential confinement in $\delta$-layers. We also find that the lower-than-theoretically-expected valley voltage can be attributed to modifications in the electronic band structure within the $\delta$-layer regions, leading to a significant band-gap narrowing induced by the high density of dopants. Finally, we extend our analyses to room temperature operation and predict that trap-assisted tunneling (TAT) facilitated by phonon interactions may become significant, leading to a complex superposition of BTBT and TAT transport mechanisms in the electrical measurements.