# Thermoelectric terahertz photodetectors based on selenium-doped black phosphorus flakes

## TL;DR

This paper reports on Se-doped black phosphorus FETs that operate as efficient terahertz photodetectors at room temperature, achieving high mobility and responsivity comparable to state-of-the-art devices.

## Contribution

It introduces a novel Se doping method for black phosphorus FETs, enhancing their transport and optical performance for terahertz detection at room temperature.

## Key findings

- Maximum hole mobility of 1780 cm2V-1s-1 at room temperature.
- Responsivity of 3 V/W at 3.4 THz.
- Optimal flake thickness for THz detection is 30-40 nm.

## Abstract

Chemical doping of bulk black phosphorus is a well-recognized way to reduce surface oxidation and degradation. Here, we report on the fabrication of terahertz frequency detectors consisting of an antenna-coupled field-effect transistor (FET) with an active channel of Se-doped black phosphorus. Our devices show a maximum room-temperature hole mobility of 1780 cm2V-1s-1 in a SiO2-encapsulated FET. A room-temperature responsivity of 3 V/W was observed, with a noise-equivalent power of 7 nWHz-1/2 at 3.4 THz, comparable with the state-of-the-art room-temperature photodetectors operating at the same frequency. Therefore, the inclusion of Se dopants in the growth process of black phosphorus crystals enables the optimization of the transport and optical performances of FETs in the far-infrared with a high potential for the development of BP-based electro-optical devices. We also demonstrate that the flake thickness can be tuned according to the target application. Specifically, thicker flakes (>80 nm) are suitable for applications in which high mobility and high speed are essential, thinner flakes (<10 nm) are more appropriate for applications requiring high on/off ratios, while THz photodetection is optimal with flakes 30-40 nm thick, due to the larger carrier density tunability.

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Source: https://tomesphere.com/paper/1903.02955