High Photoresponse Black Phosphorus TFTs Capping with Transparent Hexagonal Boron Nitride

Abstract

Black phosphorus (BP), a single elemental two-dimensional (2D) material with a sizable band gap, meets several critical material requirements in the development of future nanoelectronic applications. This work reports the ambipolar characteristics of few-layer BP, induced using 2D transparent hexagonal boron nitride (h-BN) capping. The 2D h-BN capping have several advantages over conventional Al₂O₃ capping in flexible and transparent 2D device applications. The h-BN capping technique was used to achieve an electron mobility in the BP devices of 73 cm²V^-1s^-1, thereby demonstrating n-type behavior. The ambipolar BP devices exhibited ultrafast photodetector behavior with a very high photoresponsivity of 1980 mA/W over the ultraviolet (UV), visible, and infrared (IR) spectral ranges. The h-BN capping process offers a feasible approach to fabricating n-type behavior BP semiconductors and high photoresponse BP photodetectors.

Keywords: black phosphorus (BP); hexagonal boron nitride (h-BN); n-type; photodetector; thin film transistors (TFTs).

Figure 1

Black phosphorous (BP) devices used in this study. (a) OM image of BP FET. Raman spectra of the BP and h-BN used in this study. Inset shows the peak corresponding to h-BN spectra. (b) h-BN-encapsulated BP FET.

Figure 2

Electrical characteristics of h-BN-capped BP FET devices and mechanisms underlying the formation of ambipolar BP. (a) Output curves obtained from h-BN-capped devices, as a function of the gate bias. The inset shows an OM image of the device. The scale bar indicates 5 µm. (b) Transfer curves obtained from the pristine and h-BN-capped BP devices. (c,d) A band diagram of the pristine BP FET under flat band and equilibrium state. (e) The equilibrium state of the band diagram for h-BN-capped devices. (f) Schematic diagram describing the n-doping function of the h-BN capping layer on the BP layer. The h-BN protected the BP from acceptor adsorbates, such as water or oxygen, present in the ambient air.

Figure 3

The application of the BP FETs in a photodetector. (a) The photoresponsivity of the BP device. (b) The photocurrent as a function of the incident illumination power, which shows a monotonic increase in the photocurrent. (c) The pulse photocurrent response dependent on the drain and gate bias up to 50 s. (d) The fast photocurrent response due to transparent h-BN capping effects on the barrier at the contact junction under bias application with light illumination.