Enhanced stability and performance of few-layer black phosphorus transistors by electron beam irradiation

Few layer black phosphorus (BP) has recently emerged as a potential graphene analogue due to its high mobility and direct, appreciable, band gap. The fabrication and characterization of field effect transistors (FETs) involves exposure of the channel material to an electron beam (e-beam) in imaging techniques such as transmission electron microscopy (TEM) and scanning electron microscopy (SEM), and fabrication techniques like electron beam lithography (EBL). Despite this, the effect of e-beam irradiation on BP-FET performance has not been studied experimentally. In this work, we report the first experimental study on the impact of e-beam irradiation on BP-FETs. An electron beam is known to induce defects and structural changes in 2D materials like graphene, MoS2etc. resulting in the deterioration of the device quality. However, for BP-FETs, we observe an improvement in the on-current and carrier mobility (μ) along with a decrease in threshold voltage (Vth) on exposure to an e-beam with 15 keV energy for 80 seconds. These changes can be attributed to the capture of electrons by traps near the SiO2-BP interface and reduced BP surface roughness due to e-beam exposure. Hysteresis measurements and physical characterization (i.e. atomic force microscopy (AFM), X-ray photoelectron (XPS) and Raman spectroscopies) validate these mechanisms. Reduced hysteresis indicates occupation of the traps, AFM surface scans indicate reduced surface roughness and XPS data show a reduced phosphorus oxide (POx) peak immediately after exposure. Raman measurements indicate a probable structural change due to the interaction between e-beam and BP which could result in better stability.