Preparation of High-Performance Phototransistors Combining Negative-Capacitance Effect of Gate Dielectric With WS2/MoS2 Heterojunction Channel

A heterojunction negative-capacitance (NC) phototransistor is fabricated by using Hf0.5Zr0.5O2 (HZO) as a ferroelectric layer, Al2O3 as a matching layer, and WS2/MoS2 as a heterojunction channel prepared using chemical vapor deposition (CVD) method. As a comparison, the MoS2 NC field-effect transistor (NCFET) is prepared by transferring the monolayer CVD-MoS2 onto the HZO/p+-Si substrate, and a low subthreshold swing (SS) of 50 mV/dec and a high switching ratio of 2.1
$\times \,\,10^{6}$
are obtained at room temperature. On this basis, a CVD-WS2/MoS2 heterojunction is introduced to replace MoS2 as the channel through a two-step transfer method, which results in a high electron mobility of ~20.9 cm2/Vs, a high responsivity of 559.21 A/W, and a high detectivity of 9.58
$\times \,\,10^{13}$
cmHz−1/2W−1 under the illumination of a light source with the wavelength of 520 nm due to an effective combination of the NC effect with the heterojunction effect. The qualities and performance of the deposited monolayer MoS2 and WS2, WS2/MoS2 heterojunction, and atomic layer deposition (ALD)-HZO thin film are characterized by multiple microanalysis methods. It is shown that the combination of a heterojunction energy-band engineering of two-dimension semiconductors with the NC effect of the ferroelectric thin film provides a new solution for high-performance phototransistors.