Continuous advancement in nonvolatile and morphotropic beyond-Moore electronic devices requires integration of ferroelectric and semiconductor materials. The emergence of hafnium oxide (HfO ₂ )–based ferroelectrics that are compatible with atomic-layer deposition has opened interesting and promising avenues of research. However, the origins of ferroelectricity and pathways to controlling it in HfO ₂ are still mysterious. We demonstrate that local helium (He) implantation can activate ferroelectricity in these materials. The possible competing mechanisms, including He ion–induced molar volume changes, vacancy redistribution, vacancy generation, and activation of vacancy mobility, are analyzed. These findings both reveal the origins of ferroelectricity in this system and open pathways for nanoengineered binary ferroelectrics.

Various large-area growth methods for two-dimensional transition metal dichalcogenides have been developed recently for future electronic and photonic applications. However, they have not yet been employed for synthesizing active pixel image sensors. Here, we report on an active pixel image sensor array with a bilayer MoS₂ film prepared via a two-step large-area growth method. The active pixel of image sensor is composed of 2D MoS₂ switching transistors and 2D MoS₂ phototransistors. The maximum photoresponsivity (R_ph) of the bilayer MoS₂ phototransistors in an 8 × 8 active pixel image sensor array is statistically measured as high as 119.16 A W⁻¹. With the aid of computational modeling, we find that the main mechanism for the high R_ph of the bilayer MoS₂ phototransistor is a photo-gating effect by the holes trapped at subgap states. The image-sensing characteristics of the bilayer MoS₂ active pixel image sensor array are successfully investigated using light stencil projection.

Hexagonal molybdenum diselenide (MoSe₂) multilayers were grown by chemical vapor deposition (CVD). A relatively high pressure (>760 Torr) was used during the CVD growth to achieve multilayers by creating multiple nuclei based on the two-dimensional crystal growth model. Our CVD-grown multilayer MoSe₂ thin-film transistors (TFTs) show p-type-dominant ambipolar behaviors, which are attributed to the formation of Se vacancies generated at the decomposition temperature (650 °C) after the CVD growth for 10 min. Our MoSe₂ TFT with a reasonably high field-effect mobility (10 cm²/V · s) exhibits a high photoresponsivity (93.7 A/W) and a fast photoresponse time (τ_rise ~ 0.4 s) under the illumination of light, which demonstrates the practical feasibility of multilayer MoSe₂ TFTs for photodetector applications.