Temperature- and thickness-dependence of robust out-of-plane ferroelectricity in CVD grown ultrathin van der Waals α-InSe layers

Two-dimensional (2D) ferroelectric materials with unique structure and extraordinary optoelectrical properties have attracted intensive research in the field of nanoelectronic and optoelectronic devices, such as optical sensors, transistors, photovoltaics and non-volatile memory devices. However, the transition temperature of the reported ferroelectrics in 2D limit is generally low or slightly above room temperature, hampering their applications in high-temperature electronic devices. Here, we report the robust high-temperature ferroelectricity in 2D α-InSe, grown by chemical vapor deposition (CVD), exhibiting an out-of-plane spontaneous polarization reaching above 200 °C. The polarization switching and ferroelectric domains are observed in InSe nanoflakes in a wide temperature range. The coercive field of the CVD grown ferroelectric layers illustrates a room-temperature thickness dependency and increases drastically when the film thickness decreases; whereas there is no large variance in the coercive field at different temperature from the samples with identical thickness. The results show the stable ferroelectricity of InSe nanoflakes maintained at high temperature and open up the opportunities of 2D materials for novel applications in high-temperature nanoelectronic devices. [Figure not available: see fulltext.].