Oscillatory Order-Disorder Transition during Layer-by-Layer Growth of Indium Selenide.

It is important to understand the polymorph transition and crystal-amorphous phase transition in InSe to tap the potential of this material for resistive memory storage. By monitoring layer-by-layer growth of β-InSe during molecular beam epitaxy (MBE), we are able to identify a cyclical order-disorder transition characterized by a periodic alternation between a glassy-like metastable subunit cell film consisting of < 5 sublayers (th layers = the number of subunit cell layers), and a highly crystalline β-InSe at = 5 layers. The glassy phase shows an odd-even alternation between the indium-cluster layer ( = 1, 3) and an In-Se solid solution ( = 2, 4), which suggests the ability of In and Se atoms to diffuse, aggregate, and intermix. These dynamic natures of In and Se atoms contribute to a defect-driven memory resistive behavior in current-voltage sweeps that is different from the ferroelectric switching of α-InSe.