Controllable growth of copper iodide for high-mobility thin films and self-assembled microcrystals

Copper iodide (CuI) is an emerging high-performance p-type, wide-band-gap semiconductor. However, the growth mechanisms of CuI thin films and nanocrystals are currently unclear, as they do not follow the established models. In this work, the growth mechanisms and kinetics of sputtered CuI thin films were studied, which mainly depended on adatom/ substrate interface properties driven by growth temperature and rate. A modified structure zone model was proposed to explain the two-dimensional layer-by-layer and three-dimensional island growth of CuI with different rates. The Wulff shape of the isolated CuI nanocrystals appeared to be controllable by the available iodine ion flux at high temperatures but low growth rates near the equilibrium. Moreover, smooth CuI thin films were successfully produced by combining a high substrate temperature with a high growth rate. A record-high hole mobility in a high carrier-density range was demonstrated, which was greater than twice the values reported previously. Our findings represent the essential steps toward advanced materials engineering and fabrication of CuI thin films for practical devices, as well as the self-assembly of shape-controlled CuI nano- and microcrystals.