Semiconductor thin films directly from minerals study of structural, optical, and transport characteristics of Cu2O thin films from malachite mineral and synthetic CuO

We demonstrate the proof-of-concept of using an abundantly occurring natural ore. malachite (Cu2CO3 (OH)(2)) to directly yield the semiconductor Cu2O to be used as an active component of a functional thin film based device. Cu2O is an archetype hole-conducting semiconductor that possesses several interesting characteristics particularly useful for solar cell applications, including low cost, non-toxicity, good hole mobility, large minority carrier diffusion length, and a direct energy gap ideal for efficient absorption. In this article, we compare the structural, optical, and electrical transport characteristics of Cu2O thin films grown from the natural mineral malachite and synthetic CuO targets. Growth from either source material results in single-phase, fully epitaxial cuprous oxide thin films as determined by x-ray diffraction. The films grown from malachite have strong absorption coefficients ( 10(4) cm(-1)), a direct allowed optical bandgap ( 2.4 eV), and majority carrier hole mobilities ( 35 cm(2)V(-1) s(-1) at room temperature) that compare well with films grown from the synthetic target as well as with previously reported values. Our work demonstrates that minerals could be useful to directly yield the active components in functional devices and suggests a route for the exploration of low cost energy conversion and storage technologies. (c) 2012 Elsevier B.V. All rights reserved.