Halide semiconductors stand at the very beginning of semiconductor science and technology. CuI was reported as the first transparent conductor, and the first field effect transistor was made from KBr. Although halogens are frequently used in semiconductor preparation, little use is currently made from halide semiconductors in electronics and photonics. We review past reports on the metal halide semiconductor CuI and related alloys and discuss recent progress with regard to this material including its use in organic electronics and solar cells as well as our own work on fully transparent bipolar heterostructure diodes (p-CuI/n-ZnO) with high rectification of several 107 and ideality factors down to 1.5.
γ-CuI(111) thin film on glass (1 × 1 cm2) and IV-characteristics of p-CuI/n-ZnO/a-Al2O3 bipolar heterojunction diode.