Isolated small crystals and closed epitaxial layers of CuI could be deposited on various substrates by close distance sublimation (CDS). X-ray diffraction measurements and detailed TEM studies revealed phase pure cubic γ-CuI (zincblende structure) layers and a combination of a CuI multilayer structure with γ-CuI. The multilayer structure, a 12R polytype with the space group R3m, the lattice parameters a0 = 0.4279 nm, c0 = 4.25 nm, and a twelve layers array consisting of wurtzite-like and zincblende layer sequences in combination with γ-CuI could be detected. The presence of the polytype phase was detected always together with γ-CuI. The epitaxial relationships between the CuI phases and various substrates are discussed. Low temperature (2 K) photoluminescence spectra of phase-pure γ-CuI layers show typical excitonic emission spectra in the range between 3.0 and 3.1 eV. Samples containing both, the 12R polytype and γ-CuI, additionally reveal a predominant series of intense emission lines around 3.25 eV attributed to excitonic emission from the rhombohedral phase.
