Ultra-wide spectral range (0.4-8 μm) transparent conductive ZnO bulk single crystals: a leading runner for mid-infrared optoelectronics

Transparent conductive oxides have been widely applied to solar cells, liquid crystal displays, and other optoelectronic devices because of their excellent transparent conductive properties in the visible-near infrared (Vis-NIR) region. At present, the transparent conductive oxide films (TCOFs) such as indium tin oxide (ITO), fluorine-doped tin oxide (FTO), and aluminum-doped zinc oxide (AZO) are widely noticed and used. However, a high carrier concentration (>10(20) cm(-3)) of these TCOFs leads to a result that their transparency will be affected by the plasmons effect, and thus their transparent range will generally end around 2-3 mu m. As such, they are more applicable in the Vis-NIR region but unable to meet the requirements of mid-infrared (MIR) optoelectronic devices. Faced with this situation, herein, we reported the native ZnO bulk single crystals with low background carrier concentration (10(15)-10(16) cm(-3)) and high carrier mobility (mu > 300 cm(2) V-1 s(-1)). These single crystals boast excellent transparent conductive properties (IR cutoff edge: 6-8 mu m, Rsheet: 3.7-28.5 Omega/sq) with an advantage that they can be massively produced by a hydrothermal method at a low cost. Based on these merits, the native ZnO bulk single crystals bring a new possibility of breaking the bottleneck of MIR transparent conductivity. (C) 2020 Elsevier Ltd. All rights reserved.