ZnCdO:Eu Epitaxially Grown Alloys for Self-Powered Ultrafast Broadband Photodetection

Photodetectors (PDs) are essential in imaging, communication, and sensing technologies. However, their reliance on external power makes them energy-consuming. This creates a strong need for self-powered PDs as a sustainable alternative. Zinc oxide (ZnO) is a promising semiconductor material due to its pyroelectric properties, stemming from noncentrosymmetric wurtzite crystal structure, enabling the pyro-phototronic effect that enhances response speed. Properties of ZnO can be tailored via alloying and doping. Thus, this work explores thin layers of ZnCdO:Eu random alloys grown by molecular beam epitaxy on silicon substrates with varying Cd content. The study shows that doping with Eu notably affects growth kinetics, promoting a strong [0001] orientation preference. Moreover, photoluminescence measurements confirm the successful incorporation of Eu³⁺ ions into the structure. Electrical measurements show that the introduction of Cd eliminates the problem of Schottky barrier formation at the ZnO/Au interface. The n-ZnCdO:Eu/p-Si junctions exhibit rectifying behavior and generate photocurrent across the 370-1150 nm wavelength range without external electrical bias. Utilizing the pyro-phototronic effect, these devices achieved ultrafast response times: rise time below 10 μs and decay time below 5 μs for 405 and 650 nm illumination, placing them among the fastest self-powered oxide-based detectors that do not rely on additional performance-enhancing layers.