Adsorption induced bipolar excitation at semiconductor surface

Abstract

Adsorption on metal surfaces has been shown to lead to chemisorption induced electronic excitation but direct experimental evidence of chemisorption induced excitation on semiconductor surfaces is still missing. Here, we design and use high-quality Silicon (Si) p-n diodes to in-situ probe the charge transfer process taking place during vapor and liquid phase chemisorption of iodine molecules on H-Si (100) surface. We find that the diodes can generate electricity and feed an external circuit during the chemisorption process, demonstrating chemisorption-induced electron and hole generation and the means to electrically monitor the process. A bipolar semiconductor electrochemical model where a single semiconductor surface hosts the spontaneous oxidation (electron injection) and reduction (hole injection) reactions simultaneously on its conduction and valence bands without any electrolytes is proposed to explain the observations. Our work provides new insight on the energy relaxation processes of chemisorption and also calls for further studies on the observed chemovoltaic effect. Overall, the results indicate a possibility for developing electrolyte-free vapor phase chemical energy-to-electricity converters and detectors.