Origin of persistent photoconductivity in surface conducting hydrogenated diamond films

Abstract: The p-type surface conductivity of hydrogen-terminated diamond (HD) has opened up new possibilities for the development of diamond-based electronic devices. However, the origin of the persistent photoconductivity (PPC) observed in surface-conducting HD remains unclear, an understanding that is crucial for advancing HD-based optoelectronic technologies. In this study, we investigate the underlying mechanism of PPC in surface-conducting HD films. A systematic analysis was performed by tuning the carrier density via partial oxygen termination using an ozonation process. With increasing O-termination, both the decay time and the recombination barrier of photoexcited electron-hole pairs were found to decrease significantly, from 232 to 5 seconds, and from ~ 150 to 54 meV, respectively. Temperature-dependent measurements reveal that PPC in HD is influenced by random local potential fluctuations, which delay the recombination of photoexcited carriers. Furthermore, the observed PPC behavior is closely associated with percolative transport processes within the HD film. Importantly, the dependence of PPC on sheet carrier density is correlated with Coulomb interactions between the two-dimensional hole gas and the surface adsorbate layer. This study offers new insights into the PPC mechanism in surface-conducting HD films, contributing to the broader understanding necessary for the design of advanced diamond-based optoelectronic devices.