Photocurrent mapping in optoelectronic diamond devices*

Diamond has remarkable properties that make it a promising semiconductor material for high-efficiency and high-power electronic devices. However, materials synthesis challenges and impurities, notably nitrogen, frustrate efforts to realize optimal diamond devices. On the other hand, some optically-active defect center impurities offer the possibility of in-situ characterization. Here, we use charge-sensitive optical microscopy of nitrogen-vacancy (NV) centres and photocurrent measurements to investigate the generation and propagation of charges flowing in diamond. We image photocurrent by detecting charge state conversion of NV centres, while electrically monitoring the generated photocurrent. Using optical initialization protocols, we can tailor the charge state of nitrogen impurities in the diamond on demand, and observe drastically different photocurrent and images of the current flow, ranging from narrow filaments in a space-charge dominated regime to almost ballistic trajectories when the nitrogen is charge neutral. We can use light to engineer conducting channels and space charge regions ranging from diffraction-limited to hundreds of microns, offering the prospect of reconfigurable, wide bandgap designer optoelectronics. We anticipate our approach might be extended to probe other insulators (e.g., SiC, GaN) or lower-bandgap semiconductors (GaAs, Si) relevant to present electronic technologies.