Hole conduction at H-terminated surface

Diamond is electrically a good insulator because of its large band gap (5.47 eV), but the diamond surface grown by CVD was found to be p-type and conducting. 

The hydrogen-terminated diamond surface also exhibits a p-type conduction. The surface structure, electronic properties, etc. have been extensively studied. This subject has a long history of research, and the readers can refer to Ref. [137] on this topic. Simply summarizing the results obtained so far, the thickness of the Surface conducting layer is 30-100 A, and the hole density at room temperature is approximately 10 /cm.  

---