Paper SC+EM-ThM11
Enormous Photocurrent for Hydrogenated Single-crystalline B-doped Diamond Epilayers Grown by Microwave-excited Plasma Chemical Vapor Deposition.
Diamond with energy band-gap of 5.5 eV is an attractive semiconductor for applying to a visible-blind photodetector operated at ultraviolet wavelength smaller than 240 nm. Although there have been several reports for challenges to develop such the photodetector (PD), tremendous efforts were made by applying polycrystalline diamond films to the PDs. Enormous photocurrent (PC), persistent photoconductivity (PPC), and relatively-large thermally-stimulated current (TSC) were reported by several groups to be observed for the polycrystalline diamond DUV-PDs, and the mechanisms of the PPC and TSC were proposed to be due to bulk deep levels, surface states, and/or interface states at grain boundaries in the polycrystalline diamond films. In order to understand the defect-related mechanism of the PPC and TSC, it is required to investigate the photoresponse properties of PD fabricated by single-crystalline diamond epilayer, which will lead to development of high-efficiency diamond DUV-PD with high reliability. Also, it is essential to investigate influences of diamond surfaces terminated by hydrogen and oxygen (named by hydrogenated and oxidized surfaces, respectively) on photoresponse properties, which will provide an important information on effect of surface states on the mechanism of PPC. The purpose of this paper is, as a first step to develop reliable, high-efficiency diamond PD, to explore the PC and PPC for homoepitaxial B-doped diamond epilayer with hydrogenated and oxidized surfaces. The PC's with gain larger than 105 and the long-term PPC were observed in illuminating UV-light to metal/p-diamond/ metal photodiodes fabricated on hydrogenated surfaces of the single-crystalline B-doped p-diamond epilayer. Saturation of PC with increasing applied voltages and phototransistor action against incident optical power densities were observed. The PC with large gain and the PPC were believed to be due to surface states on hydrogenated surface.