Planar‐type photosensor with SiN/a‐Si: H double layers

AbstractIt is proposed that an a‐Si:H/SiN double‐layer device is promising which has a thin SiN layer between the planar electrode and a‐Si:H so that the deficiency of the slow optical response is improved while the advantage of a high‐optical sensitivity and the easy fabrication process of the planar photoconductor device are retained. A study was carried out for the amount of PH3 inclusion with respect to SiH4 in the a‐Si:H deposition and the SiN film thickness.By using a double layer of a‐Si:H and SiN, a planar photosensor was realized which has an extinction ratio of more than two orders of magnitude (about 50 dB) and a photocurrent of more than 100 nA with an optical illumination of 150 lx. The optical response speed was more than five times that in a conventional a‐Si:H planar sensor.By varying the SiN film thickness, the threshold voltage of the photocurrent can be changed. The threshold value increased as the SiN film thickness is increased. As the PH3 concentration was increased, both the photocurrent and the dark current increased while the optical response speed decreased. The spectral sensitivity was similar to that in a conventional a‐Si:H planar sensor. Hence, no advantage of the photosensor using a‐Si:H was lost.