Characterization of Ambient Light-Induced Inversion Current in MOS(n) Tunneling Diode With Enhanced Oxide Thickness-Dependent Performance

The dark and light current mechanisms of n-type substrate MOS(n) tunneling photodiode for visible light sensing were investigated. By measuring current-voltage and capacitance-voltage curves for devices with different oxide thicknesses, we found that the light current at V
_G
= -2.5 V first decreases but then increases with oxide thickness. The turning point of oxide thickness is ~2.3 nm. We attributed this phenomenon to the oxide voltage tuning induced by the lateral diffusion current. Therefore, the photosensitivity enlarges remarkably when an oxide is thicker than 2.45 nm, and the photosensitivity and responsivity of the device with an oxide thickness of 2.5 nm reach up to 669 and 463 mA/W under the visible ambient light irradiance of 30 mW/cm
²
, respectively. MOS(n) tunneling photodiode exhibits the increasing photosensitivity with the oxide thickness, which is opposite to the behavior of MOS(p). This difference may be properly utilized as the ambient light image sensor integration in modern CMOS technology. In addition to the optoelectrical properties, the light current flow path was examined to elucidate the current mechanism and gate structural dependence.