This letter presents a CMOS-compatible photodetector displaying direct light-to-time conversion and intrinsic charge integration with a very low dark current. This device is particularly adapted for applications requiring high sensitivity such as bioluminescence detection. The effects of the physical structure, the process parameters, and the bias conditions on the device are discussed with the support of TCAD simulations and experimental measurements. The photodetector and its readout circuit are designed and implemented in standard 0.18-mu m CMOS process. The experimental study shows promising tunability and sensitivity characteristics.