Photodiode with the conventional semiconductor diodes are similar, but the photodiode can be directly exposed in the vicinity of the light source or through a transparent small window, optical fiber package, to allow light to reach the light-sensitive area of this device to detect light signals. Many used to design a photodiode using a PIN diode junction, rather than the general PN junction, to increase the response speed of the device on the signal. Photodiodes are often designed to operate in a reverse bias state.
Infrastructure is typically a photodiode PN junction or a PIN junction. When a photon with sufficient energy shock to the diode, it will excite an electron to produce free electrons and there is a positively charged holes. Such a mechanism is also known as photoconductivity. If the photon absorption occurs in the junction depletion layer, the internal electric field in the region will eliminate the barriers between them, so that the hole can move in the direction of the anode, cathode electrons toward the direction of motion, so the photocurrent arises. The actual dark current and photocurrent is integrated light generated current, and therefore the dark current must be minimized to improve device sensitivity to light.
Photovoltaic mode
When the current bias is 0:00 photodiode in photovoltaic mode, then out of the photodiode is suppressed ends a potential difference accumulated to a certain value. (Solar cell)
Photoconductive mode
When operating in this mode, the photodiode is reverse biased often dramatically reduces the response time, but the noise had to increase the cost. At the same time, the width of the depletion layer is increased, thereby reducing the junction capacitance, also makes it possible to reduce the response time. Reverse bias will cause small amounts of current (saturation current), the current and the photocurrent in the same direction. For specific spectral distribution between the photocurrent and the incident light is linearly proportional to the luminance.
Other operating modes
Conventional of avalanche photodiode having a structure similar to a photodiode, but requires much higher reverse bias voltage. This will allow the carriers of light generated by the avalanche breakdown substantial increase, resulting in internal gain in the photodiode inside, thereby further improving the response rate of the device.
