In photoconductive mode the diode is reverse biased, that is, with the cathode driven positive with respect to the anode. For optimum power output, the photovoltaic cell will be operated at a voltage that causes only a small forward current compared to the photocurrent. This mode exploits the photovoltaic effect, which is the basis for solar cells – a traditional solar cell is just a large area photodiode. If the circuit is shorted or the impedance is low, a forward current will consume all or some of the photocurrent. If the circuit is opened or has a load impedance, restricting the photocurrent out of the device, a voltage builds up in the direction that forward biases the diode, that is, anode positive with respect to cathode. In photovoltaic mode (zero bias), photocurrent flows into the anode through a short circuit to the cathode. The points of intersection with the curves represent the actual current and voltage for a given bias, resistance and illumination. The linear load lines represent the response of the external circuit: I=(Applied bias voltage-Diode voltage)/Total resistance. Photovoltaic mode I-V characteristic of a photodiode. To first order, for a given spectral distribution, the photocurrent is linearly proportional to the irradiance. The total current through the photodiode is the sum of the dark current (current that is generated in the absence of light) and the photocurrent, so the dark current must be minimized to maximize the sensitivity of the device. Thus holes move toward the anode, and electrons toward the cathode, and a photocurrent is produced. If the absorption occurs in the junction's depletion region, or one diffusion length away from it, these carriers are swept from the junction by the built-in electric field of the depletion region. This mechanism is also known as the inner photoelectric effect. When a photon of sufficient energy strikes the diode, it creates an electron– hole pair. Photodiodes are used in a wide range of applications throughout the electromagnetic spectrum from visible light photocells to gamma ray spectrometers.Ī photodiode is a PIN structure or p–n junction. This can be used for detection and measurement applications, or for the generation of electrical power in solar cells. ![]() It produces an electrical current when it absorbs photons. ![]() One Ge (top) and three Si (bottom) photodiodesĪ photodiode is a semiconductor diode sensitive to photon radiation, such as visible light, infrared or ultraviolet radiation, X-rays and gamma rays.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |