The composition of optoelectronic devices

1. Photoresistor
The most used photoelectric sensor is the photoresistor, the photoresistor in the absence of light resistance value is relatively high, when it is illuminated, the resistance value drops a lot, the conductivity is significantly strengthened. The main parameters of photoresistors are dark resistance, dark current, and corresponding to bright resistance, bright current. They are measured values in the presence of light and in the absence of light, respectively. The larger the difference between bright resistance and dark resistance, the better. When choosing a photoresistor, we should also pay attention to its light characteristics and spectral characteristics.

2. Photodiode
Under the condition of no light, the photodiode works in the cut-off state, which is similar to the general diode characteristics and has unidirectional performance. When exposed to light, the carrier concentration in the PN region increases greatly, and the carrier flow forms a photocurrent.

3. Phototransistors
The difference between the phototransistor and the ordinary triode is that the size of the emitter is relatively small, and the photocurrent is almost equal to the base current of the ordinary triode when illuminated, and the phototransistor is more sensitive than the photodiode.

4. Photocells
In fact, the photocells that are used more are silicon photocells. It converts light energy directly into electricity. An important feature of photocells is that the current when short-circuited is basically linearly proportional to the light. In the application, the load resistance is generally selected very small. The smaller the load resistance, the better the linear shape.

5. Photocell
Photocells are generally divided into vacuum photocells and gas-filled photocells. Inflated photocells are generally filled with argon gas or argon-neon mixed gas, which are inert gases and have a relatively small atomic weight. The deficiency of gas-charged photocells lies in the fast sensitivity attenuation.

6. Photomultiplier tube
The photomultiplier tube is mainly composed of a cathode chamber and a secondary emission multiplication system. The photoelectric characteristics of the photomultiplier tube are linearly when the luminous flux is small. Due to the presence of dark current in the photomultiplier tube, the minimum range for its measurement is limited.