When no light falls on the surface of the transistor, the small reverse saturation current induces on the transistor. The emitter-base junction is kept at forward biased, and the collector-base junction is at the reverse biased. Nowadays the transistor is made of a highly light effective material (like gallium and arsenides). The lens focuses the light on the surface. The small hole is made on the surface of the collector-base junction for placing the lens. Earlier, the germanium and silicon are used for fabricating the phototransistor. The construction of the phototransistor is quite similar to the ordinary transistor. The major drawback of the phototransistor is that they have low-frequency response. The base current injected the electrons in the emitter region. The movement of electrons under the influence of electric field causes the current in the base region. The generation of electron-hole pairs mainly occurs into the reverse biasing. The light enters into the base region of phototransistor generates the electron-hole pairs. In case of NPN transistor, the collector is made positive concerning emitter, and in PNP, the collector is kept negative.
The base of the phototransistor would only be used for biasing the transistor.
When the light was striking on the material, the free electrons/holes of the semiconductor material causes the current which flows in the base region. The phototransistor is made up of semiconductor material.
0 kommentar(er)
