Semiconductor photo devices utilize quantum effects on junctions, energies received by electrons that allow electrons to move from the valence tire to the conduction tire under reverse bias conditions. Semiconductor materials such as Germanium (Ge) and Silicon (Si) have 4 valence electrons, each electron in an atom is bonded so that the valence electron is even 8 for each atom, which is why the silicon crystals have low electrical conductivity, by the atomic atoms that surround it.
To form a P-type semiconductor on the material is inserted impurities of class III elements, so that the material becomes more positively charged, due to electron vacuum in the crystal structure. When a N-type semiconductor is illuminated by light, the electrons that are not attached to the crystal structure will easily escape. Then when the semiconductor is connected type P and type N and then irradiated light, then there will be a voltage difference between the two materials.
Potential differences in silicone materials generally range from 0.6 volts to 0.8 volts. Some of the characteristics of photo diodes that need to be known include: Linear dependent currents on the intensity of light. Frequency response depends on the material (Si 900nm, GaAs 1500nm, Ge 2000nm). Used as a current source Junction capacitance decreases according to the reverse bias voltage Junction capacitance determines the frequency response of the current obtained.
The photo diode sensor is a light-sensitive diode, the photodiode sensor will experience a change of resistance when receiving the light intensity and will forward the electric current as the diode in general. Photodioda sensor is one type of light sensitive sensor (photodetector). Another type of light sensitivity sensor that is often used is phototransistor. Photodiode will flow the current forming a linear function to the received light intensity. This current is generally regular against power density (Dp). The comparison between output current and power density is called current responsitivity. The current in question is the leakage current when the photodioda is irradiated and in a downturned state. Picture the symbol and the original form
The frequency response of the photodiode sensor is not broad. From that range of responses, the photodiode sensor has the best response to infrared light, precisely at light with a wavelength of about 0.9 μm. The photodiode sensor response curve is shown in the following figure.
Photodioda Frequency Response Curve
The relationship between the photodiode sensor output and the intensity of light it receives when it is rewound is to form a linear function. The relationship between the photodioda sensor output and the light intensity is shown in the following figure.
Photodiode Output Relation With Light Intensity
For example photo diode applications can be used as fire sensors. The use of photodioda sensors as a detector of the presence of fire is based on the fact that on flames are also emitted infrared light. This can not be proven by the naked eye because infrared light is invisible light, but the presence of infrared light can be felt when there is a warm or hot flame from the flame that reaches our body.