What is a photoelectric transistor? The working principle, classification, application, and testing methods of photoelectric transistors

Phototransistor is a semiconductor device that can convert optical signals into electrical signals. It is a photosensitive element based on a common transistor structure, which is a photoelectric conversion device, also known as EP2S90F1020I4N photosensitive transistor. The photoelectric transistor has the basic structure of a regular transistor, but with the addition of photosensitive materials in the base region, it can respond to light and convert optical signals into electrical signals. Phototransistors are commonly used in fields such as photoelectric control, photoelectric measurement, and photoelectric detection.

1、 Structure and Working Principle of  Phototransistor

The structure of a  Phototransistor is basically the same as that of a regular transistor, both including a base region, an emitter, and a collector. Unlike ordinary transistors,  Phototransistors add photosensitive materials in the base region, allowing them to respond to light and convert optical signals into electrical signals.

The working principle of a  Phototransistor is basically the same as that of a regular transistor, except that under illumination, photons are absorbed and excite electrons and holes, causing a change in the concentration of electrons and holes and thus altering the conductivity properties of the base region. When the base of the  Phototransistor receives light, electrons and holes are excited and recombine in the base region, causing a change in the conductivity of the base region. The change in conductivity will affect the changes in collector current and emitter current, thereby achieving the conversion of optical signals to electrical signals.

2、 Classification of Phototransistors

Phototransistors can be classified into silicon phototransistors, germanium phototransistors, GaAs phototransistors, etc. based on different photosensitive materials. Among them, silicon phototransistors and germanium phototransistors are the two most common types of phototransistors.

1. Silicon phototransistor

A silicon phototransistor is a photosensitive element based on the structure of a silicon transistor. The photosensitive material of silicon phototransistors is usually silicon, which has low sensitivity and slow response speed, but is relatively inexpensive and widely used in some low-frequency, low-speed photoelectric control, measurement, and detection fields.

2. Germanium phototransistor

Germanium phototransistor is a photosensitive element based on germanium transistor structure. The photosensitive material of germanium phototransistors is usually germanium, which has high sensitivity and fast response speed, but is relatively expensive. Germanium phototransistors are widely used in high-frequency, high-speed optoelectronic control, measurement, and detection fields.

3、 Characteristics of phototransistor

1. High sensitivity: The photoelectric transistor has high sensitivity and can respond to weak light signals.

2. Fast response speed: The photoelectric transistor has a fast response speed and can respond to optical signals within microseconds.

3. Wide linear range: The photoelectric transistor has a wide linear range and can respond linearly to the intensity of different optical signals.

4. Good stability: phototransistors have good stability and can maintain good performance under different environmental conditions.

5. Easy to integrate: Phototransistors come in various packaging forms and are easy to integrate into other circuits.

4、 The Application of phototransistors

1. Optoelectronic control: Phototransistors can convert optical signals into electrical signals, which can be used for the photoelectric control function of circuits.

2. Optoelectronic measurement: Phototransistors can efficiently convert optical signals and can be applied in the field of optoelectronic measurement.

3. Optoelectronic detection: Phototransistors can linearly respond to the intensity of different optical signals and can be applied in the field of optoelectronic detection.

4. Optoelectronic amplification: Phototransistors can amplify weak optical signals and can be applied in the field of optoelectronic amplification.

5. Optoelectronic isolation: Phototransistors can achieve the photoelectric isolation function of circuits and can be applied in some special circuit designs.

5、 Testing methods for phototransistors

1. Photocurrent testing

The photocurrent test is the most basic testing method for phototransistors, which can be used to detect the sensitivity and response speed of the device. During testing, shine the light source on the photosensitive area of the phototransistor and measure the output photocurrent. The magnitude of photocurrent is directly proportional to the intensity of the light source, and the sensitivity of the phototransistor can be tested by changing the intensity of the light source. The response speed can be evaluated by measuring the rise time and fall time of the photocurrent.

2. Photovoltaic voltage test

Photovoltage testing is a method of measuring the output voltage of a phototransistor, which can be used to detect the linearity and voltage gain of the device. During testing, shine the light source on the photosensitive area of the phototransistor and measure the output photovoltaic voltage. The magnitude of the photovoltaic voltage is directly proportional to the intensity of the light source, and the linearity and voltage gain of the phototransistor can be tested by changing the intensity of the light source.

3. Noise testing

Noise testing is a method of testing the noise index of phototransistors, which can be used to evaluate the signal-to-noise ratio and noise level of the device. During testing, shine the light source on the photosensitive area of the phototransistor and measure the output noise voltage or noise current. The magnitude of noise voltage or noise current is independent of the intensity of the light source, and the noise performance of the device can be evaluated by testing the noise level of the phototransistor.

6、 The Development Trend of Phototransistors

1. High speed

With the development of communication technology, there is an increasing demand for high-speed optoelectronic conversion devices. As a high-speed photoelectric conversion device, the photoelectric transistor has the advantage of fast response and will be widely used in high-speed communication, fiber optic communication and other fields.

2. High sensitivity

The sensitivity of a phototransistor is an important indicator for evaluating its photoelectric conversion efficiency. With the continuous development of technology, there is an increasing demand for high sensitivity of photoelectric conversion devices. Therefore, future phototransistors will pay more attention to improving their sensitivity to meet the needs of different fields.

3. Low power consumption

Low power consumption is an important development direction for future optoelectronic conversion devices. With the development of new technologies such as intelligence and the Internet of Things, the demand for low power consumption is becoming increasingly urgent. Future phototransistors will pay more attention to reducing power consumption to meet the needs of different fields.

4. Miniaturization

With the continuous development of integrated circuit technology, the demand for miniaturized devices is increasing. Future phototransistors will pay more attention to miniaturization to meet the needs of various special application fields.

7、 Summary

Phototransistor is a semiconductor device that can convert optical signals into electrical signals. Its structure and working principle are basically the same as ordinary transistors, but photosensitive materials are added to the base region, allowing it to respond to light and convert optical signals into electrical signals. phototransistors have the characteristics of high sensitivity, fast response speed, wide linear range, good stability, and easy integration, and are widely used in fields such as photoelectric control, photoelectric measurement, photoelectric detection, photoelectric amplification, and photoelectric isolation