Divided into three categories: (1) Light-emitting diodes (LED) and laser diodes (LD) : electroluminescent devices that convert electrical energy into light radiationA piece. Light emitting tube divergence Angle is large, wide spectrum range, long life, high reliability, simple modulation circuit, low cost, widely used in the rate is not too high, transmission distance is not too far communication system, as well as display and automatic control.
The types of devices now referred to as semiconductor devices are shown below. According to its manufacturing technology can be divided into discrete device semiconductor, photoelectric semiconductor, logic IC, analog IC, memory and other categories, in general, these will be divided into small categories.
Optoelectronic devices can be divided into bulk optoelectronic devices, forward and forward junction optoelectronic devices, heterojunction and multi-junction optoelectronic devices. Bulk photoelectricitySubdevice It is the simplest type of optoelectronic device in structure. Semiconductor materials absorb incident photons whose energy is greater than the bandgap width, and excite non-equilibrium electron-hole pairs (called intrinsic excitation). They are involved in conducting electricity below the field, producing photoconductivity.
Photoelectric diode, photoresistor, photosensitive diode, light emitting diode, etc. The symbol is: if the sensor, then in the upper part of the original device to hit two inward arrows, indicating the meaning of light absorption. If it is a light-emitting element, two outward arrows are played in the upper part of the original device to indicate the meaning of light.
1, the mechanism is different: the hole because of the net positive charge, so it will attract other electrons around, so that the electron movement in the semiconductor is much easier, you can find that the hole conduction seems to be a net positive charge to attract other electrons and the positive charge transfer, in fact, it is still electronic conduction, the moving hole is just the positive charge equivalent.
2, at very low temperatures, the valence band of the semiconductor is full band (see band theory), after thermal excitation, some electrons in the valence band will cross the bandgap into the higher energyThe presence of electrons in the empty band becomes a conduction band, and the absence of an electron in the valence band forms a positively charged vacancy, called a hole (Figure 1).
3, N-type semiconductor with extra electrons, P-type semiconductor with extra "holes", electrons can move between holes, from one hole to another hole, then the flow of electrons will produce current, when there is a positive current through, electrons will be combined with P-zone holes, combined at the same time release energy, This energy is in the form of photons.
4, because the majority of carriers in the semiconductor number accounts for the vast majorityThe transistor. These devices all work by using physical or chemical reactions to detect light. For example, a photoresistor is made of a photosensitive material that generates an electric current when it receives light. Photodiodes and phototransistors use light exposure to change their internal electric fields, thereby changing their conductivity.
2, the principle of photoelectric sensor is controlled by converting the change of light intensity into the change of electrical signal. Photoelectric sensor in general, there are three parts, they are divided into: transmitter, receiver and detection circuit. The transmitter fires a beam at the target. It firesLight beams generally come from semiconductor light sources, light-emitting diodes (leds), laser diodes and infrared emitting diodes. The beam is emitted without interruption, or the pulse width varies.
3, the working principle of the photodiode: the photodiode is a semiconductor device that turns the optical signal into an electrical signal. Its core part is also a PN junction, compared with ordinary diodes, the difference in structure is that in order to facilitate the acceptance of incident light, the PN junction area is as large as possible, the electrode area is as small as possible, and the junction depth of the PN junction is very shallow, generally less than 1 micron. A photodiode operates under reverse voltage.
4. Only when light illuminates the pn junction can charge carriers (electron-hole pairs) be generated in the depletion layer, and charge carriers are accelerated by the electric field in the junction to form photocurrent. The photodiode made by this principle is called depletion layer photodiode.
Prisms: Prisms are another common light distribution device that can split light into different wavelengths for spectral analysis and optical measurement. Filters: Filters can selectively transmit or absorb different wavelengths of light and are often used in lighting and image processing applications. Polarizer: Polarizers can selectively filter out polarized light in a specific direction and are commonly used in optical display and communication systems.
In the field of sensors, long-period fiber grating can be used to make sensors such as micro-bending sensors and refractive index sensors; In the field of optical communication, long period fiber gratings can be used to make bait-doped fiber amplifiers, gain flatters, mode converters, band-stop filters, etc. For a uniform fiber Bragg grating of a certain length, there are a series of side peaks on both sides of the main peak in the reflection spectrum, which are generally called the side modes of the grating.