What Is a Heterojunction?

A semiconductor heterojunction is a special PN junction formed by depositing more than two different thin films of semiconductor materials on the same substrate in sequence. These materials have different band gaps. They can be compounds such as gallium arsenide It can also be a semiconductor alloy such as silicon-germanium.

Heterojunction, an interface area formed by the contact of two different semiconductors. According to the different conductivity types of the two materials, heterojunctions can be divided into homogeneous heterojunctions (Pp or Nn junctions) and heterogeneous heterogeneous (Pn or pN) junctions. Multilayer heterojunctions are called heterostructures. Generally, the conditions for forming a heterojunction are: the two semiconductors have similar crystal structures, similar atomic distances, and thermal expansion coefficients. Heterojunctions can be fabricated using interfacial alloys, epitaxial growth, and vacuum deposition. Heterojunction often has excellent optoelectronic characteristics that cannot be achieved by the respective PN junctions of two semiconductors, making it suitable for making ultra-high-speed switching devices, solar cells, and semiconductor lasers. ^[1]

The so-called semiconductor heterostructure is the sequence of semiconductor thin films of different materials.

Heterojunction light emitting component

Because the semiconductor heterostructure can confine electrons and holes in the intermediate layer, the recombination rate of electrons and holes increases, so the efficiency of light emission is large; meanwhile, changing the width of the quantum well can also control the frequency of light emission, Semiconductor light-emitting components are mostly composed of heterostructures. Compared with other light-emitting components, the semiconductor hetero-structure light-emitting component has the advantages of high efficiency, power saving, and durability. Therefore, it is widely used in brake lights, traffic lights, outdoor display lights, etc. It is worth mentioning that in 1993, Japanese scientists developed blue light semiconductor components, so that the three primary colors of red, green, and blue can be made with semiconductors, so all colors can be obtained with semiconductor light emitting components. No wonder everyone predicts the family Incandescent lamps and fluorescent lamps will soon be replaced by semiconductor light-emitting components. ^[1]

Heterojunction laser diode

The basic structure of a semiconductor laser diode is very similar to the above-mentioned light-emitting component, except that the laser diode must consider the conditions of stimulated emission and resonance. With semiconductor heterostructures, since electrons and holes can easily fall to the intermediate layer, population inversion is easier to achieve. This is a necessary condition for excited light. Confined in the middle layer, its binding rate is large. In addition, the refractive index of the interlayer on both sides is different from that of the intermediate layer, so the light can be confined to the intermediate layer, so that the light will not be lost, and the laser intensity is increased. Therefore, the use of heterostructures to make laser diodes has great advantages. The first semiconductor heterostructure laser diode with continuous emission at room temperature was produced by a research group led by Afalov in 1970, and Kram developed the semiconductor heterostructure laser diode in 1963. principle. Semiconductor laser diodes are also used in a wide range of applications, such as laser discs, high-speed fiber-optic communications, laser printers, and laser pens. ^[1]

Heterojunction heterostructure bipolar transistor

In semiconductor heterostructures, the intermediate layer has a lower energy band, so electrons are easily injected from the adjacent interlayer. Therefore, the current from the emitter to the collector in the transistor can be greatly increased. The magnification of the transistor is also increased; at the same time, the thickness of the base can be reduced, and its doping concentration can be increased, so the reaction rate becomes larger, so a heterostructure can make a fast transistor. The proposal of using semiconductor heterostructures to make transistors and the analysis of their characteristics were put forward by Kielam in 1957. Semiconductor heterostructure bipolar transistors are widely used in satellite communications or mobile phones due to their advantages of high speed and high magnification. ^[2]

Heterojunction high-speed electron mobility transistor

High-speed electron mobility transistors use the advantages of impurities and electrons in the semiconductor heterostructure to be separated in space, so electrons have a high mobility. In this structure, by changing the voltage of the gate, the current from the source to the drain can be controlled to achieve the purpose of amplification. Because this component has the advantages of high response frequency (600GHz) and low noise, it is widely used in infinite communication with space (as shown in Figure 5), and astronomical observation. ^[2]

Other applications of heterojunctions

In addition to the semiconductor heterostructures, the semiconductor heterostructures are also widely used in other optoelectronic components, such as photodetectors, solar cells, standard resistors or photoelectric modulators. Because of the advancement of crystal growth technology, single-layer atomic thickness films can be controlled, so semiconductor heterostructures provide high-quality low-dimensional systems, allowing scientists to meet the requirements of exploring low-dimensional phenomena. In addition to the quantum and fractional quantum Hall effects observed in second-degree space, scientists have further explored the one-dimensional and zero-dimensional electronic behavior in heterostructures. It is expected that new and exciting phenomena will be discovered in the future. More novel heterostructure components emerge. ^[2]