Homogeneous junctions are semiconductor devices or interfaces that occur between similar material layers with equal bandgaps but different doping concentrations. In most cases, it occurs at the interface between n-type (called donor doped) and p-type (called acceptor doped) semiconductors, such as silicon. For example, n-type to n-type junctions can also be considered homomorphic, even if the doping level is different. In other words, a homogeneous junction is a junction formed by the same semiconductor, including a pn junction, a pp junction, and an nn junction.
What is a heterojunction?
Heterojunctions are interfaces that occur between two layers or regions of different materials/crystalline semiconductors or solid materials. A device in which multiple heterojunctions are concentrated is called a heterostructure.
The fabrication of heterojunctions generally requires the use of molecular beam epitaxy (MBE) or chemical vapor deposition (CVD) techniques. Some specialized applications of heterojunctions are:
Solar cells: In 1983, a heterojunction (HIT) solar cell structure with an inner thin layer was first developed and eventually commercialized by Sanyo/Panasonic. Intrinsically thin layer (HIT) solar cells are currently one of the most effective single junction silicon cells because of their conversion efficiency of 26.7%.
Laser: – By combining a small direct bandgap material such as gallium arsenide (GaAs) with two larger bandgap layers such as aluminum arsenide (AlAs), the carrier can be made very small, allowing laser light to occur at low threshold current at room temperature. One of the main advantages of using semiconductor lasers is that heterostructures can be used as waveguides.
Bipolar Transistors: When heterojunctions are used in bipolar crystal transistors, they will achieve extremely high forward gain and low reverse gain. This results in very good high-frequency operation (values ranging from tens to hundreds of GHz) and low leakage current. Such devices are called heterojunction bipolar transistors (HBTs).
Field Effect Transistor: – It is used in High Electron Mobility Transistors (HEMTs), which can operate at significantly higher frequencies (over 500 GHz).
In summary, a heterojunction is a special PN junction formed by depositing two or more layers of different semiconductor material films on the same substrate in turn. These materials have different energy band gaps, and they can be compounds such as gallium arsenide or semiconductor alloys such as silicon germanium.
Extended Data
Schottky junction solar cells, which utilize the Schottky barrier on the metal semiconductor interface, are called Schottky junction solar cells, or MS cells for short. Currently, it has developed into metal oxide semiconductor (MOS), metal insulator semiconductor (MIS) solar cells, etc.
Composite junction solar cells, which are formed by two or more P-N junctions, are referred to as composite junction solar cells, and are further divided into vertical multiple junction solar cells and horizontal multiple junction solar cells. For example, a high-efficiency MISNP composite junction silicon solar cell can be formed by combining a (MIS) solar cell and a P-N junction silicon cell, with an efficiency of 22%. Composite junction solar cells are often made into a cascade type, with a wide band gap material placed in the top region to absorb high-energy photons from sunlight; Using narrow band gap materials to absorb low energy photons widens the spectral response of the entire battery. Currently, the efficiency of aluminum gallium arsenide gallium arsenide silicon solar cells developed has reached 31%.
