It took many years for the material science of heterostructure fabrication to catch up with Kroemer's ideas but now it is the industry standard. By incorporating a smaller direct band gap material like GaAs between two larger band gap layers like AlAs, carriers can be confined so that lasing can occur at room temperature with low threshold currents. Lasers: Using heterojunctions in lasers was first proposed in 1963 when Herbert Kroemer, a prominent scientist in this field, suggested that population inversion could be greatly enhanced by heterostructures.HIT solar cells now hold the record for the most efficient single-junction silicon solar cell, with a conversion efficiency of 26.7%. The Heterojunction with Intrinsic Thin-Layer (HIT) solar cell structure was first developed in 1983 and commercialised by Sanyo/ Panasonic. The heterojunction is used to separate charge carriers in a similar way to a p–n junction. Solar cells: Heterojunctions are formed through the interface of a crystalline silicon substrate (band gap 1.1 eV) and amorphous silicon thin film (band gap 1.7 eV) in some solar cell architectures.ĭespite their expense, heterojunctions have found use in a variety of specialized applications where their unique characteristics are critical: A recent alternative under research is the mechanical stacking of layered materials into van der Waals heterostructures. Heterojunction manufacturing generally requires the use of molecular beam epitaxy (MBE) or chemical vapor deposition (CVD) technologies in order to precisely control the deposition thickness and create a cleanly lattice-matched abrupt interface. A more modern definition of heterojunction is the interface between any two solid-state materials, including crystalline and amorphous structures of metallic, insulating, fast ion conductor and semiconducting materials. The requirement that each material be a semiconductor with unequal band gaps is somewhat loose, especially on small length scales, where electronic properties depend on spatial properties. The combination of multiple heterojunctions together in a device is called a heterostructure, although the two terms are commonly used interchangeably. It is often advantageous to engineer the electronic energy bands in many solid-state device applications, including semiconductor lasers, solar cells and transistors. These semiconducting materials have unequal band gaps as opposed to a homojunction. A heterojunction is an interface between two layers or regions of dissimilar semiconductors.
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