Homojunctions

The first semiconductor lasers, fabricated from gallium arsenide material, were formed from a simple junction (called a homojunction because the composition of the material was the same on each side of the junction) between the type and n-ty e materials. Those devices required high electrical current density, which produced damage ia the region of the junction so that the lasers were short-Hved. To reduce this problem, a heterojunction stmcture was developed. This junction is formed by growing a number of layers of different composition epitaxially. This is shown ia Figure 12. There are a number of layers of material having different composition is this ternary alloy system, which may be denoted Al Ga his notation, x is a composition... 

Four different types of junctions can be used to separate the charge carriers in solar cebs (/) a homojunction joins semiconductor materials of the same substance, eg, the homojunction of a p—n sibcon solar ceb separates two oppositely doped layers of sibcon 2) a heterojunction is formed between two dissimbar semiconductor substances, eg, copper sulfide, Cu S, and cadmium sulfide, CdS, in Cu S—CdS solar cebs (J) a Schottky junction is formed when a metal and semiconductor material are joined and (4) in a metal—insulator—semiconductor junction (MIS), a thin insulator layer, generaby less than 0.003-p.m thick, is sandwiched between a metal and semiconductor material. 

Fabrication methods that are generaby used to make these junctions are diffusion, ion implantation, chemical vapor deposition (CVD), vacuum deposition, and bquid-phase deposition for homojunctions CVD, vacuum deposition, and bquid-phase deposition for heterojunctions and vacuum deposition for Schottky and MIS junctions. 

Although all of the preceding processes can produce a p—n homojunction, the properties required from the junction and the fabrication costs determine the fabrication method. Methods of making other kinds of junctions are similar to those used to make homojunctions, but the materials on either side of such junctions are dissimilar. 

Two different high efficiency types of GaAs cell stmctures ate being developed. These are GaAs homojunctions with a top window layer of Ga ... 

Eig. 10. Schematic of various LED and laser diode stmctures where S signifies material of a lower energy band gap (a) homojunction, (b) double-heterojunction (DH), and (c) multiquantum well (MQW) stmctures. 

Several heterostructure geometries have been developed since the 1970s to optimize laser performance. Initial homojunction lasers were advanced by the use of heterostmctures, specifically the double-heterostmcture device where two materials are used. The abiUty of the materials growth technology to precisely control layer thickness and uniformity has resulted in the development of multiquantum well lasers in which the active layer of the laser consists of one or mote thin layers to allow for improved electron and hole confinement as well as optical field confinement. 

Contacts are the elementary building blocks for all electronic devices. These include interfaces between semiconductors of different doping type (homojunctions) or of different composition (heterojunctions), and junctions between a metal and a semiconductor, which can be either rectifying (Schotlky junction) or ohmic. Because of their primary importance, the physics of semiconductor junctions is largely dealt with in numerous textbooks [11, 12]. We shall concentrate here on basic aspects of the metal-semiconductor (MS) and, above all, metal-insulator-semiconductor (MIS) junctions, which arc involved in the oiganic field-effect transistors. 

Mauriee H. Francombe and John L. Vossen, Homojunction and Quantum-Well Infrared Detectors, Volume 21, 1995. 

Semiconductor laser diodes are widely used in CD players, DVDs, printers, telecommunication or laser pointers. In the structure, they are similar to LEDs but they have a resonant cavity where laser amplification takes place. A Fabry-Perot cavity is established by polishing the end facets of the junction diode (so that they act as mirrors) and also by roughening the side edges to prevent leakage of light from the sides of the device. This structure is known as a homojunction laser and is a very basic one. Contemporary laser diodes are manufactured as double heterojunction structures. 

Homogeneous wetting, 22 111 Homogenization, 26 699 aluminum alloys, 2 329 Homogenizers, 8 703 10 127 Homoglycans, 4 697, 701 23 62-64 classification by structure, 4 723t Homo-interface, 24 71 Homo-ionic interactions, 8 77 Homojunction BJTs, 22 166 Homojunction devices, LEDs asm 173 Homojunction diode arrays, 29 163 Homojunction laser diode, 24 699 Homoleptic tetranuclear carbonyl complexes, 26 63... 

Other types of photodiodes not discussed here include the Schottky barrier, pn homojunction, and heterojunction. 

Figure 6 A schematic band diagram (electrical potential energy versus distance) of a conventional p-n homojunction solar cell at equilibrium (left) and at short circuit under spatially uniform illumination (right). The energies of the conduction- and valence-band edges are Ecb and Evb. respectively. EF is the Fermi level at equilibrium and EFn and EFp are the quasi-Fermi levels of electrons and holes, respectively, under illumination.

The most efficient silicon cells produced are based on p — n homojunctions and convert 23.1% of the energy in incident light set to simulate the global air mass (AM) 1.5 spectrum, an artificial reference spectrum used to standardize measurement of PV power, with an intensity of 1000 W/m2... 

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