Metal/insulator/semiconductor junction

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. 

MISFETs), 22 162, 192. See also Field effect transistors (FETs) Metal-insulator-semiconductor junction, 23 34... 

Flat-band potential — In the energy barrier formed for example at metal-semiconductor junctions (- Schottky barrier), metal-insulator-semiconductor junctions, and solution-semiconductor interfaces the flat-band potential corresponds to the potential at which the electric field equals zero at the semiconductor interface, i.e., there is no -+ band bending. In case of solution-semiconductor interfaces, the flat-band potential corresponds to the condition of absence of excess charge and consequently, depletion layer, in the semiconductor. See also -> Mott-Schottky plot, and -> semiconductor. 

Semiconductor materials are used to manufacture discrete devices and integrated circuits for the electronics industry. Integrated circuits and discrete devices are made of metal-semiconductor, semicondutor-semiconductor, and metal-insulator-semiconductor junctions and layered thin film structures. In general, the electrical properties of a device (IC or discrete) are determined by one or more junctions. The electrical properties of the junction are dependent on the microchemistry at and near the interface. Consequently, it is very important for the device designer/physicist to understand the electronic properties which occur both at semiconductor surfaces and at semiconductor interfaces. The study of the electronic properties of semiconductor surfaces has been accomplished by either cleaving a solid sample in ultrahigh vacuum or... 

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. 

A large fraction of the material science research, and an important chapter of solid state physics are concerned with interfaces between solids, or between a solid and a two dimensional layer. Solid state electronics is based on metal-semiconductor and insulator-semiconductor junctions, but the recent developments bring the interface problem to an even bigger importance since band gap engineering is based on the stacking of quasi two dimensional semiconductor layers (quantum wells, one dimensional channels for charge transport). 

CdSe particulate films could be transferred to solid 645 supports at any stage of their growth scanning tunneling spectroscopy on a conducting substrate indicated an n-type metal-insulator-semiconductor (MIS) junction behavior... 

In a second embodiment the imager is a metal-insulator-semiconductor, MIS, structure throughout. That is, the read lines 42, 44 and 46 and output collectors 48, 50 and 52 are MIS structures. The contiguous read lines 42, 44 and 46 and output collectors 48, 50 and 52, in another embodiment, are formed in a spaced relationship by gaps and a pulsed barrier switch is utilized to control charge flow through the gaps. The use of the pulsed barrier switch makes possible a pn-junction read line and MIS output diode, or an MIS read line and pn-junction output diode. 

Figure 4.15. Top Cross section of a MISS diode. The device can be regarded as a reverse-biased metal-insulator-semiconductor diode in series with a for-ward-biased n-p Junction. It then exhibits two stable states separated by an unstable negative resistance region. Bottom Current-voltage characteristics for a GaAs-(j -TA MISS device. The LB film thickness is approximately 9 nm...

Figure 14-3. Energy diagram of a metal-insulator-semiconductor (MIS) junction at equilibrium.

The test structures used were iridium - silicon dioxide-silicon capacitors with rather large area. Available commercial hydrogen and ammonia sensors consist, e.g., of a sensing element in the form of a transistor, a heater (a diffused resistor) and a temperature sensors (a pn-junction) on the same chip with dimensions smaller than about 1x1 mm. Research and development work is, however, in several cases most easily done on metal-insulator semiconductor capacitors mounted on a thermostatted sample holder. The description of the test structures, their fabrication and physics, given below is, however, very short. More details can be found in several of the references, e.g., ref. [1 — 3,8]. 

The phenomenon of emission of light by substances due to application of AC or DC electric field is called electroluminescence (EL). It has been observed in a number of materials in form of powder, thin films, single crystals, p-n junction and metal-semiconductor and metal-insulator-semiconductor stractures, and so on. The phenomenon of EL can be considered to be comprised of three sequential processes (i) excitation, (ii) transfer of energy from site of excitation to that of emission, and (iii) recombination. The EL involves the exciation of luminescence as a result of existence of an apphed electric potential difference across the phosphor. The EL properties of nanomaterials and nanocomposites can be significantly controlled by changing the size of the particles. 

Figure 3.25 A schematic of a typical enhancement-mode n-p-n metal-insulator-semiconductor field effect transistor. The device is normally off and eonduetion is enhanced by application of a negative gate voltage relative to the source, creating an n-type channel. The source-to-drain voltage adds to the gate bias when turned on, which is why the channel is wider at one side. The hatched area under the gate indicates an optional heavily-doped polycrystalline semiconductor region as part of the gate (see also Figure 3.27). One must further prevent current flow to the substrate as this would turn the device on as if it were a bipolar junction transistor and the base were the substrate.

The conductivity of ZnO, ITO, and Sn02 can be controlled across an extremely wide range such that they can behave as insulators, semiconductors, or metal-like materials. However, these materials are all n-type electrical conductors in nature. Their applications for optoelectronics are rather restricted. The lack of p-type conducting TCOs prevent fabrication of p-n junction composed from transparent oxide semiconductors [2], The fabrication of highly conducting p-type TCOs is, indeed, still a challenge. 

Semiconductors are materials that are characterized by resistivities intermediate between those of metals and of insulators. The study of organic semiconductors has grown from research on conductivity mechanisms and structure—property relationships in solids to include applications-based research on working semiconductor junction devices. Oiganic materials are now used in transistors, photochromic devices, and commercially viable light-emitting diodes, and the utility of oiganic semiconductors continues to increase. 

Note that this is a very simplified case. A liquid junction, dual-layer insulator, trapped charges in the insulator, surface states at the insulator/semiconductor interface, channel doping profile, and multiple connecting metals have been omitted, for the sake of simplicity. They would be present in all real devices and situations, but would not affect the thought analysis in any significant way. 

A Josephson junction consists of two closely spaced superconductors separated by a weak connection (Figure 4.6.1). This connection may be provided by an insulator, a normal metal, a semiconductor, a weakened superconductor, or some other material that weakly couples the two superconductors. The two superconducting regions may be characterized by quantum mechanical wave functions and 2 respectively. Normally a much more complicated description would be necessary because... 

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