Wide bandgap semiconductors

Gillis H P, Choutov D A and Martin K P 1996 The dry etching of Group Ill-Nitride wide bandgap semiconductors J. Mater. 48 50-5... 

Vogel R, Hoyer P, WeUer H (1994) Quantum-sized PbS, CdS, AgiS, SbiSs, and BiiSs particles as sensitizers for various nanoporous wide-bandgap semiconductors. J Phys Chem 98 ... 

Assuming that an efficient D-A type of molecule can be synthesized, it should be possible to deposit these molecules as a monolayer onto a glass slide coated with a metal such as aluminum or a wide bandgap semiconductor such as Sn(>2. With the acceptor end of the molecule near the conductor and with contact to the other side via an electrolyte solution it should be possible to stimulate electron transfer from D to A and then into the conductor, through an external circuit and finally back to D through the electrolyte. This would form the basis of a new type of solar cell in which the layer of D-A molecules would perform the same function as the p-n junction in a silicon solar cell (50). Only the future will tell whether or not this concept will be feasible but if nature can do it, why can t we ... 

The size of the bandgap can vary from a fraction of an eV (in the IR region of the spectrum) to ca. 4 eV or more (wide-bandgap semiconductors). The upper limit is somewhat arbitrary a substance commonly thought of as an insulator such as diamond has a large bandgap of 5.5 eV, but it can nevertheless be doped with elements such as B, N, or P to become an electrically-conducting semiconductor. 

J. A. Cooper, Jr., Nonvolatile Random Access Memories in Wide Bandgap Semiconductors... 

The ability to respond effectively to an event will require first responders and HAZMAT teams to coordinate thousands of details. Development of new materials for advanced telecommunications and radar could greatly improve the current response standard. Materials that can lead to faster computers, higher-density storage, and more efficient telecommunications are vital. One example of a basic area of research that could have an impact on our ability to respond to a threat is wide bandgap semiconductors, used, for instance, in phased-array radars. The development of shipboard phased-array radar systems over the past few decades has provided the military with a very high degree of situational awareness with respect to airborne targets. 

Kimg P, Razeghi M (2000) Ill-Nitride wide bandgap semiconductors, a simvey of the cimrent status and future trends of the material and device technology. Opto-Electronics Review 8(3), 201-239... 

Here, the potentiometric selectivity coefficient is given with respect to the hydroxyl ion. Single-crystal lanthanum fluoride is a wide bandgap semiconductor in which the electrical conductivity is due only to the hopping mobility of fluoride ions through the defects in the crystal. It does not respond to the La3+ ion because of the slow ion exchange of that ion. Hydroxyl ion is the only other ion that has appreciable mobility, and is the only known interference. For this reason, the measurements with a fluoride electrode are always done below pH 7, which circumvents this interference. As shown later, the consideration of ionic and/or electronic conductivity of the membrane plays a critical role also in the design of the internal contact in nonsymmetric potentiometric sensors. 

Bignozzi, C. A., Schoonover, J. R., and Scandola, F., A Supramolecular Approach to Light Harvesting and Sensitization of Wide-Bandgap Semiconductors Antenna Effects and Charge Separation. 44 1... 

Figure 33. Dye (D) sensitized electrochemical photovoltaic cell based on a wide bandgap semiconductor. Reprinted from R. Memming, Semiconductor Electrochemistry, Wiley-VCH Verlag GmbH, Weinheim (2001). Copyright 2001 with permission from Wiley-VCH Verlag GmbH.

The photoelectrochemical activity inherent in thin films of aggregated cyanine dyes permits them to act as the spectral sensitizers of wide bandgap semiconductors [69]. It is seen from Fig. 4.14 that the photoelectrochemical behaviour of semiconductor/dye film heterojunctions fabricated by deposition of 200 nm-thick films of cyanine dyes on the surface of TiC>2 and WO3 electrodes, bears close similarity to that of semiconductor electrodes sensitized by the adsorption of dye aggregates. Thus, both anodic and cathodic photocurrents can be generated under actinic illumination, the efficiency of the photoanodic and photocathodic processes and the potential at which photocurrent changes its direction being dependent on dye and semiconductor substrate [69]. 

EPR studies of metal-doped Ti02 and other oxide colloids were used for structural and functional characterization of such materials. This information is spread in many original articles, and was partially collected in [21, 220-222]. Various paramagnetic ions such as Mo5+, W5+, Cr5+, Nb4+, Ta4+, Mn4+, Mn3+, Cr3+, Fe3+, Ce3+, Al3+, Pt3+, Ni3+, Ni2+, Ni+, Co2+, Cu2+, etc., were used as spin dopants. As in the previous paragraph, Table 8.9 contents the spin-Hamittonian parameters of metal centers in Ti02 (rutile - R, anatase - A, brookite - B), and the same data concerning other wide bandgap semiconductor oxides are collected in Table 8.10. 

For wide bandgap semiconductors, such as III-V nitrides, the thermal techniques (DLTS, DDLTS, ICTS) can only detect deep levels which are energetically located within 1 eV of either bandedge for practical measurement conditions. To access deep levels near midgap optical excitation of carriers (ODLTS, OICTS) is necessary. 

While EQN (1) can be used to verify an NEA for wide bandgap semiconductors, another aspect that signals the presence of an NEA is the appearance of a sharp peak at the low kinetic energy end of the spectrum. This feature is attributed to electrons thermalised to the conduction band minimum. For a positive electron affinity, these electrons would be bound in the sample and not observed in the spectrum. 

Controlled introduction of impurities forms the basis of much of semiconductor technology indeed p-type (acceptor-doped) and n-type (donor-doped) layers and the junctions between them control carrier confinement, carrier flow and ultimately the device characteristics. Achieving both n-type and p-type conductivity has traditionally proved to be a challenge in wide-bandgap semiconductors. 

Excitation of the crystalline material, leading to the electron transfer from the VB to the CB by UV or visible light, corresponds to energy of photons in the range of approximately 1-4 eV. The materials characterized by similar bandgap energy can be classified as semiconductors or wide bandgap semiconductors. 

Gold nanoparticles are virtually not luminescent, but silver nanoparticles show plasmon emissions with reasonable quantum yields. Furthermore, the non-radiative decay, resulting in electron-hole pair generation, may be used for photosensitization of wide bandgap semiconductors (see Figure 7.5) [16,17]. Similar effects may also be observed as direct photoinduced electron transfer between metal surfaces and surface-bound molecules [18]. 

Considering the wide bandgap semiconductor crystal (there are mainly oxides, sulphides, selenides, and halides in this group of materials) the visible- or UV-light... 

Hebda M, Stochel G, Szacilowski K, Macyk W. Optoelectronic switches based on wide bandgap semiconductors. J Phys Chem B 2006 110 15275-83. 

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