Semiconductor preparation

Elements dissolved in boron influence its crystal structure. Dissolved impurities also influenee the physical and chemical properties of boron, especially the electrical properties, because boron is a semiconductor. Preparation of solid solutions in jS-rh boron requires a careful choice of crucible material. To avoid contamination, boron nitride or a cold, coinage-metal crucible should be used or the levitation or floating-zone melting techniques applied. 

Investigations carried out on specimens of the same semiconductor, prepared by different methods, have shown that there is a correlation between the catalytic activity of a specimen in relation to the hydrogen-deuterium exchange reaction and its initial electrical conductivity. Electron... 

Enhanced semiconductors -> Prepared by doping, that is, adding a small amount of impurity... 

CdTe is the most popular semiconductor prepared by electrodeposition due to its application in thin-film solar cells. A large number of papers thus discuss this process. Some examples are given below. They include all the electrolytes used for the electrodeposition of CdTe. 

Semiconductor Preparing Sensor type Gas tested Reference... 

Table 21-3 gives a smnmary of the interfacial charge injection and recombination rate constants of some organic and metal cyano compounds on semiconductor surfaces. Although the data is not directly comparable, as different semiconductor preparations, solvents, electrolytes, pH, time-scales and kinetic models were used, it provides a basis for understanding these important interfacial electron transfer processes. 

Comini, E., Baratto, C., Faglia, G., Ferroni, M., Vomiero, A., and Sberveg-lieri, G. [2009] Quasi-one dimensional metal oxide semiconductors Preparation, characterization and application as chemical sensors. Prog. 

Comini E, Baratto C, Faglia G, Ferroni M, Vomiero A, Sbtaveglieri G (2009) Quasi one dimensionale metal oxide semiconductors preparation, characterization and application as chemical sensors. Prog Mat Sci 54 1-67... 

In the discussion above, complete equilibrium was assumed at all times. However, the electronic properties of semiconductors prepared at elevated temperatures are frequently measured at room temperature or below. If a sample is cooled rapidly, the point defects... 

Undeniably, one of the most important teclmological achievements in the last half of this century is the microelectronics industry, the computer being one of its outstanding products. Essential to current and fiiture advances is the quality of the semiconductor materials used to construct vital electronic components. For example, ultra-clean silicon wafers are needed. Raman spectroscopy contributes to this task as a monitor, in real time, of the composition of the standard SC-1 cleaning solution (a mixture of water, H2O2 and NH OH) [175] that is essential to preparing the ultra-clean wafers. 

III-V compound semiconductors with precisely controlled compositions and gaps can be prepared from several material systems. Representative III-V compounds are shown in tire gap-lattice constant plots of figure C2.16.3. The points representing binary semiconductors such as GaAs or InP are joined by lines indicating ternary and quaternary alloys. The special nature of tire binary compounds arises from tlieir availability as tire substrate material needed for epitaxial growtli of device stmctures. 

There is also a possibility of preparing mixed III-V nitride alloys, e.g. GaAs connecting tire two sets of semiconductor materials. Their gap dependence on composition is tire subject of active research. 

We begin our discussion of nanocrystals in diis chapter widi die most challenging problem faced in die field die preparation and characterization of nanocrystals. These systems present challenging problems for inorganic and analytical chemists alike, and die success of any nanocrystal syndiesis plays a major role in die furdier quantitative study of nanocrystal properties. Next, we will address die unique size-dependent optical properties of bodi metal and semiconductor nanocrystals. Indeed, it is die striking size-dependent colours of nanocrystals diat first attracted... 

Silicon is prepared commercially by heating silica and carbon in an electric furnace, using carbon electrodes. Several other methods can be used for preparing the element. Amorphous silicon can be prepared as a brown powder, which can be easily melted or vaporized. The Gzochralski process is commonly used to produce single crystals of silicon used for solid-state or semiconductor devices. Hyperpure silicon can be prepared by the thermal decomposition of ultra-pure trichlorosilane in a hydrogen atmosphere, and by a vacuum float zone process. 

Epitaxial crystal growth methods such as molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) have advanced to the point that active regions of essentially arbitrary thicknesses can be prepared (see Thin films, film deposition techniques). Most semiconductors used for lasers are cubic crystals where the lattice constant, the dimension of the cube, is equal to two atomic plane distances. When the thickness of this layer is reduced to dimensions on the order of 0.01 )J.m, between 20 and 30 atomic plane distances, quantum mechanics is needed for an accurate description of the confined carrier energies (11). Such layers are called quantum wells and the lasers containing such layers in their active regions are known as quantum well lasers (12). 

The two-dimensional carrier confinement in the wells formed by the conduction and valence band discontinuities changes many basic semiconductor parameters. The parameter important in the laser is the density of states in the conduction and valence bands. The density of states is gready reduced in quantum well lasers (11,12). This makes it easier to achieve population inversion and thus results in a corresponding reduction in the threshold carrier density. Indeed, quantum well lasers are characterized by threshold current densities as low as 100-150 A/cm, dramatically lower than for conventional lasers. In the quantum well lasers, carriers are confined to the wells which occupy only a small fraction of the active layer volume. The internal loss owing to absorption induced by the high carrier density is very low, as Httie as 2 cm . The output efficiency of such lasers shows almost no dependence on the cavity length, a feature usehil in the preparation of high power lasers. 

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