Doping intentional

Doping intentionally introduces impurities into the semiconductor substrate to control its electronic... 

The other interesting challenge from a synthetic viewpoint is the synthesis of doped QDs, particularly to study their magneto-optical properties. Doping transition metal ions in bulk as well as nanoscale semi-conductors has been an important area of study for the past couple of decades. Recent studies have further shown that for several applications, dopant associated emission from semiconductor nanocrystals may be more advantageous than the usual band-edge emission. Extensive attempts have been made to dope intentional impurities in various semiconductor nanocrystals, including those in ZnSe, ... 

Point-defect ordering (e.g., vacancy-dopant pairs) leads to interesting complications. Preparation conditions themselves (e.g., oxygen partial pressure and temperature in oxides) thermodynamically define and control this defect content and structure. It is important to realize that point defects are thermodynamically allowed and defined they are not anomalous in the least. Therefore, undoped, high-purity compounds may exhibit sizable nonstoichiometry due to intrinsic point defects. Doping (intentional addition of an impurity) allows one to precisely control the point-defect content and nonstoichiometry and, thereby, the properties. Transport properties are influenced by the point defects. Electrical conduction (hole or electron transport) and solid state diffusion of atoms generally vary with the quantity and type of point defects. 

Semiconductors are a class of materials whose conductivity, while highly pure, varies witli temperature as exp (-Ag//cg7), where is tlie size of a forbidden energy gap. The conductivity of semiconductors can be made to vary over orders of magnitude by doping, tlie intentional introduction of appropriate impurities. The range in which tlie conductivity of Si can be made to vary is compared to tliat of typical insulators and metals in figure C2.16.1. 

PO7 and their rare-earth-doped compounds as starting materials for scintillation studies, with the intention of obtaining new scintillation materials with large, light yield and short decay time. 

In this sub-subsection, the Er doping of amorphous silicon is discussed. The problem of limited solubility of Er in crystalline silicon has been circumvented. However, the electrical properties of pure a-Si are poor compared to c-Si. Therefore, hydrogenated amorphous silicon is much more interesting. Besides, the possibility of depositing a-Si H directly on substrates, i.e., optical materials, would make integration possible. Both low-pressure chemical vapor deposition (LPCVD) [664] and PECVD [665, 666] have been used to make the a-Si H into which Er is implanted. In both methods oxygen is intentionally added to the material, to enhance the luminescence. 

Electric current is conducted either by these excited electrons in the conduction band or by holes remaining in place of excited electrons in the original valence energy band. These holes have a positive effective charge. If an electron from a neighbouring atom jumps over into a free site (hole), then this process is equivalent to movement of the hole in the opposite direction. In the valence band, the electric current is thus conducted by these positive charge carriers. Semiconductors are divided into intrinsic semiconductors, where electrons are thermally excited to the conduction band, and semiconductors with intentionally introduced impurities, called doped semiconductors, where the traces of impurities account for most of the conductivity. 

As mentioned in Sect. 3.4.3, very broad Knight shifted peaks were also observed by 71Ga MAS-NMR in samples of h-GaN either with unintentionally-doped shallow donors (primarily Si and O) or intentionally doped with 0.13% Ge,... 

In principle LVM spectroscopy is not the only way to evidence the presence of hydrogen in bulk materials not intentionally doped with hydrogen. Shinar et al. (1986) attributed optically detected electron nuclear double resonance (ODENDOR) lines to hydrogen associated with a PGa antisite-related defect in GaP. However the identification of these ODENDOR lines is not unambiguous as it has been recently proposed that these lines could be P-related (Watkins, 1989). 

Intentional impurities, doping After the comments previously reported on impurity effects and on the path towards higher and higher purity, a few remarks may be noteworthy on intentional addition of Impurities . To underline this point we quote... 

Exposure to toxicants can vary, producing what is known as acute or chronic poisoning. Poisoning can also be classified according to the intent of use. Poisoning can either be suicidal (non-accidental) or accidental in nature. Recreational poisoning, such as substance abuse, can be a source of harmful intoxication and, in some cases, can lead to addiction and withdrawal symptoms. Intentional harm is observed when there is criminal doping with sedative-hypnotic medicines, often associated with robberies. 

Although oxidation and diffusion are closely interrelated processes, they will be discussed separately in this chapter. However, the effects of oxidation on diffusion and those of doping on oxidation will be covered to emphasize the interrelationships that exist. The treatment of the subject is not exhaustive my intention is to give the reader a background of the subject and to inform the reader about the issues and the gaps in our knowledge of these processes. 

In order to optimize the photorefractive performance of BaTi03, it is necessary to control the centers involved in the ionization and trapping of photocarriers. This may be accomplished in part by intentionally doping the crystal with various transition metal or rare earth ions, which may exist in more than one valence state. 

Possible n-doping routes of these intrinsic QS s involve electron injection from intentionally imbibed C2042 or OH (photolytic) (Ozin, G.A. Stein, A. Stucky, G.D. Godber,J.P. J. Inch Phenom., in press.), ion exchanged Cu + (thermal) or impregnated Na (thermal or electrochemical) (25). The latter technique is summarized in the following scheme ... 

Intentionally donor-doped BaTiOj The effect of po2 on the conductivity of a donor-doped system has been studied for lanthanum-doped BaTiC>3 as shown in Fig. 2.14 for 1200 °C. The behaviour differs from that shown in Fig. 2.12 for acceptor-doped material. Firstly, there is a shift of the curves towards higher oxygen pressures. Secondly, at intermediate po2 there is a region, particularly at higher lanthanum contents, where the conductivity becomes independent of p0l. At sufficiently low pressures the curves coincide with those of the pure ceramic. 

Carbon materials, especially with low thermal history, usually include some impurities. Heteroatoms also can be considered as impurities. Importantly, many results have reported that heteroatoms can be introduced into the carbon lattice intentionally, which is defined as doping [52,53], Doping... 

Malleable materials can be beaten into sheets. Ductile materials can be pulled into wires. Lustrous materials have a shine. Oxides, hydrides, and halides are compounds with 0, H, and halogens respectively. Measures of intermolecular attractions other than melting point are also higher for metal oxides, hydrides, and halides than for the nonmetal compounds. A dopant is a small quantity of an intentionally added impurity. The controlled movement of electrons in doped silicon semiconductors carries digital information in computer circuitry. 

After a few years scientists from Japan, Israel, France, USA, and other countries followed these studies. Whereas in the first papers the diamond electrodes, although of very good crystallinity, were not intentionally doped (their conductance was attributed to some unidentified impurities or point defects imparted by special thermal treatment), turning to boron-doped diamond samples [12] gave impetus to further progress in diamond electrochemistry. The number of laboratories involved in the studies of diamond electrodes is ever increasing in the last few years. 

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