dimension (1): The dimension of a variable expresses the type of quantity being measured. This is occaisionally confused with the units of a variable. If one is discussing a distance or a length, then the measurement can be taken in any of several units, but there is a specific dimension. Feet, yards, miles, meters, and kilometers are all examples of units which measure the dimension of length. Gallons and liters are units which measure the dimension of volume (length cubed). (See also unit)
dimension (2): The dimension defines the directions through which something can move within a coordinate system. The dimension encorporates two directions: up-down, right-left, north-south, east-west, forward-backward, etc. One direction is "positive" and the other is "negative." It is generally arbitrary which is referred to as "positive," but there is usually a guiding convention for consistency.
doping: (Context: condensed matter physics) Doping is the process by which a semi-conductor is suffused with some element other than that which comprises the semi-conductor itself. This is the introduction of impurities; generally, the different elements are vastly outnumbered by the original element. (See also donor doping and acceptor doping)
doping, donor: (Context: condensed matter physics) This is the process of doping a semi-conductor with an impurity which has more protons per atom (and thus more electrons per atom). Generally, the atoms in a semicondutor will form bonds with neighboring atoms in such a manner that each atom sees a "closed shell". Since the donor atom introduces an additional electron, this electron is loosely bound; it is more free to move than the electrons which form the closed shell. This additional electron is easily put into the conduction band and can therefore conduct electricity easily. A donor-doped semiconductor is called an n-type semiconductor because it has negative charge carriers. (See also negative charge carriers and acceptor doping)
doping, acceptor: (Context: condensed matter physics) This is the process of doping a semi-conductor with an impurity which has fewer protons per atom (and thus fewer electrons per atom). Generally, the atoms in a semicondutor will form bonds with neighboring atoms in such a manner that each atom sees a "closed shell". Since the acceptor atom introduces fewer electrons, the shell is not closed; all of the electrons are tightly bound. If an additional electron can be found, it will tend to fill the shell. Occaisionally, it is possible for an electron in a neighboring closed shell to fill this shell leaving a new unclosed shell behind. The "motion" of this closed shell is referred to as the motion of the positive charge carriers. An acceptor-doped semiconductor is called a p-type semiconductor because it has positive charge carriers. (See also positive charge carriers and donor doping)