Definition:
Semiconductor statistics:
Semiconductors generally have both donors and acceptors. The electrons in the Conduction band can be made either through thermal excitation or by thermal ionization of the donors. Holes in the Valence band (VB) might be produced by interband excitation or through thermal excitation of electrons from the Valence band (VB) into the acceptor level. And in addition, electrons might fall from the donor levels to the acceptor level. The figure given below point out these different methods.
Determining the concentrations of carriers, both electrons and holes, taking all such methods into account, is quite complex. We should treat some special cases, which are frequently encountered in practice. Two areas might be differentiated based on the physical parameters comprised: The intrinsic and the extrinsic regions.
The intrinsic region:
The concentration of carriers in the intrinsic region is found out by thermally induced interband transitions. In this region n = p. The intrinsic region obtains when the impurity doping is small. If we represent the concentrations of donors and acceptors by Nd and Na, the requirement for the validity of the intrinsic condition is:
n >> Nd, Na
As 'n' increases rapidly with temperature, the intrinsic condition becomes more favorable at higher temperatures. All the semiconductors, however, become intrinsic at adequately high temperatures (that is, unless the doping is oddly high).
The extrinsic region:
Quite often the intrinsic condition is not satisfied. For the general doping encountered, around 1015 cm-3, the number of carriers supplied through the impurities is large adequate to change the intrinsic concentration appreciably at room temperature. The contributions of impurities, however, frequently go beyond those carriers which are supplied by interband excitation. Whenever this is so, the sample is in the extrinsic region.
Two different kinds of extrinsic regions might be distinguished. The first takes place if the donor concentration greatly exceeds the acceptor concentration, that is, if Nd >> Na. In this case, the concentration of electrons might be computed quite readily. As the donor's ionization energy (that is, the binding energy) is quite small, all the donors are basically ionized, their electrons going into the Conduction band (CB). Thus, to a good approximation,
n = Nd
A semiconductor in which n >> p is termed as an n-type semiconductor ('n' for negative). Such a sample is characterized, as we have observed, via a great concentration of electrons.
The other kind of extrinsic region takes place if Na >> Nd, that is, the doping is mainly via acceptors. By using an argument identical to the above, one then consists of:
p = Na
That is, all the acceptors are ionized. Such a material is termed as a p-type semiconductor. This is characterized through a preponderance of holes.
In illustrating the ionization of donors (and acceptors), we supposed that the temperature is adequately high in such a way that all of these are ionized. This is certainly true at room temperature. However if the temperature is progressively lowered, a point is reached at which the thermal energy becomes too small to cause the electron excitation. In that condition, the electrons fall from the Conduction band into the donor level, and the conductivity of the sample reduces dramatically. This is termed to as freeze-out, in that the electrons are now 'frozen' at their impurity sites. The temperature at which freeze-out occurs is Ed ~ kT that provides a temperature of around 100°K
The variation of the electron concentration having temperature in an n-type sample is represented schematically in the above figure.
Tutorsglobe: A way to secure high grade in your curriculum (Online Tutoring)
Expand your confidence, grow study skills and improve your grades.
Since 2009, Tutorsglobe has proactively helped millions of students to get better grades in school, college or university and score well in competitive tests with live, one-on-one online tutoring.
Using an advanced developed tutoring system providing little or no wait time, the students are connected on-demand with a tutor at www.tutorsglobe.com. Students work one-on-one, in real-time with a tutor, communicating and studying using a virtual whiteboard technology. Scientific and mathematical notation, symbols, geometric figures, graphing and freehand drawing can be rendered quickly and easily in the advanced whiteboard.
Free to know our price and packages for online physics tutoring. Chat with us or submit request at [email protected]
tutorsglobe.com ortho phosphoric acid assignment help-homework help by online compounds of phosphorus tutors
tutorsglobe.com mirabilis jalapa assignment help-homework help by online intermediate inheritance tutors
Our apt Feminist thought up to 1980 Assignment Help tutors assist you 24/7 to fetch you notable grades at budget-friendly prices.
tutorsglobe.com theories of wages assignment help-homework help by online wages tutors
Zoogeography-Oriental and Australasian Regions tutorial all along with the key concepts of Fauna of Oriental Region, Fauna of Australasian Region and Fauna of whole Australasian Region
TutorsGlobe.com Chemistry of Alkanes Assignment Help-Homework Help by Online Access Chemistry Tutors
atomic spectra tutorial all along with the key concepts of definition of atomic spectra, line spectra of atoms, spectrum of atomic hydrogen
tutorsglobe.com factors affecting photosynthesis assignment help-homework help by online plant physiology tutors
tutorsglobe.com criticism of marginal theory assignment help-homework help by online marginal productivity theory of distribution tutors
Chromosome theory of inheritance tutorial all along with the key concepts of Assumption of Chromosome theory of Inheritance, Evidence in Support of the chromosome Theory
avail affordable managerial economics assignment help service with 24x7 support of phd experts to score notable grades!
tutorsglobe.com choice under uncertainty assignment help-homework help by online intermediate microeconomics tutors
Essentials for success of uniform costing system, the success of the uniform costing is relies on Mutual belief and understanding, Accounting policies and principles, Classification and codification, etc.
www.tutorsglobe.com tutorials - assignment help: various elements or components of a system, introduction of a system in programming languages,
theory and lecture notes of theory of common mode rejection ratio i, all along with the key concepts of factors of cmrr, source and input impedance mismatch. tutorsglobe offers homework help, assignment help and tutor’s assistance on theory of common mode rejection ratio i.
1941708
Questions Asked
3689
Tutors
1451327
Questions Answered
Start Excelling in your courses, Ask an Expert and get answers for your homework and assignments!!