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 protein biosynthesis assignment help-homework help by online protein metabolism tutors
www.tutorsglobe.com offers Data Modelling homework help, assignment help, case study, writing homework help, online tutoring assistance by computer science tutors.
Theory and lecture notes of Sticky-Price Equilibrium all along with the key concepts of Equilibrium on the Income-Expenditure figure, Economy Move to Equilibrium, Inventories as the Balancing Item. Tutorsglobe offers homework help, assignment help and tutor’s assistance on Sticky-Price Equilibrium.
Taxes in animals tutorial all along with the key concepts of Illustrations of Taxes in animals, Aerotaxis, Chemotaxis, Energy taxis, Phototaxis, Thermotaxis, Geotaxis, Rheotaxis and Magnetotaxis
tutorsglobe.com trypanosoma cruzi assignment help-homework help by online trypanosomes tutors
tutorsglobe.com electronegativity scales assignment help-homework help by online chemical periodicity tutors
Theory and lecture notes of Exponential and Logarithmic Models all along with the key concepts of Exponential Growth, Exponential Decay, Gaussian Model, Logistics Growth Model, Logarithmic Model. Tutorsglobe offers homework help, assignment help and tutor’s assistance on Exponential and Logarithmic Models.
One or more than one coils connected in series are termed as a coil groups.
kinetics tutorial all along with the key concepts of reaction rate, average rate and instantaneous rate, factors influencing the reaction rate, concentration effects, temperature effects, phase and surface area effects, solvent effects, catalyst effects
tutorsglobe.com merits of five kingdom assignment help-homework help by online five kingdom system of classification tutors
the claims are generally categorized into - equity (owner’s claim) and liabilities (claims of outsiders). further the liabilities are classified as either current or non-current.
Theory and lecture notes of Systems of Equations and Inequalities all along with the key concepts of Linear Inequalities, Systems of Linear Inequalities, Multivariable Linear Systems, Partial Fractions. Tutorsglobe offers homework help, assignment help and tutor’s assistance on Systems of Equations and Inequalities.
theory and lecture notes of shifting, reflecting and stretching graphs all along with the key concepts of translations, shifts, scales, reflections, digression, normal & inverse behavior, effect on domain & range. tutorsglobe offers homework help, assignment help and tutor’s assistance on shifting, reflecting and stretching graphs.
www.tutorsglobe.com offers system development plan homework help, assignment help, case study, writing homework help, online tutoring assistance by computer science tutors.
tutorsglobe.com respiratory or breathing roots assignment help-homework help by online modification of taproot tutors
1947557
Questions Asked
3689
Tutors
1473693
Questions Answered
Start Excelling in your courses, Ask an Expert and get answers for your homework and assignments!!