Each trivalent impurity creates a hole in the valence band and ready to accept an electron. Ravindran, phy02e semiconductor physics, 30 january 20. The activation energy for electrons to be donated by or accepted to impurity states is usually so low that at room temperature the concentration of majority charge carriers is similar to the. The pure form of the semiconductor is known as the intrinsic semiconductor and the semiconductor in which intentionally impurities is added for making it conductive is known as the extrinsic semiconductor. Conversely, in a ptype semiconductor, holes are majority carriers and electrons are minority carriers. For an intrinsic semiconductor the number of carriers are generated by thermally or electromagnetic radiation for a pure sc. Semiconductors are categorized into one of 2 groups. If nd ni, doping controls carrier concentration extrinsic semiconductor. Pdf intrinsic carrier concentration in semiconductors.
Carrier concentrations and fermilevels in extrinsic. Temperature range in an extrinsic semiconductor where the majority carrier concentration and dopant concentration are. The impurity modifies the electrical properties of the semiconductor and makes it more suitable for electronic devices such. Silicon is doped with phosphorus atoms column v of mendeleev table with a concentration of 10 18 cm3. Difference between intrinsic and extrinsic semiconductor the intrinsic and extrinsic semiconductors are distinguished from each other considering various factors such as doping or the addition of the impurity, density of electrons and holes in the semiconductor material, electrical conductivity and its dependency on various other factors. The electron in an ntype semiconductor is called the majority carrier, whereas the hole in ntype semiconductor is termed the minority carrier. The 5th in a five valence electrons is readily freed to wander about the lattice at room temperature there is no room in the valence band so the extra electron becomes a carrier in the conduction band does not increase the number of hole concentration. The concentration of these carriers is known as intrinsic carrier concentration. In an extrinsic semiconductor the increase in one type of carrier n or p reduces the concentration of the other through recombination so that the product of the two n and p is a constant at a any given temperature. The intrinsic carrier concentration is defined as the number of electrons per unit volume in the conduction band or the number of holes per unit volume in the valence band. Fermi level of intrinsic and extrinsic semiconductors. At temperature exceeding critical temperature the extrinsic semiconductor behaves like an intrinsic semiconductor but with higher conductivity. Carrier concentrations in intrinsic, ptype and ntype semiconductors. This relationship is valid for both intrinsic and extrinsic semiconductors.
Intrinsic semiconductors ii engineering libretexts. Semiconductors doped in this way are termed ptype semiconductors. The number of charge carriers determined by the properties of the m aterial itself instead of the amount of impurities. Due to the applied voltage, the electron leaves the valence band and creates a positive hole in its place. Carriers concentration in semiconductors iv extrinsic material donation of electrons an impurity from column v introduces an energy level very near the conduction band in. Examining the consequences of fermi distribution in semiconductors. Extrinsic carrier concentrations due to doping facstaff home. One is intrinsic semiconductor and other is an extrinsic semiconductor. When electron concentrations nnumber of electronscm3 exceed the hole concentration. Temperature dependence of carrier concentration extrinsic. In intrinsic semiconductor, when the valence electrons broke the covalent bond and jumps into the conduction band, two types of charge carriers gets generated. There are two di erent types of extrinsic semiconductors. This doped semiconductor is called an extrinsic material.
Semiconductors doped with donor or acceptor atoms to engineer their conductivity are called extrinsic. Dependence on donor and acceptor impurity concentrations. Ravindran, carriers concentration in semiconductors iv uio. Temperature dependence of semiconductor conductivity. Carrier concentrations and fermilevels in extrinsic semiconductors. An intrinsic semiconductor also called an undoped semiconductor or i type semiconductor. Dopant electrons easily promoted to conduction band, increasing electrical conductivity by increasing carrier density n. It is a pure semiconductor without any significant dopant species present.
Doped semiconductors either n type or p type are known as extrinsic semiconductors. Practically in pure or intrinsic silicon crystal the number of holes p and electrons n are equal to each other, and they are equal to intrinsic carrier concentration n i. If the donor electron concentration is much greater than the intrinsic carrier concentration, then the hole concentration contributing to the. N a n d, n a n i, holes p are the majority carriers and electrons n are the minority carriers. Carrier concentration a intrinsic semiconductors inst.
Doitpoms tlp library introduction to semiconductors. The number of charge carriers present per unit volume of a semiconductor material is called carrier concentration. This will make the semiconductor an ntype material. Equilibrium charge carrier statistics in semiconductors 7. Extrinsic material this is a type of impure semiconductor that has been doped in order to enhance its conductivity. Leading to an overall decline in the total number of charge carriers. Classification of semiconductor intrinsic, extrinsic.
Ravindran, phy02e semiconductor physics, 17 january 2014. Extrinsic semiconductors 10 simple impurity with two charge states, e. An extrinsic semiconductor which has been doped with electron donor atoms is called an ntype semiconductor, because the majority of charge carriers in the crystal are negative electrons. Pdf intrinsic and extrinsic semiconductors, fermidirac. Intrinsic semiconductor and extrinsic semiconductor. Carrier concentration a intrinsic semiconductors pure singlecrystal material for an intrinsic semiconductor, the concentration of electrons in the conduction band is equal to the concentration of holes in the valence band. An electron acceptor dopant is an atom which accepts an electron from the lattice, creating a vacancy where an electron should be called a hole which can move through the crystal like a. Extrinsic semiconductors are also called impurity semiconductors or doped semiconductors. Semiconductor physics charge carriersgeneration and recombination. In intrinsic semiconductors fermi level is always lies between valence band and conduction band. Lecture 2 semiconductor physics i outline intrinsic bond model. In intrinsic or pure semiconductors, the carrier concentration of both electrons and holes at normal temperatures very low, hence to get appreciable current density through the semiconductor, a l arge electric.
For extrinsic semiconductors, we can use impurity to control the carrier concentration. Semiconductor in equilibrium density of states function, ge fermidirac distribution function, fe distribution function and fermi energy equilibrium distribution of electrons and holes n 0 and p 0 equation intrinsic carrier concentration fermi level for intrinsic semiconductor extrinsic semiconductor. Commonly, the carrier concentrations in extrinsic semiconductors are calculated on the assumption that all free carriers originate from the impurity levels. With the increase in temperature of an extrinsic semiconductor, the number of thermally generated carriers is increased resulting in increase in concentration of minority carriers. Formula for carrier concentrations in ptype and ntype semiconductors.
Carrier concentrations in intrinsic, ptype and ntype. Unlike intrinsic semiconductors, which are naturally occurring group 14 elements, extrinsic semiconductors are artificially doped with impurities that add additional electrons to the lattice, allowing increased conduction. Carrier concentrations southern methodist university. Density of charge carriers in semiconductors today. To indicate the quantitative implications of the theoretical analyses, we have performed some. This means it is the concentration of dopant atoms, since it is more than. The process of adding impurities deliberately is termed as doping and the atoms that are used as an impurity are termed as dopants. Intrinsic and extrinsic semiconductors 1 effective mass the electrons in a crystal are not free, but instead interact with the periodic potential of the lattice. Intrinsic semiconductor and extrinsic semiconductor the semiconductor is divided into two types. So the intrinsic carrier concentration in silicon at room temperature is approximately n i 1. That is, the minority carrier concentration determines the recombination rate. To determine the total carrier concentration, we must also consider spacecharge neutrality. Under thermal equilibrium conditions, the pn product remains constant, or p 0n 0n i 2, where the subscript indicates equilibrium and n i is still the intrinsic carrier concentration. The factor that generates a key difference between intrinsic and extrinsic semiconductor is that the intrinsic semiconductors are said to be pure and thus no impurity concentration is present in it.
For an intrinsic semiconductor with gap width e g 0. This is a supplement on the concepts of charge carriers, intrinsic and extrinsic semiconductors, carrier concentrations, the fermidirac distribution function and the. Drift current in semiconductors depends upon a only the electric field. Density ne is given by product of density states ne and a probability of occupying energy range fe. Intrinsic and extrinsic semiconductors, fermidirac. The semiconductor industry heavily favors the use of extrinsic. Difference between intrinsic and extrinsic semiconductor. As against, extrinsic semiconductors are said to be impure as an impurity is. Chapter 2 spring 2003 ee lecture 2, slide 2 definition of terms n number of electronscm3 p number of holescm3 ni intrinsic carrier concentration in a pure semiconductor.
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