The electron in an ntype semiconductor is called the majority carrier, whereas the hole in ntype semiconductor is termed the minority carrier. Intrinsic silicon and extrinsic silicon electrical4u. Formula for carrier concentrations in ptype and ntype semiconductors. Extrinsic carrier concentrations due to doping facstaff home.
Intrinsic and extrinsic semiconductors, fermidirac. Drift current in semiconductors depends upon a only the electric field. The number of charge carriers present per unit volume of a semiconductor material is called carrier concentration. Each trivalent impurity creates a hole in the valence band and ready to accept an electron. Pdf intrinsic carrier concentration in semiconductors. 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. Classification of semiconductor intrinsic, extrinsic. Carrier concentrations in intrinsic, ptype and ntype. We have investigated theoretically the carrier concentrations and fermilevels in extrinsic semiconductors both n and ptype, taking into account the existence of holes in valence band for ntype semiconductors and of electrons in conduction band for ptype systems. Dopant electrons easily promoted to conduction band, increasing electrical conductivity by increasing carrier density n. Examining the consequences of fermi distribution in semiconductors. 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.
Electron concentration is the number of electrons per unit volume in the conduction band of the material. 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. 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. 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. 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. N a n d, n a n i, holes p are the majority carriers and electrons n are the minority carriers. Intrinsic semiconductor and extrinsic semiconductor. Difference between intrinsic and extrinsic semiconductor.
An intrinsic semiconductor also called an undoped semiconductor or i type semiconductor. Equilibrium charge carrier statistics in semiconductors 7. To indicate the quantitative implications of the theoretical analyses, we have performed some. Carrier concentrations and fermilevels in extrinsic.
This is a supplement on the concepts of charge carriers, intrinsic and extrinsic semiconductors, carrier concentrations, the fermidirac distribution function and the. Temperature dependence of semiconductor conductivity. For extrinsic semiconductors, we can use impurity to control the carrier concentration. Semiconductors are categorized into one of 2 groups. In intrinsic semiconductors fermi level is always lies between valence band and conduction band. The impurity modifies the electrical properties of the semiconductor and makes it more suitable for electronic devices such. As against, extrinsic semiconductors are said to be impure as an impurity is. 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. Derive the expression for carrier concentration of. Intrinsic semiconductors ii engineering libretexts. Leading to an overall decline in the total number of charge carriers. Doitpoms tlp library introduction to semiconductors. Carrier concentration a intrinsic semiconductors inst. This means it is the concentration of dopant atoms, since it is more than.
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. Due to the applied voltage, the electron leaves the valence band and creates a positive hole in its place. Ravindran, phy02e semiconductor physics, 17 january 2014. 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. Derive the expression for carrier concentration of electron and holes it intrinsic and extrinsic semiconductor. The number of charge carriers determined by the properties of the m aterial itself instead of the amount of impurities. It is a pure semiconductor without any significant dopant species present. 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.
Semiconductor physics charge carriersgeneration and recombination. Silicon is doped with phosphorus atoms column v of mendeleev table with a concentration of 10 18 cm3. Dependence on donor and acceptor impurity concentrations. The process of adding impurities deliberately is termed as doping and the atoms that are used as an impurity are termed as dopants. The main purpose of this handout is to summarize how we calculate the free carrier concentrations and the position of fermi level, and their temperature dependence at various useful limits, for bulk semiconductors at thermal equilibrium. If the donor electron concentration is much greater than the intrinsic carrier concentration, then the hole concentration contributing to the. One is intrinsic semiconductor and other is an extrinsic semiconductor. For an intrinsic semiconductor with gap width e g 0. There are two di erent types of extrinsic semiconductors. 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. So the intrinsic carrier concentration in silicon at room temperature is approximately n i 1. Doped semiconductors either n type or p type are known as extrinsic semiconductors.
Intrinsic semiconductor and extrinsic semiconductor the semiconductor is divided into two types. Ravindran, carriers concentration in semiconductors iv uio. Extrinsic semiconductors 10 simple impurity with two charge states, e. 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. The semiconductor industry heavily favors the use of extrinsic. This will make the semiconductor an ntype material. The concentration of these carriers is known as intrinsic carrier concentration. For an intrinsic semiconductor the number of carriers are generated by thermally or electromagnetic radiation for a pure sc. 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. Carrier concentrations and fermilevels in extrinsic semiconductors.
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. 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. Semiconductors doped in this way are termed ptype semiconductors. If nd ni, doping controls carrier concentration extrinsic semiconductor. They are free electrons and holes the number of electrons per unit volume in the conduction band or the number of holes per unit volume in the valence band is called intrinsic carrier concentration. 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. That is, the minority carrier concentration determines the recombination rate. Temperature dependence of carrier concentration extrinsic. 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. Conversely, in a ptype semiconductor, holes are majority carriers and electrons are minority carriers. In ptype semiconductor trivalent impurity is added. Temperature range in an extrinsic semiconductor where the majority carrier concentration and dopant concentration are. Ravindran, phy02e semiconductor physics, 30 january 20. At temperature exceeding critical temperature the extrinsic semiconductor behaves like an intrinsic semiconductor but with higher conductivity.
To determine the total carrier concentration, we must also consider spacecharge neutrality. Pdf intrinsic and extrinsic semiconductors, fermidirac. 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. 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. Carrier concentrations in intrinsic, ptype and ntype semiconductors. In intrinsic semiconductor, when the valence electrons broke the covalent bond and jumps into the conduction band, two types of charge carriers gets generated.