JEE Main & Advanced Physics Semiconducting Devices Density of Charge Carriers

Density of Charge Carriers

Category : JEE Main & Advanced

Due to thermal collisions, an electron can take up or release energy. Thus, occasionally a valence electron takes up energy and the bond is broken. The electron goes to the conduction band and a hole is created. And occasionally, an electron from the conduction band loses some energy, comes to the valence band and fills up a hole. Thus, new electron-hole pairs are formed as well as old electron-hole disappear. A steady-state situation is reached and the number of electron-hole pairs takes a nearly constant value. For silicon at room temperature (300 K), the number of these pairs is about \[7\times {{10}^{15}}\,\,{{m}^{3}}\]. For germanium, this number is about \[6\times {{10}^{19}}/\,\,{{m}^{3}}\].

Densities of charge carriers

Material Type Density of conduction electrons (m- 3) Density of holes (m-3)
Copper Conductor \[9\times {{10}^{28}}\] 0
Silicon Intrinsic semiconductor \[7\times {{10}^{75}}\] \[7\times {{10}^{15}}\]
Silicon doped with phosphorus (1 part in \[{{10}^{6}}\]) N-type semiconductor \[5\times {{10}^{22}}\] \[1\times {{10}^{9}}\]
Silicon doped with aluminium (1 part in \[{{10}^{6}}\]) P-type semiconductor \[1\times {{10}^{9}}\] \[5\times {{10}^{22}}\]

 

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