Inversion (semiconductor)
When the inversion is in the semiconductor technology, both an operating state of an MIS field effect transistor as well as the general case, that, in a semiconductor, the density of the minority carriers reach the density of the majority charge carriers, or exceeds, respectively.
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When doping a semiconductor, depending on the type of dopant, either n- or p-doping occurs. The type of doping is the dominant charge carrier (majority or even the majority charge carriers called) to, at an n-type impurity are the electrons and the p-doping hole (holes). Both electrons and defect electrons always appear together in a semiconductor. During the doping, the concentration of the majority charge carriers increases, at the same time the concentration of the minority charge carriers decreases, since these recombine with the majority charge carriers .
With the help of an MIS structure such as the MOSFET , these natural conditions (equilibrium) can be changed or even reversed. For this purpose, a positive voltage is applied to the gate of an n-channel MOSFET (p-doped substrate), for example. Electrostatic attraction causes more electrons (minority charge carriers) to collect at the semiconductor-insulator boundary layer (e.g. silicon - silicon dioxide ) and recombine more intensely with the defect electrons (majority charge carriers). With increasing voltage, the concentration of the minority charge carriers increases and that of the majority charge carriers decreases. The inversion occurs when the concentration of the actual minority charge carriers (electrons in the example) at the interface between the semiconductor and the insulator is equal to or greater than the concentration of the majority charge carriers. In the case of the n-channel MOSFET, a quasi n-conducting area is formed at the interface, the n-conducting channel, the normally-off transistor is now conducting.