Discuss disadvantage of contact over normal ohmic contacts

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Reference no: EM13279561

An important advance in Si bipolar transistors is the use of polysilicon emitters. If a normal ohmic contact is made to an emitter, the injected minority density goes to zero at the ohmic contact boundary. In polysilicon emitters, heavily doped polysilicon forms the contact to the emitter. The minority density does not go to zero at the polysilicon contact, but decreases to zero well inside it. This allows one to have very thin emitter contacts for high-speed operation. Discuss the disadvantage of such a contact over a normal ohmic contact in a thin emitter. (Consider the emitter efficiency and how it is affected by a thin emitter by discussing the narrow p-n diode.)

Reference no: EM13279561

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