Semiconductors and Basic Electronic Devices flashcards

Dope silicon with a donor that has five valence electrons (phosphorus, arsenic, antimony). The loosely held fifth electron is free, so electrons are the majority carriers.

Dope silicon with an acceptor that has three valence electrons (boron, gallium, aluminum). The missing bond electron leaves a hole, so holes are the majority carriers.

No. Both are electrically neutral overall; each free carrier is balanced by a fixed dopant ion. The letter only names which mobile carrier dominates.

Forward: anode more positive than cathode; the depletion region narrows and a silicon diode conducts above about 0.6 to 0.7 V. Reverse: cathode more positive; the region widens and only tiny leakage flows.

$R=\frac{V_s-V_{LED}}{I}$: supply volts minus LED drop, divided by desired current in amperes. A 6 V supply, 2 V LED and 20 mA give 4/0.02 = 200 $\Omega$.

It is designed to conduct in reverse breakdown at its rated Zener voltage, holding that voltage nearly constant. It serves as a voltage reference or clamp and always needs a series resistor.

$\beta =\frac{I_C}{I_B}$, a unitless ratio; also $I_E=I_C+I_B$. 24 mA collector with 0.2 mA base gives 120. In saturation the outside circuit, not beta, limits $I_C$.

A BJT (emitter, base, collector) is current controlled and needs steady base current. A MOSFET (gate, drain, source) is voltage controlled; its insulated gate draws almost no steady current.