Semiconductor Devices and Electronics Flashcards
7 cards from real BEE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
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Which semiconductor device is best suited for high-power, high-frequency RF amplification due to its superior electron mobility?
Answer: GaAs MESFET
GaAs MESFETs leverage GaAs's high electron mobility (~8500 cm²/V·s vs. Si's ~1400) for superior high-frequency performance.
The gain-bandwidth product (ft) of a BJT is determined by:
Answer: The transit frequency where current gain falls to unity
ft is the frequency at which the small-signal current gain magnitude falls to 1, characterizing the transistor's high-frequency limit.
In a MOSFET, subthreshold conduction refers to:
Answer: Drain current flowing even when VGS < VT
Subthreshold current flows via diffusion even below VT and is characterized by the subthreshold slope (~60 mV/decade at room temperature).
The depletion approximation in p-n junction analysis assumes:
Answer: The depletion region has abrupt boundaries with zero free carriers inside
The depletion approximation treats the depletion region as having abrupt edges with all mobile carriers absent, simplifying Poisson's equation.
A thyristor (SCR) can be turned OFF by:
Answer: Reducing anode current below the holding current
Once latched, an SCR can only be turned off by reducing anode current below the holding current IH, not by gate control.
In an n-type semiconductor, adding acceptor impurities causes the Fermi level to:
Answer: Move closer to the valence band
Acceptors compensate donor electrons, reducing n-type character and shifting the Fermi level toward the valence band.
The Miller effect in an amplifier circuit causes the effective input capacitance to be:
Answer: Multiplied by (1 + |Av|)
Miller's theorem shows that a feedback capacitance Cf appears as (1 + |Av|)·Cf at the input, greatly increasing effective input capacitance.