Virtual Labs

High-Speed Carrier Transport and Tunneling Devices

1. In high-speed carrier transport, which factor primarily limits the drift velocity of carriers in a semiconductor?

a: Carrier recombination Explanation

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b: Velocity saturation due to scattering Explanation

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c: Tunneling probability Explanation

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d: Avalanche breakdown Explanation

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2. What is the main quantum phenomenon enabling ultrafast operation in tunnel diodes?

a: Impact ionization Explanation

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b: Thermal diffusion Explanation

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c: Quantum mechanical tunneling Explanation

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d: Drift velocity enhancement Explanation

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3. Which device uses avalanche multiplication followed by transit-time delay to generate microwave oscillations?

a: Esaki diode Explanation

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b: IMPATT diode Explanation

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c: Schottky diode Explanation

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d: Varactor diode Explanation

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4. If the transit time of carriers under drift-diffusion is τ_dd and under tunneling is τ_tun, what is typically true?

a: τ_tun ≫ τ_dd Explanation

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b: τ_tun ≪ τ_dd Explanation

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c: τ_tun = τ_dd Explanation

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d: τ_tun depends only on recombination lifetime Explanation

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5. The peak-to-valley current ratio (PVCR) in a tunnel diode characterizes:

a: Efficiency of avalanche multiplication Explanation

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b: Magnitude of negative-resistance effect Explanation

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c: Breakdown voltage stability Explanation

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d: Carrier lifetime under forward bias Explanation

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6. In an IMPATT diode, if the transit time τ_transit decreases, the oscillation frequency f_osc will:

a: Decrease proportionally Explanation

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b: Increase proportionally Explanation

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c: Remain constant Explanation

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d: Drop to zero Explanation

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7. For a tunnel barrier of width W = 10 nm, the transmission probability T roughly follows:

a: T ∝ e^(-W) Explanation

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b: T ∝ W² Explanation

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c: T ∝ 1/W Explanation

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d: T is independent of W Explanation

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8. At very high electric fields (>10^5 V/cm), carrier velocity in semiconductors tends to:

a: Increase linearly without limit Explanation

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b: Saturate at a constant value Explanation

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c: Drop to zero due to recombination Explanation

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d: Become infinite due to tunneling Explanation

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9. In an Esaki diode, negative resistance appears because:

a: Avalanche carrier multiplication dominates Explanation

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b: Electrons tunnel between overlapping conduction and valence bands Explanation

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c: Carrier lifetime is extremely short Explanation

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d: Junction temperature decreases sharply Explanation

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