Question

source V n V+ metal oxide n gate P n drain V+ channel This figure shows a typical configuration of a metal-oxide-semiconductor field effect transistor (MOSFET). The drawing shows a positive voltage at the metal gate, which activates the inversion layer, or channel, in the underlying semiconductor. (a) Using simple band diagrams, describe how a MOSFET works. In particular, explain why the current that flows between source and drain is negligible when the gate voltage is zero, but is significant when the gate voltage is large and positive. (b) In the example shown the p-type semiconductor between source and drain is labeled p to indicate a very low concentration of acceptors. Why is this important? (c) Suppose the semiconductor were a photoconductor, and the gate were replaced by a light source. Describe the behavior of the current from source to drain as the light is turned on and increased in intensity. What assumption must you make about the wavelength of the light?

          source
V
n
V+
metal
oxide
n
gate
P
n
drain
V+
channel
This figure shows a typical configuration of a metal-oxide-semiconductor field effect transistor
(MOSFET). The drawing shows a positive voltage at the metal gate, which activates the inversion layer,
or channel, in the underlying semiconductor.
(a) Using simple band diagrams, describe how a MOSFET works. In particular, explain why the
current that flows between source and drain is negligible when the gate voltage is zero, but is significant
when the gate voltage is large and positive.
(b) In the example shown the p-type semiconductor between source and drain is labeled p to
indicate a very low concentration of acceptors. Why is this important?
(c) Suppose the semiconductor were a photoconductor, and the gate were replaced by a light
source. Describe the behavior of the current from source to drain as the light is turned on and increased in
intensity. What assumption must you make about the wavelength of the light?

source
V
n
V+
metal
oxide
n
gate
P
n
drain
V+
channel
This figure shows a typical configuration of a metal-oxide-semiconductor field effect transistor
(MOSFET). The drawing shows a positive voltage at the metal gate, which activates the inversion layer,
or channel, in the underlying semiconductor.
(a) Using simple band diagrams, describe how a MOSFET works. In particular, explain why the
current that flows between source and drain is negligible when the gate voltage is zero, but is significant
when the gate voltage is large and positive.
(b) In the example shown the p-type semiconductor between source and drain is labeled p to
indicate a very low concentration of acceptors. Why is this important?
(c) Suppose the semiconductor were a photoconductor, and the gate were replaced by a light
source. Describe the behavior of the current from source to drain as the light is turned on and increased in
intensity. What assumption must you make about the wavelength of the light?

Added by Carolyn C.

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