Lecture 28

Lecture 28 - EEE 352Lecture 28 MEtal-Semiconductor...

Info iconThis preview shows pages 1–7. Sign up to view the full content.

View Full Document Right Arrow Icon
EEE 352—Lecture 28 MEtal-Semiconductor FET--MESFET A GaAs/AlGaAs Schottky-gate transistor, made at ASU. This particular device had L g ~ 45 nm. Now, we can make a field-effect transistor in a completely analogous manner to the JFET.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
METAL We first consider what happens when the semiconductor is n -TYPE doped * And its work function is SMALLER than that of the metal * Electrons are pushed AWAY from the metal forming a DEPLETION REGION, and giving rise to associated BAND BENDING Metal-Semiconductor Junctions BARRIER TO ELECTRON MOTION E F W NOTE HOW THE ENERGY BAND GAP REMAINS CONSTANT WITHIN THE SEMICONDUCTOR Electrons are depleted from the surface adjacent region. WHEN THE METAL SEMICONDUCTOR JUNCTION IS FORMED ELECTRONS MOVE INTO THE METAL THROUGH THE EXTERNAL CIRCUIT Accumulation of electrons + -
Background image of page 2
p n n For V GS < 0, the p-n junction is reverse biased. As the gate bias is increased (negatively), the width of the depletion region increases. This squeezes off the channel region, lowering the current. The current goes to zero when the depletion region reaches the back side. W D a bi A D A D a bi eN V V N N N N e V V ) ( 2 ~ ) ( 2 W - + - = ε
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Junction width increases--channel width decreases METAL W d - + Applied bias Additional depletion eV a Negative voltage, applied to the metal, relative to the semiconductor, causes additional depletion and increases the value of W, just as in the p-n junction. If the negative bias is sufficiently large, the area indicated will be totally depleted—this allows us to make a depletion-mode transistor, the MESFET.
Background image of page 4
Junction width increases--channel width decreases METAL W d - + Applied bias eV a This area of “normal” n-type semiconductor will be termed the “channel.”
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Schottky-Barrier Transistor MEtal-Semiconductor Field-Effect Transistor (MESFET) Add SOURC E and DRAIN contacts S D G=gate The SOURCE is the REFERENCE electrode V V DS
Background image of page 6
Image of page 7
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 26

Lecture 28 - EEE 352Lecture 28 MEtal-Semiconductor...

This preview shows document pages 1 - 7. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online