Lecture 27

Lecture 27 - EEE 352: Lecture 27 Metal-Semiconductor...

Info iconThis preview shows pages 1–8. Sign up to view the full content.

View Full Document Right Arrow Icon

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

View Full DocumentRight Arrow Icon

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

View Full DocumentRight Arrow Icon

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

View Full DocumentRight Arrow Icon

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

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: EEE 352: Lecture 27 Metal-Semiconductor Junctions * Metal-semiconductor junctions (Schottky barriers) Metal-n-type junction Metal-p-type junction * Band-bending * Schottky-barrier height A GaAs/AlGaAs Schottky-gate transistor, made at ASU. This particular device had L g ~ 45 nm. Drain Source Source Gate Karl Ferdinand Braun Discovered rectification in metal-PbS junctions in 1874. 1909 Nobel Prize in Physics Shared with Marconi for inventions related to wireless communications. The metal-semiconductor junction was a very good detector of radio waves. Walter Schottky In 1938, he explained how the metal-semiconductor diode worked. Today it is called the Schottky diode. We have already considered the properties of the p-n junction that is formed * When two different SEMICONDUCTORS are brought together * What if we now form a METAL-SEMICONDUCTOR junction? The problem is similar to that of a p-n junction, but depends on the TYPE of doping in the semiconductor Metal-Semiconductor Junctions E F E F E v E c METAL SEMICONDUCTOR VACUUM LEVEL m s NOTE HOW THE WORK FUNCTION OF THE SEMICONDUCTOR IS DEFINED First idea: 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 + - V appl When we apply a voltage across a capacitor, charge accumulates on the surface of the capacitor plates. In a metal, this modifies the charge density only slightly, as the number of electrons in a metal is very high. However, in the semiconductor, the number of electrons is small, we must create the charge anyway possible. METAL BARRIER TO ELECTRON MOTION E F W + - The negative voltage on the metal pushes electrons away from the surface, leaving the postively charged donorsthis creates the positive charge for the capacitor. Note that the Fermi level is constant through the junction as the current is zero. The band bending is PREDOMINANTLY restricted to the SEMICONDUCTOR, since the density of electrons here is MUCH LOWER than in the metal The depletion region is therefore much WIDER in the SEMICONDUCTOR Recall our results for the p-n diode Metal-Semiconductor Junctions...
View Full Document

This note was uploaded on 10/28/2009 for the course EEE 352 taught by Professor Ferry during the Fall '08 term at ASU.

Page1 / 32

Lecture 27 - EEE 352: Lecture 27 Metal-Semiconductor...

This preview shows document pages 1 - 8. Sign up to view the full document.

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