Lecture

MOS Junctions: Surface Potential and Band Bending

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In course

MICRO-312: Physics of semiconductors devices

Les étudiants savent expliquer la physique des composants semiconducteurs, tels que diodes, transistors et composants MOS. Ils les utilisent dans des circuits électroniques fondamentaux tels qu'inverseurs et ampli. ...

Description

This lecture discusses the operation modes of a MOS junction on an n-type substrate, focusing on the surface potential and band bending. The instructor begins by describing the flatband condition, where no charge exists due to the absence of band curvature. As a negative voltage is applied to the gate, the bands bend downwards, attracting holes and leading to accumulation. The lecture then transitions to the effects of positive voltage, which pushes the energy levels down and creates a depletion region. The instructor explains the transition to weak inversion as the energy level approaches the conduction band. The discussion continues with the behavior of the junction under an n-type substrate, detailing how positive voltage attracts electrons, leading to accumulation, while negative voltage creates a depletion region. The concepts of flatband, accumulation, depletion, and weak inversion are thoroughly examined, providing a comprehensive understanding of the electrical characteristics of MOS structures.

Instructor

Pierre-André Besse

Teaching & PhD Past EPFL PhD Students Klaus Ehrmann Courses La science quantique : une vision singulière MICRO-444 Students understand the characteristics of quantum science. They master the formalism and use it in basic quantum systems: quantum wells, wires, dots or qubits. Physics of semiconductors devices MICRO-312 The students are able to explain the physics of semiconductor devices like diodes, transistors, and MOS devices. They use such devices in fundamental electroni

Official source

Ontological neighbourhood

Physics

Condensed matter physics: Solid-state physics

Related concepts (32)

Electronic band structure

In solid-state physics, the electronic band structure (or simply band structure) of a solid describes the range of energy levels that electrons may have within it, as well as the ranges of energy that they may not have (called band gaps or forbidden bands). Band theory derives these bands and band gaps by examining the allowed quantum mechanical wave functions for an electron in a large, periodic lattice of atoms or molecules.

Band bending

In solid-state physics, band bending refers to the process in which the electronic band structure in a material curves up or down near a junction or interface. It does not involve any physical (spatial) bending. When the electrochemical potential of the free charge carriers around an interface of a semiconductor is dissimilar, charge carriers are transferred between the two materials until an equilibrium state is reached whereby the potential difference vanishes.

Transistor

A transistor is a semiconductor device used to amplify or switch electrical signals and power. It is one of the basic building blocks of modern electronics. It is composed of semiconductor material, usually with at least three terminals for connection to an electronic circuit. A voltage or current applied to one pair of the transistor's terminals controls the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal.

Depletion region

In semiconductor physics, the depletion region, also called depletion layer, depletion zone, junction region, space charge region or space charge layer, is an insulating region within a conductive, doped semiconductor material where the mobile charge carriers have been diffused away, or have been forced away by an electric field. The only elements left in the depletion region are ionized donor or acceptor impurities. This region of uncovered positive and negative ions is called the depletion region due to the depletion of carriers in this region, leaving none to carry a current.

Bipolar junction transistor

A bipolar junction transistor (BJT) is a type of transistor that uses both electrons and electron holes as charge carriers. In contrast, a unipolar transistor, such as a field-effect transistor (FET), uses only one kind of charge carrier. A bipolar transistor allows a small current injected at one of its terminals to control a much larger current flowing between the terminals, making the device capable of amplification or switching. BJTs use two p–n junctions between two semiconductor types, n-type and p-type, which are regions in a single crystal of material.

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