Editing MOSFET (section)

== Composition ==
[[file:MOSFETs.jpg|thumb|upright=1.2|Photomicrograph of two metal-gate MOSFETs in a test pattern. Probe pads for two gates and three source/drain nodes are labeled.]]

Usually the [[semiconductor]] of choice is [[silicon]]. Some chip manufacturers, most notably [[IBM]] and [[Intel]], use an [[List of semiconductor materials#Table of semiconductor alloy systems|alloy]] of silicon and germanium ([[SiGe]]) in MOSFET channels.{{Citation needed|date=July 2023}} Many semiconductors with better electrical properties than silicon, such as [[gallium arsenide]], do not form good semiconductor-to-insulator interfaces, and thus are not suitable for MOSFETs. Research continues on creating insulators with acceptable electrical characteristics on other semiconductor materials.

To overcome the increase in power consumption due to gate current leakage, a [[high-κ dielectric]] is used instead of silicon dioxide for the gate insulator, while polysilicon is replaced by metal gates (e.g. [[Intel]], 2009).<ref>{{cite web|url=http://www.intel.com/technology/architecture-silicon/45nm-core2/index.htm |archive-url=https://web.archive.org/web/20070705085953/http://www.intel.com/technology/architecture-silicon/45nm-core2/index.htm |url-status=dead |archive-date=July 5, 2007 |title=Intel 45nm Hi-k Silicon Technology |publisher=Intel}}</ref>

The gate is separated from the channel by a thin insulating layer, traditionally of silicon dioxide and later of [[silicon oxynitride]]. Some companies use a high-κ dielectric and metal gate combination in the [[45 nanometer]] node.

When a voltage is applied between the gate and the source, the electric field generated penetrates through the oxide and creates an ''inversion layer'' or ''channel'' at the semiconductor-insulator interface. The inversion layer provides a channel through which current can pass between source and drain terminals. Varying the voltage between the gate and body modulates the [[electrical conductivity|conductivity]] of this layer and thereby controls the current flow between drain and source. This is known as enhancement mode.