Majority Carrier
A majority carrier is the dominant type of mobile charge in a doped semiconductor: electrons in n-type material and holes in p-type material. Doping decides which carrier is in the majority. Adding a donor such as phosphorus to silicon supplies one extra electron per atom, adding an acceptor such as boron creates one hole per atom, and at typical doping levels of 10^15 to 10^19 atoms per cubic centimeter the majority population is many orders of magnitude larger than the thermally generated intrinsic population of about 10^10 per cubic centimeter. The majority carriers are, in effect, set by the chemistry of the dopant rather than by temperature, which is why the term is almost a synonym for how the material was doped.
Conductivity is dominated by majority carriers because they are simply more numerous. Conductivity is σ = q × (n × μn + p × μp), where n and p are the electron and hole concentrations and μn and μp their mobilities, so in n-type silicon the electron term overwhelms the hole term by many orders of magnitude and the material behaves almost like a one-carrier conductor. That is why resistivity of doped wafers is quoted from dopant concentration alone, and why the Hall effect, which gives the sign of the dominant charge, was the standard laboratory test for whether a sample was n-type or p-type. Mobility still matters: electrons in silicon move roughly three times more easily than holes, a reason n-channel transistors drive more current than p-channel ones of the same size.
Majority-carrier devices are fast because they have no minority-carrier storage. In a bipolar transistor or a pn diode, switching off requires clearing the cloud of injected minority charge, which takes a time set by the carrier lifetime. A device whose current is carried only by majority carriers has no such cloud: when the field changes, carriers already present respond, with delays set by transit time and capacitance instead of recombination. The Schottky diode, a metal-semiconductor contact whose forward current is carried by majority carriers, switches in picoseconds to nanoseconds and shows almost no reverse recovery, so it is used in high-frequency rectifiers, in clamping logic gates, and in power supplies. The field-effect transistor is the same kind of device, and field effect, majority-carrier operation and speed are linked.
This speed advantage is a large part of why the MOSFET displaced the bipolar transistor as the workhorse of digital logic. The first MOSFET was built at Bell Labs by Dawon Kahng and Mohamed Atalla in 1959-60, and although the bipolar transistor was faster and easier to make at first, a field-effect device draws almost no steady gate current and has no storage delay. Complementary MOS logic, developed in the 1960s and adopted widely by the 1980s, then added the property that it draws significant current only while switching, which made it practical to pack billions of devices onto a chip. The processors and AI accelerators of today are overwhelmingly CMOS, switching billions of times per second, and the majority-carrier channel is the reason a single transistor can switch in picoseconds while using very little energy per operation.
Calling a transistor majority-carrier does not mean minority carriers never appear. Turning on an n-channel MOSFET pulls electrons into the surface of a p-type body, which makes a thin inversion layer in which electrons are formally minority carriers of the substrate, yet they are supplied by the source and behave like a majority population in the channel, with no recombination storage. Likewise the built-in body diode of a power MOSFET is a pn junction and does inject minority carriers, which is why its reverse recovery can still limit switching in power converters. The practical rule is that the phrase describes how current is carried in the active path, not an absolute ban on the other carrier type.
Majority-carrier behavior also has costs. A device that relies only on majority carriers cannot easily achieve the conductivity modulation that bipolar devices get for free: in a high-voltage insulated-gate bipolar transistor, injected minority carriers flood the lightly doped drift region and lower its resistance, something a pure MOSFET cannot do, so high-voltage designers accept the slower switching of the IGBT. Wide-band-gap materials such as silicon carbide and gallium nitride shift this trade-off, enabling majority-carrier Schottky diodes and MOSFETs at voltages once reserved for bipolar parts, which is why they now appear in electric-vehicle inverters and fast chargers.
Read majority carrier as the default charge of a doped crystal, chosen by the dopant and carrying nearly all the current: devices that use only it, such as MOSFETs and Schottky diodes, escape the storage delay of injected charge and so set the pace of modern digital electronics, while bipolar devices accept the delay to gain amplification and conductivity modulation.