Physics · Semiconductor Electronics : Materials, Devices And Simple Circuits · NEET
A hole is not a real particle. It is the empty place left in a covalent bond after a bound electron breaks away. But we treat it as an apparent free particle with effective positive charge +q because it is much easier to track the one empty spot than to track the millions of bound electrons around it. So a hole is a bookkeeping idea that behaves like a real positive charge carrier.
A hole has an effective positive charge equal to +q (where q is the electron charge, about 1.6 x 10^-19 C). When an electron with charge -q leaves a bond, the neighbourhood it left behind is short one negative charge, so it looks positive. That is why a hole moves toward the negative side of an applied field, opposite to an electron.
A hole moves toward the negative potential (in the same direction as the applied electric field, since a positive charge moves along the field). An electron moves the opposite way, toward the positive potential. Both movements carry current in the same conventional direction, so the total current I = Ie + Ih, where Ie is electron current and Ih is hole current.
A hole moves when a bound electron from a neighbouring covalent bond jumps into the empty spot. Say the hole is at site 1. An electron from bond site 2 jumps to site 1. Now the electron is at site 1 and the empty spot (hole) is at site 2. So the hole appears to move from site 1 to site 2, opposite to the jumping electron. The originally freed conduction electron is not involved in this hole motion.
No. In a semiconductor two separate currents flow. Free conduction electrons move and give electron current Ie. Bound electrons hopping into vacancies make holes drift and give hole current Ih. The total current is I = Ie + Ih. In an intrinsic (pure) semiconductor both types are present in equal numbers, but electrons drift faster than holes.
A free electron moves on its own through the crystal. A hole moves only because bound electrons have to hop from bond to bond, which is a slower, step-by-step process. Because of this, for the same electric field electrons drift faster, so electron mobility is greater than hole mobility. This is exactly why an n-type sample carries more current than a p-type sample with the same carrier count.
In an intrinsic (pure) semiconductor, every broken bond makes one free electron and one hole together, so they are created in pairs. That means the number of holes equals the number of electrons: ne = nh = ni, where ni is the intrinsic carrier concentration. This equality only holds for pure material, not for doped (extrinsic) semiconductors.
The electron concentration in an n-type semiconductor is the same as the hole concentration in a p-type semiconductor. An external electric field is applied across each of them. Compare the currents in them.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
A hole is a vacancy left in a covalent bond by a departed electron, and it behaves like a free particle with effective positive charge +q.
A hole carries an effective positive charge of +q, equal in size and opposite in sign to the electron charge, about +1.6 x 10^-19 C.
The hole concept is used mainly for semiconductors, where broken covalent bonds create vacancies that carry current. It is a key idea for both intrinsic and doped semiconductors.
Thermal energy (heat) breaks a covalent bond, freeing an electron and leaving behind a vacancy. That electron-hole pair is created together, so one broken bond makes one electron and one hole.
Recombination happens when a free electron falls into a hole, filling the vacant bond and removing both carriers. At equilibrium the rate of generation of electron-hole pairs equals the rate of recombination.
There is no real positive particle moving. Hole current is the real motion of many bound electrons, but we describe it neatly as one positive hole drifting in the opposite direction.
