To create electron and hole pair in Si the the radiation particle need minimum of 3.6eV whereas the Light particle need energy just 1.1eV to generate electron hole pair which is the bandgap of the Si. Why there is a difference between these two?
Since Si is an indirect bandgap semiconductor, there will be some difference. But this much difference (1.1 eV- 3.6 eV) will come or not I am not sure.
As far as i know the minimum energy required to produce an electron hole pair is equal or slightly greater than the energy gap in case of direct gap and indirect energy gap material, respectively. The difference comes from the momentum offset which can affect a difference of energy of about kT of about 26 mev at 300K.
n case of substitutional diffusion of impurities in silicon such as Boron atoms, the activation energy of such process is about 3 electron volts that is about breaking three covalent bonds.
If you specify the process more precisely, one could explain this number. But this number is sufficient to break three covalent bonds and release 3 electron hole pairs.
best wishes
Don't mixed, forbidden bend and depletion region of semiconducting material.......
The energy gap is the shortest distance between the valence layer and conduction layer. This does not imply that to generate a pair electron hole have to use 1.1 eV only, as in the case of photo generation (because I think this was implicit in the question) is required more energy since phonton absorption is through an indirect gap, then part of the energy of the photon is transformed into in phonon. If it does not it have to see what kind of generation or recombination process is happening (Auger, Ionizing Impact or band by band). Below follows the silicon energy diagram:
Hi, I am working on semiconductor detectors and diamond detector for a long time from my experience, I have thought about it, For Photons the mean energy required is 1.1 eV or close to it because of indirect band gap but not 3.6 eV experimentally observed while for other electron, proton etc. It is 3.6 eV. The Physical process will include first creation of e-h pair for which energy required will be Eg, then these e-h pairs can go in any of the state in Conduction band and Valence Band. So It is sum of Eg and mean energy of electron in Conduction band and hole in Valence band.
ε = 3.6 eV, 2.96 eV, 8.9 eV and 13.6 eV for Si, Ge, GaN and Diamond. This energy is almost given by formula below.
ε = 2. 73 E g + 0. 55 eV
Note that this does not valid for Photon. Please go through the reference where It is calculated.
Ref: Electron-Hole-Pair Creation Energies in Semiconductors , PRL, Volume 35, Number 32
Hi
As far as I know, for direct bangap materials like GaAs, photon with energy = Eg or slightly greater. For indirect bandgap materials like Si, it would need > Eg for momentum mismatch and created phonons.
Good luck
I believe we are describing the wrong process here. The 3.6 eV is the average energy (per e-h pair) extracted from a fast electron. The bound electron must be excited into the conduction band to be collected at an attached electrode. So the relevant gap is from the bound state to an arbitrary momentum in the conduction band. Most of these scatters will not be to the bottom of the conduction band, indeed momentum conservation will require that an electron have more than double the band gap if it is to deliver energy to another bound electron. 3.6 eV is an average over this complex cascade.
Does anyone know the average excitation energy for amorphous Si?
Photon energy when equal to or greater than Eg ( bandgap Energy , then it is believed that photon is absorbed in a semiconductor which leads to transition of electron from valence band to conduction band. I want to know; is it possible to produce more than one electron -hole pair by the absorption of single photon. ?
The Energy required for Photon to create an e-h pair is little bit larger than band-gap in the case of indirect band-gap semiconductor.
One Photon can create more than one e-h pairs, this is the principle on which the germanium detector works for gamma (photon) spectroscopy. The number of e-h pairs created by 1.1 MeV gamma ray in Si is equal to = Energy/Band-gap=1.1x10^6 eV/1.1 eV=10^6 e-h pairs. This is how we do in high energy physics and it works experimentally verified things.
Shyam Kumar
No it is not how the germanium detector works. One photon will make a photo-electron, or a Compton-electron. This energetic electron will create electrons and vacancies. The electron-hole pair is a miss-use. The electron-hole pair is understood as a boson. Here the electron and the vacancy is not propagating as a boson. Other mistake is the fudge factor.
In silicon, at low or near zero temperature, there are no phonons and the excitation of a bound electron in Si will be from an arbitrary starting point in the uppermost dispersion curve of the valence band to the point in the dispersion curve of the lowest conduction band just above it (Delta k=0 (!)); the energy required will hence be the average vertical distance of the forbidden gap between Ev and Ec, which in the above band digram by Manoel Perez is somewhere between 3.7 and 3.8eV.
As I understand it, ~3.67 eV is the average energy taken to create an electron-hole pair in a electron-photon cascade in Si. Typically some event (e.g. incident x-ray or electron or other particle) generates an energetic electron. As that electron passes through the Si it loses energy by exciting other electrons etc. The result is that a number of electron-hole pairs are created, and in each interaction the electrons retain some kinetic energy in the conduction band, where there is essentially a continuum of states available. 3.67 eV is the average energy used in the creation of the electron-hole pairs. Below the pair-creation threshold the residual electron energy excites phonons.
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