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I have gallium arsenide (energy gap of 1.4 eV) doped with silicon in concentration of $10^{14} cm^{-3}$ and energy level very close to the conduction band so it's act like a donor. Now we put in also chromium with concentration of $10^{17}cm^{-3}$ that act like accepotr. The problem is that the energy level of the chromium is in the middle of the bang gap, so the thermal energy is not enough to create holes in the valence band. Now i need to calculate the conductivity and mobility but i don't understand how the chromium effect them, from my understanding he has no effect on the conductivity because they are very far from valence band. Any idea?

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  • $\begingroup$ How would you go about it if the chromium was close to valence band edge? You would probably calculate the occupation of the states depending on the energy level of the acceptor states. Why can't you do it in the same way now? $\endgroup$ – lmr May 15 '18 at 12:14
  • $\begingroup$ Because you will need very high temperature to overcome 0.7 eV $\endgroup$ – אבנר יעקב May 15 '18 at 18:17
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The deep chromium acceptors take away electrons from the silicon donors. As they outnumber the donors there will be no charge carriers left except for a very small number, due to thermal ionisation of the deep acceptors and E en fewer intrinsic electrons and holes. The material will have very low conductivity.

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