The number of silicon atoms per m3 is 5 × 1028. This is doped simultaneously with 5 × 1022 atoms per m3 of Arsenic and 5 × 1020 per m3 atoms of Indium. Calculate the number of electrons and holes. Given that ni = 1.5 × 1016 m–3. Is the material n-type or p-type?


Given,

Number of Silicon atoms per m3 = 5 × 1028


Number of Arsenic atoms per m3 (nAs) = 5 × 1022


Number of Indium atoms per m3 (nIn) = 5 × 1020


Intrinsic charge carrier concentration (ni) = 1.5 × 1016 m-3


So, number of electrons per m-3 (ne) = nAs – ni


i.e., ne = 5 × 1022 – 1.5 × 1016 = 4.99 × 1022 m-3


If nh is the number of holes per m-3, then according to Mass-action law,


ni2 = nenh


So, nh = ni2/ne


i.e., nh =


So, nh= 4.5 × 109 m-3


The number of electrons is higher than the number of holes. So, the given material is n-type.


NOTE: Arsenic is pentavalent and Indium is trivalent. In an n-type semiconductor, electrons are the majority charge carriers i.e., nenh. In a p-type semiconductor, holes are the majority charge carriers i.e., nh ne.


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