|Feb28-07, 05:03 PM||#1|
Band discontinuities in semiconductor heterojunctions
Two semiconductor materials have different bandgaps, different work functions, electron affinities and dielectric constants. Let's assume they are lattice matched. The larger bandgap material is doped n-type (or N-type) and the smaller doped p-type.
In the heterojunction formed epitaxially between the materials there is a discontinuity in the conduction band and a discontinuity in the valence band. This is attributed to the absolute value of the Fermi level in the bulk N-type material being higher than that of the p-type. So a number of electrons must transfer from N to p to equalise the Fermi levels of the two sides and this net charge flow across the interface causes band bending - up for the positive space-charge region in the N-type and down for the negative space-charge region in the p-type. So far so good.
I am struggling to reconcile this with the fact that there is band bending but no discontinuity in a homojunction. The Fermi levels of the n- and p-type homojunction material do not line up because they are above and below the intrinsic Fermi level, respectively, so we get net current flow, a depletion region, etc.
I have been back and forth between four textbooks looking for satisfaction. Can anybody enlighten me?
|Mar1-07, 07:06 AM||#2|
I believe that your question in answered in Chuang's book,
|Mar1-07, 06:33 PM||#3|
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