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Semiconductor Junctions: n-P Heterojunction
Written by J. Y. Wah, C. J. Hepburn.
If the narrow band gap semiconductor is doped n-type and the larger gap semiconductor is doped P-type. When they are brought together, a space charge will exist due to the diffusion and redistribution of free carriers at thermal equilibrium.
The space charge distribution r (x) is
(1)
The electric field is proportional to integal of the charge distribution, Therefore the field will be
(2)
where the boundary condition at x = 0 gives
(3)
The electrostatic potential is
(4)
where
(5)
Therefore with equations 3, 4 and 5 the depletion length of x p is as
(6)
The energy band edges function E c (x) and E v (x) can be obtained from qV(x)
(7)
(8)
nP HeteroJunction Modelling
Using the software, we show the potential, electric, field, and energy band profiles for a n-GaAs, P AlGaAs heterojunction under equilibrium conditions of zero bias and then under reversed and forward bias respectively.
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Figure 1: nP heterojunction Modelling at thermal equilibrium, i.e. V a = 0. The two figures on the bottom, on the left is the junction under reverse bias, on the right is forward bias.
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