A silicon junction is doped at ,

PHYSICS · Subjective · Fermi University Physics · Condensed Matter, Materials & Soft Matter · Semiconductor physics and devices · Semiconductor physics and devices

Condensed Matter Physics, Ch The junction: diodes, transistors, lamps and solar cells

Problem

A silicon junction is doped at

N_a=6.0\times10^{16}\,\mathrm{cm^{-3}}

N_d=2.0\times10^{16}\,\mathrm{cm^{-3}}

, giving

V_{\rm bi}=0.779\ \mathrm{V}

. A calculation for this junction treats each side separately, as if it alone had to drop the full built-in voltage,

x_n=\sqrt{\frac{2\epsilon_r\epsilon_0V_{\rm bi}}{eN_d}}\,,\qquad x_p=\sqrt{\frac{2\epsilon_r\epsilon_0V_{\rm bi}}{eN_a}}\,,\qquad W_d=x_n+x_p,

and reports

W_d=355\ \mathrm{nm}

. Find the error in this method, give the correct

W_d

, and say whether the reported answer is too large or too small.

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