A designer wants a fast silicon photodiode for light of

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

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

Problem

900\,\mathrm{nm}

, whose absorption depth in silicon is about

40\,\mu\mathrm{m}

: most photons should be absorbed inside the depletion region itself, where the field sweeps out the pairs at once, rather than deep in the neutral silicon, where collection depends on a carrier wandering unpredictably to the junction before it recombines. The diode is a symmetric junction doped at

N_a=N_d=1.0\times10^{15}\,\mathrm{cm^{-3}}

(

V_{\rm bi}=0.595\ \mathrm{V}

, unbiased width

1.24\,\mu\mathrm{m}

). Find the reverse bias needed to widen the depletion region to the full

40\,\mu\mathrm{m}

absorption depth, and the peak field that bias produces.

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