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Example 2: General Solution for Narrow Base Diode

Overview

  1. Situation where the quasi-neutral region in the solar cell is small, and therefore there is no recombination.
  2. The boundary conditions for the narrow base diode particular solution are:

    (1)

    (2)

Step 1: Solve for properties in depletion region

2元微信红包小扫雷群as in most devices, the solution for the electrostatic properties in the depletion region does not change, and so is given here.

Step 2: Solve for carrier concentration and current in quasi-neutral regions

Find U and G

2元微信红包小扫雷群we will set g equal to a constant and u=0.

Find general solution

we still start out with the same equation derived from the continuity equations. however, in this case the recombination is zero, so the equation becomes:

2元微信红包小扫雷群the general solution is:

Particular solution for narrow base diode with high recombination at edges

we need boundary conditions and these are:

at the edge of the depletion region

The excess minority carrier concentration Dn must be zero at x = W, or Dn(x = W)=0.

the first boundary condition gives :

2元微信红包小扫雷群the second boundary conditions gives :

which simplifies to

2元微信红包小扫雷群substituting these equations into the general solutions gives the equation for the carrier concentration:

2元微信红包小扫雷群the current is found by differentiating the carrier concentration:

simplifying this gives:

Step 3: Find total current

the change in the current across the depletion region is given by the general equation:

2元微信红包小扫雷群if there is a constant generation across the depletion region and no recombination, then

, where xn2元微信红包小扫雷群 is the depletion width in the p-type material.

Jn at the edge of the depletion region in the p-type material is:

Jn at the edge of the depletion region in the n-type material is:

An analogous equations exists for Jp, and the total current is: