P3 We are assuming an abrupt depletion approximation for the space charge region

Question

P3 We are assuming an abrupt depletion approximation for the space charge region. That is, no free carriers exist within the depletion region and the semiconductor abruptly changes to a neutral region outside the spae charge region. This approximation is adequate for most applications, but the abrupt transition does not exist. The space charge region changes over a distance of a few Debye lengths, where the Debye length in the n region is given by Calculate LD and find the ratio of LD/X if the p-type doping concentration is Na = 8 X 10^17 cm^-3 and the n-type doping concentration is (a) Nd = 8 X 10^14 cm^-3, (b) = 8 x 10^17 cm^-3

Explanation / Answer

Here which semiconductor we are using and at what temp. doping is done is not given.So I am explaning the formula how to calculte LD / xn .I am considering T = 300 k

We have given formula for Ld = ( Es kT/ e2 Nd )                       ----------------1

            ---------------------2

Here Vbi is the barrier potential ,   K = boltzmann constant,

ni = number density of intrinsic carrier ( which is also not given in the question)

it may be calculated as

ni2 = ne * nh       

(a) when Nd = 8* 1014 cm-3

Ld = 0.145 um, xn = 1.10 um

Ld / xn = 0.13

( B) when Nd = 8* 1017

Ld/ xn = 0.16

By putting all the values in eq 1 and 2 we can calculate the ratio of LD / xn

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