Question 213: Semiconductors and Logic Gates

Question

A potential barrier of 0.4 V exists across a p-n junction. An electron enters the junction from the n-side with a speed of 6.0 $$	imes$$ 105 ms$$-$$1. The speed with which electron enters the p side will be $${x \over 3} 	imes {10^5}$$ ms$$-$$1 the value of x is _____________.
(Given mass of electron = 9 $$	imes$$ 10$$-$$31 kg, charge on electron = 1.6 $$	imes$$ 10$$-$$19 C.)

Accepted Answer

Conserving energy,
$${1 \over 2}m{v^2} = {1 \over 2}m{(6 	imes {10^5})^2} - 0.4\,eV$$
$$ \Rightarrow v = \sqrt {{{(6 	imes {{10}^5})}^2} - {{2 	imes 1.6 	imes {{10}^{ - 19}} 	imes 0.4} \over {9 	imes {{10}^{ - 31}}}}} $$
$$ = \sqrt {36 	imes {{10}^{10}} - {{1.28} \over 9} 	imes {{10}^{12}}} $$
$$ \Rightarrow v = {{14} \over 3} 	imes {10^5}$$ m/s
$$ \Rightarrow x = 14$$

Semiconductors and Logic Gates

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