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Unformatted text preview: Lecture 14 Wednesday February 25 EE 332 Semiconductor Devices Problem Assignment Monday Æ 5.9 omit parts d , h , and i Wednesday Æ 5.14, 5.19 Friday Æ 5.16, 6.4 First PSpice problem is posted Graded Junctions Graded junctions are a natural consequence of forming pnjunctions through compensation by diffusion. There are several common mathematical models used to represent the concentration versus position. Exponential c x A A e N N λ / ) ( = Power Law N A =Gx m Linearly Graded N A-N D =-a ( x-x ) Varactor Diode Used for Voltage Variable Capacitor -Doping N d =Gx m r r n r j V V LC n m m n V C = ∝ = = → − = + = ∝ − − 2 2 3 1 1 2 if 2 1 ω Electric Fields in a Graded Junction ( ) 3 / 1 12 2 2 for ) ( = ≤ ≤ − ≅ − + − = − = − qa V w w x w qax N N n p q dx d x x a N N j A D A D ε ε ε ξ Using Poisson’s eq. Heterojunctions The junction between two semiconductors with different band gaps is called a heterojunction. Before the junction is...
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- Spring '08
- contact potential, contact potentials, Graded Junction, NA=Gxm Linearly Graded, different contact potentials