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Unformatted text preview: 2.1 (a) k = 8 . 617 10 5 eV / K n i ( T = 300 K) = 1 . 66 10 15 (300 K) 3 / 2 exp bracketleftbigg . 66 eV 2 (8 . 617 10 5 eV / K) (300 K) bracketrightbigg cm 3 = 2 . 465 10 13 cm 3 n i ( T = 600 K) = 1 . 66 10 15 (600 K) 3 / 2 exp bracketleftbigg . 66 eV 2 (8 . 617 10 5 eV / K) (600 K) bracketrightbigg cm 3 = 4 . 124 10 16 cm 3 Compared to the values obtained in Example 2.1, we can see that the intrinsic carrier concentration in Ge at T = 300 K is 2 . 465 10 13 1 . 08 10 10 = 2282 times higher than the intrinsic carrier concentration in Si at T = 300 K. Similarly, at T = 600 K, the intrinsic carrier concentration in Ge is 4 . 124 10 16 1 . 54 10 15 = 26 . 8 times higher than that in Si. (b) Since phosphorus is a Group V element, it is a donor, meaning N D = 5 10 16 cm 3 . For an ntype material, we have: n = N D = 5 10 16 cm 3 p ( T = 300 K) = [ n i ( T = 300 K)] 2 n = 1 . 215 10 10 cm 3 p ( T = 600 K) = [ n i ( T = 600 K)] 2 n = 3 . 401 10 16 cm 3 2.3 (a) Since the doping is uniform, we have no diffusion current. Thus, the total current is due only to the drift component. I tot = I drift = q ( n n + p p ) AE n = 10 17 cm 3 p = n 2 i /n = (1 . 08 10 10 ) 2 / 10 17 = 1 . 17 10 3 cm 3 n = 1350 cm 2 / V s p = 480 cm 2 / V s E = V/d = 1 V . 1 m = 10 5 V / cm A = 0 . 05 m . 05 m = 2 . 5 10 11 cm 2 Since n n p p , we can write I tot qn n AE = 54 . 1 A (b) All of the parameters are the same except n i , which means we must recalculate p . n i ( T = 400 K) = 3 . 657 10 12 cm 3 p = n 2 i /n = 1 . 337 10 8 cm 3 Since n n p p still holds (note that n is 9 orders of magnitude larger than p ), the hole concentration once again drops out of the equation and we have I tot qn n AE = 54 . 1 A 2.4 (a) From Problem 1, we can calculate n i for Ge....
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 Spring '08
 MonaHella

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