Question

Your supervisor tasked you to design a square cross-section silicon p-n junction diode with the following specifications: 1. Intrinsic concentration at 300K: n; = 1.5x 101° /cmº. 2. p-side doping: N = 1018/cm. 2. n-side doping: N = 1021/cm. 3. QNR length: W=W, = 1 um. p (a) Determine the sidelength so that the turn-on voltage of the designed diode to be 0.7V if the current rating of the diode is to be specified as 1 mA at room temperature. [Hint: You need to use necessary graphs and mathematical equations from the textbook and lectures). (b) How the performance of the diode will vary if the diffusion lengths of the electrons and holes are doubled? (c) Mention three options with scientific reasoning by which you can cut the current by half.

Answer 1

ANSWER :
0 his 1.5x 10!"/cms. No = 1021 cm3 NA = 1018 /cm3 Wp a laln=1 lm sidelength W=) wh= NA NAAND 21 1018 + 10° NATNO wn W = W= W= X 1 X um. 18 lol W = Amm 3 Drhusion length o) La Doto. of the Diffusion length is doubled Here the diffusion length depends on the carrier life time and mobility of it is doubled means the Iffe time and mobrlety also increases. > Therefore the elections and holes moves the banier at faster rate And also long diffuspon length corresponds to the long life times of election a holes

- Therefore maximum number of elections are holes are e combined. re Here Given I =IMA. of ADP QADA Lp Ln التا Post To = leakage of ADP Prot qADA Ln I = Io [e vlor Current ® sreverse saturation Current - [App nel 1) If we increase the diffusion lengths (Lo, Lp] then the Io decreases Hence the worent also reduced 2) If we decrease the cross sectional area A of Po junction then I reduces then I also reduced 3) of we increase the bias voltage to then also I will reduced to half