Question

3.13 Si pn junction Consider a long pn junction diode with an acceptor doping Naof 1018 cm-3 on the p-side and donor concentration of Nj on the n-side. The diode is forward biased and has a voltage of 0.6 V across it. The diode cross-sectional area is 1 mm2. The minority carrier recombination time, T, depends on the total dopant concentration, Ndopant (cm), through the following approximate empirical relation (5x 10-7)/(1 + 2 10-17N1°pan.) where T is in seconds. (a) Suppose that N 1015 cm-3. Then the depletion layer extends essentially into the n-side and we have to consider minority carrier recombination time, Th, in this region. Calculate the diffusion and recombination contributions to the total diode current given N, 1018cm 3 and N-10'5 cm-3 Use Table 3.3 for u, and Mn What is your conclusion? (b) Suppose that N,- .. Then W extends equally to both sides and, further, Te = Th. calculate the diffu- and Na-10 cm-3. Use sion and recombination contributions to the diode current given N-101 cm Table 3.3 for ue and u What is your conclusion?

Answer 1

Given: - Let us consider a long p_n junction diode with an acceptor doping N_a of 10^18 cm^- 3 On the p - side and donor concentration of N_d on the n - side By Using the Table values. A) Diffusion we know that Therefore KT/e = 25.86 m^2 D_e/mu_e = KT/e D_e = mu-e times KT/e = (0.02586v) (280 cm^2 v^- 1 s^- 1) = 7.2408 cm^2 s^- 1 [Here mu_e = 280 as per table where depent is 10^18 D_n = mu_n times KT/e = (478 cm^2 v^- 1 s^- 1) (0.02586 v) = 12.36 cm^2 s^- 1 Vertical-bar Here mu_n = 478 where N_d = 10^15 cm^- 3 Le = squareroot D_e T_e = squareroot 7.2408 times 23.81 times 10^- 9 = 4.152 times 10^- 4 cm T_e = 5 times 10^- 7/1 + 2 times 10^- 17 Na = 23.81 times 10^- 9 s T_n = 5 times 10^- 7/1 + 2 times 10^- 17 N_d = 490.2 times