ECE 305 1)
Spring 2015 ECE 305 Homework: Week 8 Mark Lundstrom Purdue University The sketch below shows the carrier concentrations in a PN junction at room temperature. Answer the following questions. 1a) 1b) 1c) 1d) 1e) 1f) 1g) 2)
Is the diode forward or reverse biased? Explain your answer. What is the acceptor concentration on the P-­‐side? What is the donor concentration on the N-­‐side? What is the intrinsic carrier concentration? Do low level injection conditions apply? What bias (in volts) is applied to the diode? Which is longer: the electron diffusion length on the P-­‐side of the junction or the hole diffusion length on the N-­‐side of the junction. This problem concerns the energy band diagram shown below for a diode under bias. ECE-­‐305 1 Spring 2015 ECE 305 Spring 2015 HW8 (continued): 2a) Is the diode forward or reverse biased? 2b) What is the value of the applied bias? 2c) What is the bandgap of the semiconductor? 2d) What is the built-­‐in potential of the junction. 3) A silicon diode is asymmetrically doped at N D = 1019 cm-­‐3 and N A = 1016 cm-­‐3. (Note that at N D = 1019 the semiconductor is on the edge of degeneracy, but we can assume that non-­‐degenerate carrier statistics are close enough for this problem.) Answer the following questions assuming room temperature. Assume that the minority electron and hole lifetimes are τ n = τ p = 10−6 s. The lengths of the N and P regions are L = 500 µm and L >> x p , xn . 3a) Find the zero-­‐bias depletion region capacitance per cm2 of diode area. 3b) Find the depletion capacitance at V A = −5 V (reverse biased). 3c) Find the depletion capacitance at V A = + 0.5 V (forward biased). 4)
A silicon diode is asymmetrically doped at N D = 1019 cm-­‐3 and N A = 1016 cm-­‐3. (Note that at N D = 1019 the semiconductor is on the edge of degeneracy, but we can assume that non-­‐degenerate carrier statistics are close enough for this problem.) Assume that the minority electron and hole lifetimes are τ n = τ p = 10−6 s. The lengths of the N and P regions are L = 500 µm and L >> x p , xn . 4a) Estimate the applied forward bias at which the P-­‐region enters high-­‐level injection. 4b) Compute the current density at the onset of high-­‐injection. 5)
A silicon diode is asymmetrically doped at N D = 1019 cm-­‐3 and N A = 1016 cm-­‐3. (Note that at N D = 1019 the semiconductor is on the edge of degeneracy, but we can assume that non-­‐degenerate carrier statistics are close enough for this problem.) Answer the following questions assuming room temperature. Assume that the minority electron and hole lifetimes are τ n = τ p = 10−6 s. The lengths of the N and P regions are L = 500 µm and L >> x p , xn . What is the reverse breakdown voltage of this diode? Assume a critical field for breakdown of E cr = 3× 105 V/cm. ECE-­‐305 2 Spring 2015