12.13 In connection with the npnp device of Figure 12.21, it was stated that at low Vs, the recombination in the forward-biased junction transition regions is significant. a. Explain why the recombination current is significant. b. When recombination cannot keep up with the carrier injection, what happens to the energy band diagram? Explain why the device switches to a high-current state. 12.14 We indicated that in an SCR device, applying a positive voltage pulse VG to the gate (p2 region) could turn the device to the on state. Explain how applying a negative current pulse to the nl region would have the same effect. (a) (b) (c) Ec Ey Ec Ev Ec Ev 2 n s n 2 2 n P2 Moves down because of accumulating positive charge P2 Holes P2 Electrons Moves up because of accumulating negative charge n n P PI PI 12.13 In connection with the npnp device of Figure 12.21, it was stated that at low Vs, the recombination in the forward-biased junction transition regions is significant. a. Explain why the recombination current is significant. b. When recombination cannot keep up with the carrier injection, what happens to the energy band diagram? Explain why the device switches to a high-current state. 12.14 We indicated that in an SCR device, applying a positive voltage pulse VG to the gate (p2 region) could turn the device to the on state. Explain how applying a negative current pulse to the nl region would have the same effect. (a) (b) (c) Ec Ey Ec Ev Ec Ev 2 n s n 2 2 n P2 Moves down because of accumulating positive charge P2 Holes P2 Electrons Moves up because of accumulating negative charge n n P PI PI