Question

Please explain part A in details thx!

Question 3 An n'pn Si BJT is shown in Figure Q3(a). The emitter is heavily doped with 1020 cm3 whereas the base and collector are lightly doped with 5x1018 and 3x1018, respectively. The lengths of emitter, base, and collector are 0.5um, 0.2um, and 0.5 um.. The dielectric constant of silicon is 11.8 and the intrinsic carrier concentration at 300 K is 1.5x1010 cm3. Assume that a 0.026 eV at 300 K. 0.99, e 1.6x10-19 C, kTle 0.026 V whereby kT- Depletion Base Width Depletion Wg Wcs N-Type Lightly Doped Rc P-Type Output N+ Lightly Doped N-Type 83 Heavily Doped N-type N-type NE 5x1019 cm LE = 0.5 μm P-type Lc- 0.5 m Figure Q3(a) Figure 03(b (a) Calculate the base width WB for the BJT in equilibrium. (7 marks) (b) Discuss the requirements for a good BJT base design and how the base width would change when the collector bias is increased (6 marks) (c) When the collector bias is increased to 15 V, a sharp rise in collector current Ic is observed. Discuss the reason for the above observation and propose ONE (1) way to alleviate it (4 marks) (d) The n'pn Si BJT is connected in a common emitter configuration with Rc of 5000 Ω as shown in Figure Q3(b). The BJT is biased to operate with a base current of IB = 20 μA. Apply suitable mathematical model to obtain the value of the input resistance rbe and the gain Av for the BJT (8 marks)

Answer 1

0 6 Junction υμ 2-0 l.5X1o'0 2.25 치fo Scanned with eS CamScanner

1020 )1.0983 10, & 5치 130, 5375 지0-(-20 no 10 lo 6 301 0.7s6 o. 017351 2 0.026 In 3 6 二 0.026 20" -0,026 en (6.666 ? 1016) Cs Scanned with CamScanne 1007 vait

2 3x1018 2-648 : .0.2 0.0 l07s6) L Scannew it CamScanner