Question

4.15 A PN diode with lengths much larger than the carrier diffusion length such as shown in Fig. 4-18 is called a long-base diode. A short-base diode has lengths much shorter than the diffusion lengths, and its excess carrier concentration is similar to that shown in Fig. 8-6. A uniformly doped short-base Si diode has Nd- 101cm-3and Na 1016cm3. tp n1 us, Dp 10 cms, Dn 30 cm-s, and cross-sectional area10 cm. The length of the quasi-neutral N-type and P-type regions WE -WB1 um. The diode is at room temperature under applied forward bias of 0.5 V. Answer the following questions: (a) Show that the total current and the sum of the charge stored on both N and P sides -2 of the junction are proportional to each other:-It Find the expression for ?, Use the short-base approximation, i.e., assume that the excess minority carrier concentration decreases linearly from its maximum value at the edge of the depletion region to zero at the ohmic contacts at either end of the diode. (b) t, is called the charge-storage time. Show that it is significantly smaller than Ep and Eq. (e) Which diode can operate at a higher frequency, short-based or long-based? 1.0 N side N,-2x 1017cm-3 P side N, 1017 cm-3 FIGURE 4-18 Noralized n'and p'. n(O) 2p (O) because Nd-2Na- Ln- 2Lp is assumed.

Answer 1

Fist , we need to -fnd an exp&ssfor for 9t: 30p onS ons. t Nd Na It 2 ) A shot- based dlode hos a shoes stosoye time, thus t can