Problems 129 PROBLEMS Section 3.2 3.1 A simplified pn junction is shown in Figur

Question

Problems 129 PROBLEMS Section 3.2 3.1 A simplified pn junction is shown in Figure P3.1 a. What is region "a" in Figure P3.1 known as, Why? b. Briefly describe the reason this region exists. c. When in equilibrium or open-circuit, what are the relative differences in the currents? p Figure P3.1 3.2/If a voltage is applied across the pn junction in Figure P3.1 with the positive voltage applied to the p side (i.e., forward biased): a. What happens to the depletion region? b. After equilibrium is established, what is the relationship of the drift and diffusion currents to the current in the circuit? 5k2 the out 10k2 relationship of the dnt Figure P3.4

Explanation / Answer

a) from the circuit we can clearly see that positive terminal is attached to anode the condition is forward biased and v(cathode becomes Vs(5/15) so as its always greater than 0.7 volts of diode forward drop it aways stay on as long as its connected to the diode in that manner. so the depletion region becomes narrower as the anode terminal or positive terminal is the source of positive charge carriers (holes), the positive charge carriers (holes) begins their journey at anode terminal and travel through the diode and ends at cathode terminal and the opposite happens with electrons thus forcing the depletion region to narrow down.

b)drift current: under the action of electric field the charge in the semiconductors may be poles or electons depending on the region stops moving randomly and starts to move in an orderly manner in the direction of electric field. these electrons moves in a manner that they drift tfrom atom to atom reducing their kinetic energy by each imact but still accelarates due to the applied electric field.

diffusion current: In a semiconductor there occours a state where concentration of one charge is more in a place in semiconductor but to acheive the equilibrium these charges move from high concentration areas to low concentration areas because of the production of charge gradient in one place. This current is known as diffusion current. The Drift current is more than diffusion current if its under the application of electric field. and diffusion current happens due to internal potential gradient.

so in the above circuit as the diode is is drift current will be much more greater than the diffusion current after the equilibrium is establised as the diode is in on state.

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