P24L-2003_Incourse_Test - R D = 2 k V DD = 25 V V D I D 2...

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1 DEPARTMENT OF PHYSICS P24L INCOURSE TEST WEDNESDAY, MARCH 13, 2002 - 11:00 a.m. TIME : 1 Hour ANSWER ALL QUESTIONS 1. (a) Briefly describe the difference between: (i) p-type and n-type semiconductors [2 marks] (ii) drift and diffusion currents [2 marks] (b) Calculate the intrinsic carrier concentrations n i at T = 300 o K in gallium arsenide given the following: [3 marks] Material E g (eV) B (cm -3 K -3/2 ) Gallium Arsenide (GaAs) 1.4 2.10 x 10 14 (c) Using the intrinsic carrier concentration n i found in part (b), find the concentration of electrons and holes in a sample of gallium arsenide having concentration of donor atoms equal to 5 x 10 15 cm -3 . Is the doped semiconductor p-type or n-type ? [4 marks] 2. (a) In which two regions can a JFET operate? [2 marks] Write down the conditions that must be satisfied for the JFET to operate in either region. [2 marks] (b) Determine the value of I D and V D for the Field-Effect Transistor shown in figure 2 given that Vp = -4 V and I DSS = 8 mA. [5 marks] Figure 2
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Unformatted text preview: R D = 2 k V DD = 25 V V D I D 2 3. (a) Describe, with the aid of a diagram, the current-voltage characteristic of the Zener diode. [2 marks] (b) Draw a labelled circuit diagram of a simple Zener shunt regulator and also show the circuit equivalent of the Zener diode. [2 marks] (c) A Zener shunt regulator has a resistor of 120 connected in series with the Zener diode. The p.d. across the diode is 4.92 V when the current through the diode is 10 mA and 4.98 V when the current is 25 mA. Determine the dynamic resistance of the diode [2 marks] (d) If the supply voltage was 11.0 V when the diode current was 10 mA, find the load current at that time. [4 marks] (e) If the supply voltage remains unchanged throughout, determine the load regulation of the circuit. [4 marks] 4. State the condition for a metal-semiconductor junction to act as a rectifying contact in a Schottky diode and explain with the aid of energy band diagrams how it operates. [6 marks]...
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P24L-2003_Incourse_Test - R D = 2 k V DD = 25 V V D I D 2...

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