Solid State Electronics. Final Examination

Transcription

1 The University of Toledo EECS:4400/5400/7400 Solid State Electronic Section elssf08fs.fm - 1 Solid State Electronics Final Examination Problems Points Total 40 Was the exam fair? yes no

2 The University of Toledo elssf08fs.fm - 1 Problem 1 1 points For full credit, mark your answers yes, no, or not in all of euhe given choices! 1. 1 In an intrinsic semiconductor material, x concentrations of electrons and holes are unequal, x values of effective masses of electrons and holes are unequal, x mobilities of electrons and holes are unequeal, x diffusion coefficients of electrons and holes are unequal, x amounts of lectrical charges on electrons and holes are unequal. 1. Mean life time of excess minority carriers in semiconductors can be calculated from: x the measured semiconductor material photoconductivity decay, x the measured depletion region capacity of a reverse biased pn-junction, x the measured storage delay time during a reverse recovery transient in a pnjunction, x the measured current intensity through a forward biased pn-junction. 1.3 Useful mechanisms for switching the Silicon Controlled Rectifiers from forward-blocking to forward-conducting state include: x application of an anode to cathode voltage in excess of the peak forward voltage, x application of a rapid changing gate to cathode voltage not in excess of the peak forward voltage, x "base width narrowing", x punch through of the regions n 1 or p, x positive voltage applied to the gate terminal.

3 The University of Toledo elssf08fs.fm The transferred electron mechanism is: x the consequence of a drop in mobility of free electrons with increasing electric field in InP, x responsible for the incremental negative resistance region in the current-voltage characteristic of the Tunnel diode, x the consequence of an increase in mobility of holes with increasing electric field in InP, x the consequence of a drop in mobility of free electrons with increasing electric field in GaAs, x responsible for the incremental negative resistance region in the current-voltage characteristic of the Impact Avalanch Transit Time diode. 1.5 The Hanes-Shockley experiment: x has demonstrated the drift process of minority carriers in semiconductor materials, x has demonstrated the diffusion process of minority carriers in semiconductor materials, x the random motion process of minority carriers in semiconductor materials, x provides information for calculating the mobility value of majority carriers in the semiconductor, x provides information for calculating the diffusion constant value of minority carriers in the semiconductor, 1.6 Thermal Budget is a parameter: x whose value measures the range of applicability of power semiconductor devices, x which is generally maximized in breakdown diodes, x whose value is generally minimized for control over compact doping profiles, x whose value determines whether an oxidation process satisfies the criterion for being considered as "rapid".

4 The University of Toledo elssf08fs.fm - 4 Problem 14 points Given is an abrupt silicon n + p-junction at room temperature, with the following parameters: - room temoerature T = 0 C = 93 K - junction area A = 10-7 m - junction temperature T = 0 C = 93 K - donor concentration N D = donor atoms/m 3 - acceptor concentration N A = 10 1 acceptor atoms/m 3 - intrinsic concentration n i = electron-hole pairs/m 3 - electron mobility µ n = 0.18 m /Vs - hole mobility µ p = 0.06 m /Vs Determine: Solution 1 o contact potential of the junction, o the depletion region width at thermal equilibrium condition, 3 o which junction redesign measure would double the magnitude of the given pn-junction current under forward bias, 4 o if the stated junction redesign measure would have been carried through, how wuld it have affected the following properties of a pn-junction diode which contained the redesigned junction: - the junction capacitance, - the built-in potential of the junction, - the breakdown potential of the junction, - the ohmic losses in the quasi neutral regions of the junction. Hint #1 For full credit, give answers to all questions, prepare all required circuit diagrams, write all equations for which the space is left, and show all symbolic and numerical expressions whose evaluation produces shown numerical results. An explicit demonstration of understanding the following solution steps is expected..1 Calculate the contact potential of the junction; show your work in the space reserved for equation (-1). V bo = V T ln N D N A n i = 0.05 ln = 0.7V (-1)

5 The University of Toledo elssf08fs.fm - 5. Calculate the the depletion region width; show your work in the space reserved for equation (-). W= ε s q = N A +N D Vbo N A N D = 0.94µm (-).3 State the description of the junction redesign measure which would double the magnitude of the given pn-junction current under forward bias; write your statement in the space reserved for equation (-3). Concentration of acceptor doping should be reduced by a factor of two. (-3).4 State the effect of the redesign measure proposed under part.3 on the: - pn-junction capacitance by checking the conditions on all three lines below, x pn-junction capacitance would be increased, x pn-junction capacitance would be decreased x pn-junction capacitance would not be affected,.5 State the effect of the redesign measure proposed under part.3 on the: - pn-junctionbuilt-in potential by checking the conditions on all three lines below, x pn-junction built-in potential of the junction would be increased, x pn-junction built-in potential of the junction would be decreased x pn-junction built-in potential of the junction would not be affected,.6 State the effect of the redesign measure proposed under part.3 on the: - pn-junction break down potentiale by checking the conditions on all three lines below, x pn-junction breakdown potential would be increased, x pn-junction breakdown potential would be decreased x pn-junction breakdown potential would not be affected,.7 State the effect of the redesign measure proposed under part.3 on the: - pn-junction ohmic losses by checking the conditions on all three lines below, x pn-junction ohmic losses would be increased, x pn-junction ohmic losses would be decreased x pn-junction ohmic losses would not be affected,

6 The University of Toledo elssf08fs.fm - 6 Problem 3 14 points Given is an abrupt silicon pn-junction at room temperature, with the following parameters: a) whole junction - junction area A = 10-8 m - junction temperature T = 0 C = 93 K b) n-region - donor concentration N D = donor atoms/m 3 - electron/hole mobility µ nn = 0.13 m /Vs - µ np = m /Vs - excess minority carrier life timeτ n = 0.1µs c) p-region - acceptor concentration N A = 10 3 acceptor atoms/m 3 - electron/hole mobility µ pn = 0.07 m /Vs - µ pp = 0.0 m /Vs - excess minority carrier life timeτ p = 10µs Prepare: Solution 1 o Current i D through the junction when junction is forwad biased with v D = 0.5V, o Current i D through the junction when junction is reverse biased with v D = -0.5V. Hint #1 For full credit, give answers to all questions, prepare all required circuit diagrams, write all equations for which the space is left, and show all symbolic and numerical expressions whose evaluation produces shown numerical results. An explicit demonstration of understanding the following solution steps is expected. 3.1 Calculate the values of the majority carrier concentrations in the quasi-neutra regions of the given pn-junction; show your work in the space reserved for equation (3-1). n no N D = free electrons/m 3 (3-1) p po N A = holes/m 3 3. Calculate the values of the minority carrier concentrations in the quasi-neutral regions of the given pn-junction; show your work in the space reserved for equation (3-). n po = p no = n i p = = free electrons/m 3 p 10 3 (3-) n i n n = = holes/m 3

7 The University of Toledo elssf08fs.fm Calculate the values of the minority carrier diffusion constants in the quasi-neutral regions of the given pn-junction; show your work in the space reserved for equation (3-3). D n =µ pn. V T = = = m s -1 D p =µ np. V T = = = m s -1 (3-3) 3.4 Calculate the values of the minority carrier diffusion lengths in the quasi-neutral regions of the given pn-junction; show your work in the space reserved for equation (3-4). L n= D nτ n = = 13.3 [µm] L p= D pτ p = = 106 [µm] (3-4) 3.5 Calculate the values of the reverse saturation current of the given pn-junction; show your work in the space reserved for equation (3-5). D p D n I p o = qa ( n + np ) = ( L p Ln ) = (3-5) = 1.07 fa 3.6 Calculate the value of the given pn-junction current under forward bias; show your work in the space reserved for equation (3-6). i D = I o v D V T 0.5 (3-6) ( e - 1 ) = ( - 1) = e 0.05 ( e - 1) = = 0.5µA 3.7 Calculate the value of the given pn-junction current under reverse bias; show your work in the space reserved for equation (3-7). v D i D = I V T = o ( -15 ( e - 1 ) e - 1) = ( e -0-1) = A (3-7)