Esercizi su Dispositivi elettronici ad alta velocità, Appunti di Sistemi Elettronici

Scarica Esercizi su Dispositivi elettronici ad alta velocità e più Appunti in PDF di Sistemi Elettronici solo su Docsity! High Speed Electron Devices 23 February 2011 Surname................................... Name................................... Enroll number........... Exercises 1. Describe the physical causes of Early e!ect and discuss its impact on the static characteristics of an npn BJT, pointing out the consequences on the device doping levels 2. Consider a metal-semiconductor junction between Au (work function q"M = 5 eV) and Al0.15Ga0.85As (Eg = 1.535 eV, Nc = 5.6225 ! 1017 cm!3, Nv = 1.3637 ! 1019 cm!3, !r = 12.474, q" = 3.911 eV) n doped with concentration ND = 2! 1016 cm!3. • Draw the energy band diagram at thermal equilibrium. Evaluate the potential barrier on the metal side (q"B) and on the AlGaAs side (qVbi). • Solving Poisson’s equation, derive the expressions for the electric field and depletion layer width in presence of an applied voltage V , measured on the metal side with respect to the semiconductor side. • Draw the diagrams of charge density, electric field and electrostatic potential under thermal equilib- rium, forward bias of 0.2 V, reverse bias of "1 V. Evaluate and indicate on the graphs the values of built-in potential, depletion region width and peak electric field. • Derive the expression for the depletion capacitance versus the applied bias voltage, draw its behaviour and calculate its value (per unit area) for V = 0 V, V = 0.2 V, V = "1 V. Multiple choice questions 1. In a semiconductor, electron a#nity is the distance between (a) the minimum conduction band energy and the free electron energy (b) the maximum valence band energy and the free electron energy (c) the minimum conduction band energy and the maximum valence band energy (d) the Fermi level and the free electron energy 2. A pseudomorphic epitaxial layer is formed when (a) a heterostructure is grown between materials with the same lattice constant (b) a heterostructure is grown between materials with the same doping type (c) a heterostructure is grown between materials with slightly mismatched lattice constants (d) a heterostructure is grown between materials with opposite doping types 3. In a rectifying metal-semiconductor junction, the current due to free carriers moving from the metal to the semiconductor (a) in forward bias, increases as the applied voltage increases (b) is independent of the applied voltage (c) is independent of temperature (d) keeping the applied voltage constant, decreases as temperature increases 4. A power MOSFET for switching applications typically shows (a) a periodic structure to improve the maximum con- duction drain current (b) the possibility to block both positive and negative VDS voltages (c) horizontal current flow (d) a reduced Ron because of the heavily doped n + region used to increase the breakdown voltage 5. Photodetector responsivity is (a) the ratio between the incident optical power and the generated current (b) proportional to the quantum e!ciency (c) proportional to the impinging light frequency (d) inversely proportional to the impinging light wave- length