Learning outcomes of the course unit
1) Knowledge and understanding
Attending classes and through individual study, students are to acquire:
-basic understanding of the notions of semiconductor physics required for understanding electron device operation;
- detailed knowledge and understanding of the operation of the most important semiconductor devices, in the framework of the "drift-diffusion" model.
2) Applying knowledge and understanding
- A goal of this course is providing students with the ability of applying the acquired knowledge to the first-order analysis and design of semiconductor electron devices.
- Great importance is also given to the ability of applying the analysis methods and techniques presented and used in the lectures to the qualitative as well as quantitative study of the operation of electron devices.
Students should be familiar with the notions of mathematics, physics, chemistry, electrical and electronic engineering typically acquired in first-level degrees in Information engineering (class L-8).
Course contents summary
- Part 1
1) The drift-diffusion model
2) Metal-semiconductor junctions
3) PN junctions
4) Bipolar Junction Transistors (BJTs)
5) MOS Transistor (MOSFET)
- Part 2
6) Energy bands in semiconductors
7) Charge carriers
8) Thermal equilibrium
9) Charge transport
10) Solar cells
- Part 1
1) The drift-diffusion model - 4 hrs
Semiconductors under equilibrium conditions. Mass action law. Fermi-Dirac and Maxwell-Boltzmann distributions. Density of states, Fermi level and intrinsic Fermi level. Free carriers, mobility, saturation velocity. Drift-diffusion model.
2) Metal-semiconductor junctions - 2 hrs
Metal-semiconductor junction under equilibrium conditions, forward bias and reverse bias. Interface states and Fermi level pinning. Ohmic contacts.
3) PN junctions - 8 hrs
Non-uniform doping distributions. The PN junction at equilibrium. Debye length. Reverse bias. Capacitance of a reverse-biased diode. Avalanche and Zener breakdown. Continuity equations. Shockley-Hall-Read recombination. Auger and surface recombination. I-V characteristics of the PN diode. Long-base and short-base diodes. Validity of the low-injection and quasi-equilibrium approximations. G-R currents in forward and reverse bias. Diffusion capacitance.
4) Bipolar Junction Transistors (BJTs) - 6 hrs
Forward-active region. Base transport factor. Emitter efficiency. Reverse active region, saturation, off-state. Early effect. Integrated BJTs. Low-current effects. High-injection effects: Kirk effect, base resistance. Base transit time. Frequency limitations: fT and fMAX.
5) MOS Transistor (MOSFET) - 10 hrs
Ideal MOS systems. Band structure. Accumulation, depletion, inversion, strong inversion. Threshold voltage and body effect. C-V characteristics of the ideal MOS system. Non-ideal MOS systems: cahrges in the oxide and at the interface. MOS transistors. Body effect. Bulk charge effect. Threshold voltage adjustment. Sub-threshold current. Short-channel and narrow-channel effects. Source/drain charge sharing. Drain-induced barrier lowering. Sub-surface punch-through. Mobility reduction. Velocity saturation. Drain current in short-channel MOSFETs. Effects of scaling on short-channel MOSFETs. Electric field in the saturated velocity region: quasi-2D model. Hot carrier effects: substrate and gate currents.
- Part 2
6) Energy bands in semiconductors - 4 hrs
Crystalline structure and periodic potential. Schroedinger equation. Energy bands. Reduced-zone plot. Quantum states and materials classification. Si and GaAs band structures. Crystal momentum and effective mass. Constant-energy surfaces. Effective-mass Schroedinger equation.
7) Charge carriers - 2 hrs
Generation of electrons and holes. Recombination. Carrier concentrations. Si DOS effective mass.
8) Thermal equilibrium - 2 hrs
Collisions and scattering. Fermi level. Equilibrium carrier concentrations. Mean unidirectional velocity of an equilibrium distribution.
9) Charge transport - 2 hrs
Boltzmann equation. Drift-diffusion model. Hydrodynamic model.
10) Solar cells - 2 hrs
Absorption and generation. Photocurrent. Photovoltage. Maximum power point and conversion efficiency.
- Part 1
R. S. Muller, T. I. Kamins, P. K. Ko, “Device Electronics for Integrated Circuits,” 3rd Edition, John Wiley & Sons, 2003. ISBN: 0-471-42877-9
- Part 2
D. L. Pulfrey, "Understanding modern transistors and diodes," Cambridge University Press, 2010. ISBN: 978-0-521-51460-6.
Assessment methods and criteria
Students will have to show good understanding of the physical mechanisms underlying the behavior of electron devices, and the ability to analyze their characteristics and principles of operation, also in quantitative terms.
The exam consists of two questions on the topics of part 1 (1-5), and one on those of part 2 (6-10). 24 points out of 30 are attributed based on the answers to the questions on part 1, the remaining 6 on the answer to the question on part 2.
The course web pages can be found on the Elly platform.