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
1) The drift-diffusion model
2) Metal-semiconductor junctions
3) p-n junctions
4) p-i-n diodes
5) Bipolar Junction Transistors (BJTs)
6) MOS Transistor (MOSFET)
1) The drift-diffusion model - 6 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 - 12 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) p-i-n diodes – 4 hrs
Physical structure. Static characteristics in forward and reverse bias and device design. Dynamic characteristics.
5) Bipolar Junction Transistors (BJTs) - 8 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. Basics of high-power BJTs.
6) MOS Transistor (MOSFET) - 12 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. High-power MOSFETS: structure and physics of operation; static and dynamic characteristics.
7) Solar cells – 2 hrs
Photovoltaic energy conversion. I-V characteristics of the illuminated cell and figures of merit. Solar cell technologies.
8) LEDs – 2 hrs
Light emission. Efficiency. Technologies and materials for LEDs.
1) R. S. Muller, T. I. Kamins, P. K. Ko, “Device Electronics for Integrated Circuits,” John Wiley & Sons.
2) N. Mohan, T. M. Undeland, W. P. Robbins, "Power electronics: converters, applications, and design", John Wiley & Sons.
For the academic year 2020/21 the course will be taught on-line, with streaming on the Teams platform, and recorded lectures available (at least for 3 days) on the Elly platform.
Lectures can be divided in two categories:(1) fundamental lectures: the goal is providing students with basic understanding of the physical behavior of semiconductor devices, with limited mathematical detail and by focusing on the behavioral effects of physical phenomena; (2) advanced lectures: following a physical-mathematical deductive process, the physical phenomena shaping the behavior of semiconductor devices will be treated in greater detail, in the drift-diffusion model framework.
Assessment methods and criteria
Oral exam. The exams will be held in the classroom and/or on-line depending on the regulations and indications in place at the time of the exam.
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-three questions. 24 points out of 30 are attributed based on the answers to the questions on the fundamental lecture topics, the remaining 6 on the answers to the questions on the advanced lecture topics.
The course web pages can be found on the Elly platform.