{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

note02 - Introduction to Microelectronics Chapter 2...

Info icon This preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Introduction to Microelectronics Edwin C. Kan Page 2-1 1/21/2009 Chapter 2 I NTRODUCTION TO S EMICONDUCTORS 2.1 Semiconductor Materials Semiconductor used in electronics is the class of material where the conductivity of the material can be controlled to vary over many orders of magnitude, for example, in silicon we can tune the conductivity using either doping or electric field for modulation larger than 10 10 . In contrast, metal has high conductivity and insulator has very low conductivity, both of whose conductivity can hardly be modulated even over 3 times. There are three common kinds of semiconductors: Elemental semiconductor: Si, Ge (Group IV elements) Compound semiconductor (fixed composition): SiC, GaAs, GaN, and ZnO (Group IV with equal composition, Group III-V and Group II-VI) Alloy: Si 1-x Ge x , Al 1-x Ga x As, Hg 1-x Cd x Te, etc., where x can be any number between 0 and 1 in composition. If the semiconductors cannot be made pure, then the electrical conductivity will be dominated by the uncontrollable impurity (controllable impurity is useful, as shown later), and we cannot achieve a high order of conductivity modulation. Usually for industrial grade semiconductors, the uncontrollable impurity is lower than 10 -9 in composition (or below 1013 cm-3), and there are often chemical “getters” which make the uncontrollable impurity to be electrically inactive and immobile in the material. The two solid-state materials that can be made purest are Germanium and Silicon (lucky us), and there are many known getters such as carbon and fluoride. The pure semiconductors also have charge carriers with higher electrical mobility, which will be introduced later. Semiconductors used in electronics also have very regular atomic structure called the crystal lattice, as any defect in crystal lattice behaves similarly to uncontrollable impurities that will diminish electrical conduction and its modulation. To obtain the good crystal quality, industrial-grade semiconductors are made in very high-temperature (for example, silicon at 1,450 o C) and crystallized in a controllable manner by a seed material. The dominant semiconductor for electronics today is silicon (larger than 98% market share), with SiGe, Ge and GaAs, SiC and GaN trailing far behind. This is mainly because of the cost of manufacturing and the high degree of material perfection in both Si and SiO 2 . For optoelectronics and lighting, GaAs and GaN play a more important role because silicon has low conversion efficiency from electric power to light. However, due to cost issues, solar cells today are still mostly made by silicon even though GaAs can give better efficiency. The uncontrollable impurity and defect concentrations in industry-grade silicon are less than 10 13 cm -3 , which is about 10 -9 to 10 -10 in composition as mentioned before.
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern