14.2.1. On the basis of conductivity

On the basis of the relative values of electrical conductivity (s) or resistivity (r = 1/s), the solids are broadly classified as: (i) Metals: They possess very low resistivity (or high conductivity). r ~ 10–2 – 10–8 W m s ~ 102 – 108 S m–1 (ii) Semiconductors: They have resistivity or conductivity intermediate to metals and insulators. r ~ 10–5 – 106 W m s ~ 105 – 10–6 S m–1 (iii) Insulators: They have high resistivity (or low conductivity). r ~ 1011 – 1019 W m s ~ 10–11 – 10–19 S m–1.

This chunk introduces the classification of materials based on their electrical conductivity. It explains three categories: metals, semiconductors, and insulators, along with the numerical ranges for their resistivity (r) and conductivity (s). Metals are characterized by significantly low resistivity, allowing them to conduct electricity easily. Semiconductors have a resistivity that falls between that of metals and insulators, making them versatile for electronic applications. Insulators have very high resistivity, preventing them from conducting electricity under normal conditions.

Think of metals as highways where cars (electrons) can speed through with little resistance. Semiconductors are like dirt paths where some cars can drive, but only under certain conditions, like when the weather is right (like heat or light). Insulators are more like thick forest paths where cars can't really go at all.

Our interest in this chapter is in the study of semiconductors which could be: (i) Elemental semiconductors: Si and Ge (ii) Compound semiconductors: Examples are: • Inorganic: CdS, GaAs, CdSe, InP, etc. • Organic: anthracene, doped pthalocyanines, etc. • Organic polymers: polypyrrole, polyaniline, polythiophene, etc.

This chunk delves deeper into semiconductors, identifying two main types: elemental semiconductors, like silicon (Si) and germanium (Ge), and compound semiconductors, which are made from more than one element. The examples provided include both inorganic and organic semiconductors, highlighting the diversity in semiconductor materials. These materials have unique properties that allow for various electronic applications, from simple diodes to complex integrated circuits.

Imagine elemental semiconductors like single-family homes (Si and Ge), simple and straightforward. In contrast, compound semiconductors are like apartment complexes (like CdS and GaAs), where multiple families (elements) share resources. Each type of structure serves its purpose in the neighborhood of technology, providing different capabilities based on their construction.

Most of the currently available semiconductor devices are based on elemental semiconductors Si or Ge and compound inorganic semiconductors. However, after 1990, a few semiconductor devices using organic semiconductors and semiconducting polymers have been developed signalling the birth of a futuristic technology of polymer-electronics and molecular-electronics.

This chunk discusses the practical applications of the aforementioned semiconductor materials and the emergence of new technologies through doping. Doping involves adding impurities to intrinsic semiconductors to enhance their electrical properties. This process creates two main semiconductor types: p-type (positive carrier) and n-type (negative carrier), allowing for improved conductivity and functionality. The mention of organic semiconductors illustrates the ongoing advancement in the semiconductor field, paving the way for future electronic innovations.

Think about how adding sugar to coffee changes its flavor — that’s similar to doping in semiconductors! Just as a touch of sugar improves the coffee's sweetness, adding certain elements to semiconductors enhances their ability to conduct electricity, leading to new types of technologies that could change how we use electronics.

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