We will see in Chapter 12 that semiconductors are materials that conduct electricity better than nonmetals but not as well as metals. The only two elements in the periodic table that are technologically useful semiconductors are silicon and germanium. Integrated circuits in computer chips today are based on silicon. Compound semiconductors are also used in the electronics industry. Examples are gallium arsenide, GaAs; gallium phosphide, GaP; cadmium sulfide, CdS; and cadmium selenide, CdSe. (a) What is the relationship between the compound semiconductors' compositions and the positions of their elements on the periodic table relative to Si and Ge?

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Identify the position of silicon (Si) and germanium (Ge) on the periodic table. Both are in group 14, which is also known as the carbon group.

Observe that compound semiconductors like GaAs, GaP, CdS, and CdSe are made from elements in groups 13 and 15, or groups 12 and 16.

Note that the elements in these compound semiconductors are positioned symmetrically around group 14 on the periodic table. For example, gallium (Ga) is in group 13 and arsenic (As) is in group 15.

Understand that this positioning allows these compounds to mimic the electronic structure of group 14 elements, like Si and Ge, which is crucial for their semiconductor properties.

Conclude that the relationship between the compound semiconductors' compositions and the positions of their elements on the periodic table is based on their ability to form a similar electronic configuration to that of Si and Ge, enabling them to function as semiconductors.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Semiconductors

Semiconductors are materials that have electrical conductivity between that of conductors (like metals) and insulators (like nonmetals). Their ability to conduct electricity can be altered by adding impurities, a process known as doping. This property makes them essential in electronic devices, as they can be engineered to control electrical current effectively.

Periodic Table Positioning

The position of an element in the periodic table provides insight into its chemical properties, including its conductivity. Elements in the same group often exhibit similar behaviors due to their valence electron configurations. For semiconductors, elements like silicon (Si) and germanium (Ge) are found in group 14, while compound semiconductors often consist of elements from groups 13 and 15, influencing their electronic properties.

Compound Semiconductors

Compound semiconductors are formed from two or more elements, typically from different groups of the periodic table, which allows for unique electronic properties. For example, gallium arsenide (GaAs) combines gallium from group 13 and arsenic from group 15, resulting in a material with superior electron mobility compared to silicon. These compounds are crucial in high-frequency and optoelectronic applications.

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Textbook Question

A historian discovers a nineteenth-century notebook in which some observations, dated 1822, were recorded on a substance thought to be a new element. Here are some of the data recorded in the notebook: 'Ductile, silver-white, metallic looking. Softer than lead. Unaffected by water. Stable in air. Melting point: 153 °C. Density: 7.3 g>cm3. Electrical conductivity: 20% that of copper. Hardness: About 1% as hard as iron. When 4.20 g of the unknown is heated in an excess of oxygen, 5.08 g of a white solid is formed. The solid could be sublimed by heating to over 800 °C.' (a) Using information in the text and the CRC Handbook of Chemistry and Physics, and making allowances for possible variations in numbers from current values, identify the element reported.

Textbook Question

We will see in Chapter 12 that semiconductors are materials that conduct electricity better than nonmetals but not as well as metals. The only two elements in the periodic table that are technologically useful semiconductors are silicon and germanium. Integrated circuits in computer chips today are based on silicon. Compound semiconductors are also used in the electronics industry. Examples are gallium arsenide, GaAs; gallium phosphide, GaP; cadmium sulfide, CdS; and cadmium selenide, CdSe. (b) Workers in the semiconductor industry refer to 'II–VI' and 'III–V' materials, using Roman numerals. Can you identify which compound semiconductors are II–VI and which are III–V? (c) Suggest other compositions of compound semiconductors based on the positions of their elements in the periodic table.

Textbook Question

Moseley established the concept of atomic number by studying X rays emitted by the elements. The X rays emitted by some of the elements have the following wavelengths: Element Wavelength (pm) Ne 1461 Ca 335.8 Zn 143.5 Zr 78.6 Sn 49.1 (a) Calculate the frequency, n, of the X rays emitted by each of the elements, in Hz.

Textbook Question

Moseley established the concept of atomic number by studying X rays emitted by the elements. The X rays emitted by some of the elements have the following wavelengths: Element Wavelength (pm) Ne 1461 Ca 335.8 Zn 143.5 Zr 78.6 Sn 49.1 (b) Plot the square root of n versus the atomic number of the element. What do you observe about the plot? (e) A particular element emits X rays with a wavelength of 98.0 pm. What element do you think it is?