Unit IX. Semiconductor Materials

A Semiconductor device is an electronic 1. _____ component made from a material that is neither a good conductor nor a good 2. _______. Such devices have found wide applications because of their compactness, reliability, and low cost. As discrete components, they have found use in power devices, optical sensors, and light emitters, including solid-state lasers. They have a wide range of current- and voltage-handling capabilities, with current ratings from a few nanoamperes (10 −9 ampere) to more than 5,000 amperes and voltage ratings extending above 100,000 volts. More importantly, semiconductor devices lend themselves to integration into complex but readily manufacturable microelectronic circuits. They are, and will be in the foreseeable future, the key elements for the majority of electronic systems, including communications, consumer, data-processing, and industrial-control equipment.

A. ____________

Solid-state materials are commonly grouped into three classes: insulators, semiconductors, and conductors. Conductivity or specific conductance is the 3. ______ quantity, and measures a material's ability to conduct an electric 4. _____. Insulators, such as fused quartz and glass, have very low conductivities, on the order of 10 −18 to 10 −10 siemens per centimetre; and conductors, such as aluminum, have high conductivities, typically from 10 4 to 10 6 siemens per centimetre. The conductivities of semiconductors are between these extremes.
B._____________
The conductivity of a semiconductor is generally 5. ______ to temperature, illumination, magnetic fields, and minute amounts of impurity atoms. For example, the addition of less than 0.01 percent of a particular type of impurity can increase the electrical conductivity of a semiconductor by four or more orders of magnitude (i.e., 10,000 times).
C._______________
The study of semiconductor materials began in the early 19th century. Over the years, many semiconductors have been investigated. The 6. ______ semiconductors are those composed of single species of atoms, such as silicon (Si), germanium (Ge), and gray tin (Sn) in column IV and selenium (Se) and tellurium (Te) in column VI. There are, however, numerous compound semiconductors that are composed of two or more elements. Gallium arsenide (GaAs), for example, is a binary III-V compound, which is a combination of gallium (Ga) from column III and arsenic (As) from column V.
D.__________________
7. ______ compounds can be formed by elements from three different columns, as, for instance, mercury indium telluride (HgIn 2 Te 4), a II-III-VI compound. They also can be formed by elements from two columns, such as aluminum gallium arsenide (Al x Ga 1 − x As), which is a ternary III-V compound, where both Al and Ga are from column III and the subscript x is related to the composition of the two elements from 100 percent Al (x = 1) to 100 percent Ga (x = 0). Pure silicon is the most important material for integrated circuit application, and III-V binary and ternary compounds are most significant for light emission.

E __________________________Prior to the invention of the bipolar transistor in 1947, semiconductors were used only as two-terminal 8. ______, such as rectifiers and photodiodes. During the early 1950s, germanium was the major semiconductor material. However, it proved unsuitable for many applications, because devices made of the material exhibited high leakage currents at only moderately elevated temperatures. Since the early 1960s, silicon has become a practical substitute, virtually supplanting germanium as a material for semiconductor 9. ______. The main reasons for this are twofold: (1) silicon devices exhibit much lower leakage currents, and (2) high-quality silicon dioxide (SiO 2), which is an insulator, is easy to produce. Silicon technology is now by far the most advanced among all semiconductor technologies, and silicon-based devices constitute more than 95 percent of all semiconductor hardware sold worldwide.

Many of the compound semiconductors have electrical and optical properties that are 10. _____ in silicon. These semiconductors, especially gallium arsenide, are used mainly for high-speed and optoelectronic applications.

I. Fill in the gaps with the following terms: ternary, insulator, current, absent, sensitive, circuit, elemental, fabrication, devices, reciprocal.

II. Explain the following: Solid-state materials, insulators, conductors, conductivity, voltage, compound semiconductors, ternary compounds, photodiodes, rectifiers, silicon-based.

III. Think of the possible title for each paragraph (A – E).

IV. Answer the questions:

- What is the role of semiconductors in today's technology?

- Why do we call conductivity a reciprocal quantity?

- What are the elements that semiconductors are composed of?

- What elements form ternary compounds?

- Can you speak about the development of semiconductor technologies?

- What are the advantages of silicon? What are its drawbacks?

V. Give a small oral report on semiconductors and semiconductor materials.

Date: 2015-01-02; view: 1360