Condensed-Matter Physics (1986) / Chapter Skim
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5 Semiconductors
5 Semiconductors
Pages 113-126
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From page 113... ...
instead of reaching a plateau after its initial explosive growth following the discovery of the transistor based on semiconductor physics and materials, materials research related to semiconductor technology is expected to receive another impetus to further growth from the advent of very-large-scale integration (VLS11. Alongside these exciting technological developments semiconductor physics has continued to be a surprisingly rich and fertile field of scientific inquiry.
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From page 114... ...
The tools for preparing these materials were developed for computer technology and are now used to prepare and characterize materials that may, in the future, provide even more powerful and cost-effective computer components. In this chapter, it is not our intent to discuss technology in any detail or the essential role of semiconductor materials in it, but rather we hope to convey a brief perspective of the status in semiconductor science.
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From page 115... ...
One of the more exciting areas of solid-state physics in the past few years has been the role of disorder and dimensionality on transport in solids. Lithographically produced structures, two-dimensional inversion layers, and high-mobility semiconductors have been widely used in the investigation of phenomena related to quantum transport localization, Coulomb interaction effects, and the integer and fractional quantum Hall effects.
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From page 116... ...
A combination of the results of a variety of experimental techniques using x rays, electrons, ions, and atoms has provided evidence that our understanding of the atomic arrangement at surfaces is only now beginning. In fact, it is generally agreed that only one semiconductor surface that of GaAs (1101- is currently known reliably and accurately.
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From page 117... ...
Theoretical techniques using primarily the cluster approximation, which simulates the infinite crystal by a small number of atoms, often yielded poor results. Major advances in both experimental and theoretical techniques for the study of deep centers occurred in the last decade.
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From page 118... ...
, quantum wells formed by two heterojunctions, and superlattices formed by periodic arrays of quantum wells or by periodic variations of impurity concentrations. If the confining potentials quantize the energy levels to give level spacings comparable with or greater than the thermal energy kBT and the energy level broadening, then the motion of the electrons will have a two-dimensional character.
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From page 119... ...
For example, weak localization effects and the remarkable quantized Hall conductance phenomena, both discussed in Chapter 1, have been observed in these systems. The two dimensionality of these systems also leads to a situation where the electronelectron interactions make a major contribution to the electronic energy levels, as has been verified in far-infrared spectra of silicon inversion layers.
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From page 120... ...
In the form of QWHs, monolithic, single-diode structures have achieved laser power levels from 100 mW to over 2 W In these heterostructures the large asymmetry in electron-hole behavior permits a major redesign of valence photodetectors and makes possible other unique hot-electron devices.
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From page 121... ...
Because of overconstrained bonding conditions, true glasses cannot be expected with fourfold coordination. Experimentally this is seen in the form of incomplete or dangling bonds and other local structural inhomogeneities, which lead to gap states that obscure the basic semiconducting properties of interest, for example, activated conductivity, doping, and distinct band gaps.
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From page 122... ...
We expect semiconductor research to be an active area of interest not just because of technological forces but also because of our increased experimental and theoretical capabilities. Semiconductor Surfaces and Interfaces A variety of experimental and theoretical techniques will be applied to investigate the nature of atomic rearrangement or reconstruction on semiconductor surfaces.
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From page 123... ...
Since the diffusion distance (which increases with temperature) is an intrinsic limitation on device dimension, lowtemperature processing is likely to become crucial for achieving submicrometer structures in VLSI devices.
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From page 124... ...
Defects in Semiconductors Ion implantation is currently used to introduce controlled amounts of shallow impurities in semiconductor devices. The samples are then annealed in order to redistribute the impurities to electrically active sites.
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From page 125... ...
If the precision being attained now is confirmed by additional work, the quantized Hall resistance may become a resistance standard or a secondary standard. GROWTH TECHNIQUES AND LITHOGRAPHY Continuing improvement in semiconductor growth techniques and in lithography can be expected to lead to use of a wider range of materials and to new device structures.
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From page 126... ...
THE TWO-DIMENSIONAL WIGNER CRYSTAL The elusive two-dimensional Wigner crystal, the electron crystal expected in a degenerate low-density electron system at low temperatures, may finally be observed in inversion layers at semiconductor surfaces in the coming decade, as its classical analogue was observed in electrons on liquid helium in the past decade. Exciting new possibilities arise if electrons are placed on a thin film of liquid helium on a substrate in which a periodic- or random-potential is imposed.
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