02/26/2004 -
Optoelectronic Properties of Semiconductors and Superlattices, Volume 13: III-Nitride Semiconductors, Optical Properties I (2002)
by M.O. Manasreh and H.X. Jiang
ISBN 1-56032-972-6. Taylor and Francis, London and New York. 2002. Hardcover. 417 pages. $145.
Although the title lays claim to an optical study of properties of III-N semiconductors, a major part of the results are concerned with the Raman effect commonly associated with spectroscopy. This effect is not usually linked with coherent light, which by definition is monochromatic and devoid of other spectral components. The Raman effect is well known to spectrographers and physicists who use it to study lattice and molecular properties using the light spectrum and diffracted light with smaller side bands. The fact that it also occurs in laser emissions needs explanation to the average reader; for this reason, the book is probably intended for the specialist, and the practicing spectrographer at that. Those seeking practical hints on how to evolve newer laser diodes and other light-emitting diodes will have do so independently because, while the text offers hints, and while the contributors mention band gap engineering, how this is to be done remains a black art. From an engineering point of view, the effect of the side bands is negligible (i.e., it would not affect luminosity). The study of Raman side bands, therefore, is purely diagnostic and maybe an abstruse and intellectual show of nimbleness and agility in fitting facts with theory. One contributor does mention, however, that minority phases like the hexagonal in GaN layers of zinc-blend type cannot be detected by other means, such as x-ray.
The text is divided into different topics covered by a variety of leading researchers with the stated aim of improving the laser output properties of some semiconductors (here it is focused mainly on the III-N types). Other combinations, such as II-VI and III-V, were studied earlier, from the 1950s (e.g., for thermoelectric effects and infra red detectors), but engineering these to be able to emit light as lasers was a much later development.
One of the main parameters referred to is the band gap, whereas other lattice properties related to interaction with vibrations are idealized as phonons. One might have expected to find some derivations related to the BCS theory also. There is a Raman analysis in a chapter dealing with large-band-gap wurtzite GaN relating to time-resolved effects. "Time resolved” is another buzz word that was not fully explained–is it transient, real-time, maybe? The transition times are of the order of pico and femto seconds in laser transitions. One author mentions the use of a streak camera to record such events.
Other practical applications are in optical amplifiers and for communications in consumer and military purposes. The main aim of how to enhance optical emissions was somehow lost in the haze of different physico-electronic terms and measurements. The Raman effect is known to be of use in learning about the piezoelectric field, polarization field, well-width fluctuations, alloy variation, quantum dots, and carrier transport phenomena. Improvements in p-type semiconductors only are considered.
Other topics, such as extension to superconductors, superlattice measurements and structure elucidation, optical thickness (used in radiation studies), and phase diagram studies are not found in the detail presented. One would hope that these may be included subsequently.
This book would no doubt be a good reference for practicing spectrographers and graduate students. The references are extensive and give useful leads. There is an overlap between many aspects of physics and materials science and the book is interdisciplinary with electronics fields also.
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