X-ray absorption fine-structure study of amorphous germanium under high pressure

Abstract

1087example, we have not determined yet whether in the process of observing phonon-assisted laser operation macroscopic occupation of a phonon mode occurs and whether we are operating a phonon oscillator. High-pressure measurements, among others, may help resolve these questions. In previous high-pressure measurements on QWHs we (N.H.) with H. Drickamer and our students have been able to probe, because of easily resolved confined-particle exciton states, the "inside" of an energy band and not just the band edges.21 High-Q heat sinking of a QWH and photopumping present an opportunity to observe confined-particle transitions (recombination radiation) and phonon sidebands (not just bulk-(21) Kirchoefer, S. W.; Holonyak, Jr., N.; Hess, K.; Gulino, D. A.; Drickamer, H. G.; Coleman, J. J.; Dapkus, P. D. Appl. Phys. Lett 1982, 40, 821.crystal band-edge processes) and see how they "tune" with pressure. These are experiments worth pursuing. We wish many more vigorous years for Harry Drickamer and the opportunity to do more high-pressure studies with him, including high-pressure versions of the experiments described here. Acknowledgment.We are grateful to John Bardeen for helpful discussions (N.H.) on macroscopic phonon occupation in photopumped QWHs. For technical assistance we thank B. L. Marshall, R. T. Gladin, and B. L. Payne.

Structure of crystalline and amorphous Ge probed by X-ray absorption and diffraction techniques

“…In previous papers [7,10], the precision in the XAS measurements and related determination of bond distances was insufficient to reveal such a change in the structure, but in the present case the typical error bar is estimated to be below 0.005 Å , precise enough to reveal FIGURE 3 XAS K-edge w(k) spectra of a-Ge at room temperature for increasing pressure (from the top to the bottom). The estimated uncertainty on measured pressures is AE0.1 GPa.…”

“…In amorphous Ge (a-Ge), pressurization induces modifications of the structure [6][7][8][9][10] still not completely understood.…”

Pressure and temperature dependence of EXAFS Debye–Waller factors in diamond-type and white-tin-type germanium

“…The compressibility of a coordination polyhedron of an X-ray absorbing atom can be determined by EXAFS. Some EXAFS studies on crystalline and amorphous Ge under pressure have already been presented in the literature (Kawamura et al, 1981;Shimomura & Kawamura, 1987;Freund et al, 1990). It was demonstrated by Freund et al (1990) that the local compressibility of a single GeÐGe bond in amorphous Ge is about 30% smaller than the bulk compressibility of the crystalline phase.…”

Computer analysis on the structure of low-density and high-density amorphous germanium

“…On the other hand, no significant structural changes were found in Ref. [3]. The differences among these experiments are understood in terms of the differences in the experimental conditions.…”

“…In order to elucidate the high-pressure behavior of aGe, several experimental studies have been put forward [1][2][3]. The results of these studies imply that, depending on the sample preparation and pressure-loading conditions, it is possible that different types of high-pressure structures realize.…”