skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Local Atomic Structure Of Cdse Ultra-Thin Quantum Wells Examined By X-Ray Absorption Fine Structure Experiments

Abstract

We have employed the X-ray absorption fine structure (XAFS) technique for the investigation of the local atomic structure of CdSe/ZnSe ultra-thin quantum wells (UTQWs) with 1 and 3 ML thickness. The CdSe/ZnSe system presents a large lattice mismatch of {approx}7.3 % and the pseudomorphic UTQWs are under compressive biaxial strain. The analysis of the XAFS data indicate differences in the Cd-Se bond length of the 1 and 3 ML UTQWs, as a consequence, differences in the magnitude of the strain, in significant disagreement with the usual hypothesis of thickness independent strain for pseudomorphic thin films. Furthermore, the analysis of the XAFS experiments suggests the possibility of inhomogeneous strain in the 3ML UTQW. We conclude that even for ultra-thin pseudomorphic films the strain can be inhomogeneous and depend on film thickness if this is close to the critical thickness hc.

Authors:
;  [1];  [2]
  1. Applied Physics Dept., CINVESTAV-Merida, Apdo. Postal 73., 97310, Merida, Yucatan (Mexico)
  2. Physics Department, CINVESTAV, Ave. IPN 2508, 07360 Mexico, DF (Mexico)
Publication Date:
OSTI Identifier:
21055074
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 893; Journal Issue: 1; Conference: ICPS 2006: 28. international conference on the physics of semiconductors, Vienna (Austria), 24-28 Jul 2006; Other Information: DOI: 10.1063/1.2729789; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ABSORPTION SPECTROSCOPY; BOND LENGTHS; CADMIUM SELENIDES; CRYSTAL DEFECTS; FINE STRUCTURE; INTERFACES; QUANTUM WELLS; SEMICONDUCTOR MATERIALS; STRAINS; THIN FILMS; X-RAY SPECTRA; X-RAY SPECTROSCOPY; ZINC SELENIDES

Citation Formats

Lezama-Pacheco, Juan S., Mustre, Jose, and Hernandez-Calderon, Isaac. Local Atomic Structure Of Cdse Ultra-Thin Quantum Wells Examined By X-Ray Absorption Fine Structure Experiments. United States: N. p., 2007. Web. doi:10.1063/1.2729789.
Lezama-Pacheco, Juan S., Mustre, Jose, & Hernandez-Calderon, Isaac. Local Atomic Structure Of Cdse Ultra-Thin Quantum Wells Examined By X-Ray Absorption Fine Structure Experiments. United States. doi:10.1063/1.2729789.
Lezama-Pacheco, Juan S., Mustre, Jose, and Hernandez-Calderon, Isaac. Tue . "Local Atomic Structure Of Cdse Ultra-Thin Quantum Wells Examined By X-Ray Absorption Fine Structure Experiments". United States. doi:10.1063/1.2729789.
@article{osti_21055074,
title = {Local Atomic Structure Of Cdse Ultra-Thin Quantum Wells Examined By X-Ray Absorption Fine Structure Experiments},
author = {Lezama-Pacheco, Juan S. and Mustre, Jose and Hernandez-Calderon, Isaac},
abstractNote = {We have employed the X-ray absorption fine structure (XAFS) technique for the investigation of the local atomic structure of CdSe/ZnSe ultra-thin quantum wells (UTQWs) with 1 and 3 ML thickness. The CdSe/ZnSe system presents a large lattice mismatch of {approx}7.3 % and the pseudomorphic UTQWs are under compressive biaxial strain. The analysis of the XAFS data indicate differences in the Cd-Se bond length of the 1 and 3 ML UTQWs, as a consequence, differences in the magnitude of the strain, in significant disagreement with the usual hypothesis of thickness independent strain for pseudomorphic thin films. Furthermore, the analysis of the XAFS experiments suggests the possibility of inhomogeneous strain in the 3ML UTQW. We conclude that even for ultra-thin pseudomorphic films the strain can be inhomogeneous and depend on film thickness if this is close to the critical thickness hc.},
doi = {10.1063/1.2729789},
journal = {AIP Conference Proceedings},
number = 1,
volume = 893,
place = {United States},
year = {Tue Apr 10 00:00:00 EDT 2007},
month = {Tue Apr 10 00:00:00 EDT 2007}
}
  • The anisotropy of the local structure around In atoms in high quality In{sub x}Ga{sub 1-x}N (x=0.145,0.20,0.275) single quantum wells (SQWs) was investigated by fluorescence extended x-ray absorption fine structure measurements using linearly polarized x ray whose electric field was set to be both horizontal and vertical to the SQWs. The interatomic distance was isotropic for the nearest In-N, whereas for the second nearest In-Ga and In-In, the interatomic distance for out-of-plane atoms was longer than that for in-plane atoms. From the analyses of the coordination number for In-In and In-Ga, the In atom distribution in the In{sub 0.275}Ga{sub 0.725}N SQWmore » was found to be statistically random in both directions. On the other hand, In atoms in the In{sub 0.20}Ga{sub 0.80}N SQW, corresponding to green light-emitting diodes (LEDs), were randomly distributed in the horizontal direction but aggregated in the vertical direction. Correlation was suggested between the vertical aggregation and the higher efficiency of InGaN-based blue to green LEDs.« less
  • Local structural information for the first two atomic shells surrounding Ga atoms in free standing Al{sub x}Ga{sub 1-x}N alloy films has been obtained by extended x-ray absorption fine structure spectroscopy. For an AlN mole fraction ranging from 0 to 0.6, we found that the first shell Ga-N bond length had only a weak composition dependence, roughly one quarter of that predicted by Vegard's Law. In the second shell, the Ga-Ga bond length was significantly longer than that of Ga-Al ({delta}{approx}0.04-0.065 Aa). A bond-type specific composition dependence was observed for the second shell cation-cation distances. While the composition dependence of themore » Ga-Ga bond length is {approx}70% of that predicted by Vegard's Law, the Ga-Al bond length was essentially composition independent. These results suggested that local strain in Al{sub x}Ga{sub 1-x}N was also accommodated by lattice distortion in the Al cation sublattice. (c) 1999 American Institute of Physics.« less
  • The application of near-edge surface, extended x-ray absorption fine structure to the study of a clean surface is reported. Direct evidence is found for surface recrystallization of ion-damaged (amorphized) Si, whereas no such evidence is seen for evaporated (amorphous) Si. The procedures described here are applicable to almost all clean or adsorbate-covered surfaces.
  • Extended x-ray-absorption (EXAFS) and electron-energy-loss fine-structure (EXELFS) measurements have been performed on amorphous unhydrogenated silicon carbide, a-SiC, and amorphous hydrogenated silicon carbide, a-SiC:H. Two hydrogenated samples with hydrogen concentrations corresponding, respectively, to H flows of 4 sccm (20% of argon flow) and 8 sccm (40% of argon flow) during the reactive sputtering process, were analyzed (sccm denotes standard cubic centimeters per minute at STP). It is found that short-range order (SRO), consisting of the same tetrahedrally coordinated units present in cubic crystalline c-SiC (zinc-blende structure), where a Si atom is surrounded by nearly four C atoms and vice versa, doesmore » exist in all the amorphous samples. This SRO, however, is detected only at a level of the first C and Si coordination shells in a-SiC and a-SiC:H. The structural disorder of the first Si and C coordination shells in all forms of amorphous SiC is somewhat greater than c-SiC, and it decreases appreciably as hydrogen is added. The a-SiC sample exhibits large Si and C coordination numbers, almost identical to c-SiC, a low atomic density, and virtually the same Si-C bond length as c-SiC. These results indicate that a relatively small concentration of large voids exist in a highly disordered a-SiC matrix.« less