Strain Mapping in InGaAsP Epitaxial Films by an X-Ray Diffraction Technique
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WILLIAM E.
MAYO**,
AND SIGMUND WEISSMANN**
*Mechanical Engineering Department, The Wichita State University, Wichita, KS 67208 **Department of Mechanics and Materials Science, College of Engineering, Rutgers, The State University of New Jersey, Piscataway, NJ 08854
ABSTRACT A new x-ray diffraction method is developed to determine the full elastic strain tensor and its distribution about a strain center in single crystal materials. It is based onthe recently developed Computer Aided Rocking Curve Analyzer and is particularly well suited for analysis of thin This technique will be film structures common to electronic materials. described in detail, and its application in measuring the non-uniform Also, strains in InGaAsP epitaxial film on InP substrate will be presented. possibility of using this method to measure the uniformity of film thickness will be discussed. INTRODUCTION In studies of thin film electronic materials, although many x-ray investigations have been performed [1-13], the resulting strain remains First only a few diffracting planes incomplete for two important reasons. were examined, and thus, the complete strain state could not be determined. The second shortcoming of the conventional x-ray methods of strain analysis is that these studies can estimate only the average strain in the thin films. The purpose of this paper is to present a new x-ray method which can determine all the components of the strain tensor and alst the distribution The method is a x-ray topographic technique of strains in the thin films. utilizing a double crystal diffractometer in a non-dispersive arrangement and is based on the recently developed Computer Aided Rocking Curve Analyzer (CARCA) [14]. The analysis of strain is based in part on the theory of Imura et al [15]. These authors showed that by measuring lattice parameters in six independent reflections, one can determine the complete elastic strain However, they applied this method to tensor in case of cubic crystals. determine the strain components of uniformly deformed crystals. In the present method, the analysis of Imura et al, is carried out on a point basis to measure the non-uniform strain distribution in epitaxial thin films. The operating principle of this x-ray diffraction technique will be described and its application to determine residual strain distribution in an InGaAsP thin film on InP (100 orientation) substrate deposited by liquid phase epitaxial method [16] will be presented. The quarternary alloy InGaAsP had been extensively investigated for It is an especially potential applications in double heterostructure lasers. desirable system since the lattice parameter of the thin film can be matched to the lattice parameter of the substrate by chemical control, thus proHowever, there still ducing a device which is potentially strain-free. exists a difference in thermal expansion coefficients which leads to the generation of residual elastic strains upon cooling from the deposition Another potential source of elastic strain is the variation in temperature
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