Comparative study of thermal mismatch effects in CdTe/Si,
CdTe/Ge, and CdTe/GaAs composite structures

R.N. Jacobs,1,4 L.A. Almeida,1 J. Markunas,1 J. Pellegrino,1 M. Groenert,1
M. Jaime-Vasquez,1 N. Mahadik,2 C. Andrews,2 S.B. Qadri,2 T. Lee,3 and M. Kim.3

1- U.S. Army RDECOM, CERDEC Night Vision and Electronic Sensors Directorate, Fort Belvoir, VA 22060.
2- U. S. Naval Research Laboratory, Washington, DC 20375.
3- Department of Electrical Engineering, University of Texas, Dallas, TX 75083.
4- Email: info@nvl.army.mil
 
Keywords: Residual film stress, thermal mismatch, HgCdTe, CdTe, Silicon, heteroepitaxy

Abstract
The rising interest in low-cost, large-area substrates for high performance HgCdTe infrared detectors has fueled research efforts in heteroepitaxial structures including CdTe/Si(211), CdTe/Ge(211), and CdTe/GaAs(211)B. The enormous lattice-mismatch inherent in these systems ranges from -14.6 to -19.3%, and is responsible for large dislocation densities and other defects which may limit detector performance. Though greater differences exist with regards to thermal mismatch (13.8 to -92%), the effects have not been well documented. Here, we investigate the relative contributions of lattice and thermal mismatch on CdTe film characteristics including dislocation density and residual stress. Based on x-ray techniques we consistently measure a tensile residual stress for CdTe/Si, but observe compressive residual stresses for CdTe/Ge and CdTe/GaAs. Consistent with theoretically predicted stress levels, the experimental data implies the dominance of thermal mismatch in the residual film stress characteristics. These findings may hold significance for the design and fabrication of large-format HgCdTe infrared focal plane arrays.
 
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