Properties and Strain Relaxation below Room Temperature of Epitaxial Pbse and Pb(Se,Te) on Fluoride-Covered Silicon Substrates

Abstract

ABSTRACTNarrow-gap PbSe and PbSe1−xTex films were grown by MBE on 3n-Si(111) wafers. The layers are used for IR-sensor array applications. Epitaxy was achieved by using an intermediate CaF2/BaF2 bilayer to overcome the large difference in lattice constants (14%) and thermal expansion coefficients (700%). While PbSe is rather soft, the hardness increases with x (x<0.5) in PbSe1−xTex. Thermal stresses are relieved by dislocation glide on (100)-planes, leading to slip lines on the surface. The surface morphology and step heights were studied with the scanning tunneling microscopy technique, and a model for the resulting (111)-surface structure is presented. The value of the remaining strain was determined with precision Rutherford backscattering spectrometry absolute angle measurements, X-ray diffraction and photoluminescence in the temperature range down to 10 K. It is found that no appreciable strain builds up even at cryogenic temperatures and after many temperature cycles. In contrast to PbSe, ternary PbSe1−xTex layers are strained elastically below room temperature owing to solid solution strengthening, and plastic deformation occurs only at higher temperatures.