Lattice Parameter Anomaly in an MOCVD CdTe Epitaxial Layer Grown on a GaAs Substrate

摘要

The anomalous behaviors of the CdTe and GaAs lattice parameters below 120 deg K for a composite system is reported. They concern a 3 mu m thick (1,0,0) single crystal CdTe epitaxial layer on a (1,0,0) single crystal GaAs substrate. The epilayer was deposited at 410 deg C by MOCVD. This x-ray lattice parameter study was done in the temperature range between about 8 deg K and 300 deg K. The lattice parameters of the composite system are compared to those of the corresponding bulks. The bulk lattice parameter variations as a function of the temperature were also measured and compare well with the appropriate changes of the thermal expansion coefficients taken from the literature. Our results show that the lattice parameters perpendicular to the surface of both the GaAs substrate and the CdTe epilayer shrink four times more than the corresponding bulks when the samples are cooled down to 10 deg K. It is further seen that there is no compensation effect between the elements of the composite system; that is, the lattice parameters of the two materials change in the same direction as if the composite system - the epilayer and the thickness of the substrate which is probed by the x-rays - would behave as a new material with entirely new physical properties. (ERA citation 11:036355)