Jianxiao Si

Experimental determination of valence band offset at PbTe/CdTe(111) heterojunction interface by x-ray photoelectron spectroscopy

Lattice-matched PbTe/CdTe(111) heterojunction interfaces were studied using x-ray photoelectron spectroscopy. A type-I band alignment with a valence band offset of ΔEV=0.135±0.05 eV and a conduction band offset of ΔEC=1.145±0.05 eV is concluded. Within experimental error the determined valence band offset is in agreement with theoretical prediction by inclusion of spin-orbit interaction.

Observation of phonon modes in epitaxial PbTe films grown by molecular beam epitaxy

Phonon modes of PbTe films grown by molecular beam epitaxy have been studied by micro-Raman scattering. On the as-grown PbTe surface, strong TeO2 phonon vibrational modes were detected, which obscured the observation of the longitudinal optical (LO) phonons of PbTe in early conventional Raman scattering experiments. Existence of a TeO2 layer on the PbTe surface is confirmed by observation with x-ray photoemission spectroscopy. After removal of TeO2 by chemical etching, the LO phonons for PbTe films were unambiguously observed. Misfit strain accommodated in the epitaxial films makes the lattice distorted from cubic structure, which lowers the crystal symmetry and leads to observation of what would normally be Raman inactive LO phonon modes for PbTe.

Observation of thermal-misfit strain relaxation in a PbTe semiconductor grown on Cd0.96Zn0.04Te(1?1?1)

The thermal-misfit strain relaxation in epitaxial PbTe grown on Cd0.96Zn0.04Te(1 1 1) substrates has been studied by the combined characterization of atomic force microscopy and high-resolution transmission electron microscopy. It is shown that the strain relaxes by the movement of dislocations in the 1 1 0–{1 0 0} primary glide system and leaves straight slip steps on the surface. The thermal-misfit strain relaxation is greatly affected by the growth temperature and post-growth cooling rate. Post-growth treatment with a slower cooling rate improves the crystalline quality of PbTe grown on Cd0.96Zn0.04Te(1 1 1). Because of the easy dislocation glide down to the interface in the 1 1 0–{1 0 0} primary glide system, PbTe/Cd0.96Zn0.04Te(1 1 1) heterostructures exhibit good crystal and optical qualities, which indicate that PbTe/CdZnTe heterostructures may become a promising candidate for the fabrication of PbTe-based mid-infrared optoelectronic devices.

Progress of IV-VI Semiconductor Research in China

Progress of IV-VI semiconductor (lead chalcogenides) research in China is reported. Lead chalcogenides (PbSe and PbTe) have been grown by molecular beam epitaxy (MBE). Evolution of PbSe surface morphologies with different Se/PbSe beam flux ratio has been studied by atomic force microscopy (AFM) and high-resolution x-ray diffraction (HRXRD). Interesting surface features, such as triangle holes and spirals with monolayer steps, are observed by AFM. Glide of threading dislocations in < 110> {100} -glide system and Pb-rich atom agglomeration play an important role in the formation of triangle pits. PbSe QDs grown by self-organization and mid-infrared luminescent emission of the QDs at room temperature are demonstrated. Phonon modes of PbTe and PbSe epitaxial film are studied by Raman spectroscopy in detail.