| As one of few structure-mismatched new heterostructures, PbTe/CdTe heteroj unctions (HJs) have attracted much attention. The narrow gap Ⅳ-Ⅵ semiconductor PbTe has rock-salt lattice structure and the band gap is at the L point in k-space; The Ⅱ-Ⅵ group semiconductor CdTe has zinc-blende structure and its band gap is at the Γ point. PbTe/CdTe HJs along different growth orientations ([100],[110],[111]) yield different interface structures. PbTe is a promising semiconductor material for development of mid-infrared laser and detector devices, which can be widely used in a variety of applications such as atmospheric pollution monitoring, toxic gas analysis, medical diagosing and military uses. Recently, one type of rhombocubo-octahedral PbTe quantum dots (QDs) embedded in CdTe matrix has been synthetized by annealing the (100) orientated CdTe/PbTe/CdTe quantum well (QW). The PbTe QDs have coherent (100),(110),(111) interfaces, which exhibit intensively enhanced room-temperature mid-infrared luminescence. Compared to the CdTe/PbTe(111) interface in the PbTe QDs, the epitaxial PbTe/CdTe(111) HJ interface has a different structure with both the CdTe and PbTe being polar (111) atom layers. When the CdTe epitaxial film is thin, its physical characteristics are changed by the built-in polarized electric field which could play an improtant role in the enhancement of the quantum effeciency in PbTe photoelectric devices. New types of mid-infrared devices with low threshold current and high operating temperature are expected to be developed. Besides, low dimensional structures related with PbTe/CdTe HJs would have large splitting energy of spin-orbit coupling because Pb and Te are heavy elements, which may render applictions in spintronic devices. In this thesis, the physical properities of the PbTe/CdTe HJs and the related low dimensional structures are studied both therectically and experimentally.In this thesis, the band structure parameters in the k-p envelope function model by first principle calculation are first detetmined and the splitting energy of the spin-orbit coupling in CdTe/PbTe/PbSrTe asymmetric QWs is evaluated using the simplified k·p model. Then, the growth process of the [111] orientated PbTe/CdTe HJs is simulated. To verify the calculation results, the PbTe/CdTe(111) HJs synthetized through molecular beam epitaxy (MBE) were characterized by high resolution transmission electron microscopy (HR-TEM), low temperature Hall effect measurement and in situ reflection high energy electron diffraction (RHEED). The structural optical and transport properties of the PbTe/CdTe HJs are investigated. The main results are summerized as follows:(1) The band structure parameters defined in12-band kp envelope function model are determined, which makes it possible to calculate the electronic properties in low dimensional PbTe structures more precisely. Compared to the typical Ⅲ-Ⅴ group and Ⅱ-Ⅵ group semiconductor materials, the band structure of PbTe does not have a heavy hole band while the valence and conduction bands are symmetrical. Therefore, the kp matrix can be diagonalized into two submatrice which describe the conduction and valence bands, respectively. The momentum matrix elements in the12-band kp envelope function model is calculated by first principle and the Rashba coefficient and the effective mass are given in analytical expressions.(2) The splitting energy of the spin-orbit coupling in a CdTe/PbTe/PbSrTe asymmetric QW is calculated using the simplified kp model. The CdTe/PbTe/PbSrTe QW exhibits pure Rashba splitting due to the bulk inversion symmetry in PbTe. The four energy valleys are no longer equivalent in the QW. The splitting energy in the oblique valley which has a slant angle with the growth orientation is anisotropic and gets bigger with increasing slant angle. The splitting energy in the [110] oblique valley can reach13.7meV.(3) A double external electric field correction method is proposed to simulate the polar interface. In order to simulate the growth process of PbTe/CdTe HJs, external fields should be introduced in the slab model to compensate the artificial electric field caused by the polar interfaces. Using this method, we successfully simulated the epitaxial growth of CdTe (PbTe) on the (111)-oriented PbTe (CdTe) substrate. A new twisted interface structure is predicted, which is different from the PbTe/CdTe(111) interface formed in the PbTe QDs embedded in the CdTe matrix. The interface reconstruction observed during the MBE growth is explained by our theoretical results. The predicted interface structure is confirmed by HR-TEM.(4) The electronic states of CdTe grown on PbTe(111) is simulated. The PbTe lattice is strongly distorted by the s2lone pair in Pb2+cation at the interface, which leads to the CdTe presents metallic property. The strong polarized electric field in the CdTe film lowers the conduction band edge of CdTe at the interface below the Fermi level. The partial ionization of the Pb, Cd, Te atoms causes the generation free electrons. The two dimensional electron gas (2DEG) is formed at the interface and the calculated electron density is as high as6.0×1013cm-2. For the CdTe(30nm)/PbTe(111) HJ sample, the Hall effect measurement shows the electron concentration is higher than9.0×1019cm-3, and it decreases rapidly with increasing CdTe thickness. The mobility at room temperature and77K is300-400cm2/Vs,6700cm2/Vs respectively,but the electron concentration does not change much. For the CdTe/PbTe HJ sample with75nm CdTe, the mobility at2K is20,200cm2/Vs and the electron concentration is4.5×1018cm-3. The2DEG in the CdTe/PbTe(111) HJs could keep such high mobility with elelctron density around～1013cm-2, which is rarely seen in other material system. |
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