【作者】 斯剑霄；

【导师】 吴惠桢；

【作者基本信息】 浙江大学 ， 凝聚态物理， 2009， 博士

【摘要】 以PbSe和PbTe为代表的Ⅳ-Ⅵ族窄带隙半导体材料具有一些独特的物理性质,如能带结构高度对称、重空穴带缺失,直接带隙位于布里渊区的L对称点、且具有正的温度系数关系等；Ⅳ-Ⅵ族半导体还具有俄歇复合率低的特点,比相似带隙的Ⅲ-Ⅴ族半导体低1-2个数量级。这些特性使得Ⅳ-Ⅵ族半导体成为制备中红外光电子器件的重要材料之一,并被应用到环境检测、有毒气体分析、医学诊断和国防等领域,因此研究Ⅳ-Ⅵ族窄带隙半导体材料的生长和物理特性具有重要的意义。本论文开展了Ⅳ-Ⅵ族半导体低维结构和PbTe/CdZnTe新型异质体系的分子束外延生长及其物理特性的研究工作,在BaF2(111)单晶衬底、CdZnTe(111)单晶衬底上实现了PbTe薄膜的外延生长,并在此基础上研究了PbSe量子点的生长机理。利用原子力显微镜(AFM)、高分辨X射线衍射(HRXRD)、X射线光电子能谱(XPS)以及光致发光谱(PL)等表征手段研究了PbTe薄膜、PbSe量子点以及PbTe/CdZnTe异质界面等的微结构和光电特性。取得的主要结果如下：(1)在BaF2(111)衬底上外延得到了单原子层平整表面的PbTe薄膜。通过比较不同生长温度、Te/PbTe束流比的PbTe薄膜的晶体质量和表面形貌,发现增大Te/PbTe束流比(Gr≥0.33)可以有效的改善表面形貌,得到单原子层平整的表面。同时,升高生长温度,可以有效的改善晶体质量,减少位错密度和缺陷。在不同温度下观察到了PbTe薄膜的中红外光致发光。(2)在单原子层平整的PbTe薄膜上,用分子束外延方法自组装(self-assembled)生长了PbSe量子点。通过观察不同沉积速率下的PbSe量子点生长,得到了PbSe量子点形状和分布特征,发现PbSe应力各向异性是影响量子点形状和分布的主要因素。此外在单原子层平整的PbTe薄膜上,通过电子束曝光、刻蚀,成功制备了脊背式和二维平面式PbTe薄膜微结构模板。(3)用分子束外延方法在Ⅱ-Ⅵ族Cd0.96Zn0.04Te (111)衬底上成功生长了PbTe单晶薄膜,通过比较不同生长温度、不同冷却速率下PbTe/Cd0.96Zn0.04Te薄膜的表面形貌和晶体质量,发现PbTe/Cd0.96Zn0.04Te薄膜的表面形貌主要由滑移台阶线和螺旋台阶面构成,缓慢的冷却过程可以提高PbTe/Cd0.96Zn0.04Te薄膜晶体质量。这与PbTe／和Cd0.96Zn0.04Te之间的热失配驰豫有关。实验发现在PbTe/Cd0.96Zn0.04Te界面上两种材料的(200)晶面发生了70.6。角度旋转。(4)利用X射线光电子谱(XPS),测量得到了PbTe/CdTe异质结的价带带阶为0.135±0.05 eV,同时,根据PbTe和CdTe的带隙,计算得到PbTe/CdTe导带带阶为1145±0.05eV。分析了PbTe/CdTe界面的应力、极化电荷对带阶测量的影响和PbTe/CdTe异质结带阶遵循“共阴离子”定律的原因。实验测量结果符合理论预言的带阶值。(5)研究了PbSe薄膜中声子散射对空穴迁移率的影响。通过对PbSe材料的光学波极性散射、杂质散射、声学波形变散射、声学波压电散射、光学波非极性散射的迁移率理论计算,结果表明在77-295K温度范围,PbSe的长纵光学波极性散射是影响载流子迁移率的主要散射机理。更多还原

【Abstract】 IV-VI group semiconductors (such as PbTe, PbSe) are in possession of interesting intrinsic physical natures:They have symmetric band structures with narrow direct band gaps at the L point in the Brillouin zone, positive temperature coefficients of the band gaps ((dE8)/(dT)>0). The absence of the heavy hole band and low non-radiative Auger recombination rates which are more than one order of magnitude lower in comparison withⅢ-ⅤandⅡ-Ⅵmaterials, are other unique properties. These characteristics make them as promising materials for the development of mid-infrared optoelectronic devices that could be utilized in atmospheric pollution monitoring, toxic gas analysis systems, and human breath analysis in medical diagnostics and military. Therefore, the study on the epitaxial growth and the physical properties ofⅣ-Ⅵsemiconductor is of great importance. In the thesis, we have studied the growth of new PbTe/CdZnTe heterostructures and low dimensional structures as well as their optical and electrical properties. Molecular beam epitaxy (MBE) has been used for the growth of PbTe layers and PbSe quantum dots on the BaF2(111) substrates. In addition the PbTe/CdZnTe heterostructures have also been grown by MBE. The characterization of these materials were performed by atomic force microscopy (AFM), high resolution x-ray diffraction (HRXRD), high resolution transmission electron microscopy (HRTEM), x-ray photoelectron spectroscopy (XPS) and photoluminescence (PL). The micro-structural and optoelectronic properties of the MBE grown PbSe quantum dots and PbTe/CdZnTe heterostructures were characterized by above technologies. The main conclusions are as follows:(1) Growth spirals with monolayer steps on PbTe surface are obtained by optimization of the growth parameters, such as using high Te/PbTe beam flux ratio (Gr≥0.33). It is found that the crystal qualities of PbTe grown on BaF2 substrates are improved and the defect densities are reduced as the growth temperatures increased from the 375°to 525°. The mid-infrared photoluminescence of PbTe/BaF2(111) were observed at different temperatures. (2) The self-assembled PbSe quantum dots were grown on the PbTe(111) buffer layer surfaces by molecular beam epitaxy. The shapes and sizes of PbSe quantum dots as a function of PbSe coverage were characterized using atomic force microscopy. It suggests that the high elastic anisotropy in the PbSe is main factor to impact the size and distribution of PbSe quantum dots. In addition, the stripe and two dimensional square PbTe templates were fabricated by electron beam lithography and wetting etching on the epitaxial PbTe layer.(3) Successful epitaxial growth of PbTe/Cd0.96Zn0.04Te (111) heterostructure using molecular beam epitaxy is described. The thermal misfit strain relaxation in epitaxial PbTe grown on Cd0.96Zn0.04Te (111) substrate has been studied by consideration on the effects of the growth temperature and the cooling rate. It is shown that the surface is dominated by terraces with triangular shape and anomalous spiral steps, which originate from the thermal misfit relaxation. Post-growth treatment with a slower cooling rate improves the crystalline quality of PbTe grown on Cdo.96Zn0.04Te (111). We found that the lattice fringes of the (200) plane in the PbTe rotated of 70.6°with respect to the (200) plane of Cd0.96Zn0.04Te at the interface.(4) The PbTe/CdTe (111) heterostructures were synthesized through molecular beam epitaxy and x-ray photoelectron spectroscopy has been used to measure the valence band offset at the PbTe/CdTe (111) heterostructure interface. A type-Ⅰband alignment with a valence band offset ofΔEv= 0.135±0.05 eV and conduction band offset ofΔEC=1.145 eV±0.05 eV is concluded. The piezoelectric field and band bending effects on the experimental results have been taken into consideration. Within the experimental error the directly obtained valence band offset is in agreement with theoretical prediction by the inclusion of spin-orbit interaction. In addition the origin of the nearly zero valence band offset in the PbTe/CdTe (111) heterostructure is analyzed.(5) Non-intentionally doped PbSe crystalline films were grown on insulating BaF2(111) by molecular beam epitaxy. Five scattering mechanisms limiting hole mobilities were theoretically analyzed, i.e. polar optical modes scattering, impurity scattering, acoustic mode scattering, piezoelectric acoustic modes scattering and non-polar optical modes scattering. The calculations show that in the temperatures between 77 and 295 K the scattering of polar optical phonon modes dominate the impact on the observed hole mobility in the epitaxial PbSe films.更多还原