【作者】 周志文；

【导师】 余金中； 赖虹凯；

【作者基本信息】 厦门大学 ， 凝聚态物理， 2009， 博士

【摘要】 硅基硅锗材料因其优越的性能,特别是与成熟硅微电子工艺相兼容,在硅基光电子器件如光电探测器、场效应晶体管等方面得到了广泛的应用,硅基硅锗薄膜生长及相关器件的研制引起了人们浓厚的兴趣。然而由于锗与硅的晶格失配度较大,在硅基上生长高质量硅锗和锗薄膜仍然是一个挑战性的课题,需要引入缓冲层技术。本论文采用低温缓冲层技术在UHV/CVD系统上生长出高质量硅基硅锗和锗弛豫衬底,并在此基础上研制出硅基长波长锗光电探测器。主要工作和研究成果如下:为了促进外延层应变弛豫、改善表面形貌,我们提出了低温Ge量子点缓冲层制备SiGe弛豫衬底的技术。分析了低温Ge量子点缓冲层在调节应力、湮灭位错等方面的机理,系统地研究了低温Ge量子点缓冲层制备SiGe弛豫衬底的生长条件,制备出质量良好的Si_0.72Ge_0.28弛豫衬底。Si_0.72Ge_0.28外延层的厚度仅为380nm,弛豫度高达99%,位错密度低于10⁵cm^-2,表面粗糙度小于2 nm,表面无Cross-hatch形貌,具有良好的热稳定性。系统地研究了低温Ge缓冲层的生长温度和厚度对高温Ge外延层表面形貌、应变弛豫等的影响和作用机理,探讨了低温SiGe和Ge双缓冲层对Ge外延层晶体质量改善的作用,优化了低温缓冲层生长条件,在UHV/CVD系统上生长出高质量Si基Ge薄膜。在硅衬底上制备的400nm-Ge外延层表面无Cross-hatch形貌、表面粗糙度仅为0.7 nm,X射线衍射峰的峰形对称且峰值半高宽为470 arcsec,化学腐蚀位错坑法测试位错密度为5×10⁵ cm^-2。研究了高温Ge外延层中张应变的产生机理以及对能带结构的影响。张应变主要是由于Ge和Si热膨胀系数的不同在Ge外延层从高温冷却到室温的过程中产生的,实验测量张应变的大小和理论计算值相吻合。定量计算表明张应变每增加0.1%,直接带隙将减小14 meV。设计并制备了正入射Si基长波长Ge PIN光电探测器。器件在-1 V偏压下的暗电流密度为20 mA/cm²,在波长1.55μm处-2V偏压下的响应度高达0.23 A/W。根据响应度计算Si基张应变的Ge外延层在1.55μm处的吸收系数比体Ge材料提高了3倍,达到3000 cm^-1。采用SOI衬底Ge外延层制备的探测器观测到共振增强效应。更多还原

【Abstract】 Si-based SiGe materials have been extensively applied in optoelectronic devices such as photodetectors and high mobility metal-oxide-semiconductor field effect transistors due to their advantageous properties,especially in compatibility with Si microelectronic processing.Si-based SiGe materials and their related devices have attracted great attention.However,it is a great challenge to directly deposit high-quality SiGe,especially Ge films on Si substrates due to the large lattice mismatch between Ge and Si.This thesis focuses on the growth of relaxed-SiGe and Ge virtual substrates（VSs）in ultra-high vacuum chemical vapor deposition （UHV/CVD）system using low temperature buffer technique and the fabrication of Si-based Ge photodetectors.The following are the details:An approach for the growth of relaxed-SiGe VSs with low temperature Ge （LT-Ge）islands buffer was proposed and intensively studied.The role of LT-Ge islands buffer in the mechanism of strain adjustment and dislocation annihilation was analyzed.High-quality relaxed-Si_0.72Ge_0.28films were grown on Si（100）substrates in UHV/CVD system using LT-Ge islands buffers.Si_0.72Ge_0.28film with a thickness of only 380 nm has a strain relaxation degree of 99%and a threading dislocation density less than 10⁵ cm^-2.No cross-hatch pattern is observed on the SiGe surface and the surface root-mean-square（rms）roughness is less than 2 nm.Annealing experiment indicated that SiGe films had great thermal stability.The influence of growth temperature and thickness of LT-Ge buffers on the surface morphology and strain relaxation of epitaxial Ge（epi-Ge）films was systemically investigated,and the role of LT-SiGe and Ge double buffers to improve the quality of epi-Ge films was studied.High quality relaxed-Ge films were grown on Si（100）substrates in UHV/CVD system with optimized buffer layers.X-ray diffraction peak of 400 nm-Ge epitaxially deposited on Si substrate is symmetric with a full width at half maximum（FWHM）of 460 arc sec,the threading dislocation density is measured to be 5×10⁵ cm^-2using etching pits counting method.There is no cross-hatch pattern on the Ge surface and the surface rms roughness is only 0.7 nm.The origin of tensile strain in epi-Ge and its effect on the band structure was investigated.Tensile strain was developed when cooling down due to the difference in thermal expansion coefficients between Ge and Si.The experimental data for tensile strain agrees quite well with the theoretical calculation.Tensile strain leads to the direct band-gap shrinkage of epi-Ge at a rate of 140 meV per percent calculated based on deformation potential theory.Normal-incident Si-based Ge PIN photodetectors were designed and fabricated. The dark current density is 20 mA/cm² at-1 V reverse bias.At wavelength 1.55μm, the responsivity is 0.23 A/W at-2 V reverse bias.The absorption coefficient of tensile-strained epi-Ge at 1.55μm is calculated to be 3000 cm^-1,which is 3 times that of bulk Ge.Response spectrum of epi-Ge photodetector fabricated on Silicon-On-Insulator substrate shows strong resonant enhancement effect.更多还原