| 题名 | InSb薄膜的光学热学特性研究 |
| 作者 | 蔡晓林 |
| 学位类别 | 硕士 |
| 答辩日期 | 2013 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 魏劲松 |
| 关键词 | 光学非线性 Z-扫描 InSb薄膜 物理机理 超分辨 |
| 其他题名 | Optical and thermal characteristics of InSb semiconductor thin films |
| 中文摘要 | InSb半导体薄膜被广泛用作超分辨结构（super-resolution structure）中的非线性掩膜层（mask layer），并且具有很大的发展潜力。但是，在超分辨结构中激光和InSb薄膜的相互作用机理以及超分辨的原理仍然缺乏进一步的探究。 本论文利用磁控溅射方法制备K9基片/InSb/ZnS-SiO2样品。经XRD分析发现沉积态InSb薄膜处于非晶状态，并通过真空退火热处理得到晶态样品。利用椭圆偏振光谱仪对非晶态/晶态InSb薄膜的光学常数进行测量，并分别得到光学带隙为1.30 eV和1.25 eV。 采用纳秒脉冲激光作为光源，利用改进型Z-扫描装置，测量了非晶态/晶态InSb薄膜在波长405 nm的激光作用下的非线性吸收系数和非线性折射率。通过变温椭偏方法测试了非晶态/晶态InSb薄膜折射率和消光系数随温度的变化，重点讨论了热效应对非晶态/晶态InSb薄膜的非线性吸收和非线性折射特性的贡献。通过对InSb半导体材料热学性质的测量，详细分析了其热膨胀和导热机理，为热致非线性大小的计算提供了准确的参数和物理意义。从热膨胀和带隙萎缩两个方面讨论了变温椭偏测量的热光系数的物理来源。除了热效应，根据InSb薄膜的能带结构，探讨了电子效应对非线性吸收系数和非线性折射率的贡献，包括自由载流子吸收、激发态吸收和带填充效应。另外，实验中的InSb样品是薄膜，相当于二维量子阱结构，据此初步分析了量子限制效应对非线性的增强作用。最后，对非线性饱和吸收特性诱导的超分辨效应进行了理论模拟，分析了非晶态InSb薄膜的饱和吸收对透射光斑尺寸的缩减作用。 本论文主要内容包括以下几点： 1．采用改进的Z-扫描装置测量了非晶态/晶态InSb样品在405 nm波长纳秒脉冲激光作用下的非线性吸收和非线性折射。结果表明非晶态InSb薄膜表现出饱和吸收和自聚焦特性，有效非线性吸收系数为-〖10〗^(-2) m/W数量级，非线性折射率为〖+10〗^(-9) m^2/W数量级。而晶态InSb薄膜表现出反饱和吸收和自聚焦特性，有效非线性吸收系数在〖+10〗^(-2) m/W数量级，非线性折射率也是+〖10〗^(-9) m^2/W数量级。根据非线性吸收系数，计算了非线性吸收截面的大小为〖10〗^(-17) cm^2数量级，与相关文献报道值非常接近。 2．对非晶态/晶态InSb薄膜在405 nm波长的折射率和消光系数随温度的变化进行了变温椭偏测试。对于非晶态InSb薄膜，测量结果表明在290 K到 430 K温度范围内（小于晶化温度），折射率随温度的升高而减小，线性拟合的热光系数dn/dT=-3.314×〖10〗^(-4) K^(-1)，消光系数也随着温度的升高而逐渐减小，线性拟合得到dk⁄dT=-3.610×〖10〗^(-4) K^(-1)，换算为相应的吸收系数变化为dα⁄dT=-1.12×〖10〗^4 〖m^(-1) K〗^(-1)。对于晶态InSb薄膜，在400 K到600 K温度围内，折射率随着温度的升高而增大，热光系数dn/dT=8.03×〖10〗^(-4) K^(-1)，消光系数随着温度的升高而减小，dk⁄dT=-1.25×〖10〗^(-3) K^(-1)，相应的吸收系数变化为dα⁄dT=‒3.86×〖10〗^4 〖m^(-1) K〗^(-1)。 3．对InSb半导体的几个主要热学性能进行了测量，包括热重、比热容、热扩散系数、热膨胀系数和热导率。结果表明比热容和热膨胀系数在温度升高的过程中几乎保持不变，热扩散系数和热导率随着温度的升高逐渐减小。分别讨论了声子、电子和光子辐射对热导率的贡献，发现在300 K到800 K温度范围内，声子热导率占据主导地位，这也是为什么热导率的测量结果随温度增加而减小的原因。与其它Sb基和Te基材料的热学参数进行对比，发现InSb的导热性能比其它相变材料优越。这些结果为发展InSb器件提供了重要热学信息，也为研究热效应对非线性的贡献提供了一些有用的热学参数。 4．探究了InSb薄膜光学非线性的物理机理。分析表明非晶态InSb薄膜在405 nm波长的饱和吸收特性主要来源于纳秒脉冲激光作用下的热效应，而晶态InSb薄膜的反饱和吸收特性主要来源于自由载流子吸收导致的等效双光子吸收。非晶态/晶态InSb薄膜的非线性折射特性是热致带隙萎缩和电子受激跃迁的载流子效应共同作用的结果。另外，带填充效应和量子限制效应对InSb薄膜的非线性也有贡献。 5．对饱和吸收特性诱导的超分辨效应进行理论模拟，结果表明非晶态InSb薄膜的透射光斑尺寸仅为入射光斑大小的44%。这些研究对突破衍射极限实现纳米尺寸信息存储具有重要的指导意义。 |
| 英文摘要 | InSb thin films used as active nonlinear mask layers in super-resolution structure appear to be very promising for breaking the diffraction limit due to their optical nonlinear characteristics. However, the mechanisms of interaction between the laser beam and InSb thin film as well as the super-resolution effect still require further investigation. In this dissertation, samples of InSb/ZnS-SiO2 structure are deposited on K9 glass substrate through magnetron sputtering method without substrate heating. The ZnS-SiO2 dielectric layer is employed to prevent evaporation and oxidization of the InSb layer. The as-deposited samples are verifed in amorphous state by XRD, and crystallization is achieved by annealing the as-deposited samples in an oven at Ar gas atmosphere above the crystallization temperature. Optical constants of amorphous/ crystalline InSb thin films (a-/c-InSb) are measured by a spectroscopic ellipsometer. Linear extrapolation of the absorption cuve is employed to obtain the optical band gap of a-/c-InSb thin films, which is determined to be 1.30 eV for a-InSb and 1.25 eV for c-InSb, respectively. The intensity-dependent optical nonlinear absorption and refraction of a-/c-InSb thin films are measured through well-established z-scan apparatus with nanosecond laser pulses at wavelength of 405 nm. The temperature dependence of the optical constants of a-/c-InSb thin films is investigated by variable-temperature ellipsometry measurements under Ar inert atmosphere. The contribution of thermal effect to the optical nonlinear absorption and refraction of a-/c-InSb thin films is discussed in detail. The systematical measurements of several important thermal properties of InSb semiconductor are conducted, which offer accurate thermo-physical parameters used for calculation of thermal-induced nonlinearity. The measured thermo-optic coefficient is explained from thermal expansion and band gap shrinkage. Besides, according to the band structure of InSb thin films, we investigate the contribution of carrier effects to the optical nonlinearity of a-/c-InSb thin films. Futhermore, since the InSb thin film samples in z-scan experiments are equal to quantum wells, the ehancement of optical nonlinearity due to quantum confinement effect is explored. Finally, theoretical simulation of super-resolution effect based on the strong nonlinear saturable absorption coefficient of a-InSb thin film is given. The main content of this dissertation is listed as follows: 1．The optical nonlinear absorption and refraction characteristics of a-/c-InSb thin film samples are measured by an improved z-scan method with nanosecond pulsed laser at 405 nm wavelength. Results indicate that a-InSb thin films show saturable absorption and self-focusing properties. The effictive nonlinear absorption coefficient is in the order of 〖-10〗^(-2) m/W, while the nonlinear refractive index is in the order of +〖10〗^(-9) m^2/W. From z-scan results, the c-InSb thin films exhibit reverse saturable absorption and self-focusing properties. The effective nonlinear absorption coefficient is in the order of 〖+10〗^(-2) m/W, and the nonlinear refractive index is in the order of 〖+10〗^(-9) m^2/W. Based on the nonlinear absorption coefficient, the magnitude of nonlinear optical absorption cross section is calculated to be 〖10〗^(-17) cm^2. 2．The temperature dependence of the refractive index and extinction coefficient of a-/c-InSb thin films are measured through variable-temperature ellipsometry. As for the a-InSb thin films, the results demonstrate that both the refractive index and extinction coefficient decrease with increased temperature from 290 K to 430 K bellow the crystallization temperature. The corresponding thermo-optic coefficient is provided as dn/dT=-3.314×〖10〗^(-4) K^(-1), while dk⁄dT=-3.610×〖10〗^(-4) K^(-1), or dα⁄dT=-1.12×〖10〗^4 〖m^(-1) K〗^(-1). As for the c-InSb thin films, the results reveal that the refractive index increases and extinction coefficient decreases when temperature increses during the heating process from 400 K to 600 K. The thermo-optic coefficient is dn/dT=8.03×〖10〗^(-4) K^(-1), while dk⁄dT=-1.25×〖10〗^(-3) K^(-1), the corresponding temperature dependence of absorption coefficient is dα⁄dT=‒3.86×〖10〗^4 〖m^(-1) K〗^(-1). 3．The measurements of several thermal properties of InSb semiconductor as a function of temperature are conducted systematically, including thermal gravimetry, specific heat, thermal expansion, thermal diffusivity, and thermal conductivity. Results show that the specific heat and thermal expansion coefficient remain virtually unchanged upon heating, whereas the thermal diffusivity and thermal conductivity gradually decrease with increasing temperature. The thermal conductivities from phonons, electrons, and photon radiations are investigated, respectively. Analytical results indicate that thermal conductivity from phonons is dominant for InSb when the temperature is between 300 K and 800 K. This explains why the measured thermal conductivity decreases when temterature increases. The commonly used thermal parameters of Sb-based and Te-based materials near room temperature are summarized. Compared with other Sb-based and Te-based phase-change materials, such as Sb2Te3, Ge2Sb2Te5, and AgInSbTe, InSb is markedly more thermally active, i.e., with much higher thermal conductivity. These results offer useful information for the development and performance improvement of InSb-based devices as well as provide some necessary thermo-physical parameters used in calculation of thermal- induced nonlinearity. 4．The physical mechanisms responsible for the giant optical nonlinearity are explored. Analysis indicates that the nonlinear saturable absorption of a-InSb thin films at 405 nm nanosecond laser excitation mainly stems from laser-induced thermal effect, whereas the nonlinear reverse saturable absorption of c-InSb thin films mainly results from laser-induced equivalent two-photon absorption effect rather than thermal effect. The self-focusing refraction of a-InSb thin films is from electronic nonlinearity. On the other hand, the nonlinear refraction of c-InSb thin films originates from thermal effect due to band gap shrinkage and carrier effect due to the transition process of electrons. The band filling effect and quantum confinement effect also have an influence on the optical nonlinearity characteristics. 5．Based on the strong nonlinear saturable absorption of a-InSb thin films, theoretical simulation of super-resolution effect is obtained. The results indicate that the size of transmitted spot through a-InSb nonlinear layer is only 44% of incident focusing spot size. This study prompts a different description of the photon-material interactions in super-resolution structures, and may be helpful for the future development of super-resolution optical data storage, nano-lithography, and nano-imaging. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/16765]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 蔡晓林. InSb薄膜的光学热学特性研究[D]. 中国科学院上海光学精密机械研究所. 2013. |
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