【作者】 李一；

【导师】 刘秀环；

【作者基本信息】 吉林大学 ， 通信与信息系统， 2014， 硕士

【摘要】 在电光取样技术和高速光通信系统中，对1.31μm和1.55μm波长的超短激光脉冲的测量日益显得重要。而砷化镓（GaAs）晶体是光电子学领域重要的半导体材料，其禁带宽度为1.43ev，对应的双光子响应的波长范围是0.88-1.73μm，正好覆盖了高速光电子学以及光通信领域里常用的1.31μm和1.55μm这两个重要的波长。所以GaAs双光子响应探测器将在光电子学和光通信领域发挥重要作用。本文阐述了双光子响应中的双光子吸收、倍频吸收和场致倍频吸收理论。设计了基于GaAs材料的探测器的电极结构，通过ANSYS有限元软件对不同电极结构的静电场进行了模拟，初步建立了电场分布模型，清楚地看出电场的分布情况，模拟结果显示针状电极在双光子响应敏感区将产生最强电场。而场致倍频吸收强烈依赖于直流电场，因此这将有利于我们开展实验研究工作。在表面电场的作用下，GaAs晶体表面的对称性被破坏了，通过理论分析，我们得出了GaAs晶体二阶非线性极化率张量的改变，其对称性由43m点群降为mm2点群。研究了两种铝电极结构的掺铬的半绝缘GaAs探测器在1.56μm激光照射下非线性响应特性。在外加偏压一定时，测得光电流随入射光功率呈二次方关系；当光功率一定时，测得的光电流随外加偏压变化也呈二次方关系。这说明探测器的光电流产生机理主要是GaAs样品对1.56μm的光产生了倍频吸收。对实验结果进行深入的理论分析表明，由表面电场和外加直流电场而诱导的场致倍频吸对GaAs固有的倍频吸收有很大影响。另外，在外加偏压一定的条件下，样品的非线性光响应敏感区的电极在不同极性的偏压下，探测器光电流大小的变化规律和暗电流大小的变化规律正好相反。具体来说，对于半球形GaAs样品而言，在大小相同的偏压下，当中心电极加负偏压时，样品底面中心附近的外加电场的方向和样品表面电场方向相同，造成耗尽层变宽，耗尽层中的电场增强，此时样品的等效电阻变大，光电流变大而暗电流变小。反之，当中心电极加正偏压时，外加电场的方向和样品表面电场方向相反，造成耗尽层变窄，耗尽层中的电场减弱，此时样品的等效电阻变小，光电流变小暗电流变大。我们从表面能带弯曲和表面电场理论完美地解释上述实验研究结果。更多还原

【Abstract】 The measurements of ultrashort laser pulses at1.31μm and1.55μm arebecoming increasingly important for electrooptical sampling techniques and thecharacterization of high-speed optical communication systems. The most importantsemiconductors of GaAs crystals are commonly used in optoelectronics. The bandgapof GaAs crystal is1.43eV corresponding to a wavelength range of0.88-1.73μm intwo-photon response(TPR), which covers the wavelengths of1.31μm and1.55μmcommonly used in electrooptical sampling techniques and optical communicationsystems. So, the TPR detector of GaAs will play an important role in optoelectronicsand optical communications.In this paper, the theories of two-photon absorption (TPA), the double-frequencyabsorption (DFA) and the electric field induced double-frequency absorption areelaborated in detail. We designed two different electrode configurations based onGaAs sample, and the distributions of electric field for the two different electrodeconfigurations were simulated by ANSYS software. The simulation results show thatthe electric field for the needle electrode situated at the region sensitive to TPR is thestrongest. Since the electric field induced DFA is strongly dependent on the DCelectric field, this will be helpful for us to carry out the experimental research work.We deduced the changes of second order nonlinear susceptibility for GaAs crystalunder the disturbance of surface electric field, and the symmetry of GaAs is reducedfrom43m group to mm2group. We studied the nonlinear photoresponsecharacteristics of the Cr-doped semi-insulating (SI-) GaAs photodetectors with two types of aluminum electrode configurations operating at1.56μm laser. The quadraticdependence of the photocurrent on the optical power was investigated under a fixedbiased voltage; also, the quadratic dependence of the photocurrent on the bias voltagewas investigated under a fixed incident optical power. These investigated results areproved to be dominantly responsible for the nonlinear photoresponse of the sample.With the further investigation on the nonlinear photoresponse of the sample, one canget the conclusion that the DFA induced by the surface electric field or the DCelectric field applied to the SI-GaAs has an effect on the native DFA in SI-GaAs. Inaddition, when the electrode situated at the region sensitive to TPR was biased at theconstant voltage but with two opposite polarities, the variation of the photocurrent isin reverse to that of the dark current. Specifically, for the hemispherical SI-GaAssample, biased at the same voltage, when the central electrode is negatively charged,the direction of the applied electric field in the vicinity of the bottom center isapproximately considered to be the same as that of the surface electric field inside thesemiconductor, which consequently builds up the depletion-electric field and enlargesthe depletion region, and the equivalent resistor of the sample is larger. As a result,the photocurrent tends to be larger while the dark current is smaller. However, whenthe central electrode is positively charged, the applied electric field in the vicinity ofthe bottom center is against the direction of the surface electric field, which thusdecreases the depletion-electric field and reduces the depletion region, and theequivalent resistor of the sample is smaller. Then the photocurrent tends to be smallerand the dark current is larger. Such experimental investigated results agree well withthe theories of the surface band-bending and the surface electric field.更多还原