【作者】 姜晶；

【导师】 蒋亚东；

【作者基本信息】 电子科技大学 ， 光学工程， 2013， 博士

【摘要】 晶体硅由于易提纯，易掺杂，耐高温等优点在半导体行业中有非常广泛的应用，然而由于晶体硅的反射率高和对近红外光的吸收率低这两个特点，使基于晶体硅的传统光电探测器具有灵敏度低以及不能探测近红外光等缺点。黑硅是一种新型的硅材料，它的出现为克服这些缺点提供了基础。然而采用传统的高能飞秒激光辐射的方法制备黑硅具有成本高昂、难以大面积生产以及与现有的半导体集成电路制造工艺不兼容等缺陷，因此采用其他的新技术和方法制备黑硅成为目前研究的重点和热点。本文以此为背景，提出了一种基于两步湿法腐蚀的微纳双重结构黑硅制备技术，并围绕微纳双重结构黑硅的制备与光电性能分析开展了大量的研究工作，主要包括以下几个方面：1.分别采用正交实验法优化了氢氧化钾碱腐蚀技术和金属催化酸腐蚀技术的工艺参数。通过碱腐蚀工艺前在硅片表面制备大小相等、排列规则的氮化硅圆掩膜阵列，得到在碱腐蚀处理后的硅片表面排列规则、大小相等的四面体尖锥阵列，这种尖锥阵列的存在，使得最终制备的微纳双重结构黑硅具有较好的规则性和均匀性，为单元探测器以至阵列探测器的制备提供了有利的条件。通过控制酸腐蚀工艺的腐蚀时间，可以在硅片表面得到具有不同的孔直径和孔深度的纳米孔结构，这种纳米孔结构的存在，使微纳双重结构黑硅具有了更好的减反射和增吸收的性质。2.测试和比较了晶体硅、微米和纳米结构硅以及微纳双重结构黑硅在250-2500nm波段范围的光学性能。晶体硅表面在分别经过微米结构化、纳米结构化以及微纳双重结构化后，对入射光的反射率都大量减少，其中微纳双重结构的减反射效果最佳，纳米结构次之，微米结构最差。微纳双重结构黑硅对紫外-可见光的吸收率高达98%，比晶体硅在此波段的吸收率平均值高50%；对波长大于1100nm的近红外光的吸收率高达30%，比晶体硅在此波段的吸收率平均值高28%。3.对微纳双重结构黑硅的电学性能，包括微纳双重结构黑硅的金-半接触特性、微纳双重结构黑硅的载流子浓度和迁移率以及电阻温度变化特性等进行了测试研究。在退火前，晶体硅表面在经过微纳双重结构化以后，与金属铝电极的接触特性有所改善。在退火后，晶体硅和微纳双重结构黑硅与铝电极的接触特性都有了不同程度的改善。晶体硅表面经过微纳双重结构化以后，载流子浓度和迁移率有所下降，电阻温度系数由正数值变成了负数值，且负数绝对值随着纳米结构的腐蚀时间增加而逐渐增大，体现了微纳双重结构黑硅的电阻温度系数的可调节性。当腐蚀时间为7分钟时，微纳双重结构黑硅在35-50°C的平均电阻温度系数为-3.01%，这个数值优于目前大多数热敏探测材料的热敏特性。4.采用金属-半导体-金属（MSM）这种横向表面型器件结构，利用反转胶-剥离的方法制作了基于微纳双重结构黑硅的光电探测器，制备得到的叉指电极边缘整齐、粗细均匀，而且叉指宽度和间距与设计尺寸一致。对具有不同纳米结构化时间以及不同叉指尺寸的微纳双重结构黑硅MSM探测器的光电响应特性进行了测试与分析。微纳双重结构黑硅MSM探测器的暗电流-电压曲线在某一电压附近具有负微分电阻效应，与微纳双重结构中纳米结构的量子隧穿效应有关。微纳双重结构黑硅MSM探测器的暗电流较大，通过在铝与硅之间增加一层100nm厚的SiNX薄膜，可使器件的暗电流下降至少两个数量级，在5V偏压下，该器件的暗电流密度为3.6μA/cm~2。微纳双重结构黑硅MSM探测器的响应度随着纳米结构化时间的增加以及叉指电极尺寸的优化逐渐增大，当腐蚀时间为5分钟，叉指尺寸为5:10时，微纳双重结构黑硅MSM探测器的响应度达到0.72A/W。5.利用MEDICI软件对基于微纳双重结构黑硅的MSM探测器和PIN探测器的光电响应特性进行了建模与仿真，仿真与实验结果的对比证实了MEDICI软件对微纳双重结构黑硅光电响应特性的仿真可行性。在5V的偏压下，叉指尺寸为5:10和2:10的微纳双重结构黑硅MSM探测器的峰值响应波长都为760nm，峰值响应度分别为0.89A/W和1.35A/W，峰值响应度在使用透明叉指电极后分别提高至1.31A/W和1.61A/W。晶体硅PIN探测器表面进行了1μm的微纳双重结构化后，探测器对800nm入射光的饱和光电流由1.9μA增大到2.7μA，响应度由0.337A/W增大到0.472A/W，增长幅度为40%，而响应时间基本不变，上升时间约为20ns，下降时间约为60ns。微纳双重结构黑硅PIN探测器的峰值响应波长和相对响应度曲线相较晶体硅PIN探测器而言有红移的现象，红移的宽度在5μm微纳双重结构黑硅PIN探测器中达到了60nm。基于PIN结构的微纳双重结构黑硅探测器要比基于MSM结构的微纳双重结构黑硅探测器的响应度减少53%。更多还原

【Abstract】 Silicon is the most commonly used material in semiconductor industry because itis easily purified and doped. However, the sensitivity and efficiency of silicon-basedphotodetectors are limited by two factors: silicon performs highly reflection across theelectromagnetic spectrum, and silicon is transparent to wavelengths longer than1100nm. The discovery of black silicon makes it realizable to dramatically enhance thesensitivity and efficiency of silicon-based photodetectors. Black silicon is fabricated byirradiating a silicon surface with ultrahigh energy femtosecond laser pulses. However,the femtosecond laser process is complex, and it is incompatible with mass productiontechnology and silicon-based semiconductor technology. Therefore, new methods forfabricating black silicon have attracted more and more attention recently. In this study,micro/nano two-tier structured black silicon (micro/nanostructured silicon) has beenfabricated using a simple wet chemical etching process. The optical and electricalproperties of micro/nanostructured silicon have been studied.1. The optimum parameters of alkaline anisotropic etching and metal assistedisotropic etching have been obtained from orthogonal test, respectively. The regulardistributed pyramids which are produced through alkaline anisotropic etching with amask layer are advantageous to the application of micro/nanostructured silicon in thearray photodetectors. The nanopores, whose diameters and depth are varied with theincease of etching time in metal assisted isotropic etching, are advantageous to thesuppression of reflection and enhancement of absorption of micro/nanostructuredsilicon.2. The optical properties of unstructured silicon, microstructured silicon,nanostructured silicon, and micro/nanostructured silicon have been studied. Thereflectance from the surface of silicon is dramatically decreased after micro/nanostructured, and the reflectance of micro/nanostructured silicon is the lowest. Themicro/nanostructured silicon absorbs about98%and30%of the incident light atultraviolet-visible wavelengths and near infrared wavelengths, respectively. Theabsorbance of the micro/nanostructured silicon is, on average, higher than that of unstructured silicon by50%and28%at ultraviolet-visible wavelengths and nearinfrared wavelengths, respectively.3. The electrical properties of micro/nanostructured silicon, such as contactresistance, carrier concentrations, carrier mobility, and temperature coefficients ofresistance(TCR) have been studied. The contact performance of micro/nanostructuredsilicon-aluminium are better than that of unstructured silicon-aluminium beforevacuum annealing, and the contact performance has been largely improved for allsmples after vacuum annealing. The carrier concentration is slightly reduced, whereascarrier mobility is drastically decreased after micro/nanostructuring. TCR of siliconchanges from positive value into negative value after micro/nanostructuring, and theabsolute value of TCR increases with nanostructuring duration. The capability ofmodulating TCR is one of the major advantages of micro/nanostructured silicon. HighTCR of-3.01%/°C is obtained after etching for7min, which is larger than that of mostheat sensitive materials.4. Micro/nanostructured silicon photodetectors based on metal-semiconductor-metal (MSM) structure have been fabricated and studied. Interdigital electrodes,produced by lift-off technology, are regular and uniform. The sizes of producedinterdigital electrodes are as same as the designed ones. The photoresponses ofmicro/nanostructured silicon MSM photodetectors with different nanostructuringduration and interdigital electrode sizes have been studied. Negative resistance effectcaused by quantum tunneling effect of nanostructures is observed inmicro/nanostructured silicon. The dark current of micro/nanostructured silicon MSMphotodetector is relative high, although was reduced by at least two orders ofmagnitude after introducing a100nm SiNXthin film between micro/nanostructuredsilicon and aluminium. The dark current density is3.6μA/cm~2with the bias of5V. Theresponsivities of micro/nanostructured silicon MSM photodetectors increase with theincreasing of nanostructuring duration as well as the optimizing of interdigitalelectrode sizes. Responsivity of0.72A/W is obtained after etching for5min whenInterdigital electrode size is5:10.5. Photoresponses of micro/nanostructured silicon detectors are simulated byMEDICI software. Simulation results of current density of micro/nanostructuredsilicon detector are compared with experimental values, respectively. The results indicate that MEDICI software is suitable for the simulation of properties ofmicro/nanostructured silicon photodetectors. The peak response wavelengths ofmicro/nanostructured silicon MSM photodetectors are760nm when interdigitalelectrode sizes are5:10and2:10, but the peak responsivities are0.89A/W and1.35A/W, respectively. Moreover, the peak responsivities raise to1.31A/W and1.61A/W after using transparent electrodes. The photocurrent and responsivity ofunstructured silicon PIN photodetector to incident light with wavelength of800nm is1.9μA and0.337A/W, respectively, and the values raise to2.7μA and0.472A/W afterusing micro/nanostructured silicon with thickness of1μm. The response times inunstructured silicon PIN photodetector and micro/nanostructured silicon PINphotodetectors are the same, and the rising time and dropping time are about20ns and60ns, respectively. Peak response wavelengths and response spectra of variousmicro/nanostructured silicon PIN photodetectors show different red-shifts comparedwith that of unstructured silicon PIN photodetector, and the red-shift is60nm in PINphotodetectors with5μm micro/nanostructured silicon. The responsivity ofmicro/nanostructured silicon PIN photodetector reduces about53%compared with thatof micro/nanostructured silicon MSM photodetector.更多还原