太赫兹片上系统中低温砷化镓薄膜光电导天线的研究

太赫兹时域光谱技术是一种在太赫兹频段内，广泛应用的光谱测量技术。这种技术可以用于许多物质的频谱分析，对于研究化学、半导体与生物分子等领域有着无可比拟的作用。然而用该系统进行样品探测时，受回波的影响频谱分辨率较低；受太赫兹波光斑大小以及待测样品与电磁波相互作用距离长短的影响，样品消耗量较多，并且整个系统的占用空间较大，这些局限性都限制了太赫兹时域光谱系统的进一步发展。为了突破太赫兹时域光谱系统的局限性，设计了一种将太赫兹泵浦区、探测区和传输波导集成到一个硅片上的太赫兹片上系统，该系统不仅能够解决上述系统的局限性，还能够省去样品测量前的光路准直环节，使样品的测量过程更加简便，同时集成化的系统也很大程度上提高了太赫兹波传输的稳定性。在太赫兹片上系统中，泵浦区和探测区的光电导天线是由低温砷化镓和金属电极制成，由于受到太赫兹片上系统的高度集成化和低温砷化镓晶体生长条件的限制，如何制备出低温砷化镓半导体薄膜衬底，并将其转移与键合，是太赫兹片上系统研制过程中的关键环节。首先利用分子束外延（MBE）技术制备出由半绝缘砷化镓、砷化镓缓冲层、砷化铝牺牲层和低温砷化镓层构成的外延片，然后利用盐酸溶液与砷化铝和低温砷化镓反应速度差别较大的原理，将200 nm厚的AlAs牺牲层腐蚀掉，从而得到2 μm厚的低温砷化镓薄膜。为了更加高效并且完整地得到低温砷化镓薄膜，研究了盐酸溶液在不同温度和不同浓度下与AlAs牺牲层的选择性腐蚀速率的关系。给出了低温砷化镓薄膜制备过程中盐酸的最佳体积比浓度和最佳温度，即在73 ℃下13.57%的盐酸溶液中进行砷化铝牺牲层的腐蚀。相比于已有工艺，这种腐蚀方法对实验设备的要求较低并且具有较高的安全性。最后，将单层低温砷化镓薄膜转移键合至硅片上，并制成光电导天线的结构。利用飞秒激光脉冲进行激发探测到太赫兹信号。由此说明，低温砷化镓薄膜的获取、转移与键合工艺能够满足芯片级太赫兹系统的制作要求，这为太赫兹片上系统的进一步研制打下了坚实的基础。

Study of Low-Temperature Gallium Arsenide Thin Film Photoconductive Antenna in THz On-Chip System

Terahertz time-domain spectroscopy is a widely used spectrum measurement technology in terahertz frequency domain, which can be applied to the spectrum analysis of many substances, and has an incomparable role in the research of chemistry, semiconductor and biomolecule. However, the consumption of the sample is more, and the occupied space of the whole system is larger in the terahertz time-domain spectroscopy system. These limitations hinder the further development of this system. In order to overcome the limitations of the system, a terahertz on-chip system, which integrates THz generating device, detecting device and waveguide transmission device on a silicon wafer, is designed. Due to the high integration of this system and the limitation of low-temperature gallium arsenide (LT-GaAs) of photoconductive antenna growth conditions, how to fabricate the LT-GaAs semiconductor film substrate and transfer and bond it is a key step in the THz on-chip system. The epitaxial wafer consists of semi-insulating gallium arsenide, GaAs buffer layer, AlAs sacrificial layer and LT-GaAs layer. In order to obtain LT-GaAs thin film with a thickness of 2 μm more efficiently, the selective corrosion rate of HCl solution at different temperatures and different concentrations with AlAs sacrificial layer is studied. The optimum volume ratio, concentration and optimum temperature of HCl during the preparation of LT-GaAs thin film are 13.57% and 73 ℃. Compared with the existing processes, this method has higher safety performance and lower equipment requirements. Finally, the single-layer LT-GaAs thin film is transferred and bonded to a silicon wafer. Terahertz signals generated by excitation of the photoconductive antenna structure using a femtosecond laser pulse are detected, and the experiment shows that the LT-GaAs film acquisition and transfer bonding process satisfies the production requirements of the THz on-chip system and has laid a solid foundation for the development of the THz on-chip system.