Integrated mid-infrared (MIR) photonics has been widely investigated for the past decade, where germanium (Ge) is a promising optical material in this regime. In this work, we studied the origin of optical losses in Ge waveguides on a Ge-on-insulator (GeOI) wafer fabricated using Smart-cut. We observed that the high optical loss was mainly due to the holes in Ge films, which were generated by crystal defects formed by hydrogen ion implantation for Smart-cut. Furthermore, we found that the carrier concentration profile after the splitting process in remaining Ge films depends on the hydrogen ion implantation energy and initial background doping concentration of Ge wafers. A higher proton implantation energy can lead to deeper penetration of hydrogen ions into Ge films with less damage remaining near the implantation surface, resulting in the successful fabrication of an n-type GeOI wafer with a low carrier density. As a result, we experimentally demonstrated a low-loss Ge waveguide on an n-type GeOI wafer with a propagation loss as low as 2.3 ± 0.2 dB/cm. This work suggests an approach to tailor the carrier type in a Ge film formed using Smart-cut for large-scale MIR Ge photonic integrated circuits.

中文翻译：

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n 型绝缘体上锗晶片上 2 µm 波段的低损耗锗波导

在过去的十年中，集成中红外 (MIR) 光子学得到了广泛的研究，其中锗 (Ge) 是该领域中一种很有前途的光学材料。在这项工作中，我们研究了使用 Smart-cut 制造的 Ge-on-insulator (GeOI) 晶片上 Ge 波导中光学损耗的起源。我们观察到高光损耗主要是由于 Ge 薄膜中的空穴，这是由 Smart-cut 氢离子注入形成的晶体缺陷产生的。此外，我们发现在剩余的 Ge 膜中分裂过程后的载流子浓度分布取决于氢离子注入能量和 Ge 晶片的初始背景掺杂浓度。更高的质子注入能量可以导致氢离子更深地渗透到 Ge 薄膜中，并且在注入表面附近留下的损伤更少，从而成功制造出具有低载流子密度的 n 型 GeOI 晶片。因此，我们通过实验证明了在 n 型 GeOI 晶片上的低损耗 Ge 波导，其传播损耗低至 2.3 ± 0.2 dB/cm。这项工作提出了一种为大规模 MIR Ge 光子集成电路定制使用 Smart-cut 形成的 Ge 膜中载流子类型的方法。