Final PhD Seminar

Characterizing and understanding Au-hyperdoped Si for sub-band gap optical absorption

Ms Wenjie Yang

The unparalleled technological maturity of silicon (Si) can be exploited to develop CMOS-compatible optoelectronics such as photodetectors and imaging arrays. These applications require the realization of sub-band gap photoresponse in Si, as the low-attenuation wavelengths commonly used in fiber optics (up to l~1650 nm) fall below its 1.12 eV band gap (l < 1100 nm). A promising method for achieving sub-band gap photoresponse is to add an intermediate band within the band gap by incorporating appropriate impurities into the Si lattice at high concentrations (often beyond the thermodynamic solubility limit), or hyperdoping. Indeed, Au-hyperdoped Si made by ion implantation and pulsed laser melting (PLM) has been shown to exhibit strong sub-band gap optical absorption in the near-infrared and has led to the demonstration of a Si-based near-IR photodetector. Meanwhile, other transition metals are also being investigated for Si hyperdoping.

While these results illustrate the potential of hyperdoped Si for photodetection in the near-infrared, the material properties of Au- and other transition-metal- hyperdoped Si remain elusive. With this as a premise, my PhD work has focused on characterizing and understanding the properties of Au-hyperdoped Si.

In this presentation, I will summarize the key outcomes of this work, including (1) the atom location of Au in the Si crystal, (2) unusual structural features of the hyperdoped Si lattice, especially at high local Au concentrations, (3) the optical activity of Au and other Au-induced defects, and (4) the thermal stability and relaxation mechanism of the material. Finally, I will present evidence for a vacancy trapping process which, we believe, occurs after PLM as a means to minimize local strain.

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