| Summary: | 碩士 === 國立臺灣大學 === 電子工程學研究所 === 107 === Germanium-Tin (GeSn) alloys with a high carrier mobility are a promising channel material for next-generation CMOS technology. As the Sn fraction of GeSn alloysis higher than 8 ~ 11 %, GeSn becomes a direct-bandgap material, where more electrons would populate in the Γ band, leading to a smaller effective mass and higher electron mobility. Recent works on GeSn n-MOSFET shows the best ION/IOFF ratio is merely 10 ~ 10^3 A/A possibly due to the source/substrate or drain/substrate junction leakage. In this thesis, we focus on the material quality and carrier activation by phosphorus ion implant in strained or relaxed GeSn films to investigate the effects of strains in the epitaxial GeSn films on the n+/p junction leakage.
Crystal quality will be degraded with severe Sn segregation after the ion implantation and the subsequent thermal or microwave annealing step. By X-ray diffraction, crystal quality after annealing can be evaluated. For sheet resistance and carrier activation, Hall measurements were performed. The results showed that MWA is better than RTA for carrier activation and crystal quality. To test the pn junction leakage, we fabricated Ge diodes as a baseline to evaluate the effects of process steps on the diode performance. The best JON/JOFF ratio achieved in Ge diode is 4.3 x 10^6 A/A. For GeSn diodes, by different process parameters such as implant doses, annealing temperature and microwave power, and GeSn thicknesses, it is suggested that the defects in the GeSn film would dominate the junction leakage. As the GeSn film is thicker, the leakage current is larger due to more associated defects by the strain relaxation. By MWA, the leakage current can be effectively suppressed. Furthermore, with a deep pn junction by a higher implant energy, the leakage current can be further suppressed. The record-high JON/JOFF ratios are 10^6 and 10^4 A/A for the strained and relaxed GeSn diodes, respectively.
|
|---|
