低溫製備磊晶鍺薄膜及矽基鍺光偵測器

Low Temperature Growth and Fabrication of Silicon-based Epitaxial Germanium Films and Photodetectors

侯裕瑋(Yu-Wei Hou)

指導教授 ： 張正陽

國立中央大學/理學院/光電科學與工程學系/碩士(2014年)

摘要

本文是以電子迴旋共振化學氣相沉積法(Electron Cyclotron Resonance Chemical Vapor Deposition, ECR-CVD)於單晶矽基板Si(100)上低溫磊晶成長鍺薄膜並應用其製作光偵測器。鍺相較於矽有較小的能隙及較高的載子遷移率，因此塊材鍺常被應用在矽光電子領域及高效率三五族多接面太陽能電池；吸收光之截止波長可達1550 nm，也可作為近紅外光偵測器。然而鍺基板成本約比矽貴上四倍，不利於往後發展，矽基鍺薄膜發展以取代舊有的鍺基板就越受矚目，但其高溫製程成了製程整合上的種種限制。因此本論文是以ECR-CVD在180 oC的低溫下，於矽晶片上成長磊晶鍺薄膜，並利用熱退火處理改善成膜品質，並將其應用在光偵測器上，作為光主動元件。
本研究將探討不同製程條件下，工作壓力、ECR共振區及氫氣稀釋比對薄膜特性之影響，製程後搭配後退火處理，改善薄膜品質。製程中使用光放射光譜儀(Optical Emission Spectroscopy, OES)監控電漿組成成分及其影響。薄膜特性分別利用橢圓儀、高解析度X光繞射儀(High Resolution X-Ray Diffractometer, HR-XRD)及拉曼光譜儀鑑定薄膜結構品質。最後應用製作成光偵測器，並量測分析光暗電流、響應率及二極體特性曲線。本研究中，在工作壓力30 mTorr、主磁場電流50 A、氫稀釋比(H2/GeH4)100及薄膜厚度控制在100 nm的情況下，XRD量測結果中Ge(400)半高寬為683 arcsec。光偵測器在光波長為850 nm及-1V偏壓下，響應率為0.2 A/W 及，-3V偏壓下為0.42 A/W，此外在光波長為1310 nm及-1V偏壓下。響應率為0.07 A/W 及，-3V偏壓下為0.139 A/W。同時藉由製程參數及後退火處理暗電流密度可改善至1.89 m A/cm2。

關鍵字

矽基鍺 ； 光偵測器

並列摘要

In this research, we use the electron cyclotron resonance chemical vapor deposition (ECR-CVD) to grow epitaxial germanium (Ge) thin films on single crystal silicon substrates (c-Si) and applied to the photodetector at a low temperature. Compared to Si, Ge has smaller energy band gap and higher carrier mobility, and therefore the bulk Ge is often used in the field of silicon photonics and high efficiency III-V multi-junction solar cells. The cutoff wavelength of Ge is at 1550 nm, so Ge can be used as a near-infrared photodetector. However, the cost of c-Ge is about 4 times higher than that of c-Si, so in order to reduce the cost, many researches have been doing efforts to grow high quality epitaxial Ge films on silicon substrates to replace c-Ge substrates. In this work, we use ECR-CVD to deposit epitaxial Ge on c-Si at a low temperature of 180 oC and further use rapid thermal annealing (RTA) process to improve epitaxial quality and applied it to the photodetector.
In this investigation, we analyze the effect of different parameters on the films quality. We use optical emission spectroscopy (OES) to in-situ monitor the plasma distribution during film growth and use Ellipsometry (SE), Raman Spectrometer, and X-ray Diffractometer (XRD) to characterize the thin films properties. The result shows that the XRD full width at half maximum (FWHM) of 683 arcsec can be obtained when the film thickness is 100 nm. The responsivity of photodetector in 850 nm light source is 0.2 A/W at -1V and 0.42 A/W at -3V. In 1310 nm light source, the responsivity is 0.07 A/W at -1V and 0.139 A/W at -3V. After annealing, we can reduce the dark current density to 1.89 mA/cm2.

並列關鍵字

Germanium ； Photodetector

參考文獻

1. S. Jongthammanurak, et al., "Large electro-optic effect in tensile strained Ge-on-Si films," Applied Physics Letters, vol. 89, Oct 16 2006.

2. D. Ahn, et al., "High performance, waveguide integrated Ge photodetectors," Optics Express, vol. 15, pp. 3916-3921, Apr 2 2007.

3. Y. Takada, et al., "Effect of Mesa Shape on Threading Dislocation Density in Ge Epitaxial Layers on Si after Post-Growth Annealing," Japanese Journal of Applied Physics, vol. 49, 2010.

4. Y. Ishikawa and K. Wada, "Near-Infrared Ge Photodiodes for Si Photonics: Operation Frequency and an Approach for the Future," Ieee Photonics Journal, vol. 2, pp. 306-320, Jun 2010.

5. M. T. Currie, et al., "Controlling threading dislocation densities in Ge on Si using graded SiGe layers and chemical-mechanical polishing," Applied Physics Letters, vol. 72, pp. 1718-1720, Apr 6 1998.