ISMOT 2011, June 20 - 23, Prague, Czech Republic, EU
Performance Enhancement of Microcrystalline SiGe Near Infrared Photodetector Deposited by Laser-Assisted Plasma
Enhanced Chemical Vapor Deposition
Min-Yen Tsai,1 Chun-Yen Tseng,2 Hsin-Ying Lee,3 Ching-Ting Lee2,*
1Institute of Electro-Optical Science and Engineering, National Cheng Kung University,Tainan, Taiwan 701, ROC.
2,* Institute of microelectronics, Department of Electrical Engineering, National Cheng Kung University, Tainan, Taiwan 701, ROC.
3 Department of Electro-Optical Engineering, National Cheng Kung University, Tainan, Taiwan 701, ROC.
Tel: 886-6-208-2368; Fax: 886-6-208-2368; E-mail: [email protected]
Abstract - Recently, near infrared photodetectors have been widely applied in the wireless remote monitoring system and biomedical sensors. In this work, the novel laser-assisted plasma enhanced chemical vapor deposition (LAPECVD) system was designed to deposit the silicon-germanium (SiGe) films at low temperature for the near infrared photodetectors. In the LAPECVD system, a CO2 laser was guided into the chamber of a conventional PECVD system. Because the SiH4 and GeH4 reactant gases of the SiGe films have a high absorption coefficient at a wavelength of CO2 laser (10.6 m), the reactant gases could be easily and efficiently decomposed into Si and Ge atoms by the simultaneous function of the plasma and CO2 laser. Consequently, not only were the Si-H and Ge-H bonds reduced, but the nucleation of nanoclusters was formed in the deposited SiGe films. The nanoclusters were verified as single crystalline structure measured by the transmission electron microscopy (TEM). Using the micro- Raman spectra measurement, the crystalline fraction of the laser-assisted SiGe films was 48%. The Si-H bonds and Ge-H bonds of the deposited SiGe films could be estimated by the Fourier-transform infrared (FTIR) spectrometry. The Si-H bonds of 1.18×1022 cm-3 and Ge-H bonds of 1.8×1021 cm-3 of the SiGe films deposited without laser assistance were reduced to 5.72×1021 cm-3 and 6.06×1020 cm-3 of the laser- assisted SiGe films, respectively. To investigate the function of the laser-assisted SiGe films in the near infrared photodetectors, the p-i-n-structured SiGe films were deposited on glass substrate using the LAPECVD system and the conventional PECVD system. The spectral responsivity of 330.4 mA/W was improved to 459.7 mA/W of the photodetectors with laser-assisted SiGe films. The improvement mechanisms of the laser-assisted SiGe photodetectors were attributed to the formation of microcrystalline structure and nanoclusters in the SiGe films. More mechanisms will be studied detailly.
The authors gratefully acknowledge the support from Bureau of Energy, Ministry of Economic Affairs under contract no. 99-D0204-2 and the National Science Council of Taiwan, Republic of China under contract no. NSC-99-2120-M-006-002.
Index Terms-. Fourier-transform infrared spectrometry, Laser-assisted plasma enhanced chemical vapor deposition, Near infrared photodetector, Raman spectra, Silicon-germanium films
