Germanium Quantum Dots and Bulk Germanium Photodetector
Date Issued
2006
Date
2006
Author(s)
Chang, Chieh-Chun
DOI
en-US
Abstract
In this thesis, the novel MOS tunneling diodes with high leakage current were utilized as photodetectors. In order to increase the responsivity, boron delta-doping was used in the QDIPs and QWIPs. The infrared response was significantly enhanced due to the p-type delta-doping in Ge QDs/QWs or in Si spacers because of the increase of hole concentration. The two-color broadband absorption of MOS Ge/Si QDIPs were demonstrated using boron delta-doping in the Si spacers. The peak at 3.7-6 um is due to the intersubband transition in the Ge QD layers. The other peak at 6-16 um mainly comes from the intraband transition in the boron delta-doping wells in the Si spacers. Since the atmospheric transmission windows locate at 3-5.3 um and 7.5-14 um, the two-color detection is feasible using this device. The delta-doping in Ge QDs and Si0.9Ge0.1 QWs were also investigated to identify the origin of the absorption. The peak responsivity of the QDIP and the QWIP at 15 K was found to be 0.03 mA/W and 1.3 mA/W, respectively, at a gate voltage of 1 V. The QD photoresponse in the peak wavelength range 3.5-5 um can be measured up to 100 K, while that for QW 3-7 um can only be detected up to 60 K. A higher dark current due to the lower transition energy in the QWIP limits its operating temperature as compared to the QDIP.
Since the ability of Ge to absorb in the near infrared makes it an interesting candidate for high-performance photodetector applications. Thus, the bulk Ge MOS photodetectors were also studied in this thesis. The leakage current at inversion bias was reduced by metal gate technique, and the oxide of bulk Ge MOS photodetectors was grown by LPD to reduce the thermal budget that carriers can tunnel through oxide via the assistance of multiple traps. In experiment, the novel bulk Ge PMOS photodetectors has high quantum efficiency and high responsivity at 1310 nm. Besides, the bulk Ge MOS detector can operate under 635 nm, 850 nm, 1310 nm, and 1550 nm lightwave exposure and can be applied to the optical-fiber communications. By applying external mechanical strain, we can reduce the effective bandgap of Ge and increase the photo-generated carriers. Thus, photocurrent and responsivity of the detector were significantly enhanced because more photo-generated carriers were excited. After applying 0.32% biaxial tensile strain, the bulk Ge MOS device can detect the wavelengths of 635 nm, 1310 nm, and 1550 nm with the responsivity of 25 mA/W, 210 mA/W, and 17 mA/W, respectively.
Subjects
鍺
金氧半
量子點
量子井
光偵測器
Ge
MOS
QDIP
QWIP
Photodetector
Type
thesis
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