Germanium Quantum Dot Metal-Oxide-Semiconductor Photodiodes and Poly-Si Thin-Film Transistors

• Main Authors: Sheng-Hsiung Tseng, 曾勝雄
• Other Authors: Pei-Wen Li
• Format: Others
• Language: en_US
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/25413581707109533642

博士 === 國立中央大學 === 電機工程研究所 === 98 === This thesis investigates the device physics and electrical characteristics of Ge-QD photodiodes (PDs) and hototransistors (PTs) fabricated in a complementary metal-oxide-semiconductor (CMOS) process. The main features encompass as follows. First, thermally oxidizing poly-Si0.87Ge0.13 onto a dielectric layer produces Ge QDs embedded in an SiO2 matrix to serve as an efficient absorption layer for visible to ultraviolet light. Secondly, we have successfully demonstrated the feasibility of MOS PDs including multi-layer Ge QDs in the gate oxide and elucidated the current–voltage characteristics in terms of zero, one and three Ge-QD layers. Ge-QD PDs exhibit dramatically enhanced current under light illumination in the inversion mode and amplified responsivity (quantum efficiency) from 4.64 (1.42%), through 482 (148%) to 812 (245%) mA/W, respectively, as the Ge-QD layer number increases from zero, through one to three. Shrinking Ge QD size from 9.1 nm to 5.1 nm reveals considerable blueshift in spectral peak energies, originating from the quantum confinement effect (QCE). The temperature and bias dependences on the dark current ascribe the charge transport mechanism to be percolation hopping. Thirdly, Ge-QD PTs are realized by double-gated thin-film transistors with Ge QDs in the top-gate dielectrics. Compared with the current in darkness, 405-450 nm light illumination strongly enhances drain current and improves the PTs’subthreshold characteristics, following from that only photo-excited holes within Ge QDs inject into the active channel via vertical electric field and contribute to photocurrent without the counterpart photo-generated electron-induced junction barrier lowering. Spectral responses of Ge-QD PTs are consistent with that of Ge-QD PDs, attributing the PTs’photo-absorption to QCE. Temperature-dependent and light pulse characterizations demonstrate Ge-QD PTs have great thermal stability and photo-absorption efficiency. These Ge-QD PDs and PTs offer a deterministic approach to integrate with Si-based electronics monolithically.