Fabrication and characterization of Germanium quantum dot-gated photoMOSFET

• Main Authors: Pin-chuan Chen, 陳品荃
• Other Authors: Pei-wen Li
• Format: Others
• Language: en_US
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/70805922077130062511

碩士 === 國立中央大學 === 電機工程學系 === 103 === In this thesis, Germanium quantum dots (Ge QDs) which individually surrounded SiO2 were formed by using selective oxidation of poly-crystalline SiGe pillars over the Si3N4 layer on the Si-substrate and then Ge QDs would burrowed into Si3N4 and eventually touched Si-substrate. The high quality SiO2 of 3-4 nm in thickness between Ge-QD and Si, which solves 4.2% lattice mismatch in between QD and Si-substrate, can be employed as the dielectric layer in metal-oxide-semiconductor field effect transistor. As the top SiO2 was etched until Ge QDs exposed, Ge-QD/SiO2/Si-substrate MOS structure was fabricated. Accordingly Germanium quantum dot-gated photoMOSFET which possessed tremendous photo-electrical characteristics was then realized, etching the gate dielectric thickness leads to effective reduction on RC delay time constant. Phototransistor with Ge QDs of 50 nm, 70 nm and 90 nm were fabricated, respectively, by the SiGe pillar size and time oxidation. The transistor had small subthreshold swing at darkness can be considered as a switch. Under illumination with wavelength of 850 nm and incident power of 4.38 mW, current enhancement of devices with Ge-QDs of 50 nm, 70 nm and 90 nm is 3.28×106, 2.39×106 , and 9.66×105 in off region and 8.23, 11.3, and 5.13 in on region respectively. Responsivity is 5.25 A/W, 6.26 A/W, and 6.6 A/W in off region and 1481 A/W, 2913 A/W, and 10597 A/W in on region were also observed showing great performance for near infrared ray. In the end, we investigated the effect of the QD size. The device with smaller QD size would get better subthreshold swing and amplification without illumination. Under illumination, photo current and responsivity would increase with higher Ge content because of larger Ge-QD in off region. However, the device with small QD size was determined by its amplified ability and then compensated the effect of small QD size for less Ge content, getting better photo current and responsivity.