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TY  - THES
AU  - Riazimehr, Sarah
TI  - Graphene/silicon heterojunctions for optoelectronic applications
PB  - Rheinisch-Westfälische Technische Hochschule Aachen
VL  - Dissertation
CY  - Aachen
M1  - RWTH-2020-00453
SP  - 1 Online-Ressource (xxiii, 142 Seiten) : Illustrationen, Diagramme
PY  - 2019
N1  - Veröffentlicht auf dem Publikationsserver der RWTH Aachen University 2020
N1  - Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2019
AB  - Graphene / silicon (G/Si) heterostructures are simple hybrid devices with potential for optoelectronic applications such as photodiodes, photodetectors and solar cells. Fundamental understanding of photocurrent generation in such hybrid devices is a prerequisite for designing them efficiently. This thesis presents an experimental investigation on the G/Si heterojunction junction photodetectors and proposes a simple design to improve their efficiency and performance.For this work, devices were fabricated by transferring large-area chemical vapor deposited (CVD) graphene onto prepatterned n- and p-type (Si) substrates, and their electrical and optical characteristics were investigated using several experimental techniques. The diodes fabricated on n-Si substrates showed much better rectification behavior compared to those fabricated on p-Si substrates in dark condition. Basic electrical parameters of the G/n-Si diodes, such as the Schottky barrier height (SBH), the ideality factor (n) and series resistance (RS) were obtained by analyzing the current-voltage (I-V) measurement data. Afterwards, photoconductivity of the devices was tested under white light illumination. The photodiodes displayed extraordinary sensitivity to changes in illumination. Furthermore, the local generation and distribution of photocurrent in G/n-Si photodiodes were investigated using scanning photocurrent microscopy (SPC) technique. It was observed that the G/silicon dioxide (SiO2)/Si (GIS) region, which is usually in parallel with the G/Si Schottky junction, has a significant contribution towards the measured photocurrent at reverse biases above a certain threshold voltage (Vth). This observation was explained with the formation of an inversion layer in Si underneath SiO2 using theoretical and simulation studies. Based on the findings, a concept of ‘generation area’ for genuine calculations of responsivity of graphene based photodiodes was put forth. Considering this concept, the spectral response (SR) of the diodes were measured using lock-in technique. G/n-Si photodiodes showed a substantial responsivity up to 270 mA/W within the silicon spectral range at reverse bias condition. SR measurements exhibited that Si mainly absorbs the light and graphene acts as a transparent conductive electrode.Employing these findings and invoking the ‘true’ active area, a simple interdigitated contact pattern was developed to fabricate and demonstrate highly sensitive G/n-Si heterojunction photodiodes. With this design, an external quantum efficiency (EQE) > 80
LB  - PUB:(DE-HGF)11
DO  - DOI:10.18154/RWTH-2020-00453
UR  - https://publications.rwth-aachen.de/record/780158
ER  -