Controllable Preparation And Photodetection Performance Of Two-Dimensional Ge-Based Semiconductors

Ge-based semiconductors have a great potential application in the field of photoelectric due to its advantages of environmentally friendly,rich elements,high mobility of carriers and good light adsorption performance and so on,which has become the research hot spot in recent years.However,there are some problems in the controllable preparation of 2D Ge-based semiconductors,which limit the research and development of their photoelectric performance.Based on this,the first chapter of this paper describes the research status of Ge-based semiconductors(GeSe₂,GeSe and Geas the representative).And then,this dissertation will introduce our work including their controllable preparation by chemical vapor depositon(CVD)and the research of their photoelectric performance.Firstly,the CVD preparation of ultrathin rhombic GeSe₂ nanosheets was realized by using the GeI₄ as the precursor which has a low melting point,and the layered mica as the substrate.Raman,AFM,TEM and XPS characterizations had proved the nanosheets are GeSe₂single crystal with high quality and the minimum thickness is 7 nm.Subsequently,we built the device based on GeSe₂ nanosheet.And studied the electrical transport and photoelectrical properties of GeSe₂ nanosheets.The photodetector based on a rhombic GeSe₂nanosheet is shown to exhibit a high responsivity of 2.5 A W^-1 and a fast response of?0.2 s under 450 nm light illumination.Secondly,high quality ultrathin GeSe nanosheets were prepared by CVD method through the synergistic effect of auxiliary salt and H₂ and mica as the expitaxial substrate.The high performance optoelectronic device was built with 2D GeSe nanosheet which obtained by mechanical exfoliation.The responsivity of the phototransistor based on GeSe nanosheet could reach to 1.6×10⁵AW^-1 under the contral of gate voltage.The crystal axis direction of GeSe nanosheet was determined by the polarization-dependent Raman according to the relationship between the crystal axis of GeSe nanosheet and the polarization-dependent Raman.And based on this,the anisotropy device was contstructed to study the in-plane electrical anisotropy of GeSe nanosheet.GeSe nanosheet showed obvious photoelectric anisotropy and was sensitive to changes in the polarization direction of polarized light.The peak value of photocurrent is 1.3 times of the valley value.The carrier mobility along the Armchair direction is 1.85 times higher than along the Zigzag direction.Thirdly,we designed a halide induced self-limited method to synthesize ultrathin non-layered Geflakes.The growth mechanism of Genanosheets was discussed through comparative experiments and theoretical calculation.Then,we built a phototransistor based on Genanosheet and conducted a series of study on its photoelectric performance.The phototransistor based on a Geflake shows excellent performances such as a high hole mobility of?263 cm²V^-1s^-1,a high responsivity of?200 A W^-1,and fast response rates(?_rise=70 ms,?_decay=6 ms).Fourthly,we adjusted the carrier type of Genanosheet through F induction,realized the transformation of Genanosheet from p-type to n-type semiconductor.Then we built a p-n junction device based on Genanosheet,which showed photovoltaic performance:open circuit voltage of 150 m V and an external power conversion efficiency of?8.1%.At last,we summarize the whole work and look forward to the future research in chapter six.