Electric And Optoelectronic Properties Of Black Phosphorus And Related Heterostructures

As a new member of 2D materials group, black phosphorus, which exhibits high p-type mobilit ies of ~ 200-10000 cm2/(V?s), high current on/of ratios and anisotropic transports, whos the promise as a novel candidate that could complement or exceed the electronic and optoelectronic properties of graphene or other 2D materials. Meanwhile, B-P’s bandgap and exiciton binding energy are very sensitive to the tensile strain according to the theroretical calculation. Moreover there exists ambipolar insulator- to- metal transition in B-P induced by compressive strain.Although the excellent properties of FET flexible device have been reported, the electronic, optoelectronic and mechanical properties remain unexplored experimental so far. Thus, in this thesis, we have studied these properties of black phosphorus by Scanning Probe Microscope a nd probe station. Besides, the phase transformation of black phosphorus after heat annealing has been carefully investigated by TEM and micro- Raman.Surface potential of black phosphorus increased. Surface potential of bulk B-P is approximately-51.5 m V. Meanwhile, PxOy compounds on the surface of black phosphorus prominently influence on the B-P surface potential. During the annealing process, there exists the evporation of PxOy compounds and black phosphorus. Meanwhile, there also exists the phase transformation from orthorhombic black phosphorus to monoclinic vio let phosphorus. Thus, the surface potential of black phosphorus is significantly higher after heating annealing. Hole mobility of violet phosphorus is 226.3 cm2V-1s-1, which shows an obvious p-type properties.In this thesis, force modulus of scanning probe microscope is utilized to study the mechanical properties of black phosphorus. The curve of deformation versus load expresses the phenomena of auxetic materials. Young’s modulus of black phosphorus decreases with the increase of B-P thickness. When the thickness of black phosphorus is 14.3 nm, the value of Young’s modulus is 276 ± 32.4 GPa. With the increase of B-P thickness, Young’s modulus approaches the value of bulk black phosphorus. Besides, fractured strain is above 25 GPa and the elongation percentage is above 8%, which satisfies the requirement of flexible devices. Meanwhile, friction forces of B-P and Mo S2 have been investigated by Lateral Force Microscope. Compared with isotropic Mo S2, the friction force of B- P is anisotropy. The direction of maximal force friction is perpendicular to that of minimum value. The maximum and minimum directions namely correspond to [100] and [010] crystal orientation.We report an optoelectronic study of B-P/Si heterostructures by conductive atomic force microscope. Under the illumination, there exist obvious photocurrents of B-P/p-Si in the forwards and reverse bias. The photocurrent significantly rises with the increase of light intensity. When the wavelength is 460 nm and light intensity is 106 m W/cm2, the maximum value of photocurrent is 11 n A under the 3V bias. In addition, B-P/p-Si heterostructures are sensitive to 460 nm illumination. The photoresponsivity is above 4.5 A/W. The optoelectronic properties of B-P/n-Si heterostructures are lower than those of B-P/p-Si. Under the forwards bias, there exists negative differential resistance effect of B-P/n-Si. At last, we established band structures of B-P/Si heterostructures and separated mechanism of phot o- generated carriers.