Study On Molecular Beam Epitaxy Growth Of Gesn Film And Performance Of Photodetector

In the past few decades,the epitaxial quality of SiGe heterojunction has been greatly developed.However,because Si and Ge are all indirect band gap semiconductors,the transition of the electron from valence band to the conduction band is not direct and requires additional recombination process,which reduceing the performance of its photoelectric devices and limits their applications in optoelectronic devices.At this time,a new type of alloy material,GeSn alloy,has attracted our interests.Silicon based GeSn infrared detectors can be applicated in high efficiency photonic devices and infrared optoelectronic devices worldwide because its bandgap can be tunable caused by the change of Sn content,and GeSn materials can reduce the effective quality of carrier,which could greatly enhance the carrier mobility.Graphene is a promising material for ultra wideband photodetectors.Its absorption spectrum covers the whole spectra band from ultraviolet to far-infrared.Due to the non-band structure of graphene,the carrier has a very high fluidity.However,it is its zero band gap structure and weak optical absorption capacity that limit its application.Therefore,it is of great importance to improve the light absorption ability of itself.If the advantages of graphene can be retained and its shortcomings can be overcomed,graphene could get a stronger role in the optoelectronic field.The GeSn PIN photodetectors and graphene / bismuth nanorods heterojunction photodetectors were fabricated.The surface morphology,spectral absorption and photoelectric properties were studied.The optimal growth conditions of GeSn films and the design and manufacture of the longitudinal structured PIN junction are studied detailedly: the influence of the temperature of Sn in molecular beam epitaxy process on the composition of Sn in GeSn alloy was studied.Then the detector was fabricated through semiconductor lithography and etching process.At last the surface microstructure,I-V curves and On-Off curves of the device were tested.As the result the magnitude of the photocurrent is about 100 times of the dark current.In the design of silicon based graphene / bismuth nanorods heterojunction photodetector,the methods of bandgap opening in graphene and the growth of bismuth nanorods are mainly considered.The surface morphology of nanorods and the stress exerted by nanorods to grapheme were tested.As the results,raphene / bismuth nanorods heterojunction photodetector performs excellent photoelectric effect,because its dark currents are 3 to 4 orders of magnitude lower than that of silicon / graphene photodetectors,and the ratio of photocurrent to dark current is increased by more than 30 times.