Preparation And Photoelectrical Properties Study Of The CdSe Nanobelts And Er Doped CdSe Nanobelts

CdSe is an important ?-? direct bandgap semiconductor material,and itis also an optoelectronic material with excellent performance.The CdSe 1-D nanostructures have emerged as building blocks for a variety of optoelectronicdevices.In this paper,the electron transport and optoeletronic properties of Er-doped CdSe nanobelts and their counterparts were studied.It showed that Er-doping can improve the carrier concentration of the CdSe nanobelts and then improve the photoelectric properties.The main work included preparing pure CdSe nanobelts and Er-doped CdSe nanobelts,and studying their morphology,structureand optical properties.Then a single nanobelt photosensitive device was fabricated.The photosensitive properties of pure CdSe and Er doped CdSe nanobelts were studied,and the effect of Er doping on the properties of CdSe nanobelt devices was analyzed.The main results are as follows:?1?Pure CdSe and Er doped CdSe nanobelts were successfully synthesized by a thermal evaporation method using gold as catalyst.The crystal structure and microstructure of the samples were characterized by X-ray diffraction and SEM.The surface of the nanobelts is smooth.The morphology and crystallization of single nanobelt showed that the nanobelt was grown under the VLS mechanism.XRD showed that the pure CdSe and Er doped CdSe nanobelts were still wurtzite structure.Selected area electron diffraction proved the obtained samples are the ideal crystal structure.Doping the rare earth element Er into CdSe nanobelts was verified by energy dispersive X-ray spectrometer and X-ray photoelectron spectrum.?2?Raman spectra of pure and Er-doped CdSe nanobelt were similar under an excitation of 785 nm laser.Almost all the positions of Raman peaks positionwere unchanged exceptthe two Raman peaks of LO1 and 2LO1,which shifted higher frequency 0.7 cm-1 and 2.9 cm-1respectively.The intensity of LO1 in Er doped CdSe nanobelts is much stronger than that of the pure CdSe nanobelts,which may be due to the incorporation of Er elements.Unlike 785 nm,there is no Raman signal in samples under the excitations of 532 nm and 325 nm that is due to the resonance effect between the band gap of CdSe?1.74 eV?and the radiation photon energy?785 nm?.The absorption spectra showed that the blue shift incurred in Er-doped and pure CdSe nanobelts compared to bulk CdSe.The shift is 12 nm and 16 nm and the bandgap is1.65 eV and 1.67 eV,respectively.The photoluminescence spectra of the pure CdSe nanobelts showed a symmetrical and strong peak at 713.2 nm,which accord to the band edge of CdSe.The photoluminescence spectra of Er doped CdSe nanobelts depicted two peaks at 713.7 nm and 731.6 nm by Gauss fitting respectively.The emission peak at 731.6 nm is caused by the doping of Er³⁺ ions into the CdSe nanobelts,which is corresponding to the 4F7/2?4I13/2 transition of Er³⁺ ions.The CL showed that the peaks intensity increased with the decrease of temperature,accompanied by the blue shift phenomena in pure and Er doped CdSe nanobelts.CL of Er doped CdSe nanobelts revealed the blue shift compared to that of pure CdSe nanobelts at room and low temperature.The peak at 2100.2 nm appeared at77 K,which is associated with Er doping.?3?Almost no signal in a single pure CdSenanobelt device can be detected in the darkness under 1V bias.The dark current is about 0.1 pA.However,the current of Er doped CdSe nanobelt was 0.4 nA,and the conductivity increases by about 3 orders of magnitude.Under the irradiation of incandescent lamp,the current of pure CdSe nanobelt deviceis 0.17 ?A and 10.6 ?A for the Er doped CdSe nanobelt device,which is two orders of magnitude higher than that of its counterpart.Er doped CdSe nanobelt devices has a larger light dark current ratio,ILight/IDarkis about 2.5 l?104.When the bias voltage is 1 V,the maximum photoresponse of the pure CdSe nanobelts is observed at 688 nm,while the Er doped CdSe nanobelt 695 nm.When the wavelength of the incident light is constant,the photocurrent increases with the increase of the power density.When the bias voltage is 1 V,the Er doped CdSe device has a high sensitivity and good stability.When the Er doped CdSe nanobelts were irradiated with695 nm?4.89 mW?14?cm2?light,the optical response was about 1.04?103 A/W,and the external quantum efficiency?EQE?was about 1.85?103,and the photoconductivity?Gph?was about 82 S/cm?V?.The above results show that the Er doped CdSe devices exhibit good optical detection performance.And the photoelectric performance of nanobelts device is better than that of single nanobelt device,the conductivity increased by nearly 3 orders under the dark.