Research Of Intelligent Thin Film Photodetector

Photodetectors have been widely and intensively studied in recent years,because of various commercial and military applications including communications,sensing,environmental rotection,and imaging,etc.After being excited by light with a photon energy larger than the band gap of a semiconductor,the electron–hole pairs are generated in photoactive materials and therefore the external current increases,which is used as a signal for the detection of the irradiated light in photoconductive devices.This work principle clearly shows that the detected light wavelength depends on the band gap of photoactive semiconductors.Therefore,the ultraviolet,visible,infrared and other photodetectors require the photoactive semiconductors with corresponding band gaps,such as ZnS,CdS,PbS and so on.In other words,for a given photoactive semiconductor with a fixed band gap,all the light with a photon energy larger than the semiconductor band gap makes a contribution to the detected signal,which means that the fine light wavelength is unable to be identified by the detected signal based on the above-mentioned work principle.For CdS based visible light photodetectors,for example,UV and visible light are both able to generate the photoexcited carriers,and thus it seems to be impossible to figure out whether the detected light is UV or visible lightHerein,we design an intelligent photodetector based on graphene/ZnS/ CdS hybrids,in which the response time displays a visible variation at different wavelength range and thus can be utilized to identify the detected light wavelength.Our recent work and other group's work have shown that hybridizing semiconductor films with graphene with an ultrahigh carriermobility,providing a fast transport channel for the photo generated carriers of photoactive materials through charge transfer,allows us to achieve high performance photodetectors.Between grapheme and CdS films with a band gap of 2.4 eV corresponding to visible light,ZnS films with a band gap of 3.7 eV corresponding to UV light are intentionally inserted,On one hand,the inserted ZnS films act as barriers for the charge transfer of the visible-light-generated carriers from CdS to grapheme and therefore prolong the response time compared with graphene/CdS based photodetectors.On the other hand,ZnS films are supposed to replace CdS films for the detection of UV light with a response time similar to that of graphene/CdS films.Thus,the similar response time for UV and visible light detection of graphene/CdS photodetectors is intentionally tuned by inserting ZnS films to produce graphene/ZnS/CdS based photodetectors,which can be used as a characteristic parameter to distinguish the detected UV and visible light.Moreover,it can be expected that the amount of response time variation increases with the increase of ZnS film thickness.