Investigation On Preparation Of Large Area Few Layer Black Phosphorus And The Electrical Properties Of Black Phosphorus

In recent years,black phosphorus has attracted much attention as an attractive two-dimensional semiconductor material with its excellent application prospects in electronic and optoelectronic devices.Black phosphorus is a natural p-type semiconductor material with a band gap that can be continuously adjusted from about 0.3 eV for a block to about 2 eV for a single layer.The hole mobility and current on/off ratio at room temperature can reach 1000 cm2V-1s-1 and 105,respectively.The band gap just fills the gap between the zero-band gap graphene and the wide band gap transition metal sulfide.Black phosphorus electrical devices are often prepared by few layer black phosphorus,but the direct growth of few layer black phosphorus is not mature compared to graphene and molybdenum disulfide that could be prepared by mature chemical vapor deposition.So,obtaining high quality few layer black phosphorus relies on the random mechanical exfoliation method.In addition,due to the bipolar transport property of the black phosphorous transistor,the effective regulation of bipolar property will undoubtedly pave the way for the preparation and integration of n-type and p-type black phosphorus field effect transistors(FETs).And this will make it possible to fabricate black phosphorus-based metal oxide semiconductor(CMOS)devices.Based on this,this paper has carried out related research work around these issues.Firstly,high-quality black phosphorus single crystal was successfully grown by our improved chemical vapor transport method,and a method for preparing large-area few-layer black phosphorous by metal-assisted mechanical exfoliation was developed.Then,ZnO and MgO were used to perform surface charge transfer implantation on black phosphorus,and our field effect transistor fabrication process was improved to improve its electrical performance.The following innovative results were achieved:(1)The process of preparing black phosphorous by traditional chemical vapor transport method was improved.The black phosphorus single crystal with high quality and high conversion rate of raw materials was successfully prepared by temperature gradient method and constant temperature method.(2)A method using metal-assisted mechanical exfoliation to prepare few-layer or even single layer of black phosphorus with high yield and large sample area has been developed.Compared with the conventional mechanical exfoliation method,the yield of the few-layer of black phosphorus prepared by the metal assisted mechanical method is increased by at least 100 times,and the sample size is more than 50 ?m.Based on this,field effect transistors based on the few layer black phosphorus were fabricated.The detailed electrical performance test and analysis were carried out.The hole mobility was 68.6 cm2V-1s-1,and the current on/off ratio was 105.It shows the electrical properties of the high-quality few layer black phosphorus.(3)Surface charge transfer injection of black phosphorus with ZnO and MgO,the experiment proves that both can be performed and the MgO effect is better.The electron mobility can reach 123 cm2V-1s-1,the electronic on/offf ratio reaches 17000,and the hole mobility reaches 203 cm2V-1s-1.The hole on/off ratio is up to 10000.(4)It was found that the black phosphorus structure was slightly damaged during the sputter deposition of MgO.In order to avoid such damage,we developed a method of depositing MgO with mica encapsulation,which can effectively protect black phosphorus and still carry out surface charge transfer injection.The hole mobility is 53.3 cm2V-1s-1,the electron mobility is 34.8 cm2V-1s-1,and the on/off ratio is on the order of hundreds.And the fabrication process of the black phosphorus field effect transistor is optimized to obtain the intrinsic black phosphorus transport properties.In summary,we have done a systematic work in the growth of black phosphorus single crystal,the preparation of large areas of black phosphorus and the improvement and regulation of the performance of black phosphorus field effect transistors,and also tried to improve the performance of black phosphorus field effect transistor.Some valuable research results have been obtained,which laid a foundation for further research on black phosphorus.