A method for preparing large area monolayer tungsten selenide single crystal

The present invention relates to the field of microelectronics technology, in particular to a Chemical vapor deposition (CVD) method for the preparation of a single crystal of monolayer tungsten diselenide (WSe2).
Background technology:
With molybdenum disulfide (MoS2), two dock selenide (WSe2) represented by a two-dimensional function of transition metal chalcogenide materials in the process of multi-layer to single layer, can be achieved by indirect band gap to direct band gap, with its unique physical and chemical properties make it in electronic devices, optoelectronic devices, and other fields has great application potential and wide attention by the researchers. Compared with MoS2, WSe2 has more characteristic luminescence characteristics. Currently, the preparation of large-area monolayer WSe2 mainly adopts CVD method, which requires selenium source and tungsten source as precursors. The tungsten source commonly used by CVD method is WO3. However, due to the high evaporation temperature of WO3, it is difficult to steam out WO3, so WO3 only exists in some places. At the same time, the temperature of the selenium source must be precisely controlled to realize the stable evaporation of the selenium source.
Literature 1 “j. – K.H uang, j. p. u, c. – L.H su, m. – H.C hiu, z. – Y.J uang, y. – H.C hang, w. – H.C hang, Y.I wasa, T.T akenobu and l. – J.L I, ACS Nano 8 (1), 923-930 (2013). The.” The preparation of single layer WSe2 with WO3 as precursor system by CVD method is reported. This method is typical in two-dimensional materials. In the process, hydrogen and argon are used as carrier gas. However, the side length of the WS2 triangular single crystal grown by this method is only below 20 m, and the number of layers cannot be precisely controlled, which limits the device application of the material.
Technical realization elements:
The purpose of the present invention is to present a method for preparing large-area monolayer tungsten selenide single crystal in order to reduce the production cost and increase the area of growing single crystal thin film.
The technical key of the present invention is to realize the nucleation and growth process control of CVD reaction by using a pipette gun to precisely control the amount of NaCl added, and finally achieve the large area and controllable growth of WSe2. The implementation steps are as follows:
(1) two substrates were selected and cleaned by standard RCA cleaning process. Two quartz boats were selected as tungsten and selenium boats.
(2) dissolve 1-100mg NaCl in 5mL deionized water to make a salt solution, drop 2-20l salt solution on the front end of the first substrate, and heat it on the hot plate until deionized water is completely gasified;
(3) after placing 3-300mg WO3 in the center of the first substrate, place it in the tungsten boat, cover the second substrate in the position of 1mm-10mm above WO3, then place the tungsten boat in the high temperature area of the tube furnace, then add 10-500mg selenium powder into the selenium boat, and place the selenium boat in the low temperature area of the tube furnace;
(4) the high-temperature zone was heated to 100-150℃, and the reaction chamber was purged with argon gas with a flow of 100-1000 SCCM for 15 minutes to 2 hours;
(5) adjust the flow of argon to 10scm-200sccm, and rapidly raise the temperature of the high temperature area to 300-700℃;
(6) reduce the heating rate. When the temperature in the high temperature zone reaches 600-850℃, the low temperature zone is heated independently to melt Se and react with WO3 for 3-60 minutes.
(7) naturally cool down, wait for the temperature to drop below 100℃, take out the sample and seal it, that is, complete the preparation of a single crystal of monolayer tungsten selenide.

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