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Utilizing first-principles calculations, charge transfer doping process of single layer tin selenide (SL-SnSe) via the surface adsorption of various organic molecules was investigated. Effective p-type SnSe, with carrier concentration exceeding 3.59 × 1013 cm−2, was obtained upon adsorption of tetracyanoquinodimethane or 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane on SL-SnSe due to their lowest unoccupied molecular orbitals acting as shallow acceptor states. While we could not obtain effective n-type SnSe through adsorption of tetrathiafulvalene (TTF) or 1,4,5,8-tetrathianaphthalene on pristine SnSe due to their highest occupied molecular orbitals (HOMO) being far from the conduction band edge of SnSe, this disadvantageous situation can be amended by the introduction of an external electric field perpendicular to the monolayer surface. It is found that Snvac will facilitate charge transfer from TTF to SnSe through introducing an unoccupied gap state just above the HOMO of TTF, thereby partially compensating for the p-type doping effect of Snvac. Our results show that both effective p-type and n-type SnSe can be obtained and tuned by charge transfer doping, which is necessary to promote its applications in nanoelectronics, thermoelectrics and optoelectronics.

In order to study the optimal N:Al flux ratio during the deposition of AlN, the effects of N:Al flux ratio on the crystal quality (crystallinity and surface roughness) of homoepitaxial AlN are investigated. The growth temperature ranges from 1600 K to 2000 K with an increment of 200 K. When the N:Al flux ratios are changed from 0.8 to 2.8, the good crystallinity is obtained at 1600 K with the N:Al flux ratio of 2.4, while it is obtained at 1800 K with the N:Al flux ratio of 2.4 and with the N:Al flux ratio of 2.0 at 2000 K. The crystallinity at 1800 K with N:Al flux ratio of 2.4 stands out among these three. At 1800 K with varied N:Al flux ratios, the minimum surface roughness is also obtained at the N:Al flux ratio of 2.4. Further more, the distribution of deposited Al atoms at 1800 K is explored, the result shows that the uniform distribution of Al atoms appears at N:Al flux ratio of 2.4.

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