Abstract
Recently, owing to the large surface-area-to-volume ratio of nanowires (NWs), manipulation of their surface states becomes technologically important and being investigated for various applications. Here, an in-situ surfactant-assisted chemical vapor deposition is developed with various chalcogens (e.g. S, Se and Te) as the passivators to enhance the NW growth and to manipulate the controllable p-n conductivity switching of fabricated NW devices. Due to the optimal size effect and electronegativity matching, Se is observed to provide the best NW surface passivation in diminishing the space charge depletion effect induced by the oxide shell and yielding the less p-type (i.e. inversion) or even insulating conductivity, as compared with S delivering the intense p-type conductivity for thin NWs with the diameter of ~30 nm. Te does not only provide the surface passivation, but also dopes the NW surface into n-type conductivity by donating electrons. All of the results can be extended to other kinds of NWs with similar surface effects, resulting in careful device design considerations with appropriate surface passivation for achieving the optimal NW device performances.
Highlights
Due to their superior carrier mobilities and tunable bandgaps, III-V compound semiconductors are widely investigated as the active channel materials for transistors beyond silicon complementary metal-oxide-semiconductor (CMOS) technology and highly efficient photovoltaics[1,2,3,4,5,6,7,8,9,10]
Apart from GaAs NWs, the surface states will as well form an electron accumulation layer on the InAs NW surface, leading to surface Fermi level pinned above the conduction band and making the p-type conductivity challenging
Because of the optimal size effect and electronegativity, Se is found to provide a better surface passivation to the GaAs NWs and their parallel NW arrays in diminishing the space charge depletion effect induced by the native oxide shell, and yielding less p-type or even insulating conductivity, as compared with S delivering intense p-type conductivity for the thin NWs with the diameter of ~30 nm
Summary
Due to their superior carrier mobilities and tunable bandgaps, III-V compound semiconductors are widely investigated as the active channel materials for transistors beyond silicon complementary metal-oxide-semiconductor (CMOS) technology and highly efficient photovoltaics[1,2,3,4,5,6,7,8,9,10]. Crystalline InP shells have been successfully grown onto the InAs NW core to lessen the effect of Fermi level pinning in order to achieve the p-type conductivity there[37] All these passivation techniques still suffer from the need of ex-situ operating procedures (e.g. immersing fabricated NWs into solution) making the subsequent process integration questionable, or the sophisticated in-situ schemes (e.g. overgrowing NWs with crystalline shell layers) restricting practical utilization of NWs, it is highly desirable to develop facile, effective and versatile in-situ surface passivation methods for the further applications of III-V NWs. In the past study, an in-situ sulfur surfactant assisted approach has been established in the chemical vapor deposition (CVD) of GaSb NWs, in which the S atoms can effectively passivate the reactive surface Sb constituents, facilitating the growth of thin (e.g. below 20 nm in the diameter), long and uniform GaSb NWs with the hole mobility approaching the theoretical limit[38,39,40]. All these designate the effectiveness of controllable p-n switching of thin GaAs NWs by in-situ chalcogen surface passivation, which is promising to further III-V nanomaterials for next-generation electronics and optoelectronics
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