Bandgap engineering is important for realizing high-performance semiconductor devices. In this paper, an investigation on the nanowire diode with a tapered InAs/InP core-shell structure was carried out. The strain distribution along the nanowire can be changed via the shell thickness and the gradient of the tapering. Due to the misfit-strain between InAs/InP, a strain-induced bandgap variation of 0.21 eV along the tapered InAs wire, which results in the rectifying I-V characteristic of the diode, was realized with an InP shell thickness of 6.5 nm. Moreover, due to the optimized shell thickness and strain-induced built-in electric field (including piezoelectric field), a recorded room-temperature electron mobility of 22300 cm 2 V À1 s À1 was achieved. This concept of bandgap engineering would enable the designing of a new kind of nanowire device.
:The DOF (degree of freedom) analysis is carried out for the symmetrical and asymmetrical composite unit mechanism based on the 3RR-3URU tetrahedral element and the deployable composite unit structure based on the 3UU-3URU tetrahedral basic element. Firstly, the DOF and properties of 3RR-3URU tetrahedral basic element are analyzed based on the link-demolishing and equivalent method. The basic elements are combined into symmetric 3RR-3URU composite unit and asymmetric 3RR-3URU composite unit. Then, the structures and the geometric constraints of the two composite units are analyzed, and the screw theory and G-K formula are applied to analyze the DOF of the two composite units. Secondly, in view of the problem that the composite unit based on 3RR-3URU cannot satisfy the large deployable antenna mechanism, the 3UU-3URU basic element and its composite unit are proposed, and the DOF of which are obtained according to G-K formula. Finally, the simulation models of three composite units are established, and the ADAMS simulation software is used to simulate the motion of the three combined units. The simulation results verify the correctness of the DOF analysis. The results provide an important theoretical basis for the design and analysis of tetrahedral deployable antenna mechanism.
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