Technical Insight
Adatom Diffusion Can Control InAs Nanowire Structures
The researchers say that this should be possible by using GaAs NWs of different length as the basis for growing InAs nanowires (NWs).
Researchers at Beijing University of Posts and Telecommunications (BUPT) claim that the crystal structure of InAs nanowires (NWs) can be controlled by tuning the contributions of adatom diffusion (ADD).
For growth along the most favorable (111)B direction, NWs made from III-V materials (such as GaAs, GaP, InP and InAs) normally show randomly distributed stacking faults perpendicular to the growth direction.
These crystalline defects limit the optical and electronic properties of the NWs due to carrier scattering by the defects, resulting in an intermixing structure of wurtzite (WZ) and zinc blende (ZB). Thus, control of the phase purity is now considered as one of the major challenges in NW technology.
ADD and precursor direct impingement (DIM) are two major contributions for vapor-liquid-solid (VLS) growth of NWs. The researchers found that a pure ZB structure is favored when DIM contributions dominate, while the WZ structure is more beneficial when ADD contributions dominate.
Moreover, without changing the NW diameter or growth parameters (such as temperature and V/III ratio), a transition from ZB to WZ structure can be realized by increasing the ADD contributions. The scientists have demonstrated these results for InAs NWs, and proposed a nucleation model to explain the experimental results.
For the InAs NWs grown on GaAs NWs with a length of 5.5μm, the crystal structure is pure ZB and the length is diameter-independent. This say the researchers, indicates the DIM process made dominant contributions during growth. For the InAs NWs grown on GaAs NWs with a length of 0.8μm, the crystal structure is WZ and the length is nearly inversely proportional to the diameter. This indicates the ADD made dominant contributions during growth.
Based on the experimental results, it is natural to assume that DIM and ADD contributions should play different roles in nucleation. This difference has not yet been considered in the current nucleation model proposed for VLS growth. Thus, a complementary nucleation model is proposed in which ADD and DIM contributions play different roles in determining the location and phase of the nucleus.
In the future, the researchers hope to apply this growth method to other III-V nanowires to control phase purity.
Further details of this work are published in the paper “Control of the crystal structure of InAs nanowires by tuning contributions of adatom diffusion”, by Hui Huang, Xiaomin Ren, Xian Ye, Jingwei Guo, Qi Wang, Xia Zhang, Shiwei Cai and Yongqing Huang, Nanotechnology 21 (2010) 475602.
