Controllable Growth And Characterization Of Planar Si,Ge Nanowire And Superconducting Al Film

One-dimensional Si and Ge nanowires are significant candidate material systems for post-Molar sub-10 nm nodes.Moreover,Si and Ge can be engineered by isotopic purification into nuclear spin-free materials ²⁸Si and ⁷²Ge,which provides an ideal basis of materials for the preparation of high-performance quantum bits with long coherent time in semiconductor quantum computing.Ge nanowires,in particular,have high hole mobility,strong spin-orbit coupling,and electrically modulated g factor,which hold promise to enable a fast all-electrical hole-spin qubit manipulation.Nanowires obtained by the traditional VLS method usually have a random distribution of positions and different sizes,which cannot realize the large-scale integration of devices.Therefore,it is crucial to synthesize highly uniform Si and Ge arrays that are addressable and scalable.Another material system that is of great importance to all-solid quantum computing is superconductors,especially Al.The superconducting quantum circuit based on the Al/Al O_x/Al Josephson junction is undoubtedly one of the most mature systems at present,and researchers are currently developing a 100-qubit supercomputing chip.Supporting by the advanced semiconductor manufacturing technology,the superconducting quantum circuit of preparing Al on Si substrate is expected to significantly improve the integration level and fast the research progress.Besides,combining superconductor Al with semiconductors such as Si and Ge is expected to not only fabricate a resonator that couples multiple long-distance qubits,but also produce exotic quantum states,such as Majorana zero modes and Andreev bound states,which hold promise to build a robust topologic quantum computing.Based on the two points above,in this paper,we introduce the research work of obtaining site-controlled high-uniform Si and Ge nanowire arrays,and the high-quality Al epitaxial films on Si and Ge substrates,the details as follows:First,we introduce a nano-fabrication method to obtain a<110>-oriented Si nanowire array with high uniformity on the 8-inch Si wafer.Such Si nanowires show an inverted triangular cross-section with a minimum mean width of only 20 nm.By changing the dimensions of patterns,one can simultaneously fabricate Si nanowires with multiple widths and lengths.Combination of epitaxy,we have obtained{111}-faceted Si nanowire.Further,by changing the specific growth conditions we can control the morphologies and widths of nanowires.Moreover,we also introduce a suspended Si epi-nanowire and As-assistant Si nanowire with a larger dimension.Next,we perform the heteroepitaxy research of SiGe and Ge based on the Si epi-nanowire.We demonstrate the formation of the conformal SiGe NWs and Ge NWs with{113}facets on the diamond-shaped Si NWs with{111}facets and truncated Si NWs,respectively.Characterization data indicate both nanowires of excellence uniformity and high crystal quality.Furtherly,we studied the epitaxial growth of Al on Si and Ge substrates and realized single-crystal growth of Al films on Si(111)and Ge(111)substrates.On the(001)substrate,the Al film is polycrystalline with a rough surface on both Si and Ge substrate.The Al film on Si(001)shows a(110)bi-crystal.On the other hand,the Al film on Ge(001)presents a polycrystalline structure of Al(001)and Al(110),accompanied by the diffusion of Ge along Al grain boundaries.On the(001)substrate,the Al films both on Si and Ge exhibit a monocrystalline Al(111)structure with a smooth surface.The Al film obtained on Ge(111)substrate shows the best result of surface smoothness and crystal quality in this experiment,where the RMS of roughness of the 20 nm thick Al film is only 0.33 nm,and the FHMW of the rocking curve is only 517.3 arcsec.Besides,we have analyzed the Al/Si and Al/Ge interfaces by TEM characterization and found that they form 4 Al:3 Si and 7 Al:5 Ge epitaxial relations.The results also show that the monocrystalline Al film can effectively inhibit the generation of Al and Ge intermixing.Finally,the superconductivity of Al films has been characterized.The T_c of the monocrystal Al film increases significantly with the decrease of thickness,while that of polycrystalline Al film increases slowly,besides there is an abnormal decrease of T_c for the polycrystalline Al film with a thickness of 3 nm.TEM analysis of the related samples shows that the abnormal decrease is due to the poor film-forming property of the polycrystalline Al film.It is found that the vertical critical magnetic field is more sensitive to the formation of continuous films.With the decrease of the thickness of Al monocrystalline or polycrystalline film,the increase of₍(8?)is not obvious,but when the uncovered regions are generated in the film,the₍(8?)will be dramatically increased.On the other hand,for the parallel₍(8?),both monocrystalline and polycrystalline Al films show a trend of significant increase with the decrease of thickness.For the 3 nm thick films,the₍(8?)of both monocrystal and polycrystal are close to 4.5 T.