Xianghai Ji

InAs/GaSb core-shell nanowires grown on Si substrates by metal-organic chemical vapor deposition

We report the growth of InAs/GaSb core-shell heterostructure nanowires with smooth sidewalls on Si substrates using metal-organic chemical vapor deposition with no assistance from foreign catalysts. Sb adatoms were observed to strongly influence the morphology of the GaSb shell. In particular, Ga droplets form on the nanowire tips when a relatively low TMSb flow rate is used, whereas the droplets are missing and the radial growth of the GaSb is enhanced due to a reduction in the diffusion length of the Ga adatoms when the TMSb flow rate is increased. Moreover, transmission electron microscopy measurements revealed that the GaSb shell coherently grew on the InAs core. The results obtained here show that the InAs/GaSb core-shell nanowires grown using the Si platform have strong potential in the fabrication of future nanometer-scale devices and in the study of fundamental quantum physics.

Switching from Negative to Positive Photoconductivity toward Intrinsic Photoelectric Response in InAs Nanowire

Negative photoconductivity (NPC) and positive photoconductivity (PPC) are observed in the same individual InAs nanowires grown by metal-organic chemical vapor deposition. NPC displays under weak light illumination due to photoexcitation scattering centers charged with hot carrier in the native oxide layer. PPC is observed under high light intensity. Through removing the native oxide layer and passivating the nanowire with HfO2, we eliminate the NPC effect and realize intrinsic photoelectric response in InAs nanowire.

Controlled-Direction Growth of Planar InAsSb Nanowires on Si Substrates without Foreign Catalysts

We describe the controlled growth of planar InAsSb nanowires (NWs) on differently oriented Si substrates without any foreign catalysts. Interestingly, the planar InAsSb NWs grew along four criss-crossed ⟨110⟩ directions on an [100]-oriented substrate, two ⟨100⟩ directions plus four ⟨111⟩ directions on an [110]-oriented substrate, and six equivalent ⟨112⟩ directions on an [111]-oriented substrate, which correspond to the projections of ⟨111⟩ family crystal directions on the substrate planes. High-resolution transmission electron microscopy (HRTEM) reveals that the NWs experienced a transition from out-of-plane to in-plane growth at the early growth stage but still occurred on the {111} plane, which has the lowest surface energy among all the surfaces. Furthermore, the NWs exhibit a pure zinc-blende crystal structure without any defects. A growth model is presented to explain growth of the NWs. In addition, conductive atomic force microscopy shows that electrically rectifying p-n junctions form naturally between the planar InAsSb NWs and the p-type Si substrates. The results presented here could open up a new route way to fabricate highly integrated III-V nanodevices.

All-metal electrodes vertical gate-all-around device with self-catalyzed selective grown InAs NWs array

With the scaling down of field-effect transistors (FETs) to improve their performance, 3D vertical surrounding gate structure has drawn great attention. On the other hand, concerning the channel materials, InAs nanowires (NWs) have been demonstrated to have great potential in FET due to their high mobility and other excellent electrical properties. Here, we report the first all-metal electrodes vertical gate-allaround (VGAA) FET fabricated using self-catalyzed selective grown InAs NWs array grown by metal organic chemical vapor deposition. A typical transistor we fabricated has an on-state current larger than 37 μA/μm when the drain voltage and gate voltage are +0.6 V and +3.0 V, respectively, and an on-off ratio over 3 orders of magnitudes. We have measured 34 transistors in total, and most of them have the on-off ratio between 102 and 104. Annealing is observed to improve the contact property, increase the on-state current, but decrease the on-off ratio. The ways to improve the performance of InAs NW VGAA FET are discussed.

Defect-free InAsSb nanowire arrays on Si substrates grown by selective-area metal–organic chemical vapor deposition

We report the realization of defect-free InAsSb nanowire (NW) arrays on Si substrates by selective-area metal-organic chemical vapor deposition. We studied the effects of growth temperature and the morphology of patterned Si/SiO2 substrates on the formation of InAsSb NW arrays, and found that both the morphology and the yield of the NW arrays were sensitive to the growth conditions. By optimizing the growth conditions, we achieved high-quality InAsSb NW arrays, which exhibited a pure zinc-blende crystal structure without any defects. In addition, based on the as-grown NWs, we fabricated back-gated field effect transistors devices that showed an electron mobility of 2000 cm2 V-1 s-1 at room temperature.