| 1. |
- Webb, J. L., et al.
(författare)
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Imaging Atomic Scale Dynamics on III-V Nanowire Surfaces during Electrical Operation
- 2017
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- As semiconductor electronics keep shrinking, functionality depends on individual atomic scale surface and interface features that may change as voltages are applied. In this work we demonstrate a novel device platform that allows scanning tunneling microscopy (STM) imaging with atomic scale resolution across a device simultaneously with full electrical operation. The platform presents a significant step forward as it allows STM to be performed everywhere on the device surface and high temperature processing in reactive gases of the complete device. We demonstrate the new method through proof of principle measurements on both InAs and GaAs nanowire devices with variable biases up to 4 V. On InAs nanowires we observe a surprising removal of atomic defects and smoothing of the surface morphology under applied bias, in contrast to the expected increase in defects and electromigration-related failure. As we use only standard fabrication and scanning instrumentation our concept is widely applicable and opens up the possibility of fundamental investigations of device surface reliability as well as new electronic functionality based on restructuring during operation.
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| 2. |
- Troian, Andrea, et al.
(författare)
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InAs-oxide interface composition and stability upon thermal oxidation and high-k atomic layer deposition
- 2018
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 8:12
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Tidskriftsartikel (refereegranskat)abstract
- Defects at the interface between InAs and a native or high permittivity oxide layer are one of the main challenges for realizing III-V semiconductor based metal oxide semiconductor structures with superior device performance. Here we passivate the InAs(100) substrate by removing the native oxide via annealing in ultra-high vacuum (UHV) under a flux of atomic hydrogen and growing a stoichiometry controlled oxide (thermal oxide) in UHV, prior to atomic layer deposition (ALD) of an Al2O3 high-k layer. The semiconductor-oxide interfacial stoichiometry and surface morphology are investigated by synchrotron based X-ray photoemission spectroscopy, scanning tunneling microscopy, and low energy electron diffraction. After thermal oxide growth, we find a thin non-crystalline layer with a flat surface structure. Importantly, the InAs-oxide interface shows a significantly decreased amount of In3+, As5+, and As0 components, which can be correlated to electrically detrimental defects. Capacitance-voltage measurements confirm a decrease of the interface trap density in gate stacks including the thermal oxide as compared to reference samples. This makes the concept of a thermal oxide layer prior to ALD promising for improving device performance if this thermal oxide layer can be stabilized upon exposure to ambient air.
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| 3. |
- Liu, Yen Po, et al.
(författare)
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Low temperature scanning tunneling microscopy and spectroscopy on laterally grown InxGa1-xAs nanowire devices
- 2020
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 117:16
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Tidskriftsartikel (refereegranskat)abstract
- Laterally grown InxGa1-xAs nanowires (NWs) are promising candidates for radio frequency and quantum computing applications, which, however, can require atomic scale surface and interface control. This is challenging to obtain, not least due to ambient air exposure between fabrication steps, which induces surface oxidation. The geometric and electronic surface structures of InxGa1-xAs NWs and contacts, which were grown directly in a planar configuration, exposed to air, and then subsequently cleaned using atomic hydrogen, are studied using low-temperature scanning tunneling microscopy and spectroscopy (STM/S). Atomically flat facets witha root mean square roughness of 0.12 nm and the InGaAs (001) 4 × 2 surface reconstruction areobserved on the top facet of the NWs and the contacts. STS shows a surface bandgap variation of 30 meV from the middle to the end of the NWs, which is attributed to a compositional variation of the In/Ga element concentration. The well-defined facets and small bandgap variations found after area selective growth and atomic hydrogen cleaning are a good starting point for achieving high-quality interfaces during further processing.
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| 4. |
- Mousavi, S. Fatemeh, et al.
(författare)
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Atomic Hydrogen Annealing of Graphene on InAs Surfaces and Nanowires : Interface and Morphology Control for Optoelectronics and Quantum Technologies
- 2022
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Ingår i: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 5:12, s. 17919-17927
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Tidskriftsartikel (refereegranskat)abstract
- Folding two-dimensional graphene around one-dimensional III-V nanowires yields a new class of hybrid nanomaterials combining their excellent complementary properties. However, important for high-quality electrical and optical performance, needed in many applications, are well-controlled oxide-free interfaces and a tight folding morphology. To improve the interface chemistry between the graphene and InAs, we annealed the samples in atomic hydrogen. Using surface-sensitive imaging, we found that the III-V native oxides in the interface can be reduced at temperatures that maintain the graphene and the III-V nanostructures. Transferring both single- and multilayer graphene flakes onto InAs NWs, we found that single layers fold tightly around the NWs, while the multilayers fold weakly with a decline of only a few degrees. Annealing in atomic hydrogen further tightens the folding. Together, this indicates that high-quality morphological and chemical control of this hybrid material system is possible, opening for future devices for quantum technologies and optoelectronics.
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