III−V semiconductors, such as InAs, with an ultrathin high-κ oxide layer have attracted a lot of interests in recent years as potential next-generation metal−oxide− semiconductor field-effect transistors, with increased speed and reduced power consumption. The deposition of the high-κ oxides is nowadays based on atomic layer deposition (ALD), which guarantees atomic precision and control over the dimensions. However, the chemistry and the reaction mechanism involved are still partially unknown. This study reports a detailed time-resolved analysis of the ALD of high-κ hafnium oxide (HfO x ) on InAs(100). We use ambient pressure X-ray photoemission spectroscopy and monitor the surface chemistry during the first ALD half-cycle, i.e., during the deposition of the metalorganic precursor. The removal of In and As native oxides, the adsorption of the Hf-containing precursor molecule, and the formation of HfO x are investigated simultaneously and quantitatively. In particular, we find that the generally used ligand exchange model has to be extended to a two-step model to properly describe the first half-cycle in ALD, which is crucial for the whole process. The observed reactions lead to a complete removal of the native oxide and the formation of a full monolayer of HfO x already during the first ALD half-cycle, with an interface consisting of In−O bonds. We demonstrate that a sufficiently long duration of the first half-cycle is essential for obtaining a high-quality InAs/HfO 2 interface.

and unique band structures. [1] Semiconducting monolayers of the TMDs, such as MoS 2 and WSe 2 , possess a direct band gap and excellent photoresponsivity. [2,3] In addition, single-layer MoS 2 is moderately easy to attain Ohmic contact with various metals [4][5][6][7] and graphene, [8] and the singlelayer MoS 2 field-effect transistors (FETs) show decent performances on the mobility (tens of cm 2 V −1 s −1 ) [9,10] and the on-off current ratio (exceeding 10 8 ) [4,10] at room temperature, suggesting that the monolayer MoS 2 holds greater potential for flexible nanodevices and optoelectronic applications. The huge surface-to-volume ratio of the atomically thin TMDs makes their performances extremely sensitive to the surface and interface conditions. The low-frequency electrical noise of devices often discloses the influences from the surface [11] and the interface conditions and has been widely adopted as a nondestructive tool to study the interface conditions. The subthreshold slope of the FETs and the photo response time of the MoS 2 photodetectors are significantly determined by the interfacial traps. [12] Unlike the thermal noise and shot noise that possess a constant power spectral density, low-frequency noise typically has a 1/f spectrum, and its effect on the accuracy of a device cannot be reduced by increasing the averaging time. [13] Such noise manner causes a critical issue of applications of the TMDs in the signal sensing and processing, [14] and raises numerous interests in investigating the 1/f noise in the TMD-based devices for identifying its origin and for reducing its strength.The first study of low-frequency electrical noise in exfoliated monolayer MoS 2 [15] claimed that the noise has a 1/f spectrum and is mainly explained by fluctuation of the mobility. By contrast, the 1/f noise in the exfoliated MoTe 2[16] with the ambipolar transport behaviors and many other TMD FETs [17][18][19][20] is further described as fluctuation of the carrier density. Finding a clear picture of the possible factors contributing to the 1/f noise, including the external adsorbates on the devices, [15] the defect states at the metal/TMD contacts, [17] and the trappingdetrapping centers in the substrate near the TMD channel, [18,21] remains a challenging issue because of the lack of Ohmic contacts, ideal material quality, and an effective control of the carrier density. Recently, the high-quality chemical-vapor-deposited (CVD) MoS 2 monolayers show the comparable electrical

When an intense, few-cycle light pulse impinges on a dielectric or semiconductor material, the electric field will interact nonlinearly with the solid, driving a coherent current. An asymmetry of the ultrashort, carrier-envelope-phase-stable waveform results in a net transfer of charge, which can be measured by macroscopic electric contact leads. This effect has been pioneered with extremely short, single-cycle laser pulses at low repetition rate, thus limiting the applicability of its potential for ultrafast electronics. We investigate lightwave-driven currents in gallium nitride using few-cycle laser pulses of nearly twice the duration and at a repetition rate two orders of magnitude higher than in previous work. We successfully simulate our experimental data with a theoretical model based on interfering multiphoton transitions, using the exact laser pulse shape retrieved from dispersion-scan measurements. Substantially increasing the repetition rate and relaxing the constraint on the pulse duration marks an important step forward towards applications of lightwave-driven electronics.

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 with a root mean square roughness of 0.12 nm and the InGaAs (001) 4 × 2 surface reconstruction are observed 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.