Surface State Dynamics Dictating Transport in InAs Nanowires

Abstract

Because of their high aspect ratio, nanostructures are particularly susceptible to effects from surfaces such as slow electron trapping by surface states. However, nonequilibrium trapping dynamics have been largely overlooked when considering transport in nanoelectronic devices. In this study, we demonstrate the profound influence of dynamic trapping processes on transport in InAs nanowires through an investigation of the hysteretic and time-dependent behavior of the transconductance. We observe large densities (∼10 cm) of slow surface traps and demonstrate the ability to control and permanently fix their occupation and charge through electrostatic manipulation by the gate potential followed by thermal deactivation by cryogenic cooling. Furthermore, we observe a transition from enhancement- to depletion-mode and a 400% change in field-effect mobility within the same device when the initial gate voltage and sweep rate are varied, revealing the severe impact of electrostatic history and dynamics on InAs nanowire field-effect transistors. A time-dependent model for nanowire transconductance based on nonequilibrium carrier population dynamics with thermally activated capture and emission was constructed and showed excellent agreement with experiments, confirming the effects to be a direct result of the dynamics of slow surface traps characterized by large thermal activation barriers (∼ 700 meV). This work reveals a clear and direct link between the electrical conductivity and the microscopic interactions of charged species with nanowire surfaces and highlights the necessity for considering dynamic properties of surface states in nanoelectronic devices.

Ionic‐Liquid Gating of InAs Nanowire‐Based Field‐Effect Transistors

“…Temperature and gate‐voltage sweep rates can influence the measured transport properties of InAs NW‐based devices: this is particularly true for the present case of ionic‐liquid gating. In general, however, a transport regime characterized by negligible hysteresis during a cycle of gate sweep is desirable: we searched for this regime in parameter space by investigating the hysteretic features displayed by our devices as a function of temperature and liquid‐gate voltage‐sweep rate.…”

Rethinking the Characterization of Nanoscale Field‐Effect Transistors: A Universal Approach

“…When considering the gate voltage dependence of transport properties, the experimental V g sweep rate ( V ′) is often ignored in literature, which affects the determination of transport characteristics due to electrical hysteresis (i.e., G ( V g ) depends on the direction and value of V ′). This is observed in various semiconductor NWs, [ 24,40–45 ] thin films, [ 46–48 ] and carbon nanotubes, [ 49–54 ] and is often related to slow localized states. These states exchange charge with the conduction band at a delayed rate causing time dependent measurements of G ( V g ).…”

Threshold Switching in Single Metal‐Oxide Nanobelt Devices Emulating an Artificial Nociceptor

“…The high aspect ratio of the nanobelt implies that the performance of the single nanobelt device can be susceptible to the presence of surface trapping sites. [49] This would result in an I-V behavior that could be independent of the electrodes. To test this possibility, we fabricated single TiO 2 nanobelt devices on different electrodes.…”

“…This phenomenon has been widely explored in one dimensional (1D) semiconductor nanomaterial-based devices. [49,[59][60][61] Furthermore, due to the highly defective nature of the TiO 2 nanobelts, oxygen vacancies or hydroxide groups on the surface function as localized charge-carrier centers providing paths for injected electrons to hop from one localized site to another when an external electric field is applied. At low electric field in Stage I, the temperature dependence of the resistance of the TiO 2 nanobelt device can be described using a Mott-variable range hopping (VRH) conduction mechanism according to the equation [62]…”

“…Filling of deep trap states will also lead to an upward shift of the Fermi level (E F ), rendering shallow trap states closer to the E F in Stage III. [69,70] Thus, it is suggested that from Stage II to Stage III, this nonequilibrium trapping dynamics by the defect states of the TiO 2 nanobelts causes the difference in the current response from the same trap-assisted tunneling mechanism, leading to observed hysteresis in current, [49] that is, resistive switching behavior. This assumption is supported by the sweeping voltage dependent hysteresis behavior shown in Figure 2d,3 and Figures S2 and S3, Supporting Information.…”