Low-dimensional Semiconductor Devices Research Articles

Механизмы электронного транспорта в низкоразмерных полупроводниковых структурах: обзор

Background: Low-dimensional semiconductor structures such as quantum wells, wires, and dots have sparked widespread attention due to their distinct electron transport properties that differ dramatically from bulk materials. These characteristics are critical for advances in nanoscale electrical and optoelectronic devices. Objective: The article aims to summarize current knowledge of electron transport processes in low-dimensional semiconductor devices, focusing on the impact of reduced dimensionality on electron behaviour. Methods: A thorough literature analysis was carried out, emphasizing experimental and theoretical investigations that shed light on electron transport dynamics in quantum wells, wires, and dots. The analysis looked into scattering mechanisms, quantum confinement effects, and the significance of material composition and structure. Results: The findings show that quantum confinement produces discrete energy states that drastically change electron mobility and conductivity. Furthermore, electron scattering by phonons, contaminants, and surfaces is shown to be heavily impacted by decreased dimensionality, which either enhances or suppresses electron transport depending on the precise configuration and size of the structures. Conclusion: Low-dimensional semiconductor structures have complex electron transport behaviours that differ significantly from their bulk counterparts. Understanding these mechanisms is critical for designing and developing future electronic devices, and this overview serves as a starting point for ongoing articles on this technologically significant topic.

The structure, and electronic and magnetic properties of MX (M=GA, IN; X=S, SE, TE) nanoribbons

We used the first principle of density functional theory to perform detailed calculations regarding the structure, and the electronic and magnetic properties of MX (M[Formula: see text]=[Formula: see text]Ga, In; X[Formula: see text]=[Formula: see text]S, Se, Te) nanoribbons. The armchair nanoribbons (ARNs) are nonmagnetic semiconductors, which have even or odd oscillations of bandgaps. All small-sized zigzag nanoribbons (ZRNs) were found to break the six-membered ring structure and move to the center, thereby exhibiting nonmagnetic semiconductor behavior owing to the quantum confinement effect. However, among the large ZRNs, which are all metals, MTe ZRNs are nonmagnetic; this differs from the case of graphene, MoS2 and Ti2CO2 nanoribbons. MX (M[Formula: see text]=[Formula: see text]Ga, In; X[Formula: see text]=[Formula: see text]S, Se) ZRNs exhibited ferromagnetism owing to the presence of the unpaired electrons on the metal-edge side and the magnetic moment of each pair of molecules, which was controlled by the size of the nanoribbons. The results provided a theoretical reference that can be used in the future to produce MX materials for application in low-dimensional semiconductor devices, spin electron transport devices and new magnetoresistance devices.

Density of defect states retrieved from the hysteretic gate transfer characteristics of monolayer MoS2 field effect transistors

Defect states play an important role in low-dimensional semiconductor devices. However, it becomes increasingly challenging to find the density of defect states for ultra-scaled devices using traditional capacitive techniques such as capacitance-voltage (CV) method and deep level transient spectroscopy (DLTS). Here, we proposed a model to quantitatively retrieve the density of defect states from the hysteretic gate transfer characteristics of field effect transistors (FETs), and applied it to monolayer MoS2 FETs before and after superacid treatment. We found that the superacid treatment significantly reduced the density of deep level defects. As a result, the photoluminescence was enhanced 19 folds due to the suppression of non-radiative recombination via deep level defects.

Nanocontact Disorder in Nanoelectronics for Modulation of Light and Gas Sensitivities.

To fabricate reliable nanoelectronics, whether by top-down or bottom-up processes, it is necessary to study the electrical properties of nanocontacts. The effect of nanocontact disorder on device properties has been discussed but not quantitatively studied. Here, by carefully analyzing the temperature dependence of device electrical characteristics and by inspecting them with a microscope, we investigated the Schottky contact and Mott’s variable-range-hopping resistances connected in parallel in the nanocontact. To interpret these parallel resistances, we proposed a model of Ti/TiOx in the interface between the metal electrodes and nanowires. The hopping resistance as well as the nanocontact disorder dominated the total device resistance for high-resistance devices, especially at low temperatures. Furthermore, we introduced nanocontact disorder to modulate the light and gas responsivities of the device; unexpectedly, it multiplied the sensitivities compared with the intrinsic sensitivity of the nanowires. Our results improve the collective understanding of electrical contacts to low-dimensional semiconductor devices and will aid performance optimization in future nanoelectronics.

Observation of Asymmetric Magnetoconductance in Strained 28-nm Si MOSFETs

We have measured gate current components off the axis perpendicular to the surface. The measured gate oxide magnetoconductance exhibits a pronounced magnetic asymmetry, which indicates that the gate current is flowing into different crystallographic orientations with different effective masses and hole mobilities. By identifying and monitoring the different gate current axis components, we have enhanced the understanding of the physics for Si-oxide interface charge transfer and channel conductance in low-dimensional semiconductor devices.

Magneto-modulation of gate leakage current in 65 nm nMOS transistors: Experimental, modeling, and simulation results

We introduce experimental results that reveal a small static and a slowly varying-dynamic magnetic field B induces a magneto-modulation of the gate leakage current of a 65 nm nMOSFET. For the case of a 100 mT (mili-Tesla) static B field a variation of the 6% (1.5 nA/27 nA) of the gate current is observed. For a 5 Hz slowly varying (±100 mT) square pulsed magnetic field, the gate current dynamic variation raises up to 18% (4.8 nA/27 nA). These experimental observations are explained in terms of space and time modulation of the two-dimensional surface inversion layer charge. The static B field dependent model is validated through Minimos-NT numerical simulations, while the dynamic B field experimental observations are reproduced with a SPICE macro-model, which uses the static device model as initial condition for the dynamic model. With this model we are able to predict the impact of small static and dynamic B fields on the gate leakage current and channel current interference of low-dimensional MOS transistors. We also propose this electro-magnetic experimental technique as an alternative for detailed exploration of the Si–SiO 2 interface properties for 2 nm or thinner gate oxides, as well as for low-dimensional semiconductor devices.

Valence band structures of GaAs/AlAs lateral superlattices

In the framework of effective-mass envelope function theory, the valence energy subbands and optical transitions in lateral superlattices (LSLs) have been calculated by the plane-wave expansion method. The effects of finite offset and valence band mixing are taken into account. The modulations of several types of lateral potential are also evaluated; they indicate that the out-of-phase modulation on either side of the wells is the strongest while the in-phase modulation is the weakest. The lateral modulation periods have a weak effect on the lowest hole energy levels. When one is making LSLs, the fabrication can be tailored to make the lateral modulation period fairly large, which is favourable for technological applications. Our calculations also show that the effect of the difference between the effective masses of holes in different materials on the valence subband structures is significant. Our theoretical results are in agreement with the available experimental data and have great significance as regards investigating and making low-dimensional semiconductor devices.