Hfo2 Capping Enhances Quantum Transport in Atomically Thin MoS2, Modifying Low-Temperature Electronic Behavior

The behaviour of semiconductors strongly depends on their surrounding environment, a relationship becoming increasingly important in atomically thin materials where electrons interact intensely with their surroundings. Jaroslaw Pawlowski, Dickson Thian, and Repaka Maheswar, along with colleagues at their institutions, now demonstrate how applying a high-k dielectric material dramatically alters electron transport in these ultra-thin semiconductors. Their research reveals that capping monolayer molybdenum disulfide with a high-k dielectric switches the transport mechanism from classical, scattering-dominated behaviour to a quantum regime exhibiting phase-coherent transport, evidenced by clear interference patterns. This achievement demonstrates that careful dielectric engineering offers a powerful method for controlling the fundamental properties of these materials and opens new avenues for designing advanced electronic devices.

They fabricated devices both with and without a capping layer of hafnium oxide (HfO2), a high-κ dielectric material known for its insulating properties, and then meticulously compared how electrons move through the material. The research focuses on understanding the transition from classical to quantum diffusive transport. Measurements of electron mobility and transconductance at varying temperatures reveal crucial insights into the transport mechanisms.

Researchers observed that uncapped MoS2 exhibits classical diffusive scattering, while devices capped with HfO2 display clear Fabry-Perot interference patterns, indicating phase-coherent transport. This interference arises from electrons behaving as waves and reinforces the presence of quantum effects. The team developed a computational model, a tight-binding interferometer, to simulate electron behavior within the MoS2 channel. This model accounts for how the dielectric layer alters conductive modes and facilitates coherent transport, even in the presence of imperfections. Simulations demonstrate that HfO2 partially restores the electronic structure of MoS2, enabling electrons to maintain a defined phase relationship. Detailed experiments confirm the model’s accuracy, reproducing characteristic Fabry-Perot interference patterns in both simulations and experimental data. These findings demonstrate that careful dielectric engineering offers a powerful route to control transport regimes in two-dimensional materials and realize coherent quantum transport.

Dielectric Effects on Molybdenum Disulfide Transport

Researchers investigated how surrounding materials influence the electronic properties of atomically thin molybdenum disulfide (MoS2), a two-dimensional semiconductor, at low temperatures. To explore this, the team fabricated devices both with and without a capping layer of hafnium oxide (HfO2), a high-κ dielectric material. They then meticulously compared the transport characteristics of these devices, focusing on how electrons move through the material. The study pioneered a tight-binding interferometer model, a computational technique used to simulate electron behavior within the MoS2 channel. This model accounted for the effects of the dielectric layer on conductive modes, essentially mapping how electrons travel through the material.

Researchers used this model to predict how HfO2 would alter electron pathways and facilitate coherent transport, where electrons maintain a defined phase relationship. The simulations demonstrated that the dielectric layer partially restores subband structure, enabling coherent transport, even in the presence of defects. To validate the simulations, the team performed detailed experiments measuring the electrical conductance of the MoS2 devices. They observed that uncapped devices exhibited classical diffusive scattering, while devices capped with HfO2 displayed clear Fabry-Perot interference patterns, indicative of phase-coherent transport. By varying gate voltage and source-drain bias, the team reproduced characteristic Fabry-Perot interference patterns in simulations and experiments, confirming the model’s accuracy. These findings demonstrate that careful dielectric engineering offers a powerful route to control transport regimes in two-dimensional materials and realize coherent quantum transport.

Dielectric Engineering Enables Phase-Coherent Transport in MoS2

This work details a breakthrough in understanding electron transport in atomically thin molybdenum disulfide (MoS2), demonstrating how dielectric engineering can control the behavior of charge carriers at extremely low temperatures. Scientists investigated single-layer MoS2 devices, comparing those without a capping layer to those covered with a 30 nanometer layer of hafnium oxide (HfO2), a high-k dielectric. Experiments revealed a fundamental difference in transport mechanisms, with uncapped devices exhibiting classical diffusive scattering, while those capped with HfO2 displayed clear evidence of phase-coherent transport, indicated by Fabry-Perot interference patterns. Measurements of electron mobility as a function of temperature pinpointed a crossover temperature of approximately 330 Kelvin in the uncapped MoS2, where the dominant scattering mechanism shifts from phonon scattering at higher temperatures to impurity scattering at lower temperatures.

In contrast, the HfO2-capped MoS2 exhibited a metal-insulator transition at 175 Kelvin, and a significant shift in the crossover temperature, indicating a reduction in impurity scattering. The team extracted field-effect mobility values, demonstrating that the HfO2 cap effectively screens impurities, thereby enhancing electron transport. Further analysis at temperatures below 30 Kelvin revealed pronounced conductance oscillations in the capped devices, a phenomenon absent in the uncapped samples. This observation confirms the emergence of quantum effects enabled by the dielectric screening. The team established that the crossover temperature shifts with varying impurity and phonon scattering strengths, and that the HfO2 cap alters this relationship, demonstrating control over the dominant scattering mechanisms. These findings establish dielectric engineering as a powerful route to control transport regimes in two-dimensional materials, with implications for both scalable nanoelectronics and next-generation quantum technologies.

Dielectric Control of Quantum Transport in MoS2

This research demonstrates the crucial role of the surrounding dielectric environment in determining both classical and quantum transport properties within single-layer molybdenum disulfide. By comparing devices with and without a hafnium oxide capping layer, scientists observed a clear transition from classical, diffusive transport to a quantum-coherent regime. The presence of the high-κ dielectric suppresses scattering from impurities, enabling the emergence of Fabry-Pérot interference patterns at low temperatures, a direct indication of phase-coherent transport. Temperature-dependent mobility measurements corroborate these findings, revealing reduced impurity-limited scattering in devices incorporating the hafnium oxide layer.

To further understand these observations, the team developed a tight-binding interferometer model, which confirms that the dielectric layer modifies conductive modes and facilitates the observed quantum coherence. These results establish that careful engineering of the dielectric environment offers a powerful means to not only enhance device performance but also to control the fundamental quantum behavior of charge carriers in two-dimensional semiconductors. This work establishes high-κ dielectrics as a versatile tool for realizing coherent quantum transport and provides a pathway for the design of future nanoelectronic and quantum devices based on transition metal dichalcogenides.