Si Substrates Research Articles

Manipulation of Helicity-Dependent Photocurrent and Stokes Parameter Detection in Topological Insulator Bi2Te3 Nanowires.

Helicity-dependent photocurrent (HDPC) and its modulation in topological insulator Bi2Te3 nanowires have been investigated. It is revealed that when the incident plane of a laser is perpendicular to the nanowire, the HDPC is an odd function of the incident angle, which is mainly contributed by the circular photogalvanic effect originating from the surface states of Bi2Te3 nanowire. When the incident plane of a laser is parallel to the nanowire, the HDPC is approximately an even function of the incident angle, which is due to the circular photon drag effect coming from the surface states. It is found that the HDPC can be effectively tuned by the back gate and the ionic liquid top gate. By analyzing the substrate dependence of the HDPC, we find that the HDPC of the Bi2Te3 nanowire on the Si substrate is an order of magnitude larger than that on SiO2, which may be due to the spin injection from the Si substrate to the Bi2Te3 nanowire. In addition, by applying different biases, the Stokes parameters of a polarized light can be extracted by arithmetic operation of the photocurrents measured in the Bi2Te3 nanowire. This work suggests that topological insulator Bi2Te3 nanowires may provide a good platform for opto-spintronic devices, especially in chirality and polarimtry detection.

Influence of XeCl excimer laser annealing on the ferroelectric nondoped HfO2 formation deposited on Si(100) substrate

Abstract In this research, we have investigated the effect of excimer laser annealing (ELA) on the ferroelectric nondoped HfO2 (FeND-HfO2) formation deposited on Si(100) substrate. The XeCl (λ: 308 nm) ELA was irradiated as post-deposition annealing (PDA) in the N2 ambient to the 10 nm thick HfO2 deposited by RF-magnetron sputtering without substrate heating. The C-V characteristics of Al/HfO2/p-Si(100) metal/ferroelectrics/Si (MFS) diodes were gradually improved with the energy density of ELS from 170 mJ/cm2 to 270 mJ/cm2 irradiated at 200 Hz for 200 shots although charge-injection type hysteresis of 0.2-0.3 V was remained. The post-metallization annealing (PMA) at 400oC/5 min in N2/4.9%H2 ambient for Al/HfO2/p-Si(100) MFS diodes markedly improved the C-V characteristics, and negligible hysteresis with ideal flat-band voltage (VFB) was realized. The memory window (MW) of 0.42 V was achieved by the program/erase (P/E) operation with the input pulses of +3 V/100 ms and -8 V/100 ms for the MFS diode with ELA energy density of 270 mJ/cm2 at 200 Hz for 200 shots followed by the PMA..

Neutron Reflectivity Study on the Adsorption Layer of Polyethylene Grown on Si Substrate.

To investigate the structure of the interface between polyethylene films and substrates, the neutron reflectivity (NR) of deuterated polyethylene (dPE) thin films deposited on Si substrates was measured, demonstrating water accumulation at the interface, even under ambient conditions. After leaching the thermally annealed dPE films in hot p-xylene, NR measurements were conducted on the layers remaining on the substrate, clearly revealing that the adsorption layer of dPE grew during annealing and consisted of two layers, an inner adsorption layer and an outer adsorption layer, as previously proposed for amorphous polymers. The inner adsorption layer was approximately 3.7 nm thick with a density comparable to that of the bulk. The outer adsorption layer was several nanometers thick and appeared to grow insufficiently on top of the inner adsorption layer under the annealing conditions examined in this study. This study clarifying the growth of the adsorption layer of polyethylene at the interface with an inorganic substrate is useful for improving the performance of polymer/inorganic filler nanocomposites due to the wide utility of crystalline polyolefins as polymer matrix materials in nanocomposites.

InGaN/GaN Hybrid‐Nanostructure Light Emitting Diodes with Emission Wavelength Green and Beyond

Three sets of InGaN/GaN nanowire (NW) heterostructures are grown on Si(111) substrates under different growth conditions. A quasi‐two‐dimensional p‐GaN layer is grown on top of those structures using the epitaxial lateral overgrowth (ELOG) technique. Finally, the light‐emitting diodes (LED) are fabricated using these hybrid nanostructures following standard fabrication techniques. Electroluminescence (EL) measurement confirmed the emission wavelengths of 530.0 nm (green), 608.3 nm (orange), and 632.5 nm (red). The knee voltages of the devices are estimated to be in the range of 2.18–2.89 V, with higher knee voltages for samples emitting lower wavelengths. Further analysis of forward bias electrical characteristics suggests the dominance of tunneling current and an increase in the defect density in the heterostructures emitting higher wavelengths.

High-efficiency electroluminescence devices containing Si nanocrystals/SiC multilayers via improved carrier injection and recombination process

Realizing high efficiency of all Si-based light-emitting devices is currently one of interesting issues in order to develop monolithic opto-electronic integration on chips. Here, we report an electroluminescence device based on phosphorus (P)-doped silicon nanocrystals (Si NCs)/silicon carbide (SiC) multilayers by modulating carrier injection and recombination process. The p+-Si substrate is used instead of p-Si substrate for facilitating the hole injection into Si NCs. Additionally, the influences of annealing temperature on the device performance have been studied, and the optimized annealing temperature is achieved by balancing the crystallinity, defect state density, and recombination process.

The Evaluation of Interface Quality in HfO2 Films Probed by Time-Dependent Second-Harmonic Generation

Time-dependent second-harmonic generation (TD-SHG) is an emerging sensitive and fast method to qualitatively evaluate the interface quality of the oxide/Si heterostructures, which is closely related to the interfacial electric field. Here, the TD-SHG is used to explore the interface quality of atomic layer deposited HfO2 films on Si substrates. The critical SHG parameters, such as the initial SHG signal and characteristic time constant, are compared with the fixed charge density (Qox) and the interface state density (Dit) extracted from the conventional electrical characterization method. It reveals that the initial SHG signal linearly decreases with the increase in Qox, while Dit is linearly correlated to the characteristic time constant. It verifies that the TD-SHG is a sensitive and fast method, as well as simple and noncontact, for evaluating the interface quality of oxide/Si heterostructures, which may facilitate the in-line semiconductor test.

Robustness of linear bands in epitaxial planar silicene heterostructure against surface doping

In this study, we investigate the electronic structure of epitaxial planar silicene heterostructure grown on ultrathin gold films on the Si(111) substrates, covered by 0.1 monolayer of silver, antimony and lead. Angle-Resolved Photoemission Spectroscopy measurements reveal that the electronic structure of planar silicene, that shows bands with linear dispersion, remains largely unaffected by the presence of these dopants, with only a slight energy shift observed in the case of antimony. Density functional theory calculations corroborate these experimental observations, confirming the robustness of the epitaxial planar silicene heterostructure against surface doping. The results suggest that the intrinsic electronic properties of planar silicene are well-protected against surface contamination.

Covalent Functionalization of Silicon with Plasma-Grown "Fuzzy" Graphene: Robust Aqueous Photoelectrodes for CO2 Reduction by Molecular Catalysts.

Carbon electrodes are ideal for electrochemistry with molecular catalysts, exhibiting facile charge transfer and good stability. Yet for solar-driven catalysis with semiconductor light absorbers, stable semiconductor/carbon interfaces can be difficult to achieve, and carbon's high optical extinction means it can only be used in ultrathin layers. Here, we demonstrate a plasma-enhanced chemical vapor deposition process that achieves well-controlled deposition of out-of-plane "fuzzy" graphene (FG) on thermally oxidized Si substrates. The resulting Si|FG interfaces possess a silicon oxycarbide (SiOC) interfacial layer, implying covalent bonding between Si and the FG film that is consistent with the mechanical robustness observed from the films. The FG layer is uniform and tunable in thickness and optical transparency by deposition time. Using p-type Si|FG substrates, noncovalent immobilization of cobalt phthalocyanine (CoPc) molecular catalysts was employed for the photoelectrochemical reduction of CO2 in aqueous solution. The Si|FG|CoPc photocathodes exhibited good catalytic activity, yielding a current density of ∼1 mA/cm2, Faradaic efficiency for CO of ∼70% (balance H2), and stable photocurrent for at least 30 h at -1.5 V vs Ag/AgCl under 1-sun illumination. The results suggest that plasma-deposited FG is a robust carbon electrode for molecular catalysts and suitable for further development of aqueous-stable Si photocathodes for CO2 reduction.

A scandium doped aluminum nitride thin film bulk acoustic resonator

Currently, we stand at the forefront of revolutionary advancements in communication technology. The escalating demands of advanced communication necessitate enhanced performance from materials and radio frequency devices. This paper aims to enhance film performance by depositing scandium-doped aluminum nitride (ScAlN) directly onto a Si substrate. Additionally, ScAlN was deposited on SiO2/AlN/Mo functional layers for comparison purposes. The ScAlN directly deposited on Si demonstrated superior performance in terms of crystalline quality and surface roughness, with a full width at half maximum of 1.7° and a roughness of 1.76 nm. Furthermore, a film bulk acoustic resonator (FBAR) based on the ScAlN film directly deposited on Si was successfully fabricated through thin-film transfer, with critical processes achieved via bonding and wet-etching of the substrate. The ScAlN in the fabricated resonator exhibited a favorable c-axis preferred orientation. The resulting ScAlN-based FBAR displayed a quality factor of 429. This study lays the groundwork for exciting opportunities in the development of higher-performance piezoelectric materials and devices.

Low‐Defect Quantum Dot Lasers Directly Grown on Silicon Exhibiting Low Threshold Current and High Output Power at Elevated Temperatures

The direct growth of III‐V materials on silicon is a key enabler for developing monolithically integrated lasers, offering substantial potential for ultradense photonic integration in vital communications and computing technologies. However, the III‐V/Si lattice and thermal expansion mismatch pose significant hurdles, leading to defects that degrade lasing performance. This study overcomes this challenge, demonstrating InAs/GaAs‐on‐Si lasers that perform on par with top‐tier lasers on native GaAs substrates. This is achieved through a newly developed epitaxial approach comprising a series of rigorously optimized growth strategies. Atomic‐resolution scanning tunneling microscopy and spectroscopy experiments reveal exceptional material quality in the active region and elucidate the impact of each growth strategy on defect dynamics. The optimized III‐V‐on‐silicon ridge‐waveguide lasers demonstrate a continuous‐wave threshold current as low as 6 mA and high‐temperature operation reaching 165 °C. At 80 °C, critical for data center applications, they maintain a 12 mA threshold and 35 mW output power. Furthermore, lasers fabricated on both Si and GaAs substrates using identical processes exhibit virtually identical average threshold current. By eliminating the performance limitations associated with the GaAs/Si mismatch, this study paves the way for robust and high‐density integration of a broad spectrum of critical III‐V photonic technologies into the silicon ecosystem.

Native Oxide Layer Role during Cryogenic‐Temperature Ion Implantations in Germanium

Herein, the structural properties and chemical composition of Ge samples implanted with tellurium at cryogenic temperatures are analyzed, focusing on the role of the native oxide. For germanium, cryogenic‐temperature implantation is a requirement to achieve hyperdoped impurity concentrations while simultaneously preventing surface porosity. In this work, the critical role of the thin native germanium oxide is demonstrated when performing ion implantations at temperatures close to the liquid nitrogen temperature. The structural and chemical composition of tellurium‐implanted samples as a function of the implanted dose from 5 × 1014 to 5 × 1015 cm−2 is analyzed. After a laser melting process, the incorporated oxygen is diffused to the surface forming again a GeOx layer which retains a large fraction of the total implanted dose. These detrimental effects can be eliminated by a selective etching of the native oxide layer prior to the ion implantation process. These effects have been also observed when implanting on Si substrates. This work identifies key aspects for conducting implantations at cryogenic temperatures, that are otherwise negligible for ion implanting at room temperature.

Native Oxide Layer Role during Cryogenic‐Temperature Ion Implantations in Germanium

Herein, the structural properties and chemical composition of Ge samples implanted with tellurium at cryogenic temperatures are analyzed, focusing on the role of the native oxide. For germanium, cryogenic‐temperature implantation is a requirement to achieve hyperdoped impurity concentrations while simultaneously preventing surface porosity. In this work, the critical role of the thin native germanium oxide is demonstrated when performing ion implantations at temperatures close to the liquid nitrogen temperature. The structural and chemical composition of tellurium‐implanted samples as a function of the implanted dose from 5 × 1014 to 5 × 1015 cm−2 is analyzed. After a laser melting process, the incorporated oxygen is diffused to the surface forming again a GeOx layer which retains a large fraction of the total implanted dose. These detrimental effects can be eliminated by a selective etching of the native oxide layer prior to the ion implantation process. These effects have been also observed when implanting on Si substrates. This work identifies key aspects for conducting implantations at cryogenic temperatures, that are otherwise negligible for ion implanting at room temperature.

Stable chalcogenide Ge-Sb-Te heterostructures with minimal Ge segregation.

Matching of various chalcogenide films shows the advantage of delivering multilayer heterostructures whose physical properties can be tuned with respect to the ones of the constituent single films. In this work, (Ge-Sb-Te)-based heterostructures were deposited by radio frequency sputtering on Si(100) substrates and annealed up to 400°C. The as-deposited and annealed samples were studied by means of X-ray fluorescence, X-ray diffraction, scanning transmission electron microscopy, electron energy loss spectroscopy and Raman spectroscopy. The heterostructures, combining thermally stable thin layers (i. e. Ge-rich Ge5.5Sb2Te5, Ge) and films exhibiting fast switching dynamics (i. e. Sb2Te3), show, on the one side, higher crystallization-onset temperatures than the standard Ge2Sb2Te5 alloy and, on the other side, none to minimal Ge-segregation.

Stable chalcogenide Ge-Sb-Te heterostructures with minimal Ge segregation.

Matching of various chalcogenide films shows the advantage of delivering multilayer heterostructures whose physical properties can be tuned with respect to the ones of the constituent single films. In this work, (Ge-Sb-Te)-based heterostructures were deposited by radio frequency sputtering on Si(100) substrates and annealed up to 400°C. The as-deposited and annealed samples were studied by means of X-ray fluorescence, X-ray diffraction, scanning transmission electron microscopy, electron energy loss spectroscopy and Raman spectroscopy. The heterostructures, combining thermally stable thin layers (i. e. Ge-rich Ge5.5Sb2Te5, Ge) and films exhibiting fast switching dynamics (i. e. Sb2Te3), show, on the one side, higher crystallization-onset temperatures than the standard Ge2Sb2Te5 alloy and, on the other side, none to minimal Ge-segregation.

Improving the ferroelectric properties of Lu doped Hf0.5Zr0.5O2 thin films by capping a CeO x layer

Lu doped Hf0.5Zr0.5O2 (HZO) ferroelectric films were prepared on Pt/TiN/SiO2/Si substrate by chemical solution deposition method, and an interfacial engineering strategy for improving the ferroelectric property was explored by capping the Lu doped HZO films with a cerium oxide layer. Compared with the Lu doped HZO film without the CeO x coating layer, the Lu doped HZO film with the CeO x coating layer has a larger remanent polarization (2P r = 34.72 µC cm−2) and presents weaker wake-up behavior, which result from the higher orthogonal phase ratio and the lower oxygen vacancy of the CeO x coated Lu doped HZO film. In addition, the CeO x coating can remarkably improve the fatigue resistance and retention performance of the Lu doped HZO films. It is hoped that the results can provide an effective approach for the realization of high-performance and highly reliable hafnium oxide based ferroelectric thin films.

Nucleation of InP on Si under Micro-Crucibles at Ultra-High Vacuum using a Two-Step VLS Process

Abstract We reported nucleation mechanisms of InP directly on Si (8% lattice mismatch) under confined structures, called micro-crucibles, at ultra-high vacuum (UHV) by chemical beam epitaxy (CBE). These micro-crucibles are used to induce lateral growth in the presence of a micro-scale Au catalyst. It is found that at this UHV condition, the kinetics is dictated predominantly by adatom surface diffusion. Using a two-step growth process ((1) In-only exposure, then, (2) simultaneous In and P exposures), InP islands have been successfully nucleated on Si substrates under micro-crucible structures. The nucleation of these InP islands strongly depends on the metal catalyst location relative to the micro-crucible opening with metal catalysts residing closer to the opening having a higher chance to get incorporated with In and P atoms. Importantly, we found that using smaller micro-crucibles with double openings can increase the possibility of having metal catalysts reside near either opening and nucleate InP under micro-crucibles.

Efficient In Situ Doping of Strained Germanium Tin Epilayers at Unusually Low Temperature

AbstractEfficient p‐ and n‐type in situ doping of compressively strained germanium tin (Ge1‐xSnx) semiconductor epilayers, grown by chemical vapor deposition on a standard Si(001) substrate, is demonstrated. Materials characterization results reveal unusual impact of dopants manifesting via a pronounced reduction of Sn content in the epilayer, accompanied by an enhancement of the growth rate, due to increasing p‐type doping concentration. Furthermore, the opposite behavior for n‐type doping is observed, resulting in a less pronounced increase of Sn concentration and no effect on growth rate. Nevertheless, a very high density of electrically active holes up to ≈4 × 1020 cm−3 is obtained in p‐type doped Ge1‐xSnx epilayer resulting in the lowest resistivity of 0.15 mΩ cm among all in situ doped epitaxial and strained group‐IV semiconductors. Also, the metal‐to‐insulator transition in Ge1‐xSnx is experimentally demonstrated for doping levels above 1 × 1017 cm−3, which is substantially lower than in any group‐IV semiconductor, and theoretically predict it to be as low as ≈1 × 1017 cm−3. The findings enabled by the doping regime explored in this work can open novel prospects to engineer low resistivity contacts and charge current injection in applications covering next‐generation transistors, qubits, diodes, electrically driven light sources, sensors and hybrid quantum devices.

Study of temperature-dependent copper iodide thin film by thermal evaporation system

Abstract The development of heterostructure devices has gained significant attention towards scientific communities in the present time. This article reports on the effective use of the horizontal thermal evaporation (TE) method to successfully fabricate copper iodide (CuI) films on silicon (Si) substrates. By using the TE technique, CuI-based heterojunctions have been fabricated here. CuI exhibits semiconductor qualities of the p-type, making it a promising option for optoelectronic devices in the future. The temperature was varied from room temperature (RT) to 230 °C to synthesise the CuI/Si heterojunction. The structural, morphological, optical, and electrical analyses have been carried out with various substrate temperatures. The X-ray diffraction (XRD) data show that CuI films have demonstrated a polycrystalline character and have lattice parameters of 6.03 Å. The Raman spectroscopy study shows the microstructural analysis of CuI films. The field emission scanning electron microscopy (FESEM) study reveals the variation of grain size and shape with synthesis temperature. The atomic force microscope (AFM) was used to estimate the surface roughness. The CuI films were found to be p-type by the Hall effect measurement. The sample synthesised at 130 °C shows the highest mobility of 83.12 cm2 V-1 s-1 with a carrier concentration of 1019 cm-3. The UV-visible (UV-Vis) spectroscopy measurements show good absorption of UV light by the CuI thin films. The CuI/Si heterojunctions are rectifying, as demonstrated by the I-V measurements, and they respond well to UV light irradiation.

Electroplating of Palladium‐Based Integrated Reactive Multilayer Systems (iRMS)

Bonding with integrated reactive material systems enables joining of heterogeneous substrates at room temperature. The increasing diversity of electronic modules raises the demand for low temperature bonding processes for heat sensitive components. In this article, fundamental steps for the deposition of Pd/In multilayers from a single bath electrolyte are presented. It furthermore describes the deposition of Pd/Sn reactive multilayers for bonding application on ceramic substrates and introduces a new semi‐automated plating tool for Pd/Sn multilayers. The Pd/Sn multilayers can be deposited reproducible on silicon and ceramic substrates. While a bilayer period of 425 nm enables stable ignition and bonding of Si substrates, the bilayer period for ceramics has to be increased to 620 nm to compensate the higher heat dissipation into the substrate. By integrating 2.5–9 μm thick Sn compensation layers beneath the integrated reactive multilayer systems (iRMS) to smoothen the surface profile of the printed metallization and improved bonding processes with wedge compensation, a homogeneous bond along the whole interface can be achieved.

Epitaxial Growth of the Large-Scale, Highly-Ordered 3D GaN-Truncated Pyramid Array Toward an Ultrahigh Rejection Ratio and Responsivity Visible-Blind Ultraviolet Photodetection.

The micro- and nanostructures of III-nitride semiconductors captivate strong interest owing to their distinctive properties and myriad potential applications. Nevertheless, challenges endure in managing the damage inflicted on crystals through top-down processes or achieving extensive control over the large-area growth of these microstructures via bottom-up methods, thereby impacting their optical and electronic properties. Here, we present novel epitaxially grown 3D GaN truncated pyramid arrays (TPAs) on patterned Si substrates, devoid of any catalyst. These GaN TPAs feature highly ordered, large-scale structures, attributed to the utilization of 3D Si substrates and thin AlN interlayers to alleviate epitaxial strains and limit dislocation formation. Comprehensive characterization via scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and cathodoluminescence attests to the superior structural and optical attributes of these crystals. Furthermore, photoluminescence and ultraviolet (UV)-visible diffuse reflectance spectroscopy reveal sharp band-edge emission and significant light trapping in the UV bands. Employing these GaN TPAs, we constructed metal-semiconductor-metal visible-blind UV photodetectors (PDs) incorporating Ti3C2 MXene as Schottky electrodes. These PDs display exceptional responsivity, achieving 5.32 × 103 mA/W at 255 nm and an ultrahigh UV/visible rejection ratio (R255nm/R450nm) approaching 106, which are 1-2 orders of magnitude higher than most recently reported works. This exploration showcases novel GaN-based microstructures characterized by uniformity, ordered geometry, and exemplary crystalline integrity, paving the way for developing optoelectronic applications.