N-type Substrates Research Articles

Performance Comparison of Al2O3 Gate Dielectric Grown on 4H-SiC Substrates via Thermal and Plasma-Enhanced Atomic Layer Deposition Methods

Abstract This study systematically compared the material and electrical properties of Al2O3 films deposited on n-type 4H-SiC substrates using thermal and plasma-enhanced atomic layer deposition (ALD), referred to as PE-Al2O3 and T-Al2O3, respectively. Atomic force microscopy data indicates that the roughness of Al2O3 deposited on SiC substrates by both ALD procedures is low. X-ray photoelectron spectroscopy analysis suggests that the proportion of hydroxides on T-Al2O3 surfaces is greater than that on PE-Al2O3. Based on O 1s energy loss spectra and fitting of absorption spectra, the bandgap of Al2O3 films ranges from 6.1 to 6.2 eV, with PE-Al2O3 exhibiting a slightly higher bandgap. As for C-V data analysis of MOS capacitors, PE-Al2O3/SiC possesses a lower interface defect density and border traps in oxide layer than T-Al2O3/SiC. Further I-V testing demonstrates that the breakdown field of PE-Al2O3 is 8.7 MV/cm, with leakage current maintained at the order of 10-8 A/cm2. In contrast, T-Al2O3 displays a breakdown field of 7.2 MV/cm and a significant “soft” breakdown. The effective barrier height of PE-Al₂O₃/SiC is determined to be 1.10 eV based on Fowler-Nordheim tunneling mechanism fitting, which is greater than 0.952 eV for T-Al2O3. These results confirm the advantages of using the PEALD method.

Dual Influence of Size and Electric Field on Gold Nanoparticles: Insights into 2D Monolayer Assembly.

Self-assembled gold nanoparticles (Au-NPs) possess distinctive properties that are highly desirable in diverse nanotechnological applications. This study meticulously explores the size-dependent behavior of Au-NPs under an electric field, specifically focusing on sizes ranging from 5 to 40 nm, and their subsequent assembly into 2D monolayers on an n-type silicon substrate. The primary objective is to refine the assembly process and augment the functional characteristics of the resultant nanostructures. Utilizing a multifaceted analytical approach encompassing X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDXS), atomic force microscopy (AFM), and COMSOL multiphysics simulation, this work yields comprehensive insights. Results reveal that the electric field and nanoparticle size critically influence assembly dynamics due to variations in surface energy and electrostatic interactions. Larger Au-NPs (20, 30, and 40 nm) experience enhanced dipolar interactions and more substantial polarizability, enabling more efficient alignment and organization under an applied electric field. This leads to the formation of structured, uniform monolayers with minimal vacancies and smoother surfaces. In contrast, smaller Au-NPs (5, 10, and 15 nm) exhibit lower polarizability, which hampers alignment and promotes clustering and voids. XRD analysis delineates notable disparities in peak intensities and positions: smaller Au-NPs exhibit diminished (111) peak intensities, indicative of uneven distribution and crystallinity, whereas larger particles manifest higher intensities and well-defined peaks across multiple crystallographic planes. SEM images portray diverse surface coverages with AFM corroborating that larger Au-NPs achieve uniform and continuous monolayers with minimal height variations. COMSOL simulations substantiate these findings by illustrating the efficient alignment and settling of larger Au-NPs under the electric field. This study bridges critical gaps in understanding how nanoparticle size modulates assembly dynamics and the resultant properties of 2D Au-NP monolayers, offering pivotal insights into engineering advanced nanostructured materials tailored to specific applications in electronics, coatings, photonics, and catalysis.

Oxygen Partial Pressure Effect on Nickel Oxide Thin Films and NiO/Si Diode Performance

In this work, nickel oxide thin films were grown on glass and n-type Si substrates using RF-magnetron sputtering in an oxygen-rich environment. The effects of elevated oxygen on the optical...

Study of the photoluminescence properties as a function of the temperature of porous silicon layer obtained from an N-type substrate

Study of the photoluminescence properties as a function of the temperature of porous silicon layer obtained from an N-type substrate

Tailoring Superatomic Stability with Transition Metals in Silicon Cages: Shrinking to M@Si15 (M = Re, Os, Ir).

The design of materials with intriguing electronic properties is crucial for advancing nanoscale technologies, where precise control over atomic structure and electronic behavior is essential. Metal-encapsulating silicon cage superatoms (SAs) provide a new paradigm for molecular-scale material design, allowing fine-tuning of both structure and electronic characteristics. The formation of superatoms mimicking halogens, noble gases, and alkali metals has been well-studied, particularly with M@Si16, where early transition metals from groups 3 to 5 stabilize within a Si16 cage, achieving a 68-electron configuration. For late transition metals with excess electrons, a Si15 cage offers enhanced stability by fulfilling the 68-electron rule with one fewer Si atom. This research synthesizes Si15 cage-SAs with rhenium (Re) from group 7 and iridium (Ir) from group 9 on p-type and n-type organic substrates. The stability of Re@Si15 and Ir@Si15 is evaluated via oxidative reactivity with X-ray photoelectron spectroscopy and theoretical calculations, including osmium (Os) from group 8. Re@Si15-, Os@Si150, and Ir@Si15+ exhibit superatomic behaviors similar to halogens, noble gases, and alkali metals due to the 68-electron shell closure. Among them, Re@Si15- on p-type organic substrates shows superior electronic and geometric properties. These findings advance our understanding of M@Sin systems for transition metals, addressing longstanding questions about their properties at n = 15 and 16.

Cost-effective self-powered heterostructure π-SnS/Si photodetector with superior sensitivity for near-infrared light

Photodetectors generally require external power supplies to facilitate the separation of charge carriers and the generation of photocurrents. This significantly enlarges the device's dimensions and weight, limiting its applicability in real-time medical therapy monitoring and wireless environmental sensing. To address this limitation, extensive research focuses on developing self-powered photodetectors that operate autonomously without external power sources. The heterojunction structure photodetector, characterized by a sufficient built-in potential, facilitates the separation of photo charge carriers and the generation of photocurrent, leading to self-powered photodetectors. In this study, a novel and straightforward heterostructure photodetector was developed using a tin monosulfide (π-SnS) film and silicon (Si). This device exhibited a barrier height of 0.82 eV, which effectively separates photogenerated carriers and results in a highly sensitive (5.7 × 104) self-powered photodiode for near-infrared light. The SnS film was deposited onto an n-type Si wafer substrate using a simple and cost-effective chemical bath deposition method. The photoresponse characteristics were controlled and tuned by adjusting the operating bias voltage and illumination power density. At a bias voltage of 5 V, the photodiode demonstrated high responsivity (3863 mA/W) and detectivity (7.2 × 1011 Jones). The π-SnS/Si self-powered heterojunction photodetector, with its superior sensitivity, holds promise for advancing the technological implementation of optoelectronic devices.

Free-standing n-type phosphorus-doped diamond

n-type diamond substrates are highly desired for diamond electronics and quantum technology based on NV centers. In this work, we investigate the high growth rates obtained using plasma with high-power densities in a commercial bell-jar chemical vapor deposition reactor equipped with a gas panel for diamond doping with phosphorus impurities. We evidence that the diamond growth rate is increased by adding phosphorus precursor in the gas mixture, up to 21.6 μm/h. We found conditions for growing extremely thick (up 580 μm) phosphorus doped (100) diamond homoepilayers keeping a n-type character as shown by optical spectroscopy. From such films we succeed in slicing a free-standing phosphorus-doped diamond plate, showing the feasibility of n-type diamond substrate fabrication for further use in optoelectronics and quantum devices.

Nanometer-thick TiO2 channel thin film transistors as radical monitors for plasma enhanced atomic layer deposition

Nanometer-thick-TiO2-channel thin-film transistors (TFTs) are examined as oxidizing-agent monitors for room-temperature atomic layer deposition (RTALD). RTALD is a plasma-based process using plasma-excited humidified argon where OH radicals oxidize the precursor-gas adsorbed surface. In the TFT, the anatase TiO2 channel, with a thickness of 16 nm, is attached to a 300 nm thick gate capacitor of SiO2, while the channel surface is exposed to the ALD ambient. A heavily doped n-type Si substrate attached to the gate SiO2 is used as the gate electrode. The gate width and length are 1000 and 60 μm, respectively. When the TFT is installed in the RTALD chamber, the drain-current waveform is recorded in the course of the metal organic gas adsorption, evacuation of the residual gas, oxidization, and evacuation. In the present study, three kinds of metal organic (MO) precursors, tetrakis(dimethyl)amino titanium, tris(dimethyl)amino silane, and trimethyl aluminum are examined. The drain current exhibits strong responses upon the exposure of the plasma excited humidified argon. This suggests that OH radicals in the plasma might oxidize the adsorbed MO precursors to produce the OH moieties, where the surface polarization of OH moieties might enhance channel conductivity. The experimental results suggest the applicability of the present TFT as a plasma monitor in RTALD.

Time-resolved cathodoluminescence measurement of the effects of α -particle-related damage on minority hole lifetime in free-standing n-GaN

Time-resolved cathodoluminescence using 30 keV ultrafast electron pulses has been used to perform direct measurements of the minority hole lifetime τh as a function of 3.7 MeV α-particle fluence in high-quality free-standing n-type GaN substrates. The lifetime damage factor K calculated from these measurements was found to monotonically decrease from 6.9 × 10−2 to 6.4 × 10−4 cm2 s−1 ion−1 with increasing α-fluence from 108 to 1012 cm−2, implying a reduction in trap cross section and/or an aggregation of α-induced traps. The small, ∼200–300 nm, hole diffusion length estimated from the minority hole lifetime for the highest α-fluence necessitates the deployment of α-voltaic device strategies and architectures that emphasize depletion and drift over diffusion for effective charge collection and optimal power conversion efficiency.

Substrate Induced p-n Transition for Inverted Perovskite Solar Cells.

The p- or n-type property of semiconductor materials directly determine the final performance of photoelectronic devices. Generally, perovskite deposited on p-type substrate tends to be p-type, while perovskite deposited on n-type substrate tends to be n-type. Motived by this, a substrate-induced re-growth strategy is reported to induce p- to n-transition of perovskite surface in inverted perovskite solar cells (PSCs). p-type perovskite film is obtained and crystallized on p-type substrate first. Then an n-type ITO/SnO2 substrate with saturated perovskite solution is pressed onto the perovskite film and annealed to induce the secondary re-growth of perovskite surface region. As a result, p- to n-type transition happens and induces an extra junction at perovskite surface region, thus enhancing the built-in potential and promoting carrier extraction in PSCs. Resulting inverted PSCs exhibit high efficiency of over 25% with good operational stability, retaining 90% of initial efficiency after maximum power point (MPP) tracking for 800h at 65°C with ISOS-L-2 protocol.

Fully vertical AlN-on-SiC Schottky barrier diodes

We demonstrated fully vertical Schottky barrier diodes (SBDs) that have a Si-doped AlN drift layer directly grown on an n-type 4H-SiC substrate by metal-organic CVD. The AlN SBD with a Ni anode showed a clear rectifying characteristic at 300–500 K and a rectification ratio of about 10–2. We found that the leakage current of the vertical AlN-on-SiC devices is affected by defects in the AlN drift layer and Schottky interface.

Investigation of the performance and stability of self-powered polythiophene-based photodiodes under UV and visible light illumination

In this study, we fabricated polythiophene (PTh) and silver-decorated polythiophene (Ag@PTh) films on n-type silicon substrates using the electrochemical deposition method to investigate their electrical and photoelectrical properties in metal/interlayer/n-Si heterostructures under various conditions. The physical properties of the films were comprehensively investigated through UV-Vis, Raman, XPS and SEM analysis. The results from these analyses confirmed the successful deposition and formation of the films on the n-Si substrates. Additionally, a comparison of the current-voltage (I-V) characteristics of the PTh/n-Si and Ag@PTh/n-Si devices was conducted under both dark conditions and illumination with visible and UV light. While both devices exhibited typical rectifying diode behavior, the Ag@PTh/n-Si device demonstrated greater rectification with a RR of 2.49 x 105 at ± 2 V under dark conditions. In addition, the Ag@PTh/n-Si device, with self-powered property, displayed notably enhanced performance metrics, including a significantly higher ON/OFF ratio, responsivity, and detectivity, particularly evident under UV light illumination when compared to white light. Furthermore, to assess the long-term reliability of these devices, stability tests were conducted by repeating the I-V measurements after 90 days under identical conditions. The Ag@PTh/n-Si device exhibited considerably better stability over time than the PTh/n-Si device, maintaining consistent performance without notable degradation. So, in light of the findings, it can be concluded that the Ag@PTh/n-Si device has substantial potential for advancing optoelectronic technology.

Exploration of room temperature magnetodielectric behavior in Nd0.5Dy0.5FeO3 thin films and transmission line resonators in GHz frequency range

This study explores the room-temperature magnetodielectric (MD) and magnetoresistance (MR) properties of Nd0.5Dy0.5FeO3 thin films on n-type silicon substrates from 4 Hz to 2 MHz. The observed MD effect registers a change of ∼23 %, and the MR effect manifests a change of ∼11 % when subjected to an applied magnetic field of 2.5 T at a frequency of 177 Hz. Interestingly, the MD effect was absent at 1 T across all frequencies. However, we observed an MR of 6 % at 1 T, implying the possibility of an intrinsic MD effect or the co-existence of both intrinsic and extrinsic contributions to the MD effect. To comprehensively gauge the dielectric properties of the thin film at higher frequencies, a 5-GHz microstripline resonator was fabricated. Coupled with experimental data and simulations, this study reveals a dielectric constant of ∼56 for the Nd0.5Dy0.5FeO3 thin film at 5 GHz and 300 K.

Facile synthesis and characterization of Cu2Se thin films and self-powered p-Cu2Se/n-Si heterojunction with high-performance photoresponse

A facile, cost-effective, and scalable chemical vapor deposition technique was used to synthesize p-type Cu2Se thin films on glass and n-type Si substrates. Thorough characterization confirmed the films’ β-phase structure with the correct stoichiometric ratio and exceptional crystalline quality, exhibiting behavior akin to a degenerate semiconductor. Measurements unveiled a work function of 4.83 eV and a bandgap of 2.13 eV for Cu2Se. The fabrication of a p-Cu2Se/n-Si heterojunction was achieved by depositing the p-type Cu2Se thin film onto the n-type Si substrate. The resulting heterostructure displayed rectification behavior, and its energy band diagram resembled a Schottky diode. Further exploration into its photoelectric properties showcased the p-Cu2Se/n-Si heterostructure’s favorable self-powered attribute, characterized by fast, steady, reproducible, sensitive, and robust photoresponsive performance. Consequently, it proves highly suitable for applications in high-frequency photodetectors. Additionally, the p-Cu2Se/n-Si heterojunction’s photovoltaic power conversion efficiency exceeded the reported values of the CuO/Si and Cu2O/Si systems. Here, this study contributes significantly to the pivotal evaluation of p-Cu2Se/n-Si heterostructures for promising optoelectronic applications.

Correlation between photoluminescence and radiative defects in silicon oxycarbide films due to the growth temperature effect

In this work, the effect of growth temperature (678–988 °C) on silicon oxycarbide (SiCxOy) samples obtained by hot filament chemical vapor deposition (HFCVD) is reported. The samples were deposited on silicon (Si) n-type (100) and quartz substrates for optical and structural studies. At a lower temperature (678 °C), silicon oxycarbide powders were formed on Si substrates due to the homogeneous reaction occurring in the gas phase. However, for temperatures between 804 and 988 °C, silicon oxycarbide films were formed on Si substrates. By changing the temperature from 678 to 988 °C, both carbon (C) concentration (21.2–17.7 wt.%) and the relative percentage of Si–C bond density (%RtSi-C = 11.34–3.47 %) decreased, as demonstrated by EDS and FTIR measurements, respectively. On the other hand, the content of relative Si–O–Si bonds located around 1060 cm−1 remained dominant in all cases, resulting in SiCxOy films with an amorphous SiOx-type structure. These films exhibited strong photoluminescence (PL) centered in the blue region (∼3 eV), where Si–NOVS radiative centers were preferentially responsible for PL emission. At a lower temperature (678 °C), the PL intensity decreased. The determination of optical bandgap energy (Eopt) using Tauc Plots coincided with the emission due to luminescent centers (∼3 and ∼2.7 eV) observed in PL, indicating that the radiative transitions were due to defects. The AFM measurements showed an increase in roughness from 5.01 to 16.20 nm as the growth temperature decreased, as expected according to SEM measurements.

Structural and optical properties of epitaxial ScxAl1−xN coherently grown on GaN bulk substrates by sputtering method

Three scandium aluminum nitride (ScAlN) thin films with different Sc compositions of 6%, 10%, and 14% were heteroepitaxially grown on n-type GaN bulk substrates by a low-temperature sputtering method. Atomically flat and smooth surfaces were observed by atomic force microscopy. The ScAlN films were coherently grown on GaN, and the c-axis lattice constants increased with increase in the Sc composition, confirmed by x-ray diffraction. The refractive index and the extinction coefficient of ScAlN were extracted by variable angle spectroscopic ellipsometry. The refractive index slightly increased and the extinction coefficient showed red shift with increase in the Sc composition. The optical bandgap of the ScAlN films was also extracted, which slightly shrunk with increase in the Sc composition.

Van der Waals epitaxial growth of few layers WSe2 on GaP(111)B

2D material epitaxy offers the promise of new 2D/2D and 2D/3D heterostructures with their own specific electronic and optical properties. In this work, we demonstrate the epitaxial growth of few layers WSe2 on GaP(111)B by molecular beam epitaxy. Using a combination of experimental techniques, we emphasize the role of the growth temperature and of a subsequent annealing of the grown layers under a selenium flux on the polytype formed and on its structural and morphological properties. We show that a low growth temperature promotes the formation of the 1T′ and 3R phases depending on the layer thickness whereas a higher growth temperature favours the stable 2H phase. The resulting layers exhibit clear epitaxial relationships with the GaP(111)B substrate with an optimum grain disorientation and mean size of 1.1° and around 30 nm respectively for the 2H phase. Bilayer 2H WSe2/GaP(111)B heterostructures exhibit a staggered type II band alignment and p-doped character of the epi-layer on both p and n-type GaP substrates. This first realisation of stable p-type WSe2 epi-layer on a large-area GaP(111)B substrate paves the way to new 2D/3D heterostructures with great interests in nanoelectronic and optoelectronic applications, especially in the development of new 2D-material p-n junctions.

Enhanced photocatalytic U(VI) reduction via double internal electric field in CoWO4/covalent organic frameworks p-n heterojunction

Photoreduction of highly toxic U(VI) to less toxic U(IV) is crucial for mitigating radioactive contamination. Herein, a CoWO4/TpDD p-n heterojunction is synthesized, with TpDD serving as the n-type semiconductor substrate and CoWO4 as the p-type semiconductor grown in situ on its surface. The Fermi energy difference between TpDD and CoWO4 provides the electrochemical potential for charge-hole separation. Moreover, the Coulombic forces from the distinct carrier types between the two materials synergistically facilitate the transfer of electrons and holes. Hence, an internal electric field directed from TpDD to CoWO4 is established. Under photoexcitation conditions, charges and holes migrate efficiently along the curved band and internal electric field, further enhancing charge-hole separation. As a result, the removal capacity of CoWO4/TpDD increases from 515.2 mg/g in the dark to 1754.6 mg/g under light conditions. Thus, constructing a p-n heterojunction proves to be an effective strategy for remediating uranium-contaminated environments.

Laser ablation fingerprint in low crystalline carbon nanotubes: A structural and photothermal analysis

Carbon nanotubes (CNT) hold promise as photothermal materials due to their cost-effectiveness, stability, and broad optical absorbance. Here, we investigate the structural and morphological modifications in low-crystalline vertically aligned CNT synthetized via chemical vapor deposition on n-type Si substrates at 750 °C, followed by annealing treatment with near-infrared laser radiation. Raman spectroscopy revealed laser-induced amorphous regions, facilitating identification of ablation thresholds. Time-dependent nonlinear photothermal emission, associated with CNT ablation, showed a stable thermodynamic equilibrium with broad-band radiation from an electron-hole plasma. We propose a model based on Raman spectra and positional scans of the ablation fingerprint, enabling correlation with the beam temperature profile. This study offers insights into laser beam characterization, with potential applications in plasma and optics disciplines.

Influence of the Incorporation of Nd in ZnO Films Grown by the HFCVD Technique to Enhance Photoluminiscence Due to Defects

In this work, optical–structural and morphological behavior when Nd is incorporated into ZnO is studied. ZnO and Nd-doped ZnO (ZnO-Nd) films were deposited at 900 °C on Silicon n-type substrates (100) by using the Hot Filament Chemical Vapor Deposition (HFCVD) technique. For this, pellets were made by from powders of ZnO(s) and a mixture of ZnO(s):Nd(OH)3(s). The weight percent of the mixture ZnO:Nd(OH)3 in the pellet is 1:3. The gaseous precursor generation was carried out by chemical decomposition of the pellets using atomic hydrogen which was produced by a tungsten filament at 2000 °C. For the ZnO film, diffraction planes (100), (002), (101), (102), (110), and (103) were found by XRD. For the ZnO-Nd film, its planes are displaced, indicating the incorporation of Nd into the ZnO. EDS was used to confirm the Nd in the ZnO-Nd film with an atomic concentration (at%) of Nd = 10.79. An improvement in photoluminescence is observed for the ZnO-Nd film; this improvement is attributed to an increase in oxygen vacancies due to the presence of Nd. The important thing about this study is that by the HFCVD method, ZnO-Nd films can be obtained easily and with very short times; in addition, some oxide compounds can be obtained individually as initial precursors, which reduces the cost compared to other techniques. Something interesting is that the incorporation of Nd into ZnO by this method has not yet been studied, and depending on the method used, the PL of ZnO with Nd can increase or decrease, and by the HFCVD method the PL of the ZnO film, when Nd is incorporated, increases more than 15 times compared to the ZnO film.