Hydrogen Annealing Research Articles

Increased Mobility in 4H-SiC MOSFETs by Means of Hydrogen Annealing

Enhancement-mode 4H-SiC MOSFETs utilising an aluminium oxide (Al2O3) dielectric without the requirement for an underlying silicon oxide (SiO2) layer have been shown to have a field effect mobility of 150 cm2V−1s−1 and a subthreshold swing of 160 mV/dec. The fabricated devices utilised a forming gas (3% H2 in N2) anneal immediately prior to the deposition of the Al2O3 by Atomic Layer Deposition (ALD). A comparison MOSFET using an identical Al2O3 deposition process with a 0.7 nm SiO2 layer had a field effect mobility of approximately 20 cm2V−1s−1. The hydrogen annealed device had a lower density of interface traps (Dit), a lower subthreshold swing, and a significantly reduced hysteresis in the transconductance data than the thin SiO2 sample. This finding solves the issue of inconsistency of device performance using thin film gate dielectric as an interfacial layer by offering a simple and controllable process.

Synergy effect of microwave annealing and high-pressure hydrogen annealing on Poly-Si thin-film transistor

Grain boundary (GB) is a significant factor that deteriorates the transfer characteristics of poly-Si thin-film transistors (TFTs). In this study, we utilized the synergistic effect of microwave annealing (MWA) and high-pressure hydrogen annealing (HPHA) to effectively reduce grain boundary trap (GBT) density, resulting in improved field-effect mobility (μ) and subthreshold swing (SS). To investigate the synergistic effect of MWA and HPHA, the transfer characteristics of rapid thermal annealing and forming gas annealing devices were compared and analyzed as control devices. Furthermore, the mechanism of SS and mobility enhancement can be quantitatively understood by lowering the GB barrier height. In addition, Raman spectroscopy proved that poly-Si crystallinity was improved during MWA. Our results showed that MWA and HPHA play a vital role in reducing GBT density and improving poly-Si TFT characteristics.

Regulating the surface of anion-doped TiO2 nanorods by hydrogen annealing for superior photoelectrochemical water oxidation

Dedications to achieve the highly efficient metal oxide semiconductor for the photoelectrochemical water splitting system have been persisted to utilize the TiO2 as the promising photoanode material. Herein, we report notable progress for nanostructured TiO2 photoanodes using facile sequential one-pot hydrothermal synthesis and annealing in hydrogen. A photocurrent density of 3.04 mA·cm−2 at 1.23 V vs. reversible hydrogen electrode was achieved in TiO2 nanorod arrays annealed in hydrogen ambient, which is approximately 4.25 times higher than that of pristine TiO2 annealed in ambient air. 79.2% of incident photon-to-current efficiency at 380 nm wavelength demonstrates the prominence of the material at the near-UV spectral range region and 100 h chronoamperometric test exhibits the stability of the photoanode. Detailed studies regarding crystallinity, bandgap, and elemental analysis provide the importance of the optimized annealing condition for the TiO2-based photoanodes. Water contact angle measurement displays the effect of hydrogen annealing on the hydrophilicity of the material. This study clearly demonstrates the marked improvement using the optimized hydrogen annealing, providing the promising methodologies for eco-friendly mass production of water splitting photoelectrodes.Graphical

(Invited, Digital Presentation) Interface Charge Trapping and Scattering in SiC MOSFET Channels

The channel conductivity of SiC MOSFETs is severely limited by charge trapping at interface states and mobility limiting scattering processes. In this talk, the status of interface state passivation for both n- and p-channel 4H-SiC MOSFETs will be presented. First, results from capacitance-based methods to extract interface state density (Dit) across the entire 4H-SiC band gap for thermally grown nitrided silicon dioxide gate dielectrics will be presented, emphasizing the critical importance of the SiO2(N)/SiC interface composition and nitrogen bonding. Next, the scattering mechanisms for channel electrons and holes in these devices will be analyzed and contrasted by Hall measurements. [1] The transport will be characterized as a function of temperature and substrate-bias within an effective transverse electric field model. The final part of the talk will focus on latest development on deposited dielectrics for 4H-SiC. Deposited dielectrics are an attractive alternative to thermal oxidation as it minimizes the release of carbon and the perturbation of surface crystal structure and opens the possibility of ‘high-k’ dielectrics with higher permittivity than SiO2. Herein, the key importance of 4H-SiC surface control prior to dielectric deposition will highlighted using results obtained for atomic layer deposition (ALD) of Aluminum Oxide (Al2O3) [2]. To this end, a systematic variation of SiC surface termination with processes involving oxygen, hydrogen and nitrogen will be presented. The composition of the deposited films and the interfacial bonding will be characterized for various deposition processes and correleated with electrical measurements . It will be demonstrated that surface nitridation followed by H2 annealing prior to ALD results in a factor of 2 higher channel mobility than typical NO annealed thermal SiO2. This is due to the formation of stable sub-nm SiON layers that passivates the surface and enables the formation of high-quality interfaces between SiC and deposited dielectric. In addition, the results indicate that clean Si-H terminated surfaces formed by hydrogen etching and annealing, prior to dielectric deposition leads to uniform nucleation of Al2O3. The reduction of Dit is also accompanied by improvements in oxide charge trapping and bias instability, but dielectric leakage current is significantly higher for Al2O3 compared to SiO2 due to bulk trap-assisted tunneling in Al2O3. The reliability is a significant challenge that need to be overcome to exploit the enhanced mobilities and make deposited dielectrics competitive with traditional nitrided SiO2.Acknowledgments: The authors acknowledge support from the US Army Research Laboratory (grant ARMY-W911NF-18-2-0160) and US Department of Energy (subcontracted to National Renewable Energy Laboratory, grant NREL-AHL-9-92632-01). The authors also acknowledge the support Dr. Leonard C. Feldman (Auburn, Rutgers) and Mr. Hengfei Gu (Rutgers) for help with XPS measurements. The authors also deeply thank Ms. T Isaacs-Smith, Ms. Lu Wang (Auburn), Dr. K. Ramadoss and Dr. D. Morisette (Purdue Univ.) for useful discussions and help with fabrication.[1] S. Das et al., J. Appl. Phys. 130, 225701, (2021).[2] I. U. Jayawardhena et al., J. Appl. Phys. 129, 75702, (2021) Figure 1

Improvement of imaging performance of silicon micropore X-ray optics by ultra long-term annealing.

We have been developing a light-weight X-ray telescope using micro electro mechanical systems technologies for future space missions. Micropores of 20 µm width are formed in a 4-inch Si wafer with deep reactive ion etching, and their sidewalls are used as X-ray reflection mirrors. The flatness of the sidewall is an important factor to determine the imaging performance, angular resolution. It is known that hydrogen annealing is effective to smooth a Si surface. We tested 150 hour annealing to achieve the ultimately smooth sidewalls. After 50 hour, 100 hour, and 150 hour annealing, the angular resolution improved 10.3, 4.0, and 2.6 arcmin in full width at half maximum (FWHM) and 17.0, 14.5, and 10.8 arcmin in half-power width (HPW). In spite of this improvement, the edge shapes of the sidewall were rounded. Therefore, both edges of the sidewall were ground and polished, and then the angular resolution was improved further to 3.2 arcmin (FWHM) and 5.4 arcmin (HPW).

Large coercivity of 13 kOe in L10-ordered CoPt on Si/SiO2 substrates by hydrogen annealing

L10-ordered CoPt with a large coercivity (H c) of 13 kOe was demonstrated on Si/SiO2 substrates by hydrogen annealing. Equiatomic 11.2 nm thick (Co/Pt)4 multilayer thin films were fabricated by electron-beam evaporation and were annealed at 500 °C–900 °C for 10–90 min under an Ar/H2 mixed gas atmosphere. The annealing temperature and time dependences of the crystal structures, magnetic properties, and surface morphologies of the films were systematically analyzed based on the experimental results obtained from grazing incidence X-ray diffraction (GI-XRD), vibrating sample magnetometer, and scanning electron microscope, respectively. Hydrogen annealing effectively promoted the out-of-plane c-axis orientation of L10-ordered CoPt compared to the vacuum annealing according to the GI-XRD patterns. A maximum H c of 13.3 kOe was obtained in L10-ordered CoPt with angular-outlined isolated grains by hydrogen annealing at 800 °C for 60 min, where the c-axis of L10-ordered CoPt was randomly distributed.

Development of the ZnO:Ga nanorod arrays as an alpha particle scintillation screen for the associated particle neutron generator

The development of associated alpha particle scintillation screen that takes into account high spatial resolution, ultrafast temporal resolution, and high signal-to-noise ratio is the key to promote the “fingerprint” technology in the field of explosive detection—the deuterium–tritium (D–T) reaction associated particle neutron generator (APNG). Herein, the highly uniform and densely packed ZnO:Ga nanorod arrays, as designed alpha particle scintillation screen for the APNG, is proposed and prepared on a ZnO-seeded substrate by a radio frequency magnetron sputtering and hydrothermal method. The simulation results show that the theoretical cutoff thickness is 7.6 μm for 3.5 MeV alpha particles, and the increase in array spacing is conducive to suppress transverse light output and improve its light output efficiency and spatial resolution simultaneously. Through hydrogen annealing treatment, the slow decay component is completely suppressed and the integrated intensity of the fast decay component with a rising edge response of 1 ns is significantly enhanced by nine times.

Hydrogen implantation-induced blistering in diamond: Toward diamond layer transfer by the Smart Cut™ technique

The effect of H+ implantation and annealing of diamond (100) monocrystalline substrates has been studied by ToF-SIMS, cathodoluminescence, transmission spectroscopy and TEM. Blistering conditions suitable for the Smart Cut™ technology have been identified in monocrystalline diamond, using two sets of hydrogen implantation and annealing. A first hydrogen implantation followed by a first annealing leads to amorphization of a buried layer without hydrogen exodiffusion. Blisters and exfoliations appear at the surface of the diamond samples, after a second hydrogen implantation inside the pre-amorphized diamond layer and a final annealing, as evidenced by TEM and optical microscopy. Demonstration of hydrogen-induced blistering is a major step to adapt the Smart Cut™ process on diamond material. This process is compatible with wafer bonding before the second annealing and therefore open the way for thin diamond layer transfer on a bonded receiver wafer, still not achieved to date.

Hydrogen annealing induced physical properties of ZnTe thin films

The ZnTe material has an unprecedented role in the fabrication of high efficiency CdTe thin film solar cells and optimization of hydrogen annealing induced physical properties of ZnTe films is next required step. Consequently, in the present work, the impact of Hydrogen annealing temperature on the structural, optical, electrical, topographical, morphological, and compositional properties of ZnTe films is explored. The ZnTe thin films (having 300 nm thickness) are grown via electron-beam evaporation technique on glass and ITO substrates followed by annealing at different temperatures under a Hydrogen atmosphere. The ZnTe films are found to crystallize in cubic phase with (111) predominant peak having crystallite size in the range of 19–28 nm, whereas annealed films demonstrated lower optical transmittance vis-à-vis to pristine films. The PL spectra exhibit two luminescence peaks with a stronger band at ∼351 nm and a weaker band at ∼450 nm. Ohmic behavior of ZnTe films is assured through I–V characteristics, while the AFM images revealed hill-like surface topographies. The FESEM image of pristine films demonstrated a homogeneous surface comprising spherical grains whereas annealed films have spherical, stone, and blisters like morphologies. The EDS patterns assured the Te element richness as well as successful ZnTe films deposition. The observed findings signify that the Hydrogen annealing at different temperatures notably modified the physical properties of ZnTe films. • Hydrogen annealing induced physical properties of ZnTe films are investigated. • The crystallite size is augmented from 19 to 28 nm for hydrogenated ZnTe films. • The straight lines to I–V characteristics ensure formation of Ohmic contacts. • Direct optical energy band gap is found within range of 2.00–2.51 eV for ZnTe films. • Surface topography revealed hill-like structures with varied surface roughness.

Anomalous Hall effect in electrolytically reduced PdCoO2 thin films

PdCoO2, being highly conductive and anisotropic, is a promising material for fundamental and technological applications. Recently, reduced PdCoO2 thin films were shown to exhibit ferromagnetism after hydrogen annealing. Here, we demonstrate that when PdCoO2 film is used as a cathode for dissociation of water, hydrogen generated around the film reduces the material and leads to the emergence of anomalous Hall effect (AHE). Moreover, we demonstrate that the sign of the AHE signal can also be changed with the electrolytic process. Electrolytically-modified PdCoO2 films may open a door to applications in spintronics.

Fabrication and analysis of mischmetal MM-Fe-B magnetic alloy

Mischmetal (MM30Nd70)30.4Fe68.2Al0.4Cu0.2B0.8 bulk magnets have been prepared with strip casting method followed by hydrogen decrepitating, jet milling, sintering and annealing. Process conditions to achieve optimum magnetic properties have been established through experimentations. XRD studies revealed main tetragonal RE2Fe14B phase and less RE-rich and CeFe2 phases. Microscopic examinations elucidated that magnet microstructure composed of main magnetically MM2Fe14B hard phase, RE-rich intergranular phase and magnetically soft CeFe2 phase. Henkel plot demonstrated the existence of exchange coupling between magnetic phase grains. Thermal studies showed Curie temperature of 278 °C for the Mischmetal (MM30Nd70)30.4Fe68.2Al0.4Cu0.2B0.8 magnet. Magnetic evaluations provoked coercivity Hcj of 619kA/m, remanenec Br of 1.15 T and maximum energy product density of 241 kJ/m3 for the (MM30Nd70)30.4Fe68.2Al0.4Cu0.2B0.8 magnetic alloy.

Influence of the Titanium Nitride Deposition Duration during Vacuum Ion-Plasma Treatment on the Resistance of Coatings in a Hydrogen Atmosphere

In this work, the insulating properties of nitride coatings against the hydrogen penetration into semi-finished or finished products made of VT6 titanium alloy during hydrogenation annealing have been studied. It has been established that an increase of the duration of titanium nitride deposition for more than 30 minutes leads to the formation of pores and cracks in the coating and, as a consequence, to a decrease in the «protective» properties of such coating. It is shown that during linear gradient structure creation, the nitride coating effectively “protects” alloy from penetration of up to 0.5 wt%. of hydrogen.

Insulator-to-semiconductor conversion of solution-processed ultra-wide bandgap amorphous gallium oxide via hydrogen annealing

Developing semiconducting solution-processed ultra-wide bandgap amorphous oxide semiconductor is an emerging area of research interest. However, obtaining electrical conduction on it is quite challenging. Here, we demonstrate the insulator-to-semiconductor conversion of solution-processed a-Ga2O x (E g ∼ 4.8 eV) through hydrogen annealing. The successful conversion was reflected by the switching thin-film transistor with saturation mobility of 10−2 cm2 V−1s−1. We showed that H incorporated after hydrogen annealing acts as a shallow donor which increased the carrier concentration and shifted the Fermi level (E F) closer to the conduction band minimum.

Improvement of structural quality of AlN layers grown on c-plane sapphire substrate by metal–organic vapor phase epitaxy using post-growth annealing with trimethylgallium

AlN layers were grown on a c-plane sapphire substrate by metal–organic vapor phase epitaxy (MOVPE) at 1350 °C. The structural quality of the grown AlN layers was drastically improved by post-growth annealing in mixed hydrogen, ammonia, and trimethylgallium ambiance at 1350 °C. As a first step, we grew the AlN layers exhibiting a double-domain structure with an in-plane rotation angle of ∼4°. Then, the domain structure was changed from double to single by the post-growth annealing. After 20 min post-growth annealing, the surface possessed an atomically flat step-and-terrace structure with a root-mean-square value of ∼0.11 nm measured across 5 × 5 µm2. The full-width at half maximum values for 0002 and 101̄4 AlN reflections using x-ray diffraction were as small as ∼75 and ∼280 arcsec, respectively. Since this work provides a simple continuous MOVPE growth procedure to improve the structural quality of AlN/sapphire, it is advantageous to the industrial fabrication of AlxGa1−xN-based ultraviolet light-emitters.

Modeling and Prediction of Hydrogen-Assisted Morphological Evolution in Silicon Utilizing a Level-Set Approach

Predicting the shape transformation of micro- and nano-scale structures in bulk silicon and silicon-on-insulator (SOI) material in a hydrogen annealing process can be challenging due to the volume segmentation that is likely to occur for longer process times and the long-ranging surface diffusion of silicon atoms. We present a method that allows to accurately predict the shape transformation in such a process, including the modeling of any volume segmentation. This method allows determining the geometry and size of a silicon feature before hydrogen annealing in order to obtain a desired structure after the process. The presented approach allows validating the outcome of a hydrogen annealing process of a given, pre-patterned silicon structure. Experimental results of hydrogen-annealed micro-and nano-scale structures are presented alongside their simulated counterparts to verify the applicability of the proposed method further. [2021-0016]

Thermal annealing ambiance effect on phosphorus passivation and reactivation mechanisms in silicon-based Schottky diodes hydrogenated by MW-ECR plasma

The main objective of this work is to investigate the effect of thermal annealing in forming gas atmosphere on the mechanism of deactivation and reactivation of phosphorus in silicon-based Schottky diodes. Firstly, the microwave plasma power, initial phosphorus concentration in the samples and hydrogen flux were fixed as 650 W, 1015 cm–3, and 30 sccm, respectively, to investigate the behavior of different working parameters of diodes, specifically the duration and temperature of hydrogenation. Secondly, few samples hydrogenated at 400 °C for 1 h were annealed under the forming gas (10% H2 + 90% N2) within the temperature range from 100 to 700 °C for 1 h. The profiles of active phosphorus concentration were monitored by evaluating the change in concentration of phosphorus after hydrogenation or thermal annealing in a forming gas environment through capacitance-voltage measurements. The obtained results depict the temperature and duration of hydrogenation, which ultimately reveals the complex behavior of phosphorous and hydrogen in silicon. However, the phosphorus passivation rate is homogeneous over all the depths measured at 400 °C. The thermal annealing in a forming gas indicates the increase in passivation rate of phosphorus as a function of annealing temperature, till the passivation rate attains saturation in the sample annealed at 400 °C. At higher temperatures, a decrease in the concentration of phosphorous-hydrogen complexes is observed due to the dissociation of these complexes and reactivation of phosphorus under thermal effect.

Combined experimental and theoretical studies on enlarged bandgap and improved photoelectrochemical properties of reduced graphene oxide film by hydrogen annealing

• Relationship between thermal annealing, sp 2 domain, bandgap and properties in RGO. • Correlation between experimental data with calculations (GFN2-xTB, sTD-DFT). • The significant increase of 45.8% in the PEC hydrogen evolution for RGO1100 films. The effect of thermal annealing on the recovery of sp 2 carbon networks in the reduced graphene oxide (RGO) and its consequent bandgap enlargement and electrical conductivity improvement were thoroughly studied, experimentally and theoretically correlated. The annealed RGO film at 1100 °C (designated as RGO1100) exhibited a low sheet resistance (1250 Ω.cm −2 ) with a wide bandgap of 2.82 eV. The photoelectrochemical (PEC) experiments in 1 M H 2 SO 4 solution under solar simulation light (1.5 AM) showed photocurrent densities of 48 and 70 μA.cm −2 for non-annealed RGO (72.5% sp 2 fraction) and RGO1100 (87% sp 2 fraction) respectively, equivalent to an increase of 45.8% for RGO1100. The bandgap widening as well as electrical conductivity increase of RGO1100 were closely interpreted on the basis of sp 2 domain restoration, electronic and molecular orbital structures obtained from extensive experimental data as well as elaborated Geometry, Frequency, Noncovalent Extended Tight-binding (GFN2-xTB) and simplified Tamm-Dancoff density functional theory (sTD-DFT) calculations. The correlation between the electronic structure and the PEC performance of the RGO was also evaluated when the impact of the spatial distribution of oxidation and reduction regions on the recombination rate between photogenerated electrons and holes had been taken into account. The findings shed light on the structure-PEC relationship of RGO1100, which will definitely assist in designing and tailoring RGO-based, highly active materials for PEC applications.

Electronically induced defect creation at semiconductor/oxide interface revealed by time-dependent density functional theory

Carrier induced defect creation at the semiconductor-oxide interface has been known as the origin of electronic device degradation for a long time, but how exactly the interface lattice can be damaged by carriers (especially low-energy ones) remains unclear. Here we carry out real-time time-dependent density functional theory simulations on concrete $\mathrm{Si}/\mathrm{Si}{\mathrm{O}}_{2}$ interfaces to study the interaction between excited electrons and interface bonds. We show that the normal interface Si-H bonds are generally resistant to electrons due to the delocalized nature and high energy level of the Si-H antibonding states, and due to the high-energy barrier to break the Si-H bond. However, if an additional hydrogen atom exists by attaching to a nearby oxygen atom (forming a ``Si-H\ifmmode\cdot\else\textperiodcentered\fi{}\ifmmode\cdot\else\textperiodcentered\fi{}\ifmmode\cdot\else\textperiodcentered\fi{}H-O'' complex), the Si-H bond will be greatly weakened, including the reduction of energy barrier for bond breaking, and the lowering of the antibonding state energy level which favors electron injection. Together with the multiple vibrational excitation process, the corresponding Si-H bond can be broken much more easily. Thus we propose that the Si-H\ifmmode\cdot\else\textperiodcentered\fi{}\ifmmode\cdot\else\textperiodcentered\fi{}\ifmmode\cdot\else\textperiodcentered\fi{}H-O complex will be the center for defect creation and device degradation. We also explain why such a center might be relatively easy to form during the hydrogen annealing process.

The Effects of Hydrogen Annealing on Carbon Nanotube Field-Effect Transistors.

We have systematically investigated the effects of hydrogen annealing on Ni- and Al-contacted carbon nanotube field-effect transistors (CNTFETs), whose work functions have not been affected by hydrogen annealing. Measured results show that the electronic properties of single-walled carbon nanotubes are modified by hydrogen adsorption. The Ni-contacted CNTFETs, which initially showed metallic behavior, changed their p-FET behavior with a high on-current over 10 µA after hydrogen annealing. The on-current of the as-made p-FETs is much improved after hydrogen annealing. The Al-contacted CNTFETs, which initially showed metallic behavior, showed unipolar p-FET behavior after hydrogen annealing. We analyzed the energy band diagrams of the CNTFETs to explain experimental results, finding that the electron affinity and the bandgap of single-walled carbon nanotubes changed after hydrogen annealing. These results are consistent with previously reported ab initio calculations.

Fully Bottom-Up Waste-Free Growth of Ultrathin Silicon Wafer via Self-Releasing Seed Layer.

The fabrication of ultrathin silicon wafers at low cost is crucial for advancing silicon electronics toward stretchability and flexibility. However, conventional fabrication techniques are inefficient because they sacrifice a large amount of substrate material. Thus, advanced silicon electronics that have been realized in laboratories cannot move forward to commercialization. Here, a fully bottom-up technique for producing a self-releasing ultrathin silicon wafer without sacrificing any of the substrate is presented. The key to this approach is a self-organized nanogap on the substrate fabricated by plasma-assisted epitaxial growth (plasma-epi) and subsequent hydrogen annealing. The wafer thickness can be independently controlled during the bulk growth after the formation of plasma-epi seed layer. In addition, semiconductor devices are realized using the ultrathin silicon wafer. Given the high scalability of plasma-epi and its compatibility with conventional semiconductor process, the proposed bottom-up wafer fabrication process will open a new route to developing advanced silicon electronics.