2S Treatment Research Articles

Inhibition of Cancer Cell Migration and Invasion In Vitro by Recombinant Tyrosine-Sulfated Haemathrin, A Thrombin Inhibitor.

Thrombin, a key enzyme in the regulation of hemostasis, has been implicated in cancer progression. This study explored the effect of recombinant tyrosine-sulfated haemathrin on cancer cell behavior and signaling pathways compared to wild-type (WT) haemathrin 2. The recombinant proteins, tyrosine-sulfated haemathrin 2 (haemathrin 2S), and WT haemathrin 2 were produced in Escherichia coli and subsequently purified and applied to SKOV3 and MDA-MB-231 cells with and without thrombin stimulation. Cell migration and invasion were assessed using wound healing and Transwell assays, respectively. Haemathrin 2S treatment significantly diminished cell migration and invasion promoted by thrombin in both SKOV3 and MDA-MB-231 cells (p < 0.05). Additionally, haemathrin 2S effectively inhibited thrombin-induced phosphorylation of serine/threonine kinase (Akt) in both cell lines (p < 0.05), while WT haemathrin 2 had this effect only in MDA-MB-231 cells. Furthermore, haemathrin 2S significantly reduced thrombin-activated phosphorylation of extracellular signal-regulated kinases (ERK) and p38 in both cell lines (p < 0.05) and reversed E/N-cadherin expression in thrombin-treated MDA-MB-231 cells (p < 0.05), which were not observed with WT haemathrin 2. Overall, haemathrin 2S was more effective than WT haemathrin 2 in reducing cancer cell migration and invasion, indicating that targeting thrombin with sulfated haemathrin is a promising strategy for cancer therapy. However, further in vivo studies are needed to confirm these results.

Synergistic role of melatonin and hydrogen sulfide in modulating secondary metabolites and metal uptake/sequestration in arsenic-stressed tomato plants

The multifunctional roles of melatonin (ML) and hydrogen sulfide (H2S) as plant gasotransmitters are well understood. However, their interaction in defensive responses is still unclear. Here, we assessed how the ML-H2S interaction impacts tomato plants exposed to arsenic (As, 10 mg/L) toxicity. The results showed that ML and ML+H2S treatments alleviated As toxicity by inducing the transcription of ANS, PAL, DFR, CHS, F3H, and CHI and an enhanced accumulation of phenolic and anthocyanin compounds. ML and ML+H2S led to a drop in the transcription of PT2 and Lsi1, resulting in reduced As uptake and subsequent movement to the leaves. ML and ML+H2S treatments resulted in high GSH1, PCS, and ABC1 transcription. This led to elevated levels of glutathione and phytochelatins, facilitating As sequestration in the roots and protecting root and leaf cells against As. ML and ML+H2S treatments enhanced tomato growth under As treatments by optimizing chlorophyll metabolism, increasing internal H2S, and amplifying the antioxidant machinery function. In contrast to the sole use of ML treatment, ML+H2S exhibited more pronounced positive impacts on As-stressed tomatoes, indicating synergistic/interactive effects between these two substances. On the other hand, the use of hypotaurine, an H2S scavenger, demonstrated the inhibition of the beneficial impact of ML and ML+H2S treatments in stimulating defensive responses, which highlights the substantial involvement of H2S in the signaling pathway activated by ML during As stress. Hence, we can conclude that ML requires the presence of endogenous H2S to mitigate the adverse effects of As on tomato seedlings.

(NH4)2S-induced improvement of interfacial wettability for high-quality heterojunctions to boost the chloride-assembled CZTSSe solar cells.

Concernin the crucial interfacial issues in multi-layered kesterite Cu2ZnSn(S,Se)4 (CZTSSe) solar cells, (NH4)2S treatment has been proven to be effective in eliminating surface secondary phases. While for the CZTSSe absorbers without impurity phases, what can the low-temperature (NH4)2S treatment do to the absorbers, thus to the device performance? Herein, the chloride-fabricated CZTSSe absorbers are surface treated with the (NH4)2S solution at room temperature, and its influence on the device performance is investigated in detail. Surprisingly, such treatment can make the absorbers' surface become nearly super-hydrophilicity, greatly decreasing the surface wetting angle from 63.1° ± 3.4° to 7.3° ± 0.6° after 50 min-treating, and thus lead to marked differences in the interfacial properties of the CdS/CZTSSe heterojunctions deposited in a chemical bath. Consequently, for the best-performing CZTSSe cells, combining the passivated interfacial defects, increased carrier concentration, reduced carrier recombination, and prolonged minority lifetime, the efficiency is improved from 6.54% to 9.88%, together with the 37 mV and 7.9% increase in VOC and FF, respectively. This study confirms the newfound results that the (NH4)2S treatment can effectively adjust the wettability of the absorbers to form high-quality heterojunctions to boost the device efficiency, which would be valuable for an in-depth understanding of the intrinsic mechanisms of interfacial processing.

Surface morphology engineering of metal oxide-transition metal dichalcogenide heterojunction

ABSTRACT A tremendous effort has been made to develop 2D materials-based FETs for electronic applications due to their atomically thin structures. Typically, the electrical performance of the device can vary with the surface roughness and thickness of the channel layer. Therefore, a two-step surface engineering process is demonstrated to tailor the surface roughness and thickness of MoSe2 multilayers involving exposure of O2 plasma followed by dipping in (NH4)2S(aq) solution. The O2 plasma treatment generated an amorphous MoOx layer to form a MoOx/MoSe2 heterojunction, and the (NH4)2S(aq) treatment tailored the surface roughness of the heterojunction. The ON/OFF current ratio of MoSe2 FET is about 1.1 × 105 and 5.7 × 104 for bare and chemically etched MoSe2, respectively. The surface roughness of the chemically treated MoSe2 is higher than that of the bare, 4.2 ± 0.5 nm against 3.6 ± 0.5 nm. Conversely, a 1-hour exposure of the multilayer MoOx/MoSe2 heterostructure with the (NH4)2S(aq) solution removed the amorphous oxide layer and scaled down the thickness of MoSe2 from ~92.2 nm to ~38.9 nm. The preliminary study shows that this simple two-step strategy can obtain a higher surface-area-to-volume ratio and thickness engineering with acceptable variation in electrical properties.

CZTSSe/Zn(O,S) heterojunction solar cells with 9.82% efficiency enabled via (NH4)2S treatment of absorber layer

AbstractThe replacement of CdS buffer layer is desirable for the development of nontoxic, environmentally friendly kesterite thin‐film solar cells (TFSCs). Recently, several ternary compound semiconductors have been extensively investigated as an alternative buffer layer for Cd‐free TFSCs. Herein, the effectiveness of (NH4)2S treatment on the surface properties of the absorber, as well as the device performance of atomic layer deposited (ALD) Zn(O,S) buffer‐based CZTSSe solar cells, has been investigated. X‐ray photoelectron spectroscopy (XPS) results showed that the elemental compositions of CZTSSe surface were significantly influenced by (NH4)2S treatment, whereas the surface morphologies of the CZTSSe‐absorber layers remained unaffected. The XPS results further suggested that the (NH4)2S solution treatment substantially removed the native oxide layer from the CTZSSe absorber surface. The fabricated CZTSSe/Zn(O,S) device without (NH4)2S treatment displayed an initial cell efficiency of 7.46%. The energy conversion efficiency increased significantly to 9.82% after the (NH4)2S treatment of absorber layers for an optimum duration of 1 min; to the best of our knowledge, this is the highest efficiency achieved to date for Zn(O,S) buffer‐based kesterite solar cells. The improved device performance is predominantly attributed to the pronounced increase in the fill factor (FF) of TFSCs resulting from the removal of oxides/hydroxides from the CZTSSe surface and passivation of absorber surface with sulfur species. However, increasing the treatment duration to 3 or 5 min resulted in the deterioration of cell efficiency, primarily due to the progressive degradation in the FF of the device. This study demonstrates a plausible route to improve the performance of Zn(O,S) buffer layer‐based kesterite solar cells through a simple surface treatment of the absorber layers using (NH4)2S solution.

Combined Iodine- and Sulfur-Based Treatments for an Effective Passivation of GeSn Surface

GeSn alloys are metastable semiconductors that have been proposed as building blocks for silicon-integrated short-wave and mid-wave infrared photonic and sensing platforms. Exploiting these semiconductors requires, however, the control of their epitaxy and their surface chemistry to reduce non-radiative recombination that hinders the efficiency of optoelectronic devices. Herein, we demonstrate that a combined sulfur- and iodine-based treatments yields effective passivation of Ge and Ge0.9Sn0.1 surfaces. X-ray photoemission spectroscopy and in situ spectroscopic ellipsometry measurements were used to investigate the dynamics of surface stability and track the reoxidation mechanisms. Our analysis shows that the largest reduction in oxide after HI treatment, while HF+(NH4)2S results in a lower re-oxidation rate. A combined HI+(NH4)2S treatment preserves the lowest oxide ratio <10 % up to 1 hour of air exposure, while less than half of the initial oxide coverage is reached after 4 hours. These results highlight the potential of S- and I-based treatments in stabilizing the GeSn surface chemistry thus enabling a passivation method that is compatible with materials and device processing.

Interface state density and barrier height improvement in ammonium sulfide treated Al2O3/Si interfaces

The HF treatment removes the native oxide and lays behind the dangling bonds over the Si surface which causes the increment in density of interface traps (Dit) through the direct deposition of high-k dielectric on Si. Here, we propose the facile method for reduction of interface traps and improvement in barrier height with the (NH4)2S treatment on Al2O3/Si interfaces, which can be used as the base for the non-volatile memory device. The AFM was used to optimize the treatment time and surface properties, while XPS measurements were carried out to study the interface and extract the barrier height (ΦB). The short period of 20 s treatment shows the improvement in the barrier height (1.02 eV), while the one order reduction in the Dit (0.84 × 1012 cm2/eV) of sulfur passivated Al/Al2O3/Si MOS device. The results indicate the favorable passivation of the dangling bonds over the Si surfaces covered by sulfur atoms.

Contact Engineering of Layered MoS2 via Chemically Dipping Treatments

AbstractThe performance of electronic/optoelectronic devices is governed by carrier injection through metal–semiconductor contact; therefore, it is crucial to employ low‐resistance source/drain contacts. However, unintentional introduction of extrinsic defects, such as substoichiometric oxidation states at the metal–semiconductor interface, can degrade carrier injection. In this report, controlling the unintentional extrinsic defect states in layered MoS2 is demonstrated using a two‐step chemical treatment, (NH4)2S(aq) treatment and vacuum annealing, to enhance the contact behavior of metal/MoS2 interfaces. The two‐step treatment induces changes in the contact of single layer MoS2 field effect transistors from nonlinear Schottky to Ohmic behavior, along with a reduction of contact resistance from 35.2 to 5.2 kΩ. Moreover, the enhancement of ION and electron field effect mobility of single layer MoS2 field effect transistors is nearly double for n‐branch operation. This enhanced contact behavior resulting from the two‐step treatment is likely due to the removal of oxidation defects, which can be unintentionally introduced during synthesis or fabrication processes. The removal of oxygen defects is confirmed by scanning tunneling microscopy and X‐ray photoelectron spectroscopy. This two‐step (NH4)2S(aq) chemical functionalization process provides a facile pathway to controlling the defect states in transition metal dichalcogenides (TMDs), to enhance the metal‐contact behavior of TMDs.

Facile Process for Surface Passivation Using (NH4)2S for the InP MOS Capacitor with ALD Al2O3.

Ammonium sulfide ((NH4)2S) was used for the passivation of an InP (100) substrate and its conditions were optimized. The capacitance–voltage (C–V) characteristics of InP metal-oxide-semiconductor (MOS) capacitors were analyzed by changing the concentration of and treatment time with (NH4)2S. It was found that a 10% (NH4)2S treatment for 10 min exhibits the best electrical properties in terms of hysteresis and frequency dispersions in the depletion or accumulation mode. After the InP substrate was passivated by the optimized (NH4)2S, the results of x-ray photoelectron spectroscopy (XPS) and the extracted interface trap density (Dit) proved that the growth of native oxide was suppressed.

Re-examination of effects of sulfur treatment on Al2O3/InGaAs metal-oxide-semiconductor interface properties

The effects of wet chemical treatments before treatment using (NH4)2S solutions in atomic layer deposition Al2O3/InGaAs metal-oxide-semiconductor (MOS) interfaces are experimentally examined. It is found that no chemical treatment before sulfur passivation leads to high interface state density (Dit) in spite of the (NH4)2S treatment. Furthermore, the value of Dit is dependent among the pretreatments using NH4OH, HCl, and BHF solutions before the sulfur treatment. HCl + (NH4)2S and BHF + (NH4)2S combinations show the lowest values of Dit. In addition, all of the Al2O3/InGaAs MOS interfaces with the sulfur treatment show a small amount of arsenic oxide. Thus, much higher Dit of the interfaces with the sulfur treatment indicates that the amount of arsenic oxide is not a deterministic factor for Dit. On the other hand, the amount of arsenic oxide before the sulfur treatment is found to correlate with Dit after sulfur treatment. Also, the interfaces with higher Dit after the sulfur treatment show a larger number of sulfur atoms remaining at the interfaces. These experimental results mean that there is a strong correlation among Dit, the amount of arsenic oxide, and the number of sulfur atoms remaining at the Al2O3/InGaAs interfaces. As a result, we can interpret for the present experimental results that the sulfur treatment can have two opposite impacts on Dit at the Al2O3/InGaAs interfaces: the decrease in Dit due to etching of native oxides and suppression of oxidation by sulfur passivation and the increase in Dit due to defect generation through some interaction between sulfur and arsenic oxide.

Improvement of electrical properties of ZnS/CdTe-HgCdTe interface by (NH4)2S treatment

Effect of 20% aqueous ammonium sulphide treatment on electrical properties of ZnS/CdTe-HgCdTe interface was studied by using high frequency capacitance-voltage (C-V) measurements showing significant improvement in surface conditions. MIS structures were fabricated on passivated HgCdTe wafers and C-V measurements were carried out. C-V curves were analysed to evaluate fast interface state distribution with energy, slow state density and fixed charged density. For the sake of comparison two HgCdTe samples were prepared under similar conditions, one was given (NH4)2S treatment after standard surface preparation by I-KI polishing and the other was untreated to act as the base sample. CdTe and ZnS layers were deposited on both the samples, A and B. It was observed that C-V characteristics of (NH4)2S treated sample show significant improvement in comparison to that of untreated sample. Fixed charge density and fast interface charge (fast and slow) density were estimated for both the samples. Average fixed charge density for sample treated with (NH4)2S (4.2 × 1010 cm−2) is reduced by a factor of ~6 compared to untreated sample (2.53 × 1011 cm−2), Average fast interface trap density for sample exposed to (NH4)2S treatment (~3.5 × 1011 cm−2eV−1) improved by a factor of ~3.5compared to untreated sample (~1.3 × 1012 cm−2eV−1) while average slow interface traps estimated for sample treated with (NH4)2S (~3.09 × 1010 cm−2) reduced by ~1.3times than that for untreated sample (~4.1 × 1010 cm−2). Surface and interface stability of the grown sulphide is also studied by repeated ellipsometry and C-V measurements respectively. It is found that it is important to deposit CdTe/ZnS passivation layers immediately after 20% aqueous ammonium sulphide treatment to achieve stable performance. Stability of (NH4)2S treatment with time was also investigated. C-V measurements after approximately 2 months showed improvement in interface properties.

H2S inhibits pulmonary arterial endothelial cell inflammation in rats with monocrotaline-induced pulmonary hypertension

This study aimed to determine whether hydrogen sulfide (H2S) inhibits pulmonary arterial endothelial inflammation in rats with monocrotaline (MCT)-induced pulmonary hypertension and its possible mechanisms. Twenty-four male Wistar rats were divided randomly into control, MCT, and MCT+H2S treatment groups. Human pulmonary arterial endothelial cells (HPAEC) were cultured and divided into four groups: control, MCT, MCT+H2S, and H2S. Pulmonary artery pressure was determined using a right cardiac catheterization procedure 3 weeks after MCT administration. Pulmonary vascular morphological changes and inflammatory infiltration were measured. Endogenous H2S levels, cystathionine-γ-lyase (CSE) expression, and inflammatory cytokines were determined both in vivo and in vitro. In addition, phosphorylation of NF-κB p65 and IκBα was detected by western blotting, and NF-κB p65 nuclear translocation, as well as its DNA-binding activity, was determined. Pulmonary hypertension and vascular remolding developed 3 wks after MCT administration, with elevated lung tissue inflammatory infiltration and cytokine level associated with activation of the NF-κB pathway, both in vivo and in vitro. However, the endogenous H2S/CSE pathway was downregulated in MCT rats. By contrast, an H2S donor markedly reduced pulmonary artery pressure, pulmonary vascular structural remolding, and increased lung inflammatory infiltration and cytokine levels of MCT-treated rats. Meanwhile, H2S reversed the activation of the NF-κB pathway successfully. The downregulated pulmonary arterial endothelial H2S/CSE pathway is involved in the pulmonary inflammatory response in MCT-treated pulmonary hypertensive rats. H2S attenuated endothelial inflammation by inhibiting the NF-κB pathway.

Impact of Premetallization Surface Preparation on Nickel-based Ohmic Contacts to Germanium Telluride: An X-ray Photoelectron Spectroscopic Study.

Surfaces of polycrystalline α-GeTe films were studied by X-ray photoelectron spectroscopy (XPS) after different treatments in an effort to understand the effect of premetallization surface treatments on the resistance of Ni-based contacts to GeTe. UV-O3 is often used to remove organic contaminants after lithography and prior to metallization; therefore, UV-O3 treatment was used first for 10 min prior to ex situ treatments, which led to oxidation of both Ge and Te to GeOx (x < 2) and TeO2, respectively. Then the oxides were removed by deionized (DI) H2O, (NH4)2S, and HCl treatments. Additionally, in situ Ar+ ion etching was used to clean the GeTe surface without prior UV-O3 treatment. Ar+ ion etching, H2O, and (NH4)2S treatments create a surface richer in Ge compared to the HCl treatment, after which the surface is Te-rich. However, (NH4)2S also oxidizes Ge and gradually etches the GeTe film. All treated surfaces showed poor stability upon prolonged exposure to air, revealing that even (NH4)2S does not passivate the GeTe surface. The refined transfer length method (RTLM) was used to measure the contact resistance (Rc) of as-deposited Ni-based contacts to GeTe as a function of premetallization surface preparation. HCl-treated samples had the highest Rc (0.036 ± 0.002 Ω·mm), which was more than twice that of the other surface treatments. This increase in Rc is attributed to formation of the Ni1.29Te phase at the Ni/GeTe interface due to an abundance of Te at the surface after HCl treatment. In general, treatments that resulted in Ge-rich surfaces offered lower Rc.

InP MOS capacitor and E-mode n-channel FET with ALD Al2O3-based high-k dielectric

The electrical characteristics of atomic-layer-deposited Al2O3/TiO2/Al2O3 on (NH4)2S-treated InP MOS capacitor and related MOSFET were studied. The electrical characteristics were improved from the reduction of native oxides and sulfur passivation on InP by (NH4)2S treatment. The high bandgap Al2O3 on TiO2 can reduce the thermionic emission, and the Al2O3 under TiO2 improves the interface-state density by self-cleaning. The high dielectric constant TiO2 is used to lower the equivalent oxide thickness. The leakage currents can reach 2.3 × 10−8 and 2.2 × 10−7 A/cm2 at ±2 MV/cm, respectively. The lowest interface-state density is 4.6 × 1011 cm−2 eV−1 with a low-frequency dispersion of 15 %. The fabricated enhancement-mode n-channel sulfur-treated InP MOSFET exhibits good electrical characteristics with a maximum transconductance of 146 mS/mm and effective mobility of 1760 cm2/V s. The subthreshold swing and threshold voltage are 117 mV/decade and 0.44 V, respectively.

High Quality of Liquid Phase-Deposited SiON on GaAs MOS Capacitor with Multiple Treatments

Silicon oxynitride (SiON) film on a p-type (100) GaAs substrate by liquid phase deposition has been characterized. Aqueous solutions of hydrofluosilicic acid, ammonia and boric acid were used as growth precursors. The electrical characteristics of SiON film are much improved on GaAs with (NH4)2S treatment. With post-metallization annealing (PMA), hydrogen ions further passivate traps in the SiON/GaAs film and interface. Both PMA and (NH4)2S treatments on a SiON/GaAs MOS capacitor produce better interface quality and lower interface state density (Dit) compared with ones without hydrogen and sulfur passivations. The leakage current densities are improved to 7.1 × 10−8 A/cm2 and 1.8 × 10−7 A/cm2 at ±2 V. The dielectric constant of 5.6 and the effective oxide charges of −5.3 × 1010 C/cm2 are obtained. The hysteresis offset of the hysteresis loop is only 0.09 V. The lowest Dit is 2.7 × 1011 cm−2/eV at an energy of about 0.66 eV from the edge of the valence band.

Electrical characteristics of TiO2/Al2O3/InP capacitor after removal of native oxides by atomic layer deposited Al2O3 self-cleaning and (NH4)2S treatments

The electrical characteristics of MOS capacitor with 5/2.9nm TiO2/Al2O3 prepared by atomic layer deposition on (NH4)2S treated InP were studied. The electrical characteristics were improved from the reduction of native oxides and sulfur passivation on InP by (NH4)2S treatment. The high dielectric constant TiO2 is used to lower the equivalent oxide thickness and the atomic force microscopy image reveals extremely flat and uniform surface. The root-mean-square roughness value of TiO2/S-InP is 0.226nm. The stack of high bandgap Al2O3 layer can reduce the thermionic emission of low bandgap TiO2 and its self-cleaning capability further improves the interface state density. For 5/2.9nm TiO2/Al2O3/S-InP stacked MOS capacitor, the leakage currents can reach 6.4×10−8 and 7.8×10−7A/cm2 at ±2MV/cm, respectively. The net effective dielectric constant is 16.7. The lowest interface state density is 3.8×1011cm−2eV−1 with a low frequency dispersion of 16%.

Reduction in interface state density of SiO2/Si-IPL/InP by fluorine and sulfur passivations

The characteristics of a liquid-phase-deposited SiO2 film on InP were investigated. The mixture of H2SiF6 and H3BO3 aqueous precursors was used as the growth solution. SiO2 on InP with (NH4)2S treatment showed good electrical characteristics owing to the reduction of native oxides and sulfur passivation. The electrical characteristics were further improved with an ultrathin Si interface passivation layer (IPL) through reductions in Fermi-level pinning and interface state density. Moreover, during the SiO2 deposition, the HF in the growth solution simultaneously and effectively removed native oxides from the Si-IPL and provided fluorine passivation on it. The Al/SiO2/Si-IPL/(NH4)2S-treated InP MOS capacitor showed superior electrical properties. The leakage current density reached 6.9 × 10−9 and 1.6 × 10−7 A/cm2 at ±2 V. The interface state density reached 3.6 × 1011 cm−2 eV−1 with low frequency dispersion of 12.3%.

Effects of Miscut Substrates on Electrical Conductivity Across InP and GaAs Wafer-Bonded Structures

Wafer bonding of GaAs and InP using an (NH4)2S treatment are investigated for the effect of the wafer offcut angle on the electrical conductivity of wafer-bonded III-V interfaces. HRTEM and STEM are used to confirm the misorientation of the bonded samples and to compare the interface morphology across the range of relative misorientations. A line ratio at the interface shows that the well-bonded crystalline regions to amorphous oxide inclusions is consistent across all bonded samples, indicating that the degree of misorientation does not affect the level of interface recrystallization at high temperatures. Fitting the zero-bias conductance over a range of temperatures reveals an increase in barrier heights for samples with greater than 4° misoriented bonded pairs. This demonstrates that the out-of-plane relative surface misorientation is a critical parameter to be monitored and thus any in-plane twist as well in order to achieve superior electrical conductivity in direct-bonded multijunction solar applications.

Characteristics of liquid phase deposited SiO2 on (NH4)2S-treated GaAs with an ultrathin Si interface passivation layer

The characteristics of liquid-phase-deposited SiO2 film on GaAs were investigated. A mixture of H2SiF6 and H3BO3 aqueous precursors was used as the growth solution. SiO2 on GaAs with (NH4)2S treatment shows good electrical characteristics owing to the reduction of native oxides and sulfur passivation. The electrical characteristics are further improved with an ultrathin Si interface passivation layer (Si IPL) from the reduction of Fermi-level pinning and interface state density. Moreover, during the SiO2 deposition, HF in the growth solution can simultaneously and effectively remove native oxides on Si IPL and provide fluorine passivation on it. The Al/SiO2/Si IPL/(NH4)2S-treated GaAs MOS capacitor shows superior electrical properties. The leakage current densities can reach 7.4 × 10−9 and 6.83 × 10−8 A/cm2 at ±2 V. The interface state density can reach a 2.11 × 1011 cm−2 eV−1 with low frequency-dispersion of 8%.

Electrical characteristics of GaAs MOS capacitor and field effect transistor with atomic layer-deposited TiO2/Al2O3 dielectrics

The (NH4)2S treatment can reduce native oxides and passivate GaAs. Atomic layer-deposited Al2O3 can further remove the residue native oxides by self-cleaning. Stacked with high dielectric constant TiO2 prepared by atomic layer deposition on Al2O3/(NH4)2S-treated GaAs MOS capacitor, the leakage current densities can reach 4.5 × 10−8 and 3.4 × 10−6 A/cm2 at ±2 MV/cm. The net effective dielectric constant of the entire stack is 18 and the interface state density is about 4.2 × 1011/cm2/eV. The fabricated enhancement-mode n-channel GaAs MOSFET exhibited good electrical characteristics with a maximum g m of 122 mS/mm and electron mobility of 226 cm2/V s.