2S Treatment Research Articles

Electrical characteristics of Al2O3/TiO2/Al2O3 prepared by atomic layer deposition on (NH4)2S-treated GaAs

The electrical characteristics of atomic layer deposited (ALD) Al2O3/TiO2/Al2O3 on (NH4)2S treated GaAs MOS capacitor were studied. The electrical characteristics were improved from the reduction of native oxides and sulfur passivation on GaAs by (NH4)2S treatment. The top high bandgap ALD-Al2O3 can further reduce the thermionic emission, and the bottom ALD-Al2O3 improves the interface state density by the self-cleaning. The high dielectric constant TiO2 is used to lower the equivalent oxide thickness. The leakage currents can reach 8.3×10−9 and 2.2×10−7A/cm2 at ±2MV/cm, respectively. The interface state density is 3.11×1011cm−2eV−1 at the energy of about 0.57eV from the edge of the valence band.

Ohmic Contacts to <I>N</I>-Face p-GaN Using Ni/Au for the Fabrication of Polarization Inverted Light-Emitting Diodes

The electrical properties of Ni-based ohmic contacts to N-face p-type GaN were investigated. The specific contact resistance of N-face p-GaN exhibits a linear decrease from 1.01 omega cm2 to 9.05 x 10(-3) omega cm2 for the as-deposited and the annealed Ni/Au contacts, respectively, with increasing annealing temperature. However, the specific contact resistance could be decreased down to 1.03 x 10(-4) omega cm2 by means of surface treatment using an alcohol-based (NH4)2S solution. The depth profile data measured from the intensity of O1s peak in the X-ray photoemission spectra showed that the alcohol-based (NH4)2S treatment was effective in removing the surface oxide layer of GaN.

AR-HPES study on chemical bonding states of high-κ/high-μ gate stacks for advanced CMOS

Hard X-ray photoemission spectroscopy experiments are attractive because they can probe more deeply. The paper reviews two topics on the non-destructive characterization of high-κ/high-μ gate stacks using hard X-ray (hν=7.94keV) photoemission spectroscopy. The first topic is the change in the compositional depth profiles and the chemical bonding states of HfO2/Si-cap/strained-Ge/Si0.5Ge0.5/Si(100) laminating structures. The second topic is the influence of various surface treatments (HF, (NH4)2S and HMDS treatments) and La2O3 interlayer insertion on the chemical bonding states at high-κ/In0.53Ga0.47As interface.

In situ study of HfO2 atomic layer deposition on InP(100)

The interfacial chemistry of the native oxide and chemically treated InP samples during atomic layer deposition (ALD) HfO2 growth at 250 °C has been studied by in situ X-ray photoelectron spectroscopy. The In-oxide concentration is seen to gradually decrease on the native oxide and acid etched samples. No significant changes of the P-oxide concentrations are detected, while the P-oxides chemical states are seen to change gradually during the initial cycles of ALD on the native oxide and the chemically treated samples. (NH4)2S treatment strongly decreases In-oxide and P-oxide concentrations prior to ALD and maintains low concentrations during the ALD process.

Surface Chemistry and Interface Formation during the Atomic Layer Deposition of Alumina from Trimethylaluminum and Water on Indium Phosphide

The surface chemistry and the interface formation during the initial stages of the atomic layer deposition (ALD) of Al2O3 from trimethylaluminum (TMA) and H2O on InP(100) were studied by synchrotron radiation photoemission spectroscopy and scanning tunneling microscopy. The effect of the ex situ surface cleaning by either H2SO4 or (NH4)2S was examined. It is shown that the native oxide on the InP surface consisted mainly of indium hydrogen phosphates with a P enrichment at the interface with InP. After a (NH4)2S treatment, S was present on the surface as a sulfide in both surface and subsurface sites. Exposure to TMA led to the formation of a thin AlPO4 layer, irrespective of the surface cleaning. The surface Fermi level of p-type InP was found to be pinned close to midgap after H2SO4 cleaning and moved only slightly further toward the conduction band edge upon TMA exposure, indicating that the AlPO4/InP interface was rather defective. (NH4)2S passivation led to a Fermi level position of p-type InP close ...

Electrical Conductivity of Direct Wafer-Bonded GaAs/GaAs Structures for Wafer-Bonded Tandem Solar Cells

Wafer bonding of GaAs using an ammonium sulfide (NH4)2S treatment is investigated for various structures. The effect of the wafer offcut angle on the electrical conductivity of III-V solar cell devices using n-GaAs/n-GaAs wafer-bonded structures is studied. High resolution x-ray diffraction is used to confirm the misorientation of the bonded samples. Additionally, we compare the electrical properties of epitaxially grown p-n junctions on GaAs to n-GaAs/p-GaAs wafer-bonded structures. High resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy (STEM) are used to compare the interface morphology across the range of relative misorientations after a 600 {degree sign}C RTP. The ratio of 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.

Characterization of SiON/InP MOS structure with sulfidation, fluorination, and hydrogenation

Liquid phase deposited SiON film on InP with (NH4)2S treatment shows superior electrical characteristics due to the reduction of native oxides and sulfur passiva- tion. Simultaneously, HF in SiON liquid phase deposition solution can effectively reduce residual native oxides on InP and provide fluorine passivation in SiON/InP film and in- terface. With post-metallization annealing (PMA), hydrogen ions can further passivate defects in SiON/InP film and inter- face. With these treatments, the PMA-LPD-SiON/(NH4)2S- treated InP MOS structure shows excellent electrical char- acteristics. With the physical thickness of 5.4 nm, the leak- age current densities can be as low as 1.25 × 10 −7 and 6.24 × 10 −7 A/cm 2 at ±2 V, and the interface state density is 3.25 × 10 11 cm −2 eV −1 .

Oxide Trapping in the InGaAs–$\hbox{Al}_{2} \hbox{O}_{3}$ System and the Role of Sulfur in Reducing the $ \hbox{Al}_{2}\hbox{O}_{3}$ Trap Density

Trap spectroscopy by charge injection and sensing method was applied to the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX"> $\hbox{In}_{0.53}\hbox{Ga}_{0.47}\hbox{As}{-}\hbox{Al}_{2}\hbox{O}_{3}$</tex></formula> system, yielding the spatial and energetic distribution of the traps inside the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{Al}_{2}\hbox{O}_{3}$ </tex></formula> layer. The trap density inside the atomic-layer-deposited (ALD) <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX"> $\hbox{Al}_{2}\hbox{O}_{3}$</tex></formula> layer was found to be significantly reduced by <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(\hbox{NH}_{4})_{2}\hbox{S}$</tex></formula> treatment of the InGaAs surface prior to the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{Al}_{2}\hbox{O}_{3}$</tex></formula> deposition. Indium concentration inside the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{Al}_{2}\hbox{O}_{3}$</tex></formula> layer was found to be reduced once the InGaAs surface is <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(\hbox{NH}_{4})_{2}\hbox{S}$</tex> </formula> treated prior to the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{Al}_{2}\hbox{O}_{3}$</tex></formula> deposition as measured by time-of-flight secondary ion mass spectroscopy, indicating indium as a possible origin of the oxide traps. The results suggest a new mechanism for the sulfur action at the InGaAs surface, which might be responsible for the transistor performance improvements observed after <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$( \hbox{NH}_{4})_{2}\hbox{S}$</tex></formula> passivation. This mechanism involves sulfur as an indium diffusion/segregation barrier stabilizing the InGaAs surface during the ALD <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$ \hbox{Al}_{2}\hbox{O}_{3}$</tex></formula> deposition, lowering the oxide trap density. This, in turn, improves the electron mobility through a reduction in the Coulomb scattering of the carriers due to border traps and improves the device drive current.

Low interface state density and low leakage current of atomic‐layer deposited TiO2/Al2O3/sulfur‐treated GaAs

AbstractThe (NH4)2S treatment can reduce native oxides and passivate GaAs. Atomic‐layer‐deposited (ALD‐Al2O3) can further remove the residue native oxides by self‐cleaning. For the first time, native oxides can be sufficiently removed by the combination of (NH4)2S treatment and ALD‐Al2O3. Stacked with high dielectric constant TiO2 prepared by atomic‐layer deposition on a Al2O3/(NH4)2S‐treated GaAs MOS capacitor, the leakage current densities can reach 1.9 × 10−8 and 3.1 × 10−6 A/cm2 at ±2 MV/cm. The dielectric constant is 25 and the interface state density is about 2.4 × 1011 cm−2 eV−1.

Low equivalent oxide thickness of TiO2/GaAs MOS capacitor

High quality TiO2 film grown by MOCVD on p-type GaAs with (NH4)2S treatment was obtained. The characteristics of TiO2/GaAs MOS capacitor were further improved by post-metallization annealing treatment. The leakage current densities can reach 1.7×10−6 and 4.5×10−5A/cm2 at ±2V (2.7MV/cm). The equivalent oxide thickness can reach 0.53nm for the physical thickness of 7.5nm. The dielectric constant is 52. The lowest interface state density is 4.7×1011cm−2eV−1 derived by the high-low frequency capacitance method.

Study on Surface Passivation Homogeneity of Gallium Antimonide using Photoluminescences

Improvement in optical and surface morphology were observed after sulphur passivation of gallium antimonide surface. The effect of surface passivation of Te-doped n-GaSb by (NH4)2S treatment was investigated by using photoluminescence (PL), Atomic Force Microscope (AFM). The optimum passivation time is around 180 s. Under this condition, the relative PL spectrum intensity of passivated sample can be approximately 10 times stronger than as-grown sample. Meanwhile, the best luminescence homogeneity and suface morphology could be obtained.

Comprehension of Postmetallization Annealed MOCVD-TiO2on(NH4)2STreated III-V Semiconductors

The electrical characteristics of TiO2films grown on III-V semiconductors (e.g., p-type InP and GaAs) by metal-organic chemical vapor deposition were studied. With (NH4)2S treatment, the electrical characteristics of MOS capacitors are improved due to the reduction of native oxides. The electrical characteristics can be further improved by the postmetallization annealing, which causes hydrogen atomic ion to passivate defects and the grain boundary of polycrystalline TiO2films. For postmetallization annealed TiO2on (NH4)2S treated InP MOS, the leakage current densities can reach2.7×10−7and2.3×10−7 A/cm2at±1 MV/cm, respectively. The dielectric constant and effective oxide charges are 46 and1.96×1012 C/cm2, respectively. The interface state density is7.13×1011 cm−2eV−1at the energy of 0.67 eV from the edge of valence band. For postmetallization annealed TiO2on (NH4)2S treated GaAs MOS, The leakage current densities can reach9.7×10−8and1.4×10−7at±1 MV/cm, respectively. The dielectric constant and effective oxide charges are 66 and1.86×1012 C/cm2, respectively. The interface state density is5.96×1011 cm−2eV−1at the energy of 0.7 eV from the edge of valence band.

Analysis of the minority carrier response of n-type and p-type Au/Ni/Al2O3/In0.53Ga0.47As/InP capacitors following an optimized (NH4)2S treatment

The electrical properties of metal-oxide-semiconductor capacitors incorporating atomic layer deposited Al2O3 on n-type and p-type In0.53Ga0.47As were investigated. A clear minority carrier response was observed for both n-type and p-type Au/Ni/Al2O3/In0.53Ga0.47As devices following an optimized ammonium sulfide (NH4)2S treatment. Capacitance-voltage and conductance-voltage measurements performed at varying temperatures allowed an Arrhenius extraction of activation energies for the minority carrier response, indicating a transition from a generation-recombination regime to a diffusion controlled response.

(Invited) XPS Study on Chemical Bonding States of high-κ/high-μ Gate Stacks for Advanced CMOS

The paper reviews the two topics on the non-destructive characterization of high-k/high-mobility gate stacks using the hard X-ray(7.94 keV) photoemission spectroscopy. The first topic is the change in the compositional depth profiles and the chemical bonding states of HfO2/Si-cap/strained-Ge/Si0.5Ge0.5/Si(100) laminating structures. The second topic is the influence of HF, (NH4)2S and HMDS treatments on In0.53Ga0.47As surface, La2O3 interlayer insertion on the chemical bonding states at high-k/In0.53Ga0.47As interface. Analyses of Ge 2p, Si 1s and Hf 3d spectra show that the strained-Ge layer is oxidized during the deposition of HfO2 in the case of 1-nm-thick Si cap layer and that strained-Ge layer is not oxidized in the case of 3 and 5-nm-thick Si cap layer. A critical Si thickness is also extracted. Analyses of measured spectra show that the oxidation of In0.53Ga0.47As is suppressed by La2O3 interlayer insertion ant that (NH4)2S treatment can suppress the oxidation of In0.53Ga0.47As surface.

Effect of Various Surface Treatments on Chemical Bonding State at La2O3/In0.53Ga0.47As and on In0.53Ga0.47As Surface

We have investigated the influence of HF, (NH4)2S and Hexa Methy Disilazane (HMDS) treatments on thermal stability of high-k/In0.53Ga0.47As interface and the chemical bonding states at high-k/In0.53Ga0.47As interface by the X-ray (hv= 1486.6eV) photoemission spectroscopy. The control of the oxide formation on In0.53Ga0.47As surface was tried by surface treatment. Analyses of As 3d, Ga 3p, In 3d, S 1s, Si 2p, N 1s, O 1s and C 1s spectra show that the oxidation of In0.53Ga0.47As was suppressed by various surface treatments.

Capacitance–Voltage Characterization of La2O3 Metal–Oxide–Semiconductor Structures on In0.53Ga0.47As Substrate with Different Surface Treatment Methods

We studied InGaAs surface treatment using hexamethyldisilazane (HMDS) vapor or (NH4)2S solution after initial oxide removal by hydrofluoric acid. The effect of each treatment on interface properties of La2O3/In0.53Ga0.47As metal–oxide–semiconductor (MOS) capacitor was evaluated. We found that HMDS surface treatment of InGaAs, followed by La2O3 deposition and forming gas annealing reduces the MOS capacitor's interface state density more effectively than (NH4)2S treatment. The comparison of the capacitance–voltage data shows that the HMDS-treated sample reaches a maximum accumulation capacitance of 2.3 µF/cm2 at 1 MHz with roughly 40% less frequency dispersion near accumulation, than the sample treated with (NH4)2S solution. These results suggest that process optimization of HMDS application could lead to further improvement of InGaAs MOS interface, thereby making it a potential routine step for InGaAs surface passivation.

Study of High-κ/In0.53Ga0.47As Interface by Hard X-ray Photoemission Spectroscopy

We have investigated the effect of La2O3 interlayer insertion on the thermal stability of a high-κ/In0.53Ga0.47As interface and the chemical bonding states at the high-κ/In0.53Ga0.47As interface by hard X-ray (hν= 7.94 keV) photoemission spectroscopy (HX-PES). The control of the oxide formation at the HfO2/In0.53Ga0.47As interface was tried by inserting La2O3, which has a large Gibbs free energy. Analyses of As 2p, Ga 2p, In 3d, Hf 3d, La 3d, and W 4f spectra show that the oxidation of In0.53Ga0.47As was suppressed by La2O3 interlayer insertion. We have also investigated the effect of surface treatment on the chemical bonding state of the In0.53Ga0.47As surface. (NH4)2S treatment can suppress the oxidation of the In0.53Ga0.47As surface.

Characterization of Fluorinated-SiO2/PMA-Treated TiO2/(NH4)2S-Treated GaAs MOS Structure

The electrical characteristics of metalorganic chemical vapor deposited TiO2 films on p-type GaAs were studied. For GaAs with (NH4)2S treatment, the electrical characteristics of TiO2/GaAs are improved from native oxide removal. The electrical characteristics can be further improved by hydrogen passivation on defects, grain boundary and interface of TiO2/GaAs via post-metallization annealing, in which the active hydrogen is produced from the reaction between aluminum (Al) contact and hydroxyl groups existed on oxide surface. The stack of liquid phase deposited high band-gap SiO2 on TiO2 film can lower the thermionic emission leakage of low band-gap TiO2 and improve the quality of stacked structure by fluorination. The leakage current densities of fluorinated-SiO2/PMA-treated TiO2/(NH4)2S-treated GaAs MOS structure can reach 5.4 × 10−9 and 4.9 × 10−7 A/cm2 at ±1.5 MV/cm. The dielectric constant and the lowest interface state density are 39.7 and 4.8 × 1011 cm−2eV−1, respectively.

Hydrogen Sulfide Causes Apoptosis in Human Pulp Stem Cells

Introduction Untreated dental caries will eventually lead to pulpal inflammation. Although much is known regarding the interaction of microbial antigens and the immunologic defense systems of pulp, many aspects of the pathogenesis of pulpitis are not fully understood. The relationship between human pulp stem cells (HPSCs) and the pathogenesis of pulpitis remains among the poorly understood areas. Many of the invading bacteria are known to produce considerable amounts of hydrogen sulfide (H 2S), which causes apoptosis in some tissues. The aims of this study were to determine whether H 2S causes apoptosis in HPSCs and to examine its signaling pathway. Methods Stem cells were isolated from human dental pulp and incubated with 50 ng/mL H 2S for 48 hours. To detect apoptosis, the cells were analyzed by using flow cytometry. The mitochondrial signaling pathway was examined by determining mitochondrial membrane depolarization. Activation of the key apoptotic enzymes caspase-9, caspase-8, and caspase-3 was assessed by using enzyme-linked immunosorbent assay. Release of cytochrome C from mitochondria was also determined. Results The number of apoptotic cells increased significantly with H 2S treatment from 1.6% to 16.3% ( P < .01). Significant increases were also measured in the amounts of caspase-9 and caspase-3 and in cytochrome C release (all P < .01) and in mitochondrial membrane depolarization ( P < .05), whereas caspase-8 activity was not found. Conclusions H 2S causes apoptosis in HPSCs by activating the mitochondrial pathway. It is suggested that H 2S might be one of the factors modifying the pathogenesis of pulpitis by causing loss of viability of HPSCs through apoptosis.

Effect of H 2S treatment on properties of CuInS 2 thin films deposited by chemical spray pyrolysis at low temperature

CuInS 2 thin films were deposited by chemical spray of aqueous solutions containing CuCl 2, InCl 3 and thiourea at substrate temperature of 250 °C in air and subjected to annealing at 530 °C in H 2S atmosphere. Structure and composition before and after annealing were studied by XRD, EDS, XPS and Raman spectroscopy. As-sprayed films were low-crystalline, showed uniform distribution of elements in film thickness and no oxygen content. For the CuInS 2 films deposited from the solutions with [Cu 2+] / [In 3+] = 1.0 and 1.1, H 2S treatment for 30 min increased the chalcopyrite content up to 73% and 51%, respectively. Cu XS phase in sprayed CIS films promotes the crystallite growth but retards the formation of chalcopyrite phase during H 2S treatment.