Plasma Hydrogen Treatment Research Articles

Thermal deformation behavior of γ-TiAl based alloy by plasma hydrogenation

The Ti–48Al–2Cr alloy was subjected to the plasma-hydrogenation treatment. Then the alloy containing minor hydrogen was prepared (0.058 wt percent, wt.%). Hot-compression experiments were carried out at temperatures ranging from 1000 to 1,150 °C and strain rates ranging from 1 to 0.001 s−1. The results show that the peak stress after the plasma-hydrogenation treatment is lower than that of the unhydrogenated one. At 1100 °C and the strain rate of 0.01 s−1, the peak stress is reduced by 32.3%. The mechanism of high-temperature softening caused by plasma-hydrogenation is examined, and the constitutive equations are established for the unhydrogenated and hydrogenated alloys. Through the constitutive equations, the high-temperature softening mechanism of unhydrogenated and hydrogenated alloys are dynamic-recrystallization, and the activation energy of hydrogenated alloy is lower than that of the unhydrogenated. Meanwhile, electron back-scatter diffraction analyses of the thermal-compressed microstructures show that the hydrogenated alloy has more recrystallized grains, less lamellar structure, and more uniform deformation than the unhydrogenated alloy.

Development of a rapid thermal annealing process for polycrystalline silicon thin-film solar cells on glass

In this report, we discuss the influence of rapid thermal annealing (RTA) on the performance of polycrystalline Si (poly-Si) thin-film solar cells on glass where the poly-Si layers are differently prepared. The first part presents a comprehensive study of RTA treatments on poly-Si thin-films made by solid phase crystallization (SPC) (standard material of CSG Solar AG, Thalheim). By varying both plateau temperature (up to 1050 °C) and duration (up to 1000 s) of the annealing profile, we determined the parameters for a maximum open-circuit voltage ( V OC). In addition, we applied our standard plasma hydrogenation treatment in order to passivate the remaining intra-grain defects and grain boundaries by atomic hydrogen resulting in a further increase of V OC. We found, that the preceding RTA treatment increases the effect of hydrogenation already at comparable low RTA temperatures. The effect on hydrogenation increases significantly with RTA temperature. In a second step we investigated the effect of the RTA and hydrogenation on large-grained poly-Si films based on the epitaxial thickening of poly-Si seed layers.

Impact of Direct Plasma Hydrogenation on Thermal Donor Formation in n-Type CZ Silicon

In this paper, the role of a direct plasma hydrogenation treatment and a subsequent air annealing at 450°C in the formation of thermal donors (TDs) in n-type Czochralski (CZ) silicon is investigated by means of a combination of capacitance-voltage (C-V) and deep-level transient spectroscopy (DLTS). The hydrogenation treatment is found to enhance the introduction rate of TDs at 450°C for shorter annealing times, reaching its maximum acceleration after 5 h and for the longest plasma hydrogenation studied (2 h). For much longer annealing times, the TD introduction rate becomes independent of the presence of hydrogen in the material. DLTS detects only one donor level having an activation energy, which lowers with increasing doping density of the material, from 0.106 to 0.093 eV. After activation energy correction for the Poole-Frenkel electric-field-enhanced emission, this trap is found to fit well with the conventional singly ionized oxygen thermal donor level. However, from C-V free carrier and DLTS trap concentrations, it is derived that other shallower donors, created by the plasma hydrogenation and 450°C anneal should play an important role in the free carrier concentration increase of the n-CZ silicon. © 2004 The Electrochemical Society. All rights reserved.

Carrier Transport and Photogeneration in Amorphous Silicon / Crystalline Silicon Heterojunctions with i/n and p/n Interfaces

ABSTRACTAmorphous hydrogenated silicon films deposited by Plasma Enhanced Chemical Vapour Deposition (PE-CVD) using standard rf-glow discharge at 13.56 MHz were used to produce amorphous silicon heterostructures. Junction properties were studied from current-voltage (IV), capacitance-voltage (C-V) and spectral response measurements. The photosensitivity of these structures was investigated for different amorphous film thicknesses and different applied bias voltages. It was shown that the output device characteristics could be improved by plasma hydrogen treatment before the deposition of the amorphous layer. The results show that ITO/a-Si:H/c-Si structures present high internal gain in the visible infra-red region and high collection efficiency in the blue range. They can be used as visible/near-IR photodiodes or for current amplifications proposes.

Atomic Force Microscopy Study of Initial Nucleation in the Deposition OF μc-Si:H

AbstractThe initial stages of microcrystalline silicon growth of n+ doped films prepared by rf plasma enhanced chemical vapor deposition (PECVD) and of intrinsic films prepared by hot-wire chemical vapor deposition (HW-CVD) are studied using atomic force microscopy, Raman spectroscopy and parallel dark conductivity measurements. The effect of the use of a plasma hydrogen treatment, of chamber conditioning prior to this treatment, of the type of substrate (glass or c-Si) used and the effects of a seed layer on the film properties are discussed.

Correlation between electron mobility and silicon-hydrogen bonding configurations in plasma-hydrogenated polycrystalline silicon thin films

This letter describes the relationship between electron mobility and Si-hydrogen bonding configurations in poly-Si thin films after plasma-hydrogenation treatment. A 50-nm-thick amorphous-Si film was crystallized by excimer laser irradiation followed by plasma hydrogenation. Measurements of the Hall effect and Raman scattering demonstrated that mobility increased under the Si-H dominant state and decreased under the Si-H2 dominant state, which were respectively caused by adjusted and excessive hydrogenation times. Mobility degradation was recovered by dissociation of excess H atoms by annealing. The origin of the correlation is discussed in terms of imperfections such as grain boundaries and in-grain defects.

Effects of hydrogen on Er/p-type Si Schottky-barrier diodes.

Metal Er was deposited onto 〈100〉-oriented B-doped p-type crystalline silicon wafers, with or without plasma hydrogen treatment, to form Er/p-type Si Schottky barriers. The current-voltage and activation energy measurements reveal that hydrogen decreases the Schottky-barrier height (SBH) of Er/p-type Si by 0.10--0.12 eV, and, at the same time, the ideality factor is decreased from 1.17 to 1.08. The reason why hydrogen decreases the SBH and the ideality factor of Er/p-type Si and increases those of Al/p-type Si [Y. Q. Jia and G. G. Qin, Appl. Phys. Lett. 56, 641 (1991)] is that the main role of hydrogen is either passivating or generating the defects on the metal-semiconductor interface in Er/p-type Si and Al/p-type Si, respectively.

Optoelectronic properties of polycrystalline silicon produced by low-temperature (600°C) solid-phase crystallization of hydrogenated amorphous silicon

Abstract We present novel data on optoelectronic properties observed in the amorphous-to-polycrystalline silicon (polysilicon) phase transition, and the effect on as-crystallized films of a simple post-hydrogenation treatment. The polysilicon thin films were produced by low-temperature (600°C) furnace crystallization of undoped hydrogenated amorphous silicon (a-Si: H). Other parameters, such as the onset of crystallization, degree of amorphization and average grain size were determined by ultraviolet reflectivity and electron microscopy. The grain size is found to increase with decreasing a-Si: H substrate temperature, and a maximum areal grain size of 0.4 μm2 is obtained. Optical absorption, d.c. conductivity and transient photoconductivity measurements are employed to examine carrier transport mechanisms. We observe a Meyer-Neldel relationship between the d.c. conductivity pre-factor [sgrave]0 and activation energy E[sgrave] . A plasma hydrogenation treatment of the as-crystallized films results in an o...

CONTROLLING Au/n-Si SCHOTTKY BARRIER CONTAI-NING HYDROGEN BY ZERO BIAS ANNEALING AND REVERSE BIAS ANNEALING

Metal Au was deposited onto oriented phosphorous doped n-type epitaxial silicon. wafers, with or without plasma hydrogen treatment, to form Au/n-Si Schottky barrier (SB). The experimental results indicate: hydrogen decreases the Schottky barrier height (SBH) of Au/n-Si by 0.13eV; the SBH of Schottcky barrier containing hydrogen (SB(H)) can be controlled by zero bias annealing (ZBA) and reverse bias annealing (RBA), i.e. ZBA decreases and RBA increases the SBH of SB(H); and the controlling of SBH is reversible in at least three ZBA/RBA cycles. The increased SBH value of SB(H) after RBA is related not only to the reverse bias used in annealiug but also to the annealing temperature.

Controlling of Schottky barrier heights for Au/n-GaAs and Ti/n-GaAs with hydrogen introduced after metal deposition by bias annealing

Up to now, in most of the research work done on the effect of hydrogen on a Schottky barrier, the hydrogen was introduced into the semiconductor before metal deposition. This letter reports that hydrogen can be effectively introduced into the Schottky barriers (SBs) of Au/n-GaAs and Ti/n-GaAs by plasma hydrogen treatment (PHT) after metal deposition on 〈100〉 oriented n-GaAs substrates. The Schottky barrier height (SBH) of a SB containing hydrogen shows the zero/reverse bias annealing (ZBA/RBA) effect. ZBA makes the SBH decrease and RBA makes it increase. The variations in the SBHs are reversible. In order to obtain obvious ZBA/RBA effects, selection of the temperature for plasma hydrogen treatment is important, and it is indicated that 100 °C for Au/n-GaAs and 150 °C for Ti/n-GaAs are suitable temperatures. It is concluded from the analysis of experimental results that only the hydrogen located at or near the metal-semiconductor interface, rather than the hydrogen in the bulk of either the semiconductor or the metal, is responsible for the ZBA/RBA effect on SBH.

Evolution of microstructures in hydrogenated silicon films prepared by diluted-hydrogen and hydrogen-atom-treatment methods

Nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy, and Raman studies on microstructures of hydrogenated silicon films that were fabricated by diluted-hydrogen and hydrogen-atom-treatment methods are presented. The diluted-hydrogen samples tend to show a very sharp line shape in the NMR spectra at substrate temperatures higher than 300 °C, and the addition of atomic hydrogen treatment can produce the same NMR spectra at a lower temperature of about 250 °C. The Raman scattering spectra show that the atomic hydrogen treatment creates the microcrystalline phase while the diluted-hydrogen method produces amorphous phase plus a small quantity of microcrystalline phase. The infrared-absorption spectra also indicate an increase of SiH2 bonding configuration and a hydrogen content reduction when atomic hydrogen treatment is employed. The relation between the origin of the sharp line shape in the NMR spectra and the formation of the microcrystalline phase is also discussed. Together with increase of dark conductivity and reduction of the photo-to-dark conductivity ratio, these samples indicate that with appropriate hydrogen incorporation during deposition, and with plasma hydrogen treatment, these films should possess a much more compact structure. These results suggest that the degree of crystallinity of hydrogenated silicon films can be systematically adjusted. A qualitative model based on our experimental data is presented to illustrate the formation procedures of microcrystalline-phase hydrogenated silicon under the influence of plasma hydrogen and hydrogen dilution.

The Study on Microstructure by NMR, FTIR, Raman, Conductivity and Optical Bandgap in Hydrogenated Amorphous Silicon Prepared by Novel Fabrication Methods

ABSTRACTIt was found that hydrogen dilution in the SiH4/H2 mixture tend to show a sharp line-shape in the NMR spectra as the substrate temperature is higher than 300 °C. The hydrogen-atom-treatment method also produces the same effect at a lower substrate temperature about 250°C. The Raman scattering spectra show that the hydrogen-atom-treatment creates the microcrystalline structure at a temperature higher than 250°C while hydrogen dilution produces mixed phases containing amorphous phase and a small quantity of micro-crystalline phase. Together with the optical bandgap narrowing, the increase of the dark conductivity and the reduction of photo-to-dark conductivity ratio, these samples indicate that with more hydrogen incorporation during deposition and plasma hydrogen treatment, these films possess a much compact structure, and the degree of crystallinity of hydrogenated silicon film was found to be systematically changed.

Polysilicon thin Films and Devices Produced by Low-Temperature (600°C) Furnace Crystallisation of Hydrogenated Amorphous Silicon (a-Si:H)

ABSTRACTIn this work, we report on the electronic properties of polysilicon thin films and devices realised via furnace crystallisation of undoped a-Si: H. The onset of crystallisation, degree of amorphisation and average grain size are determined by UV reflectivity and electron microscopy. Grain size is found to increase with decreasing a-Si:H substrate temperature, and a maximum areal grain size of 0.4μm2 is obtained. Optical absorption, DC conductivity and transient photoconductivity measurements are employed to examine carrier transport mechanisms. We observe a Meyer-Neldel relationship between the DC conductivity prefactor σ0 and activation energy Eσ. A plasma hydrogenation treatment of the as-crystallised films results in an order of magnitude increase in the DC conductivity and a similar increase in photoconductivity. This is consistent with a shift of the Fermi level position 0.06 eV towards the conduction band. Additionally, analysis of the transient photoconductivity infers a reduced density of states. We discuss the implications of our results for polysilicon TFT optimisation.

Resistivity of chemical vapor deposited diamond films

Diamond films grown by plasma chemical vapor deposition techniques display a fairly low resistivity (∼106 Ω cm). Heat treating the films causes an increase in the resistivity by up to six orders of magnitude. The low resistivity of the as-grown films is postulated to be due to hydrogen passivation of traps in the films. Annealing causes dehydrogenation resulting in the electrical activation of deep traps with an attendant increase in the resistivity. This mechanism has been confirmed by an observed reduction of the resistivity of the heat-treated films when they are subjected to a plasma hydrogen treatment.