Effect Of Hydrogen Passivation Research Articles

Effect of hydrogen passivation on charge storage in silicon quantum dots embedded in silicon nitride film

The effect of hydrogen passivation on the charge storage characteristics of two types of silicon nitride films containing silicon quantum dots (Si QDs) grown by SiH4+N2 and SiH4+NH3 plasma was investigated. The transmission electron microscope analysis and the capacitance-voltage measurement showed that the silicon nitride film grown by SiH4+NH3 plasma has a lower interface trap density and a higher density of Si QDs compared to that grown by SiH4+N2 plasma. It was also found that the charge retention characteristics in the Si QDs were greatly enhanced in the samples grown by means of SiH4+NH3 plasma, due to the hydrogen passivation of the defects in the silicon nitride films by NH3 during the growth of the Si QDs.

Hydrogen passivation effect in nitrogen-doped ZnO thin films

The role of hydrogen in nitrogen-doped ZnO thin films was studied by Fourier transform infrared (FTIR) absorption and modeled by first-principles calculations to understand the difficulty of doping ZnO p-type with nitrogen. Nitrogen-doped ZnO films were fabricated by low-pressure metal-organic chemical vapor deposition (MOCVD). High levels of nitrogen incorporation were observed, but the acceptor concentrations remained low. Theoretical analysis suggests there is a high probability that NO− and H+ charged defects combine to form the neutral defect complexes, thereby compensating the nitrogen-related acceptors. Calculated values of the vibrational frequencies of the related infrared modes agree well with the measured spectra. Thus, we believe the difficulty of achieving p-type doping in MOCVD-grown ZnO films is due, at least partially, to inadvertent passivation by hydrogen.

Effect of hydrogen passivation on polycrystalline silicon thin films

Hydrogen passivation is essential for improving the properties of polycrystalline silicon thin films. We have observed that remote plasma hydrogenation with duration up to 30 min effectively passivated the defects and improved the Hall mobility, trap density and photoluminescence intensity. Over 60 min of hydrogenation caused the photoluminescence intensity to decrease. It seems that excessive hydrogenation not only passivated defects but also created new defects (Si–H 2 bonds and hydrogen molecules) in the grains. Raman spectroscopy detected that hydrogen formed Si–H 2 bonds in the poly-Si up to 100 nm from surface. Creation of these defects corresponded to a decrease of the photoluminescence intensity. These defects might be harmful to poly-Si-based devices.

Defect passivation in multicrystalline silicon for solar cells

We report on the effect of hydrogen passivation in ribbon multicrystalline silicon (mc-Si) wafers from SiNx:H anti-reflecting layer using simultaneous rapid thermal annealing of Al back-contact and SiNx anti-reflection coating on the front (RTP-Al∕SiNx). Scanning room-temperature photoluminescence spectroscopy revealed a strong inhomogeneity in the increase of minority carrier lifetime caused by the hydrogen defect passivation in mc-Si. We present experimental evidence that RTP-Al∕SiNx processing leads to strong lifetime enhancement caused by hydrogen defect passivation in low-lifetime regions of mc-Si wafers. Additional details on the hydrogenation mechanism are revealed in a course of the dehydrogenation study. Hydrogen out-diffusion shows a different rate or activation energy between high and low lifetime regions of the wafers.

Effect of hydrogen passivation on the microstructure of silicon nanocrystals in SiO2

Effect of hydrogen passivation on the microstructure of silicon nanocrystals in SiO2

Effect of hydrogen passivation on the microstructure of silicon nanocrystals in SiO 2

Si nanocrystals were formed by implantation of Si + into SiO 2 film on (1 0 0) Si, followed by high-temperature annealing. Transmission electron microscopy (TEM) was used to examine the effect of hydrogen passivation on the microstructure of the Si nanocrystals (nc) in SiO 2 film. The size and spatial distribution of the Si nc in both non-passivated and passivated samples were investigated using dark-field imaging technique. It is shown that the size and spatial distribution of the Si nc are much similar for both samples. The concentration of Si nc in SiO 2 film was determined from the dark field images taken under different diffraction conditions. Selected area electron diffraction pattern shows that there is no preferential orientation for the Si nc in the SiO 2 film. For the passivated sample, the increase of photoluminescence intensity is attributed to the elimination of the optically inactive defects in SiO 2 matrix and around the Si nc/SiO 2 interface.

Low resistance Ohmic contacts to n-GaN by Ar plasma and forming gas ambient treatments

In this article, a scheme for fabricating low resistance Ohmic contacts to n-GaN was developed. This approach takes advantage of Ar plasma treatment and thermal annealing in forming gas ambient. As a result, the adjustment of Ar flow rate was very effective in improving the contact resistance. After proper Ar plasma treatment, the contact resistance and specific contact resistance of as-deposited Ohmic contacts were reduced to 0.362 Ω mm and 3.9×10−5 Ω cm2, respectively. Low contact resistance (0.103 Ω mm) and specific contact resistance (3.2×10−6 Ω cm2) were obtained after annealing in N2 gas ambient. By performing thermal annealing in forming gas ambient, even lower contact resistance (0.093 Ω mm) and specific contact resistance (2.6×10−6 Ω cm2) were successfully achieved, indicating that the electrical characteristics of Ohmic contacts would not be affected by the effect of hydrogen passivation of dopants in n-GaN.

Hydrogen passivation of multi-crystalline silicon solar cells

The effects of hydrogen passivation on multi-crystalline silicon (mc-Si) solar cells are reported in this paper. Hydrogen plasma was generated by means of ac glow discharge in a hydrogen atmosphere. Hydrogen passivation was carried out with three different groups of mc-Si solar cells after finishing contacts. The experimental results demonstrated that the photovoltaic performances of the solar cell samples have been improved after hydrogen plasma treatment, with a relative increase in conversion efficiency up to 10.6%. A calculation modelling has been performed to interpret the experimental results using the model for analysis of microelectronic and photonic structures developed at Pennsylvania State University.

Deep center passivation in 3C-SiC by hydrogen plasma with a grid for damage suppression

In order to passivate deep levels, hydrogen was introduced into 3C-SiC by a hydrogen plasma treatment. The effects of hydrogen were investigated by deep level transient spectroscopy (DLTS). DLTS results indicated that hydrogen passivates deep levels in the as-grown sample. However, the results also indicated that the plasma treatment simultaneously forms deep levels originated from damages in the surface region. In order to suppress the damages, we introduced a grid between the sample and the plasma source during the plasma treatment. DLTS results showed that the grid reduces the deep levels originated from the damages, retaining the hydrogen passivation effects. The defect concentration is less than 10 14 cm −3 for the sample treated by the hydrogen plasma with the grid and subsequently annealed at 300 °C.

Effects of Hydrogen on the Deep Levels in Si, ZnO and Diamond Studied by Cathodoluminescence

AbstractThe effects of hydrogen on the deep level luminescence in Si, ZnO and diamond were studied by means of cathodoluminescence. It is well known that most of the deep levels in Si are passivated by hydrogen. Scratch lines on Si surface, which do not show any characteristic luminescence, obtain so-called D-line luminescence by hydrogen plasma treatment. It indicates that only nonradiative defects are passivated but D-line luminescence is not passivated by hydrogenation. Contrarily, typical ZnO crystal shows the green emission, which is attributed to the point defects or impurities. Hydrogen completely passivates this green emission, and in turn, enhances the band edge emission. The effect of hydrogen passivation disappeared by the annealing at temperatures higher than 600 °C. Hydrogen behaves more peculiarly in diamond. The hydrogenated diamond film shows the characteristic emission around 2.3 eV in photon energy. Since it disappears by oxidization treatment, this emission is attributed to hydrogen at the subsurface region. The detailed study indicated that hydrogen in diamond has bistable states.

Growth of ultrahigh carbon-doped InGaAs and its application to InP/InGaAs(C) HBTs

Growth of ultrahigh carbon-doped p-type InGaAs lattice matched to InP by chemical beam epitaxy (CBE) using carbon tetrabromide (CBr/sub 4/) as a doping source was investigated. Effects of growth temperature, group V supply pressure, and CBr/sub 4/ supply pressure on growth rate, composition, mobility, and hole concentration of carbon-doped InGaAs were studied. Ultrahigh net hole concentration and room-temperature mobility of 2 /spl times/ 10/sup 20//cm/sup 3/ and 33 cm/sup 2//V/spl middot/sec, respectively, were achieved. Mobility of the ultrahigh carbon-doped InGaAs using CBr/sub 4/ compared favorably to those of CBE grown carbon-doped InGaAs using carbon tetrachloride (CCl/sub 4/) and molecular beam epitaxy grown beryllium (Be)-doped InGaAs grown at low temperature. The highly carbon-doped InGaAs layers grown by CBE using CBr/sub 4/ as a doping source showed a negligible hydrogen passivation effect and were used for the growth of high-performance, highly carbon-doped base InP/InGaAs heterojunction bipolar transistor epitaxial layer structures.

Effect of particle size on the photoluminescence from hydrogen passivated Si nanocrystals in SiO2

The effect of hydrogen passivation on the photoluminescence from Si nanocrystals prepared in SiO2 by ion implantation and annealing is examined as a function of nanocrystal size (implant fluence). Passivation is shown to produce a significant increase in emission intensities as well as a redshift of spectra, both of which increase with increasing fluence. These results are shown to be consistent with a model in which larger nanocrystals are assumed to contain more nonradiative defects (i.e., the defect concentration is assumed to be proportional to the nanocrystal surface area or volume). Since this results in a smaller fraction of larger nanocrystals contributing to the initial luminescence, emission spectra are initially blueshifted relative to that that might be expected from the physical nanocrystal size distribution. The contribution from larger crystallites is then disproportionately increased by passivation resulting in the observed redshift.

Optical transmission losses in polycrystalline silicon strip waveguides: Effects of waveguide dimensions, thermal treatment, hydrogen passivation, and wavelength

Signal propagation delays dominate over gate delays in the ever-shrinking ultra large scale integrated (ULSI) circuits. Consequently, silicon-based monolithic optoelectronic circuits (SMOE) with their light speed signal propagation can provide unique advantages for future generations of microprocessors. For such SMOE circuits, we need optical interconnects compatible with silicon technology. Strip waveguides consisting of polycrystalline silicon (polySi) clad with SiO2 offer excellent optical confinement and ease of fabrication that are ideal for such interconnect applications. One major challenge with using this material system, however, is its insertion loss. In this paper we provide techniques for minimizing optical transmission losses in polySi strip waveguides. Our previous work using polySi strip waveguides, showed an optical transmission loss of 15 dB/cm at λ=1.55 µm, which is a communication wavelength of choice in optical fibers because it represents an absorption minimum. Similar measurements in crystalline silicon strip waveguides1 yielded transmission losses of less than 1 dB/cm. Hitherto, in decreasing loss from 77 dB/cm to 15 dB/cm, we had minimized loss from surface scattering by improving the film surface morphology, and decreased bulk absorption with hydrogen passivation. In this paper we report a further reduction in the residual bulk loss from 15 dB/cm to 9 dB/cm. By experimenting with different waveguide core dimensions, we find that the contribution of bulk loss towards net transmission loss decreases with waveguide core thickness. Additionally, high temperature treatment provides strain relief in the polySi, decreasing transmission loss. Annealing in an oxygen ambient is not recommended because it always increases transmission loss. Hydrogen passivation improves transmission, attributable to passivation of light-absorbing dangling bond defect sites present at polySi grain boundaries. Together, these methods have resulted in the lowest measured loss value of 9 dB/cm at λ=1.55 µm. Since integrated SiGe and Ge photodetectors are more efficient at shorter wavelengths like λ=1.32 µm, transmission loss is also measured at λ=1.32 µm. Losses at the two wavelengths (1.32 µm and 1.55 µm) are similar when defects and stress in the waveguides are minimized.

Decreased low frequency noise by hydrogen passivation of polysilicon emitter bipolar transistors

The effect of hydrogen passivation by forming gas annealing (FGA) on the bipolar junction transistor low frequency noise was investigated. The results demonstrated a reduced 1/ f noise component by a factor of five after FGA, which resulted in a reduced corner frequency. An equivalent input noise spectral density ( S I B ) dependence on base current ( I B) of S I B ∼ I 2 B and on emitter area ( A E) of S I B ∼ A E −1 was observed, both before and after FGA. The interpretations of the results were (a) the 1/ f noise was due to carrier number fluctuation, (b) the noise sources were homogeneously distributed over the polysilicon/monosilicon emitter interfacial oxide, and (c) the noise sources were passivated by hydrogen.

Hydrogen passivation of AlxGa1−xAs/GaAs studied by surface photovoltage spectroscopy

We study the effect of hydrogen passivation on AlxGa1−xAs grown by liquid-phase epitaxy (LPE) on semi-insulating GaAs. Using surface photovoltage (SPV) spectroscopy and Hall measurements we investigate the effect of hydrogenation on AlxGa1−xAs epilayers with electron concentrations in the range 1016–1017cm−3. We measure the minority carrier diffusion length in the as-grown AlxGa1−xAs epilayers to be in the range 0.1–0.8 μm and to increase significantly upon hydrogenation. Hydrogen passivation of interface states at the heterojunction is demonstrated for epilayers with low carrier concentration. We apply the result from the SPV measurements to speculate on the band bending at the heterojunction.

H+ passivation of poly-si solar cells processed by different annealing processes

The effects of different annealing processes on the photovoltaic (PV) properties and the spectral response as well as minority carrier lifetime in the bulk of unanalyzed PF5 ion implantation poly-Si solar cells were investigated. The different hydrogen passivation effects of defects in poly-Si induced by three heat treatment processes are reported. We used RTA-rapid thermal annealing, YAG pulse laser annealing and CTSA-classical three-step annealing for this study. The results show that cells processed by RTA (800°C, 4 sec) achieved the best PV properties and spectral response among all annealed samples. Under this precess condition, no or few defects were induced in bulk. While RTA (>-850°C for 4 sec), CTSA as well as YAG laser processes induced defects of different nature and concentration in the bulk of cells. It is further shown that hydrogen ion implantation significantly improved, the performances of poly-Si cells. It is able to efficiently remove the YAG laser induced defects in bulk. However, it cannot completely passivate the defects induced by CTSA and RTA processes.

Study of NH 3 Plasma Damage on GaAs Schottky Diode in Inductively Coupled Plasma System

Si‐doped n‐GaAs samples were exposed to inductively coupled plasma (ICP) discharges at different chuck temperature, pressure, source powers, and rf chuck powers to simulate the effects of ion damage and hydrogen passivation during silicon nitride deposition for GaAs ICs fabrication. The ideality factor and reverse breakdown voltage of Schottky diodes were used to characterize the plasma damages. Both ideality factor and reverse breakdown voltage increase with increasing rf chuck power and ICP power because of the reduction of free carriers due to the lattice disorder created by the ion bombardment. A similar trend was observed with increasing deposition temperature and pressure; however, this is mainly due to the passivation of Si dopants in the GaAs donor layer by hydrogen free radicals and ion bombardment damage. The high temperature process enhances the hydrogen diffusion and high pressure produces more hydrogen free radicals and deposition bias voltage increases at both conditions. © 1999 The Electrochemical Society. All rights reserved.

The effect of hydrogen passivation on electrical characteristics of double-polysilicon self-aligned bipolar transistors

The influence of hydrogen passivation using forming gas annealing (FGA), on the electrical performance of double-polysilicon self-aligned bipolar junction transistors was investigated. While the collector current remained essentially unaffected after FGA, the base current decreased substantially. As a result, the peak DC current gain increased by a factor of three. Identification of the various base current components showed that the SiO 2/monosilicon interface area along the perimeter of the emitter window, were effectively passivated after FGA, both in the quasi-neutral base and in the space charge region. The FGA treatment was also found to lead to an increase in the peak cut-off frequency by up to 40%. This is explained by a decrease in emitter–base junction capacitance, which was verified experimentally.

Photoluminescence and photoconductivity in hydrogen-passivated ZnTe

Hydrogen passivation effects in undoped p-ZnTe single crystals were studied by photoluminescence (PL) and photoconductivity (PC) measurements. Samples were exposed to r.f. hydrogen plasma at for different durations. Before passivation PL peaks were observed at 2.06 eV, 1.47 eV, 1.33 eV and 1.06 eV. After 60 min of exposure, samples showed strong band edge green luminescence at 2.37 eV due to an exciton bound to a Cu acceptor. In PC studies the dark current decreased by a factor of 70 on passivation for 60 min. From the temperature dependence of PC gain, the minority carrier lifetime was found to go through a maximum of at 220 K before passivation. After 60 min of hydrogenation, remained constant at for and decreased for . The activation energies of have been determined and show marked changes on passivation for . Comparison between PL and PC studies showed that the deep acceptor level responsible for emission at 2.06 eV is passivated, giving rise to strong band edge emission at 2.37 eV, while emission due to the midgap impurity levels at 1.47, 1.33 and 1.05 eV remained unaffected. The thermal activation energies of PL peaks have also been determined and allow the construction of a defect energy level diagram for ZnTe.

Enhanced room temperature mobilities and reduced parallel conduction in hydrogen passivated Si/SiGe heterostructures

The effect of hydrogen passivation on the room temperature mobility and density is studied on n-type /strained Si modulation-doped structures. Room temperature carrier densities reduced by an order of magnitude while a threefold maximum increase in mobility was observed. By using a two-carrier analysis, it was found that, apart from parallel conduction passivation, the hydrogenation process also improves the channel mobility directly. Plasma and electrolytic hydrogenation were carried out on samples with different spacer thicknesses and mobilities. The plasma method of hydrogenation was found to be more effective when compared to the electrolytic technique. A successful removal of incorporated hydrogen and partial recovery of the control sample was shown by annealing the hydrogenated sample in vacuum at .