Charge State Of Hydrogen Research Articles

Laser illumination for manipulation of hydrogen charge states in silicon solar cells

This Letter investigates the important parameters of illumination for control of hydrogen charge states in p-type silicon solar cells. Through variations in the wavelength and intensity of illumination, evidence is provided for the importance of the neutral charge state of interstitial hydrogen, H0, for the passivation of defects in upgraded metallurgical grade (UMG) silicon. It is shown that through this approach minority carrier lifetimes may be achieved in excess of those realised through previous techniques, resulting in open-circuit voltages (iVOC) over 710 mV. (© 2015 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

Manipulation of Hydrogen Charge States for Passivation of P-Type Wafers in Photovoltaics

Passivation of defects in silicon solar cells using hydrogen has long been an area of significant interest to the photovoltaic community. In this paper, we explore the importance of the charge states of hydrogen for passivation of defects in p-type silicon and how these charge states might be manipulated using illumination. We show that by using illumination during hydrogenation processes at temperatures between 475 and 625 K, the lifetime of wafers containing high concentrations of hydrogen can be strongly increased. The magnitude of the increase depends on temperature, with the most significant increase occurring at 545 K with samples under illumination showing an average effective lifetime of 167 μs, while samples without illumination had an average lifetime of 67 μs. This increase in the lifetime with illumination is explained in terms of how the electron quasi-Fermi energy and, hence, the relative concentrations of the hydrogen charge states respond to illumination at these temperatures. We show a correlation between the predicted charge states of interstitial hydrogen and the effective lifetimes of the wafers.

Advanced Bulk Defect Passivation for Silicon Solar Cells

Through an advanced hydrogenation process that involves controlling and manipulating the hydrogen charge state, substantial increases in the bulk minority carrier lifetime are observed for standard commercial grade boron-doped Czochralski grown silicon wafers from 250-500 μs to 1.3-1.4 ms and from 8 to 550 μs on p-type Czochralski wafers grown from upgraded metallurgical grade silicon. However, the passivation is reversible, whereby the passivated defects can be reactivated during subsequent processes. With appropriate processing that involves controlling the charge state of hydrogen, the passivation can be retained on finished devices yielding independently confirmed voltages on cells fabricated using standard commercial grade boron-doped Czochralski grown silicon over 680 mV. Hence, it appears that the charge state of hydrogen plays an important role in determining the reactivity of the atomic hydrogen and, therefore, ability to passivate defects.

Hydrogen Passivation of B-O Defects in Czochralski Silicon

We report on hydrogen passivation of boron-oxygen defects through manipulation of the hydrogen charge states within the silicon. Standard hydrogenation processes which do not control hydrogen charge states do not appear to passivate a significant quantity of boron-oxygen defects and may result in a reduction in lifetime for wafers with high boron doping concentrations. An improved hydrogenation process through charge state manipulation is observed to lead to substantial improvements in the lifetimes of standard 2Ωcm commercial grade boron-doped Czochralski wafers and experimental compensated 2Ωm Czochralski grown wafers. The passivation of boron-oxygen defects using hydrogen is a fully reversible process, and hence subsequent processes can lead to a net reactivation of boron- oxygen defects if there are insufficient quantities of atomic hydrogen in the correct charge state. Through improved hydrogenation, independently confirmed open circuit voltages in excess of 680mV are demonstrated on solar cells fabricated using standard commercial grade boron-doped Czochralski grown wafers on an industrial production line.

Evaluation of the mean energy deposit during the impact of charged particles on liquid water

The DNA strand break yield due to the impact of ionizing particles on living beings is closely related to the number of inelastic events per unit absorbed dose produced by these particles. The higher this number, the higher the probability of causing DNA strand breaks per unit absorbed dose. In a previous work, it was found that the total number of events produced by primary particles and the secondary electrons is almost independent of the type and energy of the incident particle (or LET). This finding could be supported by a quasi-constant mean energy deposit by inelastic event (). In this work, was defined and determined for electrons and the non-negative charge states of hydrogen (H0, +) and helium (He0, +, 2 +) species impacting on liquid water. Ionization, excitation and charge transfer (up to two-electron transfers) processes have been included in present calculations. We found that, for liquid water, is within 13.7 ± 4.1 eV, 14.2 ± 1.7 eV and 13.8 ± 1.4 eV for electrons, hydrogen and helium species, respectively, with impact energies changing over three orders of magnitude. Unlike the mean excitation energy, the mean energy deposit per inelastic event depends not only on the target molecule but also on the projectile features. However, this dependence is relatively weak. This fact supports the quasi-independent number of inelastic events per unit absorbed dose found previously when charged particles impact on matter.

A Density Functional Theory Study of the Charge State of Hydrogen in Metal Hydrides

Density functional theory and Bader charge analyses were used to investigate the charge state of hydrogen in vanadium, niobium, tantalum, palladium, and niobium−palladium alloys. Over a range of concentrations and hydrogen-site configurations, it is found that hydrogen consistently acquires a net charge of between approximately −0.51e and −0.64e in the pure group 5 metals compared with a significantly smaller value of 0.3e in palladium. Although there is indirect evidence that the electronic charge plays a role in the solubility and diffusivity of hydrogen in the group 5 metals, this is the first work to quantify the value of the charge. Hydrogen tends to migrate to regions of the metal lattice that minimize its overall charge density, which generally corresponds to the T-site in the bcc metals. It is found that the charge of hydrogen at the O-site of vanadium can be slightly lower due to lattice deformation and may explain the occupation of both T- and O-sites in vanadium hydrides.

Changes in phase composition of Zr–Fe–V getter after hydriding and vacuum dehydriding cycles

Abstract The stability and phase composition of the commercial non-evaporable getter SAES St 707 (70% Zr, 24.6% V, and 5.4% Fe) during hydriding and vacuum dehydriding cycles were investigated. Structure and phase composition were studied using X-ray diffraction (XRD) with Co Kα and 57 Fe Mossbauer spectroscopy (MS). The samples were hydrided during annealing in pure hydrogen at 550 °C for 15 min and dehydrided in vacuum at 550 °C for 15 min. This procedure was applied 1, 5 and 10 times in the same furnace without a contact with an ambient atmosphere (air) between the cycles. Finally, the samples were removed from the furnace to an ambient atmosphere where XRD and MS experiments were performed. Cubic C15 Laves phase and α-Zr were determined from XRD measurements in the samples which were annealed in vacuum during the last heat treatment step. ZrH 2 and ZrV 2 H 3.6 phases were identified in the samples which were in the hydrogen charged state after the last step of the heat treatment. In the samples after 5 and 10 cycles a small amount of cubic and monoclinic ZrO 2 was found. These oxides nucleated already during the first step of the heat treatment in vacuum and their amounts increased by subsequent annealing steps. In situ XRD measurements during heating showed a structure amorphisation due to hydrogen absorption.

Chemical state and diffusion behavior of hydrogen isotopes in liquid lithium–lead

Hydrogen existing in liquid lithium–lead was modeled using first-principles molecular dynamics. The chemical state of hydrogen was analyzed based on the trajectory and charge of hydrogen, and the H–Li radial distribution function, as obtained from calculations. Results show that, in liquid lithium–lead, the charge state of hydrogen correlates with Li–H interatomic distance: it becomes close to H − because of a binding interaction of Li–H when the distance is short, whereas it becomes close to H 0 as a hydrogen atom dissolved in liquid lead when the distance is long. Additionally, it was observed that hydrogen diffuses in liquid lithium–lead with jumping from one site to another where the binding interaction of Li–H can be formed, which would be one of the main diffusion mechanisms.

Correlation between charge state and diffusion of hydrogen in Ti-based quasicrystals

The dependence of the charge state of hydrogen as a function of H content in the 1/1 approximant to icosahedral Ti-based quasicrystals (QCs) was studied using a first-principles method based on the density functional theory and norm-conserving pseudopotentials. It was found that the dependence is strong and non-monotonic. Hydrogen diffusion is significantly hindered in QCs with a charged hydrogen atom.

Charge state and diffusion of hydrogen in the TiZrNi icosahedral alloy

The electronic structure of a hydrogen atom in a 1/1 approximant of the Ti-Zr-Ni icosahedral quasicrystal is investigated using ab initio methods based on the density functional theory. The charge state of the hydrogen atom in Ti36Zr32Ni13 with different types of tetrahedral pores, as well as the charge state of hydrogen at a ratio H/M ≈ 1.7, is determined. The hydrogen atom is found to be in a nearly neutral state. The coefficient of hydrogen diffusion in Ti36Zr32Ni13 is calculated.

Dependence of Hydrogen Diffusion on the Electric Field in p-Type Silicon

Hydrogen was incorporated into p-type Czochralski silicon by hydrogen plasma exposure, and hydrogen-enhanced thermal donor formation was achieved. Posthydrogenation annealing treatment with and without electric field was carried out. Hydrogen diffusion after posthydrogenation annealing was investigated by spreading resistance measurements and diffusivities were determined. Direct evidence for the presence of the positive charge state of hydrogen in p-type silicon was established by the dependence of hydrogen diffusion on electric field. The conversion from neutral and positively charged hydrogen and into negatively charged hydrogen is discussed. © 2004 The Electrochemical Society. All rights reserved.

Interstitial H and H2 in SiC

The properties of hydrogen in 3C and 4H type silicon carbide (SiC) are studied theoretically at the density functional level. We find that only singly positive or negative charge states of hydrogen are thermodynamically stable in SiC. The transition from the positive to the negative charge state (+/−) is at 0.9 and 1.3 eV above the valence band maximum in 3C and 4H structures, respectively. The diffusion barrier for the proton is 0.5 eV (being, however, anisotropic in 4H). For the negative H− the diffusion barrier is found to be considerably higher, of the order of 3 eV.

Hydrogen Internal Friction Peak in Amorphous Zr-Cu-Al-Si Alloys

The hydrogen internal friction peak (HIFP) in amorphous (a-) Zr 60 Cu 40-y Al y (y = 0, 10), a-Zr 50 Cu 50 , a-Zr 40 Cu 60 and a-Zr 40 Cu 50-x Al 10 Si x (x = 0, 1, 3) are studied to pursue a high-strength and high-damping performance as well as the underlying process for the HIFP in a-alloys. The tensile strength, σ f , of a-Zr 60 Cu 30 Al 10 , a-Zr 40 Cu 50 Al 10 and a-Zr 40 Cu 49 Al 10 Si 1 increases from about 1.5 GPa to 2 GPa with increasing hydrogen concentration, C H , to 20 at%. One part of a-Zr 60 Cu 30 Al 10 , a-Zr 40 Cu 50 Al 10 and a-Zr 40 Cu 49 Al 10 Si 1 specimens show a very high HIFP beyond 3 × 10 -2 in the as hydrogen charged state, where the hydrogen induced structural relaxation (HISR) proceeds above room temperature. A maximum value of the HIFP, Q -1 p , after the HISR shows a moderate increase with increasing C H , about I x 10 -2 at C H of 10 at% The combination of σ f and Q -1 p data indicates that a-Zr 60 Cu 40 Al 10 (H), a-Zr 40 Cu 50 Al 10 (H) and a-Zr 40 Cu 49 Al 10 Si 1 (H) after the HISR are potential materials with a high-strength and high-damping performance. The peak temperature of the HIFP, Tp, at 10 at%H is 309 K, 270 K and 220 K with the measurement frequency of about 200 Hz for a-Zr 40 Cu 49 Al 10 Si 1 , a-Zr 40 Cu 50 Al 10 and a-Zr 60 Cu 30 Al 10 , respectively. It is noted that Tp found for a-Zr 40 Cu 49 Al 10 Si 1 shows a breakthrough for an elevation of T p of the HIFP in a-alloys, and that a composite material composed of these a-alloys can serve a high-damping performance in a wide temperature range or a wide frequency range. For the underlying process of the HIFP, the Q -1 p vs. C H data shows a camel's humps like change for a-Zr 50 Cu 50 and a-Zr 40 Cu 60 , suggesting that only one part of hydrogen atoms can contribute to the HIFP. In contrast, Q -1 p shows a monotonous increase with increasing C H for C H below 20 at% for a-Zr 60 Cu 40-y Al y (y = 0, 10) and a-Zr 40 Cu 50-x Al 10 Si x (x = 0, 1, 3), suggesting that most of hydrogen atoms are associated with the HIFP in the a-alloys. For the relaxation parameters of the HIFP, values of 1/τ 0 ) fall in the range expected for a simple relaxation process for a-Zr 60 Cu 40-y Al y (y = 0, 10) and a-Zr 40 Cu 50-x Al 10 Si x (x = 0, 1, 3), but are extremely high for a-Zr 50 Cu 50 and a-Zr 40 Cu 60 , where τ 0 denotes the pre-exponential factor of the relaxation time. These results are discussed in the light of the amorphous structures in the a-alloys.

Proton-induced defect generation at the Si-SiO/sub 2/ interface

We report first-principles calculations of interface trap formation in MOS structures. Hydrogen is known to passivate Si dangling bonds at the Si-SiO/sub 2/ interface, but the subsequent arrival of H+ at the interface causes depassivation of Si-H bonds. We show that, contrary to conventional assumptions, depassivation is not a two-step process, namely, neutralization of H+ by a Si electron, reaction with a Si-H bond, and subsequent formation of an H/sub 2/ molecule. Instead, we establish that H+ is the only stable charge state of hydrogen at the interface, and that H+ reacts directly with Si-H. The products of this reaction are an H/sub 2/ molecule and a positively charged dangling bond center (D/sup +/), formed via the reaction SiH + H/sup +/ /spl rArr/ D/sup +/ + H/sub 2/. Here the D/sup +/ center is most likely the positive charge state of the P/sub b/ defect. As a result, H-induced interface-trap formation depends on the electric field in the oxide to establish a preferred direction for proton drift, but does not depend on the availability of Si electrons to enable the interface reaction to occur. After the dangling bond center is formed via this process, the subsequent charge state of the interface traps is controlled by the Si surface potential. A hydrogen catalytic cycle can lead to reversible passivation and depassivation reactions at or near the interface, depending on experimental conditions.

Lattice location of hydrogen in Mg doped GaN

We have used ion channeling to examine the lattice configuration of hydrogen in Mg doped wurtzite GaN grown by metal organic chemical vapor deposition. Hydrogen is introduced by exposure to hydrogen gas or electron cyclotron resonance plasmas and by ion implantation. A density functional approach including lattice relaxation was used to calculate total energies for various locations and charge states of hydrogen in the wurtzite Mg doped GaN lattice. Results of channeling measurements are compared with channeling simulations for hydrogen at lattice locations predicted by the density functional theory.

Hydrogen effect on enhancement of defect reactions in semiconductors: example for silicon and vacancy defects

A model of interaction of the hydrogenated vacancy with silicon interstitial and different dopants (B, P and As) in crystalline silicon is considered. Quantum chemical calculations show that hydrogenation of the vacancy leads to a decrease of mechanical stresses of the silicon crystalline lattice near vacancy and consequently to a considerable decrease of the energy barrier height for the interstitial atom incorporation into the vacancy site of the crystalline lattice. The potential barriers for incorporation of the interstitial into the site and for leaving the atoms from the site have been calculated as a function of hydrogen localization in the vicinity of the vacancy (inside and outside of the vacancy), the charge state of hydrogen localized outside the vacancy (H 0 and H +), and the transport direction (〈111〉, 〈110〉 and 〈100〉) of the atoms both in and out of the vacancy. The theory is compared with the experimental results.

Lattice Location of Deuterium in Plasma and Gas Charged Mg Doped GaN

We have used ion channeling to examine the lattice configuration of deuterium in Mg doped GaN grown by MOCVD. The deuterium is introduced by exposure to gas phase or ECR plasmas. A density functional approach including lattice relaxation, was used to calculate total energies for various locations and charge states of hydrogen in the wurtzite Mg doped GaN lattice. Results of channeling measurements are compared with channeling simulations for hydrogen at lattice locations predicted by density functional theory.

Lattice Location of Deuterium in Plasma and Gas Charged Mg Doped GaN

AbstractWe have used ion channeling to examine the lattice configuration of deuterium in Mg doped GaN grown by MOCVD. The deuterium is introduced by exposure to gas phase or ECR plasmas. A density functional approach including lattice relaxation, was used to calculate total energies for various locations and charge states of hydrogen in the wurtzite Mg doped GaN lattice. Results of channeling measurements are compared with channeling simulations for hydrogen at lattice locations predicted by density functional theory.

Hydrogen Enhanced Defect Reactions in Silicon: Interstitial Atom - Vacancy

AbstractIn the paper the model of interaction of the hydrogenated vacancy with silicon interstitial and different dopants (B, P and As) in crystalline silicon is considered. Quantum chemical calculations using the SCF MO LCAO technique in the NDDO valence approach show that the hydrogenation of the vacancy leads to the considerable decrease of the energy barrier height for the interstitial atom incorporation into the vacancy site of the crystalline lattice. The potential barriers for incorporation of the interstitial into the site and for leaving the atoms from the site have been calculated as a function of hydrogen localization in the vicinity of the vacancy (inside and outside of the vacancy), the charge state of hydrogen localized outside the vacancy (HO, H+ and H-) and the transport direction (<111>, <110> and <100>) of the atoms both to the vacancy and out from it. The theory is compared with the reported experimental results.

Hydrogen passivation of nitrogen in 6H–SiC

N-doped 6H–SiC wafers have been annealed in hot hydrogen for two doping levels, corresponding to n- (n∼1017 cm−3) and n+-type (n∼1019 cm−3) material. Electron spin resonance shows little passivation of N by hydrogen in n-type material, where secondary-ion-mass spectroscopy shows better penetration of deuterium. Both observations are accounted for in terms of Fermi-level control of the hydrogen charge state.