Sex: Female
Education:
- Doctor of Philosophy in Electrical and Electronic Engineering, The University of Manchester, United Kingdom, 2021
- Master of Science in Applied Physics, University of Santo Tomas, 2011
- Bachelor of Science in Physics, University of the Philippines, Baguio, 2009
Field of Specialization
Solar Photovoltaics
Semiconductors
Nanotechnology
Raman Spectroscopy
Photoluminescence Spectroscopy
Deep Level Transient Spectroscopy
Laplace DLTS
Minority Carrier Transient Spectroscopy
Economics
Public Policy
Medical Physics
Researches:
Article title: Passivation of thermally-induced defects with hydrogen in float-zone silicon
Authors: J A T De Guzman, V P Markevich, D Hiller, I D Hawkins, M P Halsall and A R Peaker
Publication title: Journal of Physics D: Applied Physics 54(27): 275105, 2021
Abstract:
In this study, passivation of thermally-activated recombination centers with hydrogen in n-type float zone (FZ) Si containing nitrogen has been investigated. Prior to hydrogenation samples were heated to 550 °C using rapid thermal annealing and conventional furnaces. A large decrease in minority carrier lifetime occurred upon the heat-treatments confirming previous reports. A sequence of electron traps created in this process have been detected in the deep level transient spectra and characterized. Significant changes in the spectra have occurred after treatments in remote hydrogen plasma and subsequent annealing of the hydrogenated samples in the temperature range 100 °C–400 °C. A total elimination of electrical activity of the thermally induced defects has been observed in the hydrogenated samples subjected to annealing in the temperature range 150 °C–300 °C. The results obtained suggest a simple way for an effective cure of the degraded FZ-Si-based solar cells. Possible defect reactions occurring in the FZ-Si crystals and the role of nitrogen and carbon upon the performed treatments are discussed.
Full text link https://tinyurl.com/btx53u9w
Article title: Indium-Doped Silicon for Solar Cells – Light Induced Degradation and Deep Level Traps
Authors: Joyce Ann T. De Guzman, Vladimir P. Markevich, Ian D. Hawkins, Hussein M. Ayedh, José Coutinho, Jeff Binns, Robert Falster,Nikolay V. Abrosimov, Iain F. Crowe, Matthew P. Halsall, Anthony R. Peaker
Publication title: Physica Status Solidi A (PSSA), 2021
Abstract:
Indium-doped silicon is considered a possible p-type material for solar cells to avoid light-induced degradation (LID), which occurs in cells made from boron-doped Czochralski (Cz) silicon. Herein, the defect reactions associated with indium-related LID are examined and a deep donor is detected, which is attributed to a negative-U defect believed to be InsO2. In the presence of minority carriers or above bandgap light, the deep donor transforms to a shallow acceptor. An analogous transformation in boron-doped material is related to the BsO2 defect that is a precursor of the center responsible for BO LID. The electronic properties of InsO2 are determined and compared to those of the BsO2 defect. Structures of the BsO2 and InsO2 defects in different charges states are found using first-principles modeling. The results of the modeling can explain both the similarities and the differences between the BsO2 and InsO2 properties.
Full text link https://tinyurl.com/2j9xjhem
Article title: Electronic Properties and Structure of Boron–Hydrogen Complexes in Crystalline Silicon
Authors: Joyce Ann T. De Guzman, Vladimir P. Markevich, José Coutinho, Nikolay V. Abrosimov, Matthew P. Halsall, Anthony R. Peaker
Publication title: Solar RRL, 2100459, 2021
Abstract:
The subject of hydrogen–boron interactions in crystalline silicon is revisited with reference to light and elevated temperature-induced degradation (LeTID) in boron-doped solar silicon. Ab initio modeling of structure, binding energy, and electronic properties of complexes incorporating a substitutional boron and one or two hydrogen atoms is performed. From the calculations, it is confirmed that a BH pair is electrically inert. It is found that boron can bind two H atoms. The resulting BH2 complex is a donor with a transition level estimated at E c–0.24 eV. Experimentally, the electrically active defects in n-type Czochralski-grown Si crystals co-doped with phosphorus and boron, into which hydrogen is introduced by different methods, are investigated using junction capacitance techniques. In the deep-level transient spectroscopy (DLTS) spectra of hydrogenated Si:P + B crystals subjected to heat-treatments at 100 °C under reverse bias, an electron emission signal with an activation energy of ≈0.175 eV is detected. The trap is a donor with electronic properties close to those predicted for boron–dihydrogen. The donor character of BH2 suggests that it can be a very efficient recombination center of minority carriers in B-doped p-type Si crystals. A sequence of boron–hydrogen reactions, which can be related to the LeTID effect in Si:B is proposed.
Full text link https://doi.org/10.1002/solr.202100459.
Article title: Acceptor-oxygen defects in silicon: the electronic properties of centers formed by boron, gallium, indium, and aluminum interactions with the oxygen dimer
Authors: Joyce Ann T. de Guzman, Vladimir P. Markevich, Ian D. Hawkins, José Coutinho, Hussein M. Ayedh, Jeff Binns, Nikolay V. Abrosimov, Stanislau B. Lastovskii, Iain F. Crowe, Matthew P. Halsall, and Anthony R. Peaker
Publication title: Journal of Applied Physics (2021) JAP21-AR-DIS2022-05907R
Abstract:
It is well established that boron reacts with two oxygen atoms in Czochralski-grown silicon (Cz-Si) to form a defect, which is responsible for the dominant light-induced degradation (LID) in solar cells made from Cz-Si:B material. The detrimental effect of LID has stimulated a move by solar cell manufacturers to the use of silicon with other group-III dopants, particularly with gallium. Cz-Si:Ga is immune to the BO-type LID. The information available in the literature on the interactions of oxygen with either Al, Ga, or In impurities in Si is limited. We use ab initio modeling and junction spectroscopy techniques to study a family of defects with unusual electronic properties, which have been detected in Cz-Si samples doped with different shallow acceptor species. We have carried out detailed measurements of the temperature dependencies of hole emission rate, equilibrium occupancy, and hole capture kinetics for the traps observed in differently doped p-type Cz-Si samples. It is found from the analysis of the changes in magnitude of the deep-level-transient signals with temperature that the equilibrium occupancy function of the traps is characteristic for a defect with negative-U properties in all the samples. The positions of the E(−/+) occupancy level of the defects are very close in differently doped samples, E(−/+) = Ev + (0.31 ± 0.01) eV. It is argued that the oxygen dimer interacts with group-III atoms in silicon and these interactions result in the formation of AsO2 complexes (A is either B, Al, Ga, or In atom) with very similar electronic properties
Full text link https://tinyurl.com/2czs6a4s
Article title: Defect Reactions Responsible for Boron-Oxygen Degradation in Crystalline Silicon
Photovoltaics
Authors: J.A.T. De Guzman, V.P. Markevich, A.R. Peaker, M. Vaqueiro-Contreras, J. Coutinho, I.F. Crowe, I. Hawkins, S. Hammersley, M.P. Halsall
Publication title: EUPVSEC Proceedings. (145-151), 3-936338-73-6, September 2020
Abstract:
Light-induced degradation of silicon solar cells containing boron and oxygen impurity atoms (BO-LID) has been linked recently with structural transformations of the defect consisting of a substitutional boron atom and two interstitial oxygen atoms - BsO2. An atomistic model and configuration-coordinate diagram of the BsO2 defect have been proposed (M. Vaqueiro-Contreras et al, J. Appl. Phys. 125 (2019) 185704). In the present work, we have studied the transformations of the BsO2 defect between configurations with different recombination activity in n+-p-p+ diodes fabricated from Si:B+O materials with different boron concentrations using deep-level transient spectroscopy (DLTS) and Laplace DLTS. The transformations have been initiated either by minority carrier injection (MCI) by forward biasing the diodes (BO degradation) or by increasing the temperature of the diodes above 313 K in dark after the MCI treatments (BO annealing). The values of energy barriers for the forward and back processes have been determined and found to be consistent with those known from literature for BO-LID. Further, we have compared the defect reactions degrading the boron-oxygen system with similar reactions in material doped with gallium, indium or aluminium and discuss possible explanations of the reduced degradation in samples doped with group-III elements other than boron.
Full text available upon request to the author
Article title: Minority carrier traps in Czochralski-grown p-type silicon crystals doped with B, Al, Ga, or In impurity atoms
Authors: Joyce Ann T. de Guzman, Vladimir P. Markevich, Simon Hammersley, Ian D. Hawkins, Iain Crowe, Nikolay V. Abrosimov, Robert Falste, Jeff Binns, Pietro Altermatt, Matthew P. Halsall, Anthony R. Peaker
Publication title: 2020 47th IEEE Photovoltaic Specialists Conference (PVSC) (pp. 1013-1018). IEEE
Abstract:
Minority carrier traps in Czochralski-grown (Cz) silicon crystals doped with either boron, aluminum, gallium, or indium impurity atoms have been investigated by means of deep-level transient spectroscopy and other junction-related techniques. The experimental data have suggested that minority carrier trapping effects in Cz-Si samples doped with different acceptor impurities are associated with complexes incorporating a substitutional group-III impurity atom and two oxygen atoms, which are found to be negative-U defects with close locations of E(-/+) occupancy level at about Eu + 0.32 eV. We have determined the energy barriers and frequency factors for the reversible transformations of the complexes between deep donor and shallow acceptor states. These parameters are discussed in relation to light-induced degradation behavior of solar cells on p-type Cz-Si crystals.
Full text link https://tinyurl.com/2p8aw792
Article title: Formation and Elimination of Electrically-Active Thermally-induced defects in Float-Zone-Grown Silicon Crystals
Authors: De Guzman, Joyce Ann T., Markevich, Vladimir P., Mullins, Jack, Grant, Nicholas E., Murphy, John D., Hiller, Daniel, Halsall, Matthew P. and Peaker, Anthony R.
Publication title: 2021 11th International Conference on Silicon Photovoltaics – Silicon PV 2021.American Institute of Physics.
Abstract:
Understanding the origins of the phenomena that limit the minority carrier lifetime in float-zone-grown silicon (FZ-Si) is an important area in photovoltaics research. Although FZ silicon has been applauded for its stability, purity, and high minority carrier lifetime, it has been found recently that severe degradation of the minority carrier lifetime occurs in FZ-Si crystals upon thermal treatments in the temperature range 400-700 oC and upon light soaking at elevated (~ 100 oC) temperatures. In this work, deep level transient spectroscopy (DLTS) and high-resolution Laplace DLTS have been used to elucidate the formation and elimination processes of the electrically active thermally-induced defects. Float-zone-grown n-type Si crystals with and without added nitrogen from different suppliers have been studied. It has been found that the spectra of deep levels from thermally-induced defects are different in FZ-Si crystals from different manufacturers. Significant qualitative changes were observed in the DLTS spectra after heat-treatments of the FZ-Si samples at different temperatures for different treatment duration. These results indicate various defect reactions occurring upon heat-treatments in FZ-Si materials with varying ensembles of intrinsic defects, doping, and residual impurities in the as-grown state. Also, we have found that hydrogenation from a remote plasma source with subsequent low-temperature annealing has resulted in the total deactivation of thermally-induced defects in FZ silicon.
Full text available upon request to the author
Article title: On the correlation between light-induced degradation and minority carrier traps in boron-doped Czochralski silicon
Authors: Saman Jafari, Yan Zhu, Fiacre Rougieux, Joyce Ann T. De Guzman, Vladimir P. Markevich, Anthony R. Peaker, and Ziv Hameiri
Publication title: ACS Applied Materials & Interfaces 13(5), 2021
Abstract:
Boron-doped Czochralski-grown silicon wafers dominate the photovoltaic market. Light-induced degradation of these wafers is one of the most significant roadblocks for high-efficiency solar cells. Despite a very large number of publications on this topic, only a few studies have directly investigated the precursor of the defect responsible for this degradation. In this study, using the photoconductance decay measurement method, we identify the precursor of the defect responsible for light-induced degradation. By comparing the photoconductance decay of samples in the different states, we observe the presence of a minority carrier trap in the annealed state, which is not present after degradation. Trap annihilation shows a clear anticorrelation with the generation of the recombination-active boron-oxygen defect, as determined from minority carrier lifetime measurements. Furthermore, it is concluded that a model based on a single-level trap cannot explain the doping-dependent measurements, meaning that the detected trap has two or more energy levels.
Full text available upon request to the author
Article title: Boron–Oxygen Complex Responsible for Light‐Induced Degradation in Silicon Photovoltaic Cells: A New Insight into the Problem
Authors: Vladimir P. Markevich, Michelle Vaqueiro-Contreras, Joyce T. De Guzman, José Coutinho, Paulo Santos, Iain F. Crowe, Matthew P. Halsall, Ian Hawkins, Stanislau B. Lastovskii, Leonid I. Murin, and Anthony R. Peaker
Publication title: Physica Status Solidi (A) Applications and Materials 216(17), July 2019
Abstract:
Results available in the literature on minority carrier trapping and light induced degradation (LID) effects in silicon materials containing boron and oxygen atoms are briefly reviewed. Special attention is paid to the phenomena associated with “deep” electron traps (J.A. Hornbeck and J.R. Haynes, Phys. Rev. 1955, 97, 311) and the recently reported results which have linked LID with the transformation of a defect consisting of a substitutional boron atom and an oxygen dimer (BsO2) from a configuration with a deep donor state into a recombination active configuration associated with a shallow acceptor state (M. Vaqueiro‐Contreras et al., J. Appl. Phys. 2019, 125, 185704). The significance of the latter work is discussed and detailed experimental results on the electronic and dynamic properties of the BsO2 complex are presented. It is shown that the BsO2 complex is a defect with negative‐U properties and it is responsible for minority carrier trapping and persistent photo‐conductivity in non‐degraded Si:B+O samples and solar cells. It is argued that the “deep” electron traps observed by Hornbeck and Haynes are the pre‐cursors of the “slow” forming shallow acceptor defects, which are responsible for the dominant LID in boron‐doped Cz‐Si crystals. Both the deep and shallow defects are BsO2 complexes, transformations between charge states and atomic configurations of which account for the observed electron trapping and LID phenomena.
Full text link https://tinyurl.com/365h5x5p
Article title: Kinetics of Bulk Lifetime Degradation in Float‐Zone Silicon: Fast Activation and Annihilation of Grown‐In Defects and the Role of Hydrogen versus Light
Authors: Daniel Hiller,Vladimir P. Markevich,Joyce Ann T. de Guzman,Dirk König,Slawomir Prucnal,Wolfgang Bock,Jaakko Julin,Anthony R. Peaker,Daniel Macdonald,Nicholas E. Grant,John D. Murphy
Publication title: Physica status solidi (a), 217(17), 2000436, 2020
Abstract:
Float-zone (FZ) silicon often has grown-in defects that are thermally activated in a broad temperature window (≈300–800 °C). These defects cause efficient electron-hole pair recombination, which deteriorates the bulk minority carrier lifetime and thereby possible photovoltaic conversion efficiencies. Little is known so far about these defects which are possibly Si-vacancy/nitrogen-related (VxNy). Herein, it is shown that the defect activation takes place on sub-second timescales, as does the destruction of the defects at higher temperatures. Complete defect annihilation, however, is not achieved until nitrogen impurities are effused from the wafer, as confirmed by secondary ion mass spectrometry. Hydrogenation experiments reveal the temporary and only partial passivation of recombination centers. In combination with deep-level transient spectroscopy, at least two possible defect states are revealed, only one of which interacts with H. With the help of density functional theory V1N1-centers, which induce Si dangling bonds (DBs), are proposed as one possible defect candidate. Such DBs can be passivated by H. The associated formation energy, as well as their sensitivity to light-induced free carriers, is consistent with the experimental results. These results are anticipated to contribute to a deeper understanding of bulk-Si defects, which are pivotal for the mitigation of solar cell degradation processes.
Full text available upon request to the author
Article title: Electrical Characterization of Thermally Activated Defects in n-Type Float-Zone Silicon
Authors: Yan Zhu, Fiacre Rougieux, Nicholas E. Grant, Joyce Ann T. De Guzman, John D. Murphy, Vladimir P. Markevich, Gianluca Coletti, Anthony R. Peaker, and Ziv Hameiri
Publication title: IEEE Journal of Photovoltaics, 2020
Abstract:
Float-zone (FZ) silicon is usually assumed to be bulk defect-lean and stable. However, recent studies have revealed that detrimental defects can be thermally activated in FZ silicon wafers and lead to a reduction of carrier lifetime by up to two orders of magnitude. A robust methodology which combines different characterization techniques and passivation schemes is used to provide new insight into the origin of degradation of 1 Ω·cm n-type phosphorus doped FZ silicon (with nitrogen doping during growth) after annealing at 500 °C. Carrier lifetime and photoluminescence experiments are first performed with temporary room temperature surface passivation which minimizes lifetime changes which can occur during passivation processes involving thermal treatments. Temperature- and injection-dependent lifetime spectroscopy is then performed with a more stable passivation scheme, with the same samples finally being studied by deep level transient spectroscopy (DLTS). Although five defect levels are found with DLTS, detailed analysis of injection-dependent lifetime data reveals that the most detrimental defect levels could arise from just two independent single-level defects or from one two-level defect. The defect parameters for these two possible scenarios are extracted and discussed.
Full text available upon request to the author
Article title: Boron-oxygen related light-induced degradation of Si solar cells: Transformation between minority carrier traps and recombination active centers
Authors: Anthony R. Peaker, Saman JafariYan ZhuFiacre RougieuxJoyce Ann T. De GuzmanVladimir P. MarkevichZiv Hameiri
Publication title: IEEE-PVSC Proceedings, 2020
Abstract:
Light-induced degradation (LID) has a considerable impact on solar cells made from boron-doped Czochralski (Cz) grown silicon wafers. Thus, a great effort has been made to investigate this type of degradation. Recently, it has been suggested that minority carrier traps are acting as precursors to the LID-related defects and that the enhanced recombination might occur through a trap-assisted Auger process. In this study, we investigate the former suggestion using photoconductance measurement of boron-doped Cz wafers in the course of LID. A clear anti-correlation between minority carrier trap density and LID extent has been found. We detect minority carrier traps in the dark annealed state which disappear upon LID. A time constant of 55±5 min for trap annihilation under 1 sun illumination at 60 °C has been determined, in agreement with previous findings regarding the LID-related defects' formation rate. Additionally, the kinetic of the traps is studied at different temperatures ranging from 25 °C to 100 °C. This study highlights the fact that despite decades of LID-related research, new insights can be obtained when using new approaches, such as those presented in this paper.
Full text available upon request to the author
Article title: New insights into the thermally activated defects in n-type float-zone silicon
Authors: Yan Zhu, Fiacre Rougieux, Nicholas Grant, Jack Mullins, Joyce Ann De Guzman, John D. Murphy, Vladimir P. Markevich, Gianluca Coletti1, Anthony R. Peaker, and Ziv Hameiri
Publication title: AIP Conference Proceedings (Vol. 2147, No. 1, p. 140014). AIP Publishing LLC, 2019
Abstract:
Float-zone silicon has been long assumed to be bulk defect free and stable. Nevertheless, recently it was found that upon annealing between 450 °C to 700 °C detrimental defects can be activated in this material. Previous studies via deep level transient spectroscopy have identified several defect levels. However, it is still not clear which of these levels have a substantial impact on the minority carrier lifetime. In this study, we determine the recombination parameters of the dominant defect level using a combination of deep level transient spectroscopy and temperature and injection dependent lifetime spectroscopy. Additionally, we investigated the effect of hydrogenation on the thermally activated defects in n- type float-zone silicon.
Full text available upon request to the author