B2H6 Gas Research Articles

Optical properties of low-pressure DC Ar plasma torch with N2–SiH4–B2H6 gas mixture injection for Si–B–N thin film deposition

Si–B–N ceramic hard films were prepared by injecting N2+SiH4+B2H6 reaction gas into an argon DC arc plasma jet at reduced pressure. XPS, FT-IR, SEM, and microhardness tester were used to characterize the samples, and the optical properties of Ar discharge plasma jet with and without reaction gas injection were studied by a multichannel high-resolution spectroscopy and a wide spectral range spectroscopy. It is found that the deposited films are mainly composed of Si, B, N and O. The film surface presents a dense structure with hundred-nanometer-sized clusters, and the hardness of sample is greatly enhanced. When the reaction gas is injected into the plasma jet, the emission of excited atoms in the background plasma is greatly reduced, and the growth rate of Si–B–N film shows a significant downward trend as the reaction gas injection ring or substrate holder is moved away from the torch nozzle. A slight enhancement of background plasma emission is observed near the substrate surface with increasing the distance between gas injection ring and torch nozzle, which indicates that the suppression effect of the reactive gas injection on the background plasma emission and the activation efficiency of the reaction gas are weakened, thereby reducing the deposition rate.

Dehydrogenation of diborane on small Nbn+ clusters.

The reactivity of Nbn+ (1 ≤ n ≤ 21) clusters with B2H6 is studied by using a self-developed multiple-ion laminar flow tube reactor combined with a triple quadrupole mass spectrometer (MIFT-TQMS). The Nbn+ clusters were generated by a magnetron sputtering source and reacted with the B2H6 gas under fully thermalized conditions in the downstream flow tube where the reaction time was accurately controlled and adjustable. The complete and partial dehydrogenation products NbnB1-4+ and NbnB1-4H1,2,4+ were detected, indicative of the removal of H2 and likely BHx moieties. Interestingly, these NbnB1-4+ and NbnB1-4H1,2,4+ products are limited to 3 ≤ n ≤ 6, suggesting that the small Nbn+ clusters are relatively more reactive than the larger Nbn>6+ clusters under the same conditions. By varying the B2H6 gas concentrations and the reactant doses introduced into the flow tube, and by changing the reaction time, we performed a detailed analysis of the reaction dynamics in combination with the DFT-calculated thermodynamics. It is demonstrated that the lack of cooperative active sites on the Nb1+ cations accounts for the weakened dehydrogenation efficiency. Nb2+ forms partial dehydrogenation products at a faster rate. In contrast, the Nbn>6+ clusters are subject to more flexible vibrational relaxation which disperse the energy gain of B2H6-adsorption and thus are unable to overcome the energy barriers for subsequent hydrogen atom transfer and H2 release.

Catalytic Cleavage of the Dative Bond of Ammonia Borane by Polymeric Carbonyl Groups for Enhanced Energy Generation

Dissociation of the dative (B–N) bond of ammonia borane (NH3BH3/AB) is essential to prevent its thermochemical oligomerization to chemically resistant BNHx compounds, for its applicability as a fuel in high-energy propulsion systems. We show that when AB is incorporated into polymer matrices containing carbonyl functional groups, thermal activation causes the carbonyl groups to engage in nucleophilic interactions with AB. Such interactions catalyze the lysis of the dative B–N bond resulting in the decomposition of AB to NH3 and B2H6 gases, with no evidence of oligomerization. We find that the carbonyl groups function as catalysts and do not participate in any net reaction. In situ high-heating rate (∼105 K/s) characterizations demonstrate that facile-synthesized hierarchical (micro/nano) composite particles of AB/carbonyl-based polymers completely gasify to NH3 and B2H6 at ∼510 K, followed by spontaneous ignition in the air with negligible delay. Thus, the current chemical pathway enables the solid-state storage of reactive fuels, NH3 and B2H6, and their controlled on-demand release for high-energy applications.

Effects of PECVD preparation conditions and microstructures of boron-doped polysilicon films on surface passivation of p-type tunnel oxide passivated contacts

We investigate the effects of plasma-enhanced chemical vapor deposition (PECVD) preparation conditions and microstructures of the boron-doped polysilicon films on the passivation quality of p-type tunnel oxide passivated contact (p-TOPCon) integrated with plasma-assisted N2O oxidation (PANO) SiOx. The B2H6 gas flow, activation temperature, substrate temperature, H2 dilution ratio, and carbon (C)-doped polycrystalline silicon insertion layer are investigated. The best passivation based on plane-surface n-type CZ-Si lifetime sample manifests an implied open-circuit voltage (iVoc) of 706 mV, a single-sided saturation current density (J0,s) of 17.9 fA/cm2, and an effective lifetime (τeff) of 2.25 ms at 1 × 1015 cm−3, showing a slight improvement compared with the controlled sample featuring an iVoc of 703 mV. Although this passivation quality is one of the best specifications of the p-TOPCon featuring PANO SiOx so far, it is insufficient for industry application. Detailed experimental studies and a numerical simulation suggest that the passivation quality is probably weakened by the boron-induced defects located at the interfacial and beneath the SiOx, whose harmful influence is difficult to offset by the field-passivating effect. Generally, we provide new insight into the bottleneck of the p-TOPCon's passivation and then discuss the new strategies for improving the p-TOPCon's passivation in this paper.

Ultrashallow Junction (USJ) Fabrication by Advanced Ion Implantation Processes

For advanced CMOS device process, a preamorphization implant (PAI) procedure had been carried on source and drain (SD) lightly doped source and drain (LDD), heavily doped source and drain (HDD), and contact implants before an ultralow energy (ULE) beamline (BL)-based implant to depress the channeling effect for lower OFF-current and short channel effect (SCE). One-step plasma doping (PLAD) was utilized to replace this two-step BL implant process for the pMOS device because PLAD has an in situ real-time controllability for less channeling effect. The PLAD using B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas with ULE high dose regime was utilized for this application. It significantly reduces cost and increases throughput because this one low-cost PLAD module eliminates PAI BL implant. The pMOS devices also exhibit significant performance improvements, including ~30% lower contact resistances ( <b xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</b> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CS</sub> ), similar threshold voltage ( <b xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</b> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> ) and subthreshold voltage (SV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> ) characteristics, and ~8% higher drive currents (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><b>DS</b></sub> ) without degrading OFF-current (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> ).

Langmuir-Type Mechanism for In-Situ Doping in CVD Si and Si1−xGex Epitaxial Growth

In-situ doping process of B and P in CVD Si and Si1−xGex (100) epitaxial growth is investigated using SiH4–GeH4–dopant gas (B2H6 or PH3)–H2 gas mixture. For lower dopant gas partial pressure, the in situ doping is explained quantitatively by the Langmuir-type adsorption and reaction at Si–Si, Si–Ge or Ge–Ge pair sites on the (100) surface. For higher B2H6 gas partial pressure (P B2H6), it is proposed that SiH4, GeH4 and B2H6 molecules are adsorbed and react partially at the B-occupied sites where B2H6 molecules have been adsorbed on the (100) surface. For higher PH3 gas partial pressure (P PH3), it is proposed that the in situ doping and Ge incorporation are enhanced by the self-limited adsorption of PH3 molecules and the decomposition of GeH4 at the P-occupied sites where PH3 molecules have been adsorbed on the (100) surface, respectively, and that the decrease of P concentration with increasing P PH3 in high P PH3 region is caused by lower segregation coefficients of P at Si–Ge and Ge–Ge pair sites than that at Si–Si pair sites according to the Henry’s law. Fairly good agreement is obtained between all the experimental data and the modified Langmuir-type mechanism for in situ doping.

Plasma‐immersion ion implantation: A path to lower the annealing temperature of implanted boron emitters and simplify PERT solar cell processing

AbstractIon implantation is a suitable and promising solution for the massive industrialization of boron doping, which is a crucial process step for most next‐generation solar cells based on crystalline silicon (c‐Si). However, the use of ion implantation for boron doping is limited by the high temperature (in the 1050°C range) of the subsequent activation anneal, which is essential to dissolve the boron clusters and reach a high‐emitter quality. In this work, we propose the use of plasma‐immersion ion implantation (PIII) from B2H6 gas precursor instead of the standard beamline ion implantation (BLII) technique to decrease this temperature down to 950°C. PIII and BLII boron emitters were compared with annealing temperatures ranging from 950°C to 1050°C. Contrary to BLII, no degradation of the emitter quality was observed with PIII implants annealed at 950°C along with a full activation of the dopants in the emitter. At 1000°C, emitter saturation current densities (J0e) below 21 fA/cm2 were obtained using the PIII technique regardless of the tested implantation doses for sheet resistances between 110 and 160 Ω/sq. After metallization steps, the metal/emitter contact resistances were assessed, indicating that these emitters were compatible with a conventional metallization by screen‐printing/firing. The PIII boron emitters' performances were further tested with their integration in n‐type passivated emitter rear totally diffused (PERT) solar cells fully doped by PIII. Promising results already show a conversion efficiency of 20.8% using a lower annealing temperature than with BLII and a reduced production cost.

Langmuir-Type Mechanism for In-Situ Doping in CVD Silicon-Germanium Epitaxial Growth

In-situ doping process of B and P in CVD Si, Si1-xGex and Ge epitaxial growth is reviewed using a modified Langmuir-type mechanism. For lower dopant gas (B2H6 or PH3) partial pressure, growth rate, Ge fraction and dopant (B or P) concentration in the films are explained by a Langmuir-type mechanism. For higher B2H6 gas partial pressure, it is proposed that SiH4, GeH4 and B2H6 molecules are absorbed and react partially at the B-occupied sites where B2H6 molecules have been adsorbed on (100) surface. For higher PH3 gas partial pressure, it is proposed that GeH4 molecules decomposes and PH3 molecules are adsorbed at the P-occupied sites and that P atoms are incorporated into the grown film according to the Henry’s law. Fairly good agreement is obtained between all experimental data and the modified Langmuir-type mechanism for in-situ doping.

Characterization of particle generated during plasma-enhanced chemical vapor deposition on amorphous carbon layer using particle beam mass spectrometer

Nanoscale particles that can affect the process yield were generated using the plasma-enhanced chemical vapor deposition (PECVD) process. A particle beam mass spectrometer is remarkably useful to understand particle behavior in a reactor. The properties of nanoscale particles obtained from the exhaust line of PECVD during amorphous carbon layer (ACL) growth under various growth conditions were investigated. The number concentration and the size of the nanoscale particles generated were quite sensitive to growth parameters such as radio frequency (RF) plasma power, C2H2, and dopant (i.e., NH3 and B2H6) gas flow rate. For an ACL growth at higher RF plasma power, the average size of the nanoscale particles decreased as the number concentration of particles increased while they are opposingly increased in particle size and decreased in concentration for a higher C2H2 flow rate. A reduction in both the average nanoscale particle size and their number concentration occurred when NH3 gas was used for nitrogen-doped ACL. By contrast, ACL growth with increasing B2H6 gas flow for boron-doped ACL exhibited a larger average nanoscale particle size and number concentration. The particle number concentration was in the range of 106–108 cm−3 with average particle sizes of 100–400 nm. According to this study, the measurement of real-time particle size distribution can help to minimize the number of generated particles and optimize the ACL deposition process.

Selective Boron Elimination from B2H6–SiH4 Gas Mixtures for Purifying Si

A boron elimination method based on the difference in the pyrolysis temperatures of SiH4 and B2H6 is proposed for purifying metallurgical grade Si feedstock for photovoltaic applications through direct hydrogenation using high-pressure hydrogen plasma. A simple kinetic model is constructed to estimate the proposed boron elimination filter performance. The filter performance is experimentally evaluated. It is confirmed that there is a significant temperature difference between the B2H6 and SiH4 transmission behavior through the filter. However, when SiH4 and B2H6 gases are simultaneously supplied to the filter at the same flow rate of a few standard cubic centimeters per minute, the SiH4 transmission curve is affected by B2H6 and almost overlaps with the B2H6 curve. In contrast, by decreasing the B2H6 flow rate to one thousandth the SiH4 flow rate, B2H6 co-supply has little influence on the SiH4 transmission curve. The type of carrier gas (H2 and He) also affects the transmission curve. With increasing filter temperature, the B elimination effect of the filter becomes greater. The B concentration in Si films prepared by a single elimination process can be reduced to about 1/3000 of the value estimated from the concentration ratio in the unfiltered gas mixture.

21%-Efficient n-type Rear-junction PERT Solar Cell with Industrial Thin 156mm Cz Single Crystalline Silicon Wafer

We have achieved 21.2% efficiency, and 670mV open-circuit voltage(calibrated in Fraunhofer ISE) of n-type rear junction(RJ) PERT (Passivated Emitter Rear Totally-diffused) solar cell with plated Ni/Ag contacts, Al2O3 rear passivation, and screen-printed local Al BSF on industrial 180μm-thickness 6-inch n-type Czochralski (Cz) single crystalline silicon wafer. Also 21.0% efficiency and 669mV open-circuit voltages was achieved with 125μm-thickness wafer. Effects of borosilicateglass (BSG) deposited by APCVD in different B2H6 gas flow rate and the influence of O2 addition during furnace tube anneal were studied in terms of not only boron emitter quality but also impact on the cell Voc and FF. We found that, at fixed diffusion temperature, surface boron concentration could be controlled mainly by changing B2H6 flow rate during BSG deposition by APCVD and subsidiary by O2 addition in the tube furnace anneal. Additionally, as risks of n-type mass production, the 6” n-type wafer quality deviation issue and thin wafer related process issues were discussed.

Boron‐doped hydrogenated silicon carbide alloys containing silicon nanocrystallites for highly efficient nanocrystalline silicon thin‐film solar cells

AbstractBoron‐doped hydrogenated silicon carbide alloys containing silicon nanocrystallites (p‐nc‐SiC:H) were prepared using a plasma‐enhanced chemical vapor deposition system with a mixture of CH4, SiH4, B2H6 and H2 gases. The influence of hydrogen dilution on the material properties of the p‐nc‐SiC:H films was investigated, and their roles as window layers in hydrogenated nanocrystalline silicon (nc‐Si:H) solar cells were examined. By increasing the RH (H2/SiH4) ratio from 90 to 220, the Si―C bond density in the p‐nc‐SiC:H films increased from 5.20 × 1019 to 7.07 × 1019/cm3, resulting in a significant increase of the bandgap from 2.09 to 2.23 eV in comparison with the bandgap of 1.95 eV for p‐nc‐Si:H films. For the films deposited at a high RH ratio, the Si nanocrystallites with a size of 3–15 nm were formed in the amorphous SiC:H matrix. The Si nanocrystallites played an important role in the enhancement of vertical charge transport in the p‐nc‐SiC:H films, which was verified by conductive atomic force microscopy measurements. When the p‐nc‐SiC:H films deposited at RH = 220 were applied in the nc‐Si:H solar cells, a high conversion efficiency of 8.26% (Voc = 0.53 V, Jsc = 23.98 mA/cm2 and FF = 0.65) was obtained compared to 6.36% (Voc = 0.44 V, Jsc = 21.90 mA/cm2 and FF = 0.66) of the solar cells with reference p‐nc‐Si:H films. Further enhancement in the cell performance was achieved using p‐nc‐SiC:H bilayers consisting of highly doped upper layers and low‐level doped bottom layers, which led to the increased conversion efficiency of 9.03%. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Investigation of In Situ Boron‐Doping in SiGe Source/Drain Layer Growth for PMOS Devices

Embedded SiGe (eSiGe) source/drain (S/D) was studied to enhance PMOS performance. Detailed investigations concerning the effect of GeH4 and B2H6 gas flow rate on the resultant Boron‐doping of the SiGe layer (on a 40 nm patterned wafer) were carried out. Various SiGeB epitaxial growth experiments were realized under systematically varying experimental conditions. Key structural and chemical characteristics of the SiGeB layers were investigated using Secondary Ion Mass Spectroscopy (SIMS), nanobeam diffraction mode (NBD), and Transmission Electron Microscopy (TEM) itself. Furthermore, Ion/Ioff performances of 40 nm PMOS transistors are also measured by the Parametric Test Systems for the semiconductor industry. The results indicate that the ratio between GeH4 and B2H6 gas flow rates influences not only the Ge and Boron content of the SiGeB layer, but also the PMOS channel strain and the morphology of the eSiGe S/D regions which directly affect PMOS performance. In addition, the mechanism of Boron‐doping during SiGe layer growth on the pattern wafer is briefly discussed. The results and discussion presented within this paper are expected to contribute to the optimization of eSiGe stressor, aimed for advanced CMOS devices.

Effective nanoconfinement of 2LiBH4–MgH2 via simply MgH2 premilling for reversible hydrogen storages

To improve nanoconfinement of LiBH4 and MgH2 in carbon aerogel scaffold (CAS), particle size reduction of MgH2 by premilling technique before melt infiltration is proposed. MgH2 is premilled for 5 h prior to milling with LiBH4 and nanoconfinement in CAS to obtained nanoconfined 2LiBH4–premilled MgH2. Significant confinement of both LiBH4 and MgH2 in CAS, confirmed by SEM–EDS–mapping results, is achieved due to MgH2 premilling. Due to effective nanoconfinement, enhancement of CAS:hydride composite weight ratio to 1:1, resulting in increase of hydrogen storage capacity, is possible. Nanoconfined 2LiBH4–premilled MgH2 reveals a single–step dehydrogenation at 345 °C with no B2H6 release, while dehydrogenation of nanoconfined sample without MgH2 premilling performs in multiple steps at elevated temperatures (up to 430 °C) together with considerable amount of B2H6 release. Activation energy (EA) for the main dehydrogenation of nanoconfined 2LiBH4–premilled MgH2 is considerably lower than those of LiBH4 and MgH2 of bulk 2LiBH4–MgH2 (ΔEA = 31.9 and 55.8 kJ/mol with respect to LiBH4 and MgH2, respectively). Approximately twice faster dehydrogenation rate are accomplished after MgH2 premilling. Three hydrogen release (T = 320 °C, P(H2) = 3–4 bar) and uptake (T = 320–325 °C, P(H2) = 84 bar) cycles of nanoconfined 2LiBH4–premilled MgH2 reveal up to 4.96 wt. % H2 (10 wt. % H2 with respect to hydride composite content), while the 1st desorption of nanoconfined sample without MgH2 premilling gives 4.30 wt. % of combined B2H6 and H2 gases. It should be remarked that not only kinetic improvement and B2H6 suppression are obtained by MgH2 premilling, but also the lowest dehydrogenation temperature (T = 320 °C) among other modified 2LiBH4–MgH2 systems is acquired.

Effects of post-deposition treatments on transparent conducting ZnO:B thin films grown by MOCVD

In this work, the effects of post-treatments such as air-annealing (AA), light soaking (LS), and heat-light soaking (HLS) on the electrical properties of boron-doped ZnO (ZnO:B) films were investigated. The ZnO:B films were deposited by metal organic chemical vapor deposition (MOCVD) using diethyl zinc (DEZ), H2O, and low toxicity triethylboron (TEB) instead of the commonly used highly toxic B2H6 gas. Both the carrier concentration and electron mobility were increased after HLS post-treatment; thereby, the resistivity obviously decreased from 4.5 × 10−3 to 2.4 × 10−3 Ω·cm after HLS post-treatment under AM1.5, 100 mW/cm2 illumination at 130 °C for 30 min. The details of this beneficial effect from HLS post-treatment for Cu(In,Ga)Se2 solar cells are also described together with the possible reason.

Boron Elimination Filter from SiH4 and B2H6 Gas Mixture for Purification of Metallurgical Si

We have proposed the solar-grade Si film formation method from metallurgical-grade (MG) Si source by using a chemical transport induced by high-pressure hydrogen plasma1). In this method, selectivity of hydrogen induced chemical reaction was utilized to eliminate the metal impurities from MG-Si source. However, MG-Si also contains B and P which are electrically active element in Si matrix. These are difficult to remove by using above method, because they can form volatile hydrides. So, the simple process to eliminate these elements is necessary. Fortunately, it can be expected that elimination of PH3 would be easily achieved by using a molecular sieve due to the polarity of PH3 2). However, B2H6 molecule has no dipole moment in common with SiH4, hence molecular sieve is not expected to remove B2H6 efficiently from SiH4 and B2H6gas mixture.Then, in this study, we have attempted to eliminate B2H6 from the gas mixtures by using difference of the pyrolytic behavior of both gases and demonstrated that the developed filter can operate effectively as B2H6filter. EXPERIMENTAL The porous carbon plate with its thickness of 5mm was used as filter element to the benefit of its chemical inertness, electrical conductivity (162μΩcm), relatively wide specific surface area, and its porosity (30%). The plate was settled in the filter vessel and connected to the heater power source to control its temperature by electrical heating. To investigate the elimination property of the pyloritic filter precisely, the SiH4 and B2H6 gases supplying from gas cylinder were used in this study. The gas mixture ratio of SiH4 and B2H6 was controlled through mass flow controller. Moreover, H2 and He are used as carrier gas. The transmission property of SiH4 and B2H6for porous carbon filter at various temperatures was evaluated by gas phase FTIR. To ensure the Boron elimination from Si material by using the filter, Si film was formed on Si substrate by thermal CVD at 800°C through the use of gas mixture after passing through the filter and B concentration in the film was evaluated by SIMS. RESULTS AND DISCUSSION Figure 1 shows the filter temperature (Tfilter) dependence of transmission properties of SiH4 and B2H6. He carrier gas flow rate was 10 slm. During the experiment, the filter vessel pressure was kept at 200 Torr. As shown in Fig.1, B2H6 transmittance begins to decrease at 200°C and is reduced to almost zero at 350°C. On the other hand, SiH4 begins to decrease at 450°C and shows the transmittance of 10% even at 550°C. From this result, it is found that B2H6 can be eliminated efficiently without sacrifice of SiH4, if the Tfilteris kept at 400°C.Figure 2 shows the B removal performance of the porous carbon filter at various temperatures. The carrier gas flow rate was 10slm. The removal performance (RPgas/film) was defined by dividing the concentration ratio in the gas phase(([B]/[Si])gas) by that in the Si film(([B]/[Si])film). The supplying concentration ratio in gas phase was 10-3 in this study. RPgas/film exponentially increases from 60 to 3200 with increasing the Tfilter from 300°C to 500°C. This temperature dependence of RPgas/film assures that the filter operates on the basis of difference of thermochemical decomposition between SiH4 and B2H6. CONCLUSION We have proposed and developed the B eliminating filter operating on the basis of difference of pyrolitic behavior between B2H6 and SiH4. B concentration in both gas phase and Si film could be decreased by filtering the gas mixture at the Tfilterof more than 300°C.REFERENCES1) H. Ohmi et al., Appl. Phys. Lett. 95(2009) 181506-1-3.2) A. Yusa et al., J. Electrochem. Soc. 122 (1975) 1700.

High Critical Current Densities in MgB2 Films Grown on Hastelloy Tape by Hybrid Physical-Chemical Vapor Deposition

We report on the high critical current densities in MgB2 films directly grown on Hastelloy tapes without any buffer layer by using the hybrid physical-chemical vapor deposition method. MgB2 films were formed by reaction of Mg metal vapor with the incoming B2H6 gas on the heated substrates. In MgB2 films grown for 10 min at 500 °C in total working pressure 100 Torr with gas mixing ratio H2:B2H6=70:30, we observed the transport critical current density (J c) was approximately 106 A/cm2 at 4 T and 20 K in magnetic fields applied parallel to the substrate plane. This value is higher than those observed in epitaxial MgB2 films on sapphire substrates grown by using the same method. Magnetic field dependence of J c of this sample was well explained by the grain-boundary pinning model. Our result opens up a possibility that the coated conductors made of MgB2 films have a strong potential for high current applications.

Effect of Carrier Injection Stress in Thin Film Solar Cells by Impedance Spectroscopy

In amorphous silicon solar cells, degradation is directly related to V(oc), FF and cell performance. The dependence of the stability of thin film amorphous silicon solar cells is studied in terms of the volume fraction of B2H6 in the p-layer. When the volume fraction of B2H6 is increased by an order of magnitude, the doping-induced defects tend to increase quite rapidly. Low-doped p-type a-SiO(x) layers had better initial properties but rapidly degraded. Heavily doped p-type a-SiO(x) layers had lower initial properties but displayed better stability. The improvement in stability is explained in conjunction with the capacitance and resistance values of impedance spectroscopy. When the B2H6 gas flow rate is increased, the cell is degraded showing a capacitance decay decrease from 51.75% to less than 18.18%. In addition, the increase in the resistance decreased from 90.90% to 11.73%.

Valence band structure in boron-zinc oxide films characterized by secondary electron emission

Properties of the valence band structure in boron-zinc oxide (BZO) films were investigated using the secondary electron emission due to the Auger neutralization of helium ions, with respect to the application of BZO films to the development of solar cells, in which the conductivity of the BZO films plays a critical role in improving cell performance. The characteristic energy ɛ0 corresponding to the peak density of states in the valence band showed that BZO film prepared with a 3000 SCCM B2H6 gas flow rate (SCCM denotes cubic centimeters per minute at standard temperature and pressure) had a shallow characteristic energy ɛ0 = 5 eV, whereas film without boron doping had a deep characteristic energy ɛ0 = 8.2 eV, suggesting that a high concentration of boron impurity in BZO films might enhance the transition of electrons and holes through the bandgap from the valence to the conduction band in zinc oxide crystals, thereby improving the conductivity of the film. The measurement method developed here demonstrates that the secondary electron emission is very useful in the determination of the band structure in various synthetic films.

The Effect of Carrier Injection Stress on Boron-Doped Amorphous Silicon Suboxide Layers Investigated by X-ray Photoelectron Spectroscopy

In amorphous silicon solar cells, reducing degradation is one of the key issues in improving cell performance. The degradation of the p-layer can play an important role since it is directly related to the open circuit voltage (Voc) and fill factor (FF) in the cells. In this study, we investigated the changes in boron-doped p-type silicon suboxide (SiOx) layers after carrier injection stress. The boron doping level was varied by controlling B2H6 gas flow rate. When these layers were degraded, the dark conductivity decay decreased from 53% to less than 5%, and the increase in activation energy decreased from 11 to 0.5% depending on the B2H6 gas flow rate increase. Our improvements are explained in conjunction with the three- and four-fold coordinated boron atoms by the shift of the B 1s X-ray photoelectron spectrum. In this paper we present how to improve the stability of hydrogenated amorphous silicon (a-Si:H) thin-film solar cells.