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We investigate the electrical characteristics of defects at the SiO2/Si interface, within the adjacent Si crystal, and through the depth profile of the bulk defect using three-dimensional deep-level transient spectroscopy (3D-DLTS). These defects are introduced by the reactive plasma deposition technique employed for depositing transparent conductive oxides in the fabrication of carrier-selective contact-type solar cells. To control the surface potential near the Si surface, we apply a varying voltage to obtain DLTS signals as functions of both temperature and Fermi level at the SiO2/Si interface. Using machine learning for 3D-DLTS spectral analysis, we estimate the capture cross sections, energy levels, densities, and depth profiles of these process-induced defects. The experimental results indicate the existence of three types of electron traps within the bulk defects, ranging from the interface to a depth of ∼70 nm. The electrical properties of these bulk defects suggest the presence of oxygen-related defects within Si. On the other hand, regarding the properties of interface defects, the capture cross sections and the defect densities are estimated as a function of their energy levels. They suggest that the defects at the SiO2/Si interface are likely oxygen-related PL centers.

Abstract This study investigated how the SiNx refractive index (RI) and SiO2 thickness, dox, of stacked SiNx/SiO2 passivation layers of the front p+emitters of n‐type crystalline‐silicon (c‐Si) photovoltaic (PV) cells affect their polarization‐type potential‐induced degradation (PID) behaviors. We prepared six n‐type c‐Si PV cells with an RI of 2.0 or 2.2 and with dox of 9, 2, or 1 nm. Then PV modules fabricated from the cells were subjected to PID tests during which a bias of −1000 V was applied to cells with respect to the front cover glass surface. For dox of 9 or 2 nm, rapid polarization‐type PID was observed, irrespective of the RI. However, for dox of 1 nm, the RI markedly affected the degradation behavior, and cells with an RI of 2.2 showed no degradation. These findings are attributable to carrier transport between the high RI (Si‐rich) SiNx and the c‐Si substrates, which can readily occur only when the SiO2 layer is sufficiently thin for electrons to tunnel through the SiO2 layer. These results are important for elucidating polarization‐type PID mechanisms and for developing preventive measures against polarization‐type PID.

This paper proposes a new double carrier pulse deep-level transient spectroscopy (DC-DLTS) method that is applicable for evaluating metal–insulator–semiconductor (MIS) structures and the recombination centers in carrier-selective contact solar cells. Specifically, this study evaluated recombination characteristics of defects induced in bulk Si near SiO2/Si interfaces by reactive plasma deposition (RPD). In this method, a pulse voltage was first applied to inject majority carriers. Subsequently, a second pulse voltage was applied, which allowed minority carriers to be injected into the MIS structure. With these two types of carrier injections, carriers were recombined in recombination-active defects, and the DC-DLTS spectrum changed. During the injection of minority carriers, some majority carriers were thermally emitted from the defects, resulting in a decrease in the signal intensity. The recombination activity was analyzed by considering the effect of thermal emission on the change in signal intensity. The number of induced defect types and defect properties were estimated using Bayesian optimization. According to the results, three types of electron traps were generated using the RPD process. Based on the DC-DLTS results, defects with energy level 0.57 eV below the conduction band and capture cross section of ∼10−15 cm2 act as recombination centers.

Suppression of the formation of crystal defects is essential for the realization of high-efficiency solar cells. The reactive plasma deposition (RPD) process introduces defects in the silicon crystal bulk and at the passivation layer/silicon crystal interface. This study suggests that oxygen impurities can affect the generation of RPD-induced defects. Although the RPD deposition conditions were the same, the number of RPD-induced recombination centers in Cz-Si was larger than that in the Fz wafer. The increase in 950 °C pre-annealing resulted in increased peak intensity corresponding to defect level E1 in the Cz-Si MOS sample. In the case of Fz-Si, the increase in intensity with increasing pre-annealing time was slight. This indicates that oxygen precipitation might be related to the structure of RPD-induced defects.

A reactive-plasma deposition (RPD) process damage is evaluated for an indium-tin-oxide (ITO)/SiO2/Si structure in terms of the recombination properties at the interface. To calculate the surface recombination velocity (SRV), the defect density at the SiO2/Si interface (Dit), the effective total charge (Qtot) which is the sum of the charges in the SiO2 and the trapped charge at the SiO2/Si interface, and the workfunction of ITO at the ITO/SiO2 interface (ϕITO), are extracted by capacitance-voltage (C-V) analysis as a function of a postdeposition annealing (PDA) temperature. The Dit and Qtot significantly increase by the RPD process to 1.4×1012 cm-2eV-1 and 1.5×1012/q cm-2, respectively, and decrease by the PDA at 200 °C in N2 ambient to 1.4×1011 cm-2eV-1 and 1.1×1011/q cm-2, respectively. The ϕITO also varies from 4.80 eV to 4.35 eV by the PDA. The correlation is examined between the SRV values calculated based on the extended SRH model using the extracted Dit, Qtot, and ϕITO values [SRV(CV)], and the SRV ones obtained from the minority carrier lifetime measurements [SRV(LT)]. It is found that multiple sets of capture cross-sections were required for SRV(CV) values to coincide with SRV(LT) ones. The effect of variation in the Qtot and ϕITO on the band bending is almost canceled out in the present PDA condition. It is thus considered that the increase in Dit is the main cause to decrease the minority carrier lifetime.

Recently, titanium oxide has been widely investigated as a carrier-selective contact material for silicon solar cells. Herein, titanium oxide films were fabricated via simple deposition methods involving thermal evaporation and oxidation. This study focuses on characterizing an electron-selective passivated contact layer with this oxidized method. Subsequently, the SiO2/TiO2 stack was examined using high-resolution transmission electron microscopy. The phase and chemical composition of the titanium oxide films were analyzed using X-ray diffraction and X-ray photoelectron spectroscopy, respectively. The passivation quality of each layer was confirmed by measuring the carrier lifetime using quasi-steady-state photoconductance, providing an implied open circuit voltage of 644 mV. UV−vis spectroscopy and UV photoelectron spectroscopy analyses demonstrated the band alignment and carrier selectivity of the TiO2 layers. Band offsets of ~0.33 and ~2.6 eV relative to the conduction and valence bands, respectively, were confirmed for titanium oxide and the silicon interface.

The effects of residual C on cell properties are investigated from the view point of thermal budget in the n-type bifacial cell processes. Implied Voc obtained from wafers with same Oi concentration depend on the thermal budgets decreases as the Cs concentration increases. The Voc values vary depending on the wafer with different growth cooling rate. To analyze the effect of thermal budget correspond to solar cell fabrication process, CZ wafers with almost the same Oi concentrations are prepared. One of the wafers with relatively high residual Cs concentration shows the longer lifetime than the initial value after the 950 oC annealing step. On the other hand, the lifetime of a wafer with relatively low Cs concentration dramatically decreased by the same process due to the O segregation. These results suggest that it is important to choose appropriate wafer specification, starting with feedstock material, for increasing the solar cell efficiency.

The formation and evolution of rotational twin (TW) domains introduced by a stacking fault during molecular-beam epitaxial growth of GaAs on Si (111) substrates were studied by in situ x-ray diffraction. To modify the volume ratio of TW to total GaAs domains, GaAs was deposited under high and low group V/group III (V/III) flux ratios. For low V/III, there was less nucleation of TW than normal growth (NG) domains, although the NG and TW growth rates were similar. For high V/III, the NG and TW growth rates varied until a few GaAs monolayers were deposited; the mean TW domain size was smaller for all film thicknesses.

By performing capacitance transient analyses, the recombination activity at a (110)/(100) direct silicon bonded (DSB) interface contaminated with nickel diffused at different temperatures, as a model of grain boundaries in multicrystalline silicon, was studied. The trap level depth from the valence band, trap density of states, and hole capture cross section peaked at an annealing temperature of 300 °C. At temperatures ⩾400 °C, the hole capture cross section increased with temperature, but the density of states remained unchanged. Further, synchrotron-based X-ray analyses, microprobe X-ray fluorescence (μ-XRF), and X-ray absorption near edge structure (XANES) analyses were performed. The analysis results indicated that the chemical phase after the sample was annealed at 200 °C was a mixture of NiO and NiSi2.

100-nm-thick nanocrystalline silicon (nano-Si)-dot multi-layers on a Si substrate were fabricated by the sequential repetition of H-plasma surface treatment, chemical vapor deposition, and surface oxidation, for over 120 times. The diameter of the nano-Si dots was 5–6 nm, as confirmed by both the transmission electron microscopy and X-ray diffraction analysis. The annealing process was important to improve the crystallinity of the nano-Si dot. We investigated quantum confinement effects by Raman spectroscopy and photoluminescence (PL) measurements. Based on the experimental results, we simulated the Raman spectrum using a phenomenological model. Consequently, the strain induced in the nano-Si dots was estimated by comparing the experimental and simulated results. Taking the estimated strain value into consideration, the band gap modulation was measured, and the diameter of the nano-Si dots was calculated to be 5.6 nm by using PL. The relaxation of the q ∼ 0 selection rule model for the nano-Si dots is believed to be important to explain both the phenomena of peak broadening on the low-wavenumber side observed in Raman spectra and the blue shift observed in PL measurements.

The details of the process of carrier recombination via the Shockley-Read-Hall (SRH) defect level, at the grain boundaries of multicrystalline silicon, were investigated. For this, the temperature-dependent recombination velocities, as determined by experiments, were analyzed by the application of an electron beam induced current method. For the model, the misorientation angles at the grain boundaries were defined using a multi-seed casting-growth method. The results of our experiments indicated different temperature behaviors at low and high temperatures. These can be explained by controlling the process anticipated by the SRH model, that is, the process whereby minority carriers (electrons) are captured at lower temperatures, followed by the reemission of the carriers before recombination with Arrhenius behavior at higher temperatures. The minority capture process appeared to conform to the power law T-α temperature behavior. Thus, there are two candidate electron capture mechanisms, namely, cascade phonon emission capture for shallow centers and excitonic-Auger capture for deep centers. The activation energy for the reemission of carriers was around 0.1 eV. These findings regarding the temperature dependence are essentially independent of the misorientation angles, suggesting a common defect level and recombination mechanism. The difference in the recombination velocities can be regarded as being derived from the difference in the density at the defect level. [ABSTRACT FROM AUTHOR]

The incorporation of Si in GaAsN alloys grown simultaneously on (100), (311)A, (311)B, and (211)B GaAs substrates by the chemical beam epitaxy has been investigated. The decrease in electron concentration with the increasing N composition suggests the occurrence of N and Si interaction, whereas the interaction exhibits evidently different extent depending on the growth orientation. Combined with the secondary ion mass spectrometry and photoluminescence measurements, it is revealed that (311)B and (211)B are the promising substrate orientations to reduce the N-Si passivation and improve n-type Si doping in GaAsN over a wider N composition range. A surface bonding model is utilized to explain the plane polarity dependent incorporation behaviors of Si and N. [ABSTRACT FROM AUTHOR]

The hole traps associated with high background doping in p-type GaAsN grown by chemical beam epitaxy are studied based on the changes of carrier concentration, junction capacitance, and hole traps properties due to the annealing. The carrier concentration was increased dramatically with annealing time, based on capacitance-voltage (C-V) measurement. In addition, the temperature dependence of the junction capacitance (C-T) was increased rapidly two times. Such behavior is explained by the thermal ionization of two acceptor states. These acceptors are the main cause of high background doping in the film, since the estimated carrier concentration from C-T results explains the measured carrier concentration at room temperature using C-V method. The acceptor states became shallower after annealing, and hence their structures are thermally unstable. Deep level transient spectroscopy (DLTS) showed that the HC2 hole trap was composed of two signals, labeled HC21 and HC22. These defects correspond to the acceptor levels, as their energy levels obtained from DLTS are similar to those deduced from C-T. The capture cross sections of HC21 and HC22 are larger than those of single acceptors. In addition, their energy levels and capture cross sections change in the same way due to the annealing. This tendency suggests that HC21 and HC22 signals originate from the same defect which acts as a double acceptor. [ABSTRACT FROM AUTHOR]

The conversion efficiencies of crystalline silicon (Si) solar cells are increasing and the module price is dramatically going down. PERC (passivated emitter and rear cell) solar cells, which have achieved high conversion efficiencies of over 20%, are the next main focus for mass production. In the structure of a typical PERC, the minority carrier recombination rate is decreased by the rear side passivation. On the other hand, the hetero-junction of amorphous Si and crystal Si shows high passivation quality at the interface, and an increase in the open circuit voltage. The back-contact cell increases the photoinduced current density because of the shadow loss suppression. The combination of the hetero-junction and the back contact structures realize the 26.33% conversion efficiency. To reduce the fabrication cost of solar cells with high conversion efficiency, passivated contact cells have been proposed. The minority carrier recombination is suppressed by an intermediated layer, such as SiO2, between the Si crystal and the contact materials. When the light is irradiated, the current flows through this interlayer by the tunneling phenomena. High current density and high open circuit voltage are realized by adjusting the work functions of the contact materials. [ABSTRACT FROM AUTHOR]

We have used transient electron-beam-induced current (EBIC) to map minority carrier lifetime distributions in multicrystalline Silicon (mc-Si). In this technique, the electron beam from a scanning transmission electron microscope was on-off modulated while the sample was scanned. The resulting transient EBIC was analyzed to form a lifetime map. An analytical function was introduced as part of the analysis in determining this map. We have verified this approach using numerical simulations and have reproduced a lifetime map for an mc-Si wafer. [ABSTRACT FROM AUTHOR]

The lateral transport of minority carriers in the surface inversion layer of a crystalline silicon (cSi) surface for a p-aSi:H/i-aSi:H/cSi heterojunction (SHJ) solar cell was experimentally analyzed to study defects/traps at the aSi:H/cSi interface and/or on the cSi surface. To extract the lateral surface inversion layer current, a field-effect transistor type test element group device was designed and fabricated on a cSi wafer where SHJ cells were co-integrated. By analyzing the lateral surface inversion layer current, the effective surface minority carrier mobility was calculated. The extracted mobility was one order of magnitude smaller than that of a reference MoOx/i-aSi:H/cSi structure but it increased by low-temperature post-deposition annealing with respect to the reference. This method is highly sensitive to the quality of the aSi:H/cSi interface and/or the cSi surface. The density of trap sites was estimated to be of the order of 1011 cm−2 at the aSi:H/cSi interface and/or on the cSi surface. [ABSTRACT FROM AUTHOR]

In this study, the effects of oxygen precipitation on the minority carrier lifetime were evaluated in conjunction with crystal growth conditions. It was revealed that oxygen precipitates and dislocations formation are suppressed and lifetime deterioration is suppressed in Czochralski (Cz)-Si, which is maintained at high temperature, followed by rapid cooling during crystal growth. In addition, the interface at the oxygen precipitate/Si matrix and dislocations were the dominant carrier recombination centers. From the above, it was suggested that controlling oxygen precipitation by crystal growth conditions can contribute to high-efficiency solar cells. [ABSTRACT FROM AUTHOR]

We investigated the interface phenomena between the electrode by a low fire-through electrode paste and the silicon substrate in a crystalline silicon solar cell. Oblique polishing was used to evaluate the chemical bonding states in the depth direction. From the evaluation by X-ray photoelectron spectroscopy (XPS) and the hard X-ray photoelectron spectroscopy (HAXPES), we found changes in the chemical bonding states of Ag 3d, Si 2p, O 1s, and N 1s at the electrode–silicon interface. In addition, it was possible to confirm the reduction of Ag induced by the heat treatment at the interface. Thus, it became possible to evaluate the chemical bonding states at the interface between the electrode and the silicon substrate by adapting oblique polishing and XPS measurement. [ABSTRACT FROM AUTHOR]

We report on our attempt to increase the carrier density in the p-type polycrystalline silicon (poly-Si) layers grown by aluminum-induced crystallization (AIC) employing a B-doped Si target. Hall measurement revealed that we could obtain a lower-resistance and heavily doped p-type continuous poly-Si thin layer formed by AIC using B-doped a-Si. According to our evaluation of tunnel oxide passivated contact (TOPCon) solar cells with AIC-grown poly-Si, the AIC-TOPCon solar cells fabricated at 570 °C using B-doped a-Si showed higher conversion efficiency of 13.5% than that of 12.8% when using nondoped a-Si. It is considered that the cell characteristics, particularly FF and Voc, were improved owing to the lower series resistance and higher carrier density since both Al and B were successfully incorporated into the AIC-grown poly-Si. [ABSTRACT FROM AUTHOR]

In this study, we evaluated the effects of carbon and annealing process conditions on the oxygen precipitation in an n-type Czochralski (Cz) wafer for solar cells by infrared light scattering tomography (IR-LST). It was confirmed that precipitates grow larger and denser as carbon concentration increase. Thus, carbon promotes oxygen precipitation. We also evaluated the effect of oxygen precipitation on the minority carrier lifetime by photoluminescence (PL) imaging. It was confirmed that the interface between the precipitate and the Si matrix is a dominant recombination center since the surface area of the precipitate obtained by IR-LST measurement and the PL intensity show good correlation. In addition, it was also confirmed that carbon is involved in the supply of interstitial oxygen to precipitates through the formation and extinction of the thermal donor. We believe that it is important to understand and control the effect of carbon of controlling the oxygen precipitation behavior. [ABSTRACT FROM AUTHOR]

The workfunction of molybdenum oxide (MoOx) at the MoOx/SiO2 interface, which is referred to as the interface workfunction, and the process-induced damage at the SiO2/Si interface in an indium tin oxide (ITO)/MoOx/SiO2/Si structure are extracted by capacitance–voltage (C–V) analysis. The estimated interface workfunction is compared with that of the bulk determined by ultraviolet photoelectron spectroscopy (UPS). The interface workfunction of 5.59 eV for the as-grown ITO condition is 0.41 eV smaller than the bulk workfunction for the as-grown MoOx film. The reactive-plasma deposition (RPD) process induces damage at the SiO2/Si interface, with an estimated interface defect density (Dit) of 3.9 × 1011 cm−2 eV−1. The effects of postdeposition annealing in a forming gas on these parameters are also studied. The interface workfunction decreases with increasing temperature to 5.24 eV at 400 °C, while that of the bulk is 5.9 eV, suggesting a difference in the interface and bulk properties. The damage is almost removed at 250 °C. [ABSTRACT FROM AUTHOR]

Si ingots were sliced using a diamond-coated wire, and saw damage was observed even after damage removal etching and texturization. Since invisible microscopic damage was observed only under uncontrolled slice conditions, such damage was identified as saw damage. The wafers with saw damage exhibited the degradation of solar cell conversion efficiency (approximately 1–2% absolute). The results of external quantum efficiency (EQE) measurements showed a slight deterioration of EQE in the short wavelength region. Current–voltage characteristic measurements showed similar results that agreed with the EQE measurement results. In addition, EQE mapping measurements were carried out at various irradiation wavelengths between 350 and 1150 nm. Areas with dark contrasts in EQE mapping correspond to saw damage. In the cells with a low conversion efficiency, both EQE mapping and PL images exhibited dark areas and lines. On the other hand, in the cells with a high conversion efficiency, a uniform distribution of saw damage was observed even with the saw damage in the PL images. We believe that sophisticated control to suppress saw damage during sawing is required to realize higher conversion efficiency solar cells in the future. [ABSTRACT FROM AUTHOR]

Aluminum-added silver paste (Ag/Al paste) has been used for p+ emitter of n-type solar cells. The electrical losses due to shunting and recombination caused by the paste in the cells have been reported to originate from huge metallic spikes due to the aluminum. However, whether the aluminum actually induces the losses has not been clarified yet. In this study, the “floating contact method” is applied to aluminum-free silver (Al-free Ag) paste to investigate the effects of aluminum extraction from the Ag/Al paste and to understand how the aluminum principally induces the losses for the p+ emitter. Furthermore, the interfacial morphology between the Al-free Ag paste and p-type silicon is investigated. The Ag paste itself creates tiny crystallites for the p+ emitter, resulting in shunting and recombination. The result indicates that the aluminum addition to Ag paste is not the main reason for the electrical losses in the n-type solar cells. [ABSTRACT FROM AUTHOR]

The effect of substrate orientation on strain relaxation mechanisms of an InGaAs layer grown on vicinal GaAs substrates was investigated by in situ X-ray diffraction (XRD). The crystallographic tilt and indium segregation in the InGaAs layer were altered depending on the miscut direction and angle. In the case of the substrate tilted 6° toward the [110] direction, one type of misfit dislocations was formed preferentially rather than other types, especially in the rapid relaxation phase. While in the case of the substrate tilted 6° toward the direction, no anisotropies during relaxation were observed. The present finding indicates that the appropriate use of vicinal substrates may lead to a novel method of improving the crystal quality of heterolayers. [ABSTRACT FROM AUTHOR]

The effect of misorientation on the recombination activity of tilt small angle grain boundaries was studied by temperature-dependent electron beam induced current (EBIC) analyses of artificially induced grain boundaries in multicrystal grown by casting from multiple seeds. For small misorientation, there is no significant difference in the recombination of grain boundaries at the middle of a grown ingot, whereas moderate contamination on grain boundaries caused changes in the EBIC contrast, especially at room temperature. The EBIC contrast of moderately contaminated grain boundaries at room temperature has a peak at a misorientation of ∼3°, and for misorientation θ > 6°, the recombinative nature diminishes with increasing misorientation. The results indicate differences in the gettering ability of small angle grain boundaries. [ABSTRACT FROM AUTHOR]

A simulation of interdigitated back-contact silicon heterojunction (IBC-SHJ) solar cells was performed using a quantum transport model to consider the quantum effect at the crystalline/amorphous (c/a) heterojunction interface. It was found that the impact of the quantum effect on the open-circuit voltage is comparable to that of the interface defect density at the c/a interface, indicating the importance of implementation of the quantum model. The optimal back-contact design was also discussed from the viewpoint of mass production, in which the design rule is relaxed. The degradation of the conversion efficiency by widening the gap between the p- and n-aSi:H layers can be compensated by improving passivation quality at the c/a interface. [ABSTRACT FROM AUTHOR]

We investigated the electronic chemical properties and film structures in SiN passivation layers on crystalline Si by X-ray photoelectron spectroscopy (XPS) and X-ray reflectometry (XRR). From XPS analyses, a N-rich component (N–Si–N) and oxygen mixing were observed at the interface. The longest lifetime was obtained after post deposition annealing at 600 °C, where the N-rich layer was the thinnest with small peak height. Therefore, longer lifetime could be obtained as the N concentration at the interface decreased. The film consisted of three SiN layers and one SiO2 layer, as confirmed by XRR profile fitting. From the density profiles, a longer lifetime was obtained when the density gradient in the oxygen mixing layer was small. Results of XPS and XRR suggested that N at the interface significantly affected the lifetime. We believe it is important to understand the electronic chemical properties at the passivation interface to realize high-efficiency Si solar cells. [ABSTRACT FROM AUTHOR]

We have grown 50 cm2 mono Si ingots by the seed cast technique. The carbon and oxygen concentrations of the ingots have been significantly reduced by improving the gas flow condition and coating. The dislocation density was also reduced by eliminating the extra dislocation generation sources. Owing to these developments, the lifetime of wafers has reached 465 µs. Finally, the efficiency of 18.7% has been achieved, which is comparable to 18.9% of the reference Czochralski (CZ) Si wafer. [ABSTRACT FROM AUTHOR]

The formation mechanism of N–H-related defects in GaAsN grown by chemical beam epitaxy (CBE) is studied on the basis of the isotope effects on the local vibration modes (LVMs) originating from N–H. When deuterated monomethylhydrazine (MMHy) is used as the N source, LVM signals from the nitrogen–deuterium bond (N–D) are obtained. However, there are still N–H peaks in the IR absorption spectra, which have intensities similar to those of N–D peaks. When the film is grown with deuterated triethylgallium (TEGa), there are no N–D peaks. The peak intensity at 2952 cm−1 increases with increasing tris(dimethylamino)arsenic (TDMAAs) flow rate, and that at 3098 cm−1 is almost constant regardless of the flow rate. These results indicate that H atoms in the N–H-related defects originate from H directly bonded to N in MMHy and CH3 in MMHy and/or H in TDMAAs, not from TEGa. [ABSTRACT FROM AUTHOR]

We succeeded in growing Ge homoepitaxial films by metal–organic chemical vapor deposition (MOCVD) using tertiarybutylgermane (t-C4H9GeH3). We synthesized and investigated the characteristics of t-C4H9GeH3. The vapor pressure was sufficiently high in the CVD process. The precursor was sufficiently safe as it did not have a pyrophoric and explosive nature. The Ge homoepitaxial growth was achieved at 360 °C under reduced pressure on an appropriately cleaned Ge(001) substrate. [ABSTRACT FROM AUTHOR]

The photoluminescence properties of small-angle grain boundaries (SA-GBs) with various misorientation angles were evaluated before and after Fe contamination. Comparison of SA-GBs with the same misorientation angle showed that the Da1 band at 0.78 eV remain the same before and after the Fe contamination. At the SA-GBs with the misorientation angle of 5°, a strong emission existed at 0.87 eV, which has been reported as an oxygen-precipitation-related peak. The emission of this high-energy region became weaker and shifted toward lower energy for a smaller misorientation angle. The high-energy emission became weak after the Fe contamination. It is considered that the Fe contamination affected the PL spectra originating from oxygen precipitates. [ABSTRACT FROM AUTHOR]

The properties of the main acceptor state in GaAsN crystal grown by chemical beam epitaxy (CBE) are studied based on the changes of carrier concentration and temperature dependence of the junction capacitance due to the annealing. The junction capacitance in p-type films shows a significant increase between 50 and 80 K and the energy level of the acceptor defect in as-grown film was obtained at 0.161 eV above the valence band maximum. This energy level decreases and its density increases with annealing time. Therefore, this acceptor state is not thermally stable and its structure and electrical properties change by the annealing. This acceptor state is mainly responsible for the high background doping in unintentionally doped GaAsN grown by CBE, since the carrier concentration estimated by using the energy level and the density obtained by capacitance–temperature (C–T) measurements explain well the carrier concentration at room temperature provided by capacitance–voltage (C–V) results. [ABSTRACT FROM AUTHOR]

Correlations between N–H local vibrational modes (LVMs) in GaAsN grown by chemical beam epitaxy are studied by polarized Fourier transform infrared spectroscopy. The N–H bonds of LVMs at 960, 2952, 3011, and 3098 cm−1 are shown to exhibit polarizations along in the GaAsN(001) plane. By comparing the polarization degrees of those LVMs, it is shown that the four LVMs have no correlations with each other. This result indicates that there are four types of N–H complexes whose bond directions are 〈111〉. Those structures are considered to be of the bond-center or antibonding type with interstitial host atoms, antisite host atoms, and vacancies. [ABSTRACT FROM AUTHOR]

The origin of N–H related local vibration modes (LVMs) in GaAsN grown by chemical beam epitaxy is discussed on the basis of the change in peak intensity caused by annealing. The peak areas at 973 and 3124 cm−1 increase as the annealing temperature increases. Their ratio is almost one, independent of the annealing temperature and time. On the other hand, the intensities at 960, 2952, 3014, and 3098 cm−1 decrease owing to annealing. Although the peak area at 960 cm−1 becomes half after annealing at 700 °C, those at 2952, 3014, and 3098 cm−1 to almost zero. These results indicate that the wagging mode at 973 cm−1 and the stretching mode at 3124 cm−1 are originated from the same N–H related defect in GaAsN, and that the wagging mode at 960 cm−1 does not correspond to the stretching modes at 2952, 3014, and 3098 cm−1. [ABSTRACT FROM AUTHOR]