Ga Source Research Articles

Study on the thickness effect of wide-bandgap CuGaSe2 thin films for applications with tandem solar cells

For application on the top cell of a tandem structure, chalcopyrite CuGaSe2 (CGS) thin films were prepared on as-deposited 200-nm-thick indium-tin-oxide (ITO) thin films grown by using radiofrequency (RF) magnetron sputtering. CGS thin films with a wide bandgap of 1.63 eV for use in high open-circuit-voltage solar cells were deposited by using a three-stage co-evaporation process with Cu, Ga, and Se elemental sources with compositional ratios of Cu/Ga = 0.88 and Se/(Cu + Ga) = 0.98. In this study, we examined the effect of the thickness of the top-cell CGS thin films on the tandem cell performance, which is a key factor for improving the cell’s efficiency for optimum light absorption. The film thickness was varied from 0.5 μm to 2 μm in intervals of 0.5 μm by controlling the process time to confirm the optical and the electrical properties of solar cells. Based on our experimental results as a function of the CGS film’s thickness, we achieved a solar cell efficiency of 5.77% with a 1.5-μm-thick CGS thin film in the cell structure fabricated as Al/ZnO: Al/i-ZnO/CdS/CGS/ITO/SLG.

Detrital zircons from Neoproterozoic sedimentary rocks in the Yili Block: Constraints on the affinity of microcontinents in the southern Central Asian Orogenic Belt

The Yili Block is one of the Precambrian microcontinents dispersed in the Central Asian Orogenic Belt (CAOB). Detrital zircon U–Pb ages and Hf isotopic data of Neoproterozoic meta-sedimentary rocks (the Wenquan Group) are presented to constrain the tectonic affinity and early history of the Yili Block. The dating of detrital zircons indicates that both the lower and upper Wenquan Groups have two major populations with ages at 950–880Ma and 1600–1370Ma. Moreover, the upper Wenquan Group has two minor populations at ~1100Ma and 1850–1720Ma. According to the youngest age peaks of meta-sedimentary rocks and the ages of related granitoids, the lower Wenquan Group is considered to have been deposited during the early Neoproterozoic (900–845Ma), whereas the upper Wenquan Group was deposited at 880–857Ma. The zircon εHf (t) values suggest that the 1.85–1.72Ga source rocks for the upper Wenquan Group were dominated by juvenile crustal material, whereas those for the lower Wenquan Group involved more ancient crustal material. For the 1.60–1.37Ga source rocks, however, juvenile material was a significant input into both the upper and lower Wenquan Groups. Therefore, two synchronous crustal growth and reworking events were identified in the northern Yili Block at ca. 1.8–1.7Ga and 1.6–1.3Ga, respectively. After the last growth and reworking event, continuous crustal reworking took place in the northern Yili Block until the early Neoproterozoic. Comparing the age patterns and Hf isotopic compositions of detrital zircons from the Yili Block and the surrounding tectonic units indicates that the Yili Block has a close tectonic affinity to the Chinese Central Tianshan Block in the Precambrian. The Precambrian crustal evolution of the Yili Block is distinct from that of the Siberian, North China and Tarim Cratons. Such difference therefore suggests that the Yili Block and the Chinese Central Tianshan Block may have been united in an isolated Precambrian microcontinent within the CAOB rather than representing two different blocks rifted from old cratons on both sides of the Paleo-Asian Ocean.

Effects of the composition of diffusion source on the surface concentration and effective surface diffusivity of Zn in n-GaSb

Understanding the Zn diffusion behavior in GaSb is very important to accurately control the distribution of Zn during the fabrication of photoelectric devices. The surface concentration and effective surface diffusivity are two key parameters for modeling the Zn profile in GaSb. The experimental results indicated that when the diffusion temperature and time are kept unchanged, the diffusion profiles with pure Zn, Zn–Sb, and Zn–Ga sources differ in the surface concentration and effective surface diffusivity. To quantitatively explain the effects of source composition on the two parameters, the relationship between the two parameters and the vapor pressure surrounding the GaSb wafer in the diffusion process was deduced based on a surface-equilibrium assumption and the substitutional-interstitial mechanism. The Ga/Sb/Zn ternary phase diagram was calculated and discussed for determining the vapor pressures in different source cases. The ratio of surface concentrations and that of effective surface diffusivities between different sources were obtained to quantitatively explain the experiment results. The theoretical and experimental results both indicated that adding Sb to pure Zn source keeps the surface concentration unchanged while slightly decreases the effective surface diffusivity, and that adding Ga to pure Zn source significantly decreases both the surface concentration and effective surface diffusivity.

Growth and characterization of β-Ga2O3 nanowires obtained on not-catalyzed and Au/Pt catalyzed substrates

In recent years, a large interest has been reported on low-dimensional β-Ga2O3 structures, like nanowires, nanobelts, nanorods or nanosheets, because of their peculiar and sometimes superior properties. These properties, however, can be strongly affected by the growth procedure, especially if metal growth catalysts are used. In this work we report the successful synthesis of β-Ga2O3 nanowires/nanobelts using a simple combination of thermal evaporation of a metallic Ga source and controlled oxidation. The same growth procedure has been used to grow nanostructures on different kind of substrates (silicon and alumina), without catalyst as well as with Au or Pt deposited on the substrates, in order to promote the nucleation of nanowires. The morphological, structural and optical properties of the obtained nanostructures have been characterized and compared. Different growth distributions on the substrates and possible growth mechanisms have been highlighted, while a strong increase in luminescence intensity has been observed on samples grown with Au and Pt catalysts.

Structural and optical properties of β-Ga2O3 thin films grown by plasma-assisted molecular beam epitaxy

Epitaxial beta-gallium oxide (β-Ga2O3) has been deposited on c-plane sapphire by plasma-assisted molecular-beam epitaxy technique using two methods. One method relied on a compound Ga2O3 source with oxygen plasma while the second used elemental Ga source with oxygen plasma. A side-by-side comparison of the growth parameters between these two methods has been demonstrated. With various substrate temperatures, pure phase (2¯01) oriented β-Ga2O3 thin films were obtained using both sources. Reflection high energy electron diffraction patterns displayed a threefold reconstruction during the growth. X-ray photoelectron spectroscopy analysis showed a shift in the binding energy of the Ga 2p peaks consistent with a Ga being in a +3 oxidation state. For transparent oxide like β-Ga2O3, it is important to determine the index of refraction (n) and its functional dependence on the wavelength. The Cauchy dispersion relation was employed to evaluate the refractive index, film thickness, roughness values, and extinction coefficient. The band gap energies of the thin films were calculated to be ∼5.02 eV by extrapolating the linear portion of Tauc-plot analysis and the refractive index is ∼1.89 at the wavelength (λ) of 6328 Å, suggesting high structural quality and packing density of the oxide films.

Comparative study of the role of Ga in CIGS solar cells with different thickness

Cu(In, Ga)Se2 (CIGS) thin films with thickness of 1μm and 2μm are prepared by co-evaporation process, and the different Ga/(Ga+In) are achieved by varying the temperature of Ga source. The morphology, structure, minimum band gap, and performance of solar cells are comparatively studied. As Ga/(Ga+In) increases, little changes can be observed in the crystal quality of 1μm CIGS films, while the grain size of 2μm films decreases significantly. (112) diffraction peak intensities of the 1μm and 2μm films decrease and increase, respectively. In the case of the same Ga/(Ga+In), the minimum band gap values of 1μm films are larger than that of 2μm films, and the difference becomes large with Ga/(Ga+In) increasing. The minimum band gap values of 1μm films are more sensitive to variation of the Ga/(Ga+In). As Ga/(Ga+In) increases, a more improvement of the efficiency of solar cells with thickness of 1μm is obtained due to the large enhancement of the open-circuit voltage, and the efficiency reaches the maximum value when Ga/(Ga+In) is about 0.37.

Zircon U–Pb ages and Hf isotopic compositions indicate multiple sources for Grenvillian detrital zircon deposited in western Laurentia

Combined U–Pb ages and Hf isotopic data from 1.0 Ga to 1.3 Ga (Grenvillian) detrital zircon in Neoproterozoic and Cambrian siliciclastic sedimentary rocks in southwest North America, and from igneous zircon in potential Mesoproterozoic source rocks, are used to better assess the provenance of detrital zircon potentially transported across Laurentia in major river systems originating in the Grenville orogenic highlands. High-precision hafnium isotopic analyses of individual ∼1.1 Ga detrital zircon from Neoproterozoic siliciclastic sedimentary rocks in Sonora, northern Mexico, reveal that these zircons have low εHf(0) (−22 to −26) and were most likely derived from ∼1.1 Ga granitic rocks embedded in local Mojave Province Paleoproterozoic crust. In contrast, Grenvillian detrital zircons in Cambrian sedimentary rocks in Sonora, the Great Basin, and the Mojave Desert, have generally higher εHf(0) (−15 to −21) as demonstrated both by high precision solution-based, and by lower precision laser ablation, ICPMS data and were likely derived from more distal sources further to the east/southeast in Laurentia. Comparison to new and existing zircon U–Pb geochronology and Hf isotopic data from Grenvillian crystalline rocks from the Appalachian Mountains, central and west Texas, and from Paleoproterozoic terranes throughout southwest North America reveals that zircon in Cambrian sandstones need not entirely represent detritus transported across the continent from Grenville province rocks in the vicinity of the present-day southern Appalachian Mountains. Instead, these zircons could have been derived from more proximal, high εHf(0), ∼1.1 Ga, crystalline rocks such as those exposed today in the Llano Uplift in central Texas and in the Franklin Mountains of west Texas. Regardless of the exact source(s) of the Grenvillian detrital zircon, new and existing whole–rock Nd isotopic data from Neoproterozoic to Cambrian siliciclastic sedimentary rocks in the Mojave Desert demonstrate that the occurrences of higher εHf(0), Grenvillian detrital zircons are decoupled from the sources of the bulk of the sedimentary detritus in which the zircons are entrained. The Cambrian Wood Canyon Formation and the underlying “off craton” Neoproterozoic Johnnie Formation and Stirling Quartzite all contain higher εHf(0), Grenvillian detrital zircon, in some cases as the dominant detrital zircon population. However, only portions of the Wood Canyon Formation have whole rock Nd isotopic compositions consistent with a bulk sediment source in ∼1.1 Ga sources rocks. Whole rock Nd isotopic compositions of the remaining portions of this unit, and all of the Johnnie Formation and Stirling Quartzite, require bulk sediment sources principally in Paleoproterozoic continental crust. We consider the observed decoupling in the sources of Grenvillian detrital zircon and bulk sediment in the Wood Canyon Formation and underlying siliciclastic sediments as a demonstration that detrital zircon U–Pb and Hf isotopic data alone can provide an incomplete picture of the source of sediments that comprise a given siliciclastic stratigraphic unit.

Study of the structural quality of GaN epitaxial layers obtained by hydride vapor phase epitaxy using a low-temperature buffer layer

The structural quality and surface morphology of low-temperature (LT) buffer layers after deposition and high-temperature (HT) annealing and HT GaN layers grown on LT buffer layers by hydride vapor phase epitaxy have been investigated. The HCl flow rate through the Ga source varied from 0.3 to 2 L/h, and the carrier gas N2 flow rate was either 18 or 60 L/h. It is established that the structural quality of LT GaN buffer is determined to a great extent by the HCl and N2 flow rates; the best results are obtained at HCl and N2 flow rates of 0.3 and 18 L/h, respectively. These GaN layers are characterized by a mirror surface and a rocking curve half-width of 360". It is suggested that the layer structure is improved due to the increase in the lateral growth rate.

U–Pb age and Hf isotope composition of detrital zircons from Neoproterozoic sedimentary units in southern Anhui Province, South China: Implications for the provenance, tectonic evolution and glacial history of the eastern Jiangnan Orogen

Neoproterozoic sedimentary units at the southeastern margin of the Yangtze Block, South China, record a complex geological history including development of the Jiangnan Orogen during assembly of the Yangtze and Cathaysia blocks and later episodes of glacial activity. The timing of these events is controversial, and we have used U–Pb–Hf compositions of detrital zircons from the Lantian type section to constrain their ages in southern Anhui Province, at the eastern end of the Jiangnan Orogen. This section comprises the Xikou Group below an angular unconformity, and the Xiuning Formation and overlying glacial Leigongwu Formation above the unconformity. Detrital zircons in all three units are dominated by 2.6–2.4Ga, 2.1–1.9Ga and 960–740Ma age populations suggesting erosion from similar source regions, and an increasing proportion of older grains up through the sequence reflects a change in depositional environment from syn-collisional to extensional. Pre-Neoproterozoic zircon grains were derived from the Yangtze Block basement, much of which is now concealed by younger rocks, while the Neoproterozoic population was eroded from local igneous rocks in the Jiangnan Orogen. Zircon Hf isotope compositions indicate that 2.6–2.4Ga source rocks were a mix of juvenile and reworked crust, while 2.1–1.9Ga source rocks were dominated by reworked crust. Neoproterozoic sources show a switch from 960–860Ma juvenile crust to 860–740Ma juvenile and reworked crust, reflecting a transition in the Jiangnan Orogen from subduction to collision and extension. The youngest detrital grains in the Xikou Group and overlying Xiuning Formation indicate deposition after ca. 810Ma and ca. 732Ma, respectively, correlating closely with comparable sequences elsewhere in the Yangtze Block. This demonstrates that the unconformity in South Anhui is part of a regional erosion surface that formed more or less synchronously throughout the orogen at 830–800Ma, consistent with it dating the end of collision between the Yangtze and Cathaysia blocks. The age of the overlying glacial Leigongwu Formation is difficult to constrain from detrital zircons because of a paucity of post-720Ma source rocks, but our data suggest the Leigongwu diamictite in the Lantian section is a single Marinoan-age glacial unit deposited after 649±13Ma. It follows that a carbonate layer in the middle of the Leigongwu diamictite in the Lantian section most likely reflects later faulting, rather than two separate glacial sequences, although we cannot rule out the presence of both Sturtian and Marinoan diamictite elsewhere in South Anhui.

(Ga,In)P nanowires grown without intentional catalyst

We have grown (Ga,In)P nanowires through the MOCVD method without a intentional catalyst. The organometallic precursor triethylgallium ((C2H5)3Ga), used as Ga source, is transported by the N2 gas carrier to the reactor chamber where reacts with the InP vapor pressure producing the nanowires. Two different reactor pressures (70 and 740Torr) were used leading to nanowires with different In contents. The nanowires are straight or wool-like and exhibit a twinned structure. They emit an intense orange to red color visible even to the naked eyes. Interface tunneling process at Ga1−xInxP/Ga1−yInyP interfaces (x≠y) is proposed to explain this efficient light emission mechanism.

The geology of the Matala Dome: an important piece of the Pan-African puzzle in Central Zambia

The Matala Dome (MD), an ENE-trending structure located at the junction between the Pan-African Lufilian and Zambezi belts, is cored by a Gneiss-Schist Unit with uncertain age overlain by a metasedimentary section (Quartzite-Schist Unit, Marble Unit and Carbonate-Siliciclastic Unit) of the Neoproterozoic to Cambrian Katanga Supergroup. The top of the Katangan stratigraphy is represented by synorogenic sedimentary rocks—Upper Siliciclastic Unit. An early event D1 resulted in the development of shallow-dipping metamorphic foliation S1 and pre- to syntectonic growth of garnet and kyanite in the schists of the Quartzite-Schist Unit. Pseudosections and garnet isopleth modelling on schist from this unit defined the peak metamorphism at P = 7.5–9.3 kbar and T = 620–700 °C. U–Pb detrital zircon dating revealed ca. 2.7 Ga source and a high-grade metamorphism during Pan-African times. The S1 foliation was affected by upright folding F2 with ENE-trending axes and associated subvertical crenulation fabric S2 development. The syn-D2 retrogression in the schists is marked by post-S1 staurolite crystallisation and further by chloritisation followed by sericitisation. The D2 event is interpreted to have exhumed the orogenic middle crust and to be responsible for the domal structure of the MD. 40Ar/39Ar dating of muscovite at 529.3 ± 5.6 to 526.3 ± 6.2 is interpreted to date the exhumation event. D2 is correlated with regional N–S shortening event at ca. 530–520 Ma. Based on the lithology, structural record, and time and facies of the metamorphism, a correlation between the MD and the northern part of the Zambezi Belt is suggested.

Practical Issues for Atom Probe Tomography Analysis of III-Nitride Semiconductor Materials

Various practical issues affecting atom probe tomography (APT) analysis of III-nitride semiconductors have been studied as part of an investigation using a c-plane InAlN/GaN heterostructure. Specimen preparation was undertaken using a focused ion beam microscope with a mono-isotopic Ga source. This enabled the unambiguous observation of implantation damage induced by sample preparation. In the reconstructed InAlN layer Ga implantation was demonstrated for the standard "clean-up" voltage (5 kV), but this was significantly reduced by using a lower voltage (e.g., 1 kV). The characteristics of APT data from the desorption maps to the mass spectra and measured chemical compositions were examined within the GaN buffer layer underlying the InAlN layer in both pulsed laser and pulsed voltage modes. The measured Ga content increased monotonically with increasing laser pulse energy and voltage pulse fraction within the examined ranges. The best results were obtained at very low laser energy, with the Ga content close to the expected stoichiometric value for GaN and the associated desorption map showing a clear crystallographic pole structure.

R면 사파이어 위에 HVPE로 성장된 a면 GaN 에피층의 성장온도 효과 및 1000℃에서의 V/III족 비의 효과

The effects of the growth temperature on the properties of a-plane GaN epi-layer on r-plane sapphire by HVPE were studied, when the constant V/III ratio and the flow rate of HCl for the Ga source channel was fixed at 10 and 700 sccm, respectively. Additionally the effects of V/III ratios for source gasses were studied when growth temperature and the flow rate of HCl for the Ga source channel was fixed at 1000 C and 700 sccm, respectively. As the growth temperature was increased, the values of Full Width Half Maximum (FWHM) for Rocking curve (RC) of a-plane GaN (11-20) epi- layer were decreased and thickness of a-plane GaN epi-layer were increased. As V/III ratios were increased at 1000 C, the values of FWHM for RC of a-plane GaN (11-20) were declined and thickness of a-plane GaN epi-layer were increased. The a-plane GaN (11-20) epi-layer grown at 1000 C and V/III ratio = 10 showed the lowest value FWHM for RC of a- plane GaN (11-20) for 734 arcsec and the smallest dependence of Azimuth angle for FWHM of (11-20) RCs.

GaSb/GaAs quantum dots and rings grown under periodical growth mode by using molecular beam epitaxy

GaSb/GaAs quantum dots (QDs) and quantum rings (QRs) are investigated. By using periodical growth interrupts, precise coverage control can be achieved for GaSb QD growth by using a single Ga source. With direct As irradiation to the substrate surface during the post soaking time, the soaking time can be effectively reduced while full ring morphologies and room-temperature QR luminescence can still be obtained by using this method.

Growth of GaN layers using Ga2O vapor obtained from Ga and H2O vapor

In this study, we performed growth of GaN layers using Ga2O vapor synthesized from Ga and H2O vapor. In this process, we employed H2O vapor instead of HCl gas in hydride vapor phase epitaxy (HVPE) to synthesize Ga source gas. In the synthesis reaction of Ga2O, a Ga2O3 whisker formed and covered Ga, which impeded the synthesis reaction of Ga2O. The formation of the Ga2O3 whisker was suppressed in H2 ambient at high temperatures. Then, we adopted this process to supply a group III precursor and obtained an epitaxial layer. X-ray diffraction (XRD) measurement revealed that the epitaxial layer was single-crystalline GaN. Growth rate increased linearly with Ga2O partial pressure and reached 104 µm/h.

Vapor–Solid growth of InP and Ga2O3 based composite nanowires

InP/Ga 2 O 3 core-shell nanowires were grown on Si substrate at 400 oC in the hydrazine (N 2 H 4 ) vapor diluted with 3 mol. % H 2 O. The crystalline InP and solid Ga served as source materials for the growth of nanowires. According to TEM and EDX data the nanowires consisted of wurtzite InP core with an amorphous Ga 2 O 3 shell. The minimum diameter of NWs was 14 nm, while the maximum lengths reached several micrometers. The twinned planes appeared in WZ InP core at increased nanowire diameters. Based on the obtained results and possible chemical reactions, the following mechanism was proposed for the growth of core-shell nanowires: pyrolytic decomposition of hydrazine caused the appearance of intermediate NH 2 , NH and H species in the vapor. At elevated temperatures the crystalline InP source was also dissociated to In droplets and phosphorus precursors. At source temperatures close to 600 oC, due to the interaction of In and Ga sources with water molecules and hydrazine decomposition products the volatile Ga 2 O and In 2 O were formed. These molecules reached the Si substrate which was heated to 400oC. The final chemical reaction involved Ga 2 O 3 , I 2 O 3 and phosphorus precursors. As a result of a spontaneous reaction the Ga 2 O 3 and InP phases were produced and segregated. The InP crystallized as a core while Ga 2 O 3 created the amorphous shell, because the growth temperature was insufficient for its crystallization.

Provenance and paleogeographic reconstruction of a mesoproterozoic intracratonic sag basin (Upper Espinhaço Basin, Brazil)

The Mesoproterozoic Conselheiro Mata Group is the uppermost sequence of the Proterozoic intracontinental Espinhaço basin that developed on the Congo-São Francisco Paleoplate. This sequence is represented by a marine shallow-water platform that experienced a sag phase followed by a rift phase in the Upper Espinhaço. We used combined sedimentological-stratigraphic descriptions of sections, whole-rock (WR) geochemistry and U-Pb detrital zircon dating to develop a regional paleogeographic evolution model of the sag phase. The succession corresponds to transgressive-regressive cycles in the following ascending order: 1) offshore to lower shoreface facies represented by quiescent periods and episodic sediment supply (Santa Rita Formation); 2) upper shoreface to foreshore and coastal desert facies with a reworking of the underlying units (Córrego dos Borges Formation); 3) lower shoreface with fallout of suspended fine sediments and a combination of unidirectional and oscillatory flows generated by storm waves (Córrego da Bandeira Formation); 4) tidal-influenced upper shoreface to foreshore facies with the migration of subaqueous dunes, wave swash in a beach environment and cycles of neap-spring tides (Córrego Pereira Formation); and 5) the resumption of lower-shoreface sedimentation and the subsequent development of a stromatolitic carbonate-siliciclastic platform (Rio Pardo Grande Formation). The geochemical data indicate that the studied units contain input from felsic rocks and sedimentary rocks. The basal marine to eolian sediments of the Galho do Miguel Formation are dominated by Rhyacian sources (2.1Ga). The basal and intermediate units of the Conselheiro Group contain Archean, Rhyacian, Statherian and Calymmian-Ectasian (1.6–1.33Ga) zircon grains, whereas Orosirian (1.9–2.0Ga) sources dominate in the upper strata of the group. The study of this Stenian (Mesoproterozoic) intracratonic sequence provides clues to understanding the history of sedimentation and the potential source areas on the São Francisco Craton and adjacent areas, which are very useful for comparison to Phanerozoic intracratonic basins and the reconstruction of Paleoproterozoic and Mesoproterozoic supercontinents.

Improved utilization efficiency of Ga source and flatness of GaN layer by pulsed-GaCl flow modulation on hydride vapor phase epitaxy

This paper presents the results of pulsed-GaCl flow modulation epitaxy (FME) on hydride vapor phase epitaxy (HVPE) at various interval times, supply times, and V/III ratios under a constant NH3 flow. The best performance was observed at an interval time of 30s, GaCl gas supply time of 10s in one cycle and V/III ratio of 10. As compared to the conventional HVPE growth, the utilization efficiency of the GaCl gas improved by 2.5 times in the present method and the root-mean-square (RMS) values reduced to one-fifth of the original, without degradation of crystalline quality. We concluded that the dynamic change in the V/III ratio in one cycle of an FME sequence contributed to a change in the growth mode, resulting in an improved utilization efficiency of the GaCl gas.

Detrital zircons in basement metasedimentary protoliths unveil the origins of southern India

Coupled U-Pb and Hf isotopic analysis of detrital zircons from metasedimentary rocks of the Southern Granulite terrane (India) provides provenance information that helps unravel their paleotectonic position before Gondwana amalgamated. The metasedimentary packages of the Salem block (southernmost extension of Dharwar craton) record a restricted juvenile late Archean to early Paleoproterozoic (2.7–2.45 Ga) source provenance and epsilon Hf values between +0.3 and +8.8. Similar late Archean juvenile crust is found throughout the Dharwar craton and represents a likely source for the Salem block metasedimentary rocks. By contrast, the metasedimentary rocks of the Madurai block (south of the Salem block) show a predominantly Archean to Paleoproterozoic provenance (3.2–1.7 Ga) in the northern part of the Madurai block and a largely late Mesoproterozoic to Neoproterozoic provenance (1.1–0.65 Ga) in the southern part of the Madurai block. Collectively, the Madurai block metasedimentary rocks record a mixture of reworked Archean and Paleoproterozoic sources, as well as juvenile Paleoproterozoic, late Mesoproterozoic, and evolved Neoproterozoic sources. These detrital signatures best fit the combined basement ages of the Congo-Tanzania-Bangweulu block and central Madagascar (Azania), thus linking the tectonic evolution of the southernmost tip of India to these domains throughout much of the Proterozoic. The diachroneity of metamorphic ages obtained from the rims of Madurai block detrital zircons attests to their poly-metamorphic history that is different from that of the Salem block. The contrasting metamorphic and depositional histories between the Salem and Madurai blocks place them on opposite sides of the Mozambique Ocean until the latest Neoproterozoic when they came together to form Gondwana.

Influences of Ga gradient distribution on Cu(In, Ga)Se2 film

One of the traditional methods of preparing Cu (In, Ga) Se2 (CIGS) is the three-step co-evaporation. Using this technique, four elements of Cu, In, Ga, and Se form a parabolic Ga gradient distribution through their inter-diffusion and interaction. In this paper, CIGS films and solar cells with different Ga gradient distributions are prepared through adjusting the temperature of Ga source. The effects of different Ga gradients on structural and electrical properties of CIGS film surface and back surface are studied through a variety of measurement methods. The influences of surface conduction band offset value and back surface electric field on the performance of solar cell are investigated and analysed. Finally, an optimal Ga gradient distribution is obtained, where the spectral response is improved, and the solar cell shows better performance.