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We investigate the synthesis of kesterite Cu2ZnSnS4 (CZTS) polycrystalline thin films using cosputtering from binary sulfide targets followed by annealing in sulfur vapor at 500 {\deg}C to 650 {\deg}C. The films are the kesterite CZTS phase as indicated by x-ray diffraction, Raman scattering, and optical absorption measurements. The films exhibit (112) fiber texture and preferred low-angle and Sigma3 grain boundary populations which have been demonstrated to reduce recombination in Cu(In,Ga)Se2 and CdTe films. The grain growth kinetics are investigated as functions of temperature and the addition of Na. Significantly, lateral grain sizes above 1 um are demonstrated for samples grown on Na-free glass,demonstrating the feasibility for CZTS growth on substrates other than soda lime glass.

Copper zinc tin sulfide (CZTS) is a promising Earth-abundant thin-film solar cell material; it has an appropriate band gap of ∼1.45 eV and a high absorption coefficient. The most efficient CZTS cells tend to be slightly Zn-rich and Cu-poor. However, growing Zn-rich CZTS films can sometimes result in phase decomposition of CZTS into ZnS and Cu 2 SnS 3 , which is generally deleterious to solar cell performance. Cubic ZnS is difficult to detect by XRD, due to a similar diffraction pattern. We hypothesize that synchrotron-based extended X-ray absorption fine structure (EXAFS), which is sensitive to local chemical environment, may be able to determine the quantity of ZnS phase in CZTS films by detecting differences in the second-nearest neighbor shell of the Zn atoms. Films of varying stoichiometries, from Zn-rich to Cu-rich (Zn-poor) were examined using the EXAFS technique. Differences in the spectra as a function of Cu/Zn ratio are detected. Linear combination analysis suggests increasing ZnS signal as the CZTS films become more Zn-rich. We demonstrate that the sensitive technique of EXAFS could be used to quantify the amount of ZnS present and provide a guide to crystal growth of highly phase pure films.

This study investigates the synthesis of chalcopyrite Cu 2 Si 1−x Sn x S 3 (CSTS) thin films for photovoltaic solar cell absorber layers. Preliminary results indicate that layered sputtering of Cu, Sn, and Si followed by annealing in a sulfur atmosphere at 500°C does not provide adequate mixing or sulfur incorporation. Annealing/sulfurizing a homogeneous co-sputtered film of Cu, Sn, and S lead to CSTS formation, although low sulfur incorporation and undesired copper sulfide phase formation resolved. Sputtering from sulfide targets may lead to formation of CSTS.

Cu2ZnSnS4 (CZTS) is an alternative material to Cu(In,Ga)Se2 (CIGSe) for use in thin film photovoltaic absorber layers composed solely of commodity elements [1,2]. Thus, if similar material quality and performance can be realized, its use would allow scale-up of terrestrial thin film photovoltaic production unhindered by material price or supply constraints. Here we report on our research on the deposition of CZTS by RF sputtering from a single CZTS target and co-sputtering from multiple binary sources on Mo-coated glass. We find some samples delaminate during post-sputtering furnace annealing in S vapor. Samples on borosilicate glass (BSG) delaminate much more frequently than those on soda-lime glass (SLG). We investigate the influences of the formation of frangible phases such as MoS2 at the CZTS/Mo interface and residual and thermal mismatch stress on delamination. We implicate fracture in a layer of MoS2 as the mechanism of delamination between the Mo and CZTS layers using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Wafer curvature measurements show significant (˜400 MPa) deposition stress for minimally optimized Mo deposition; however nearly stress-free Mo layers with good adhesion can be deposited using a multi-step Mo deposition recipe. Co-sputtering CZTS adds 100 MPa of stress on both BSG and SLG, however delamination is nearly absent for samples deposited on low-stress Mo layers. We investigate metallic diffusion barrier layers to prevent the formation of MoS2 at the interface. Lastly we discuss the importance of removing Mo oxide by sputter etching before CZTS deposition and its effects on adhesion and series resistance.

CuInSe2 (CIS) is commercially processed using energy intensive vacuum processes such as sputtering and thermal evaporation followed by thermal annealing. In order to reduce the cost of fabricating CIS photovoltaic absorber layers we need fast and cheap processing methods. We have investigated the use of non-vacuum electrochemical deposition (ED) followed by ultra violet pulsed laser annealing (UV-PLA). We report here on the results of ns pulsed KrF irradiation of ED CIS films and ED CIS films which were first annealed in a Se atmosphere.

A systematic investigation of ferromagnetic resonance (FMR) was carried out on ${\text{Ga}}_{1\ensuremath{-}x}{\text{Mn}}_{x}\text{As}$ layers synthesized by Mn ion implantation into GaAs followed by pulsed laser melting. Angular and temperature dependences of FMR were measured on layers prepared on GaAs (001), (110), and (311) surfaces. The observed angular dependence of FMR can be understood in terms of contributions from cubic anisotropy fields defined by the crystal symmetry of ${\text{Ga}}_{1\ensuremath{-}x}{\text{Mn}}_{x}\text{As}$ and uniaxial anisotropy fields perpendicular or parallel to the film plane. For completeness, the angular dependence of the FMR linewidth was also investigated and was found to be dominated by broadening ascribed to local inhomogeneities in magnetic anisotropy. Our results show that both the magnetic anisotropy and the FMR linewidth in (Ga,Mn)As prepared by ion implantation are similar to those observed on ${\text{Ga}}_{1\ensuremath{-}x}{\text{Mn}}_{x}\text{As}$ samples grown by low-temperature molecular beam epitaxy, indicating that the two very different growth methods lead to materials with fundamentally similar magnetic properties.

We employ Faraday and Kerr effect spectroscopy in the infrared range to investigate the electronic structure of ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}$ near the Fermi energy. The band structure of this archetypical dilute-moment ferromagnetic semiconductor has been a matter of controversy, fueled partly by previous measurements of the unpolarized infrared absorption and their phenomenological impurity-band interpretation. Unlike the unpolarized absorption, the infrared magneto-optical effects we study are intimately related to ferromagnetism, and their interpretation is much more microscopically constrained in terms of the orbital character of the relevant band states. We show that the conventional theory of the disordered valence band with an antiferromatnetic exchange term accounts semiquantitatively for the overall characteristics of the measured infrared magneto-optical spectra.

Utilizing three-terminal tunnel emission of ballistic electrons and holes, we have developed a method to self-consistently measure the bandgap of semiconductors and band discontinuities at semiconductor heterojunctions without any prerequisite material parameter. Measurements are performed on lattice-matched GaAs/AlxGa1-xAs and GaAs/(AlxGa1-x)0.51In0.49P single-barrier heterostructures. The bandgaps of AlGaAs and AlGaInP are measured with a resolution of several meV at 4.2 K. For the GaAs/AlGaAs interface, the measured Gamma band offset ratio is 60.4:39.6 (+/-2%). For the GaAs/AlGaInP interface, this ratio varies with the Al mole fraction and is distributed more in the valence band. A non-monotonic Al composition dependence of the conduction band offset at the GaAs/AlGaInP interface is observed in the indirect-gap regime., 4 pages, 4 figures, submitted to Phys. Rev. Lett.

We report the effect of dilute alloying of the anion sublattice with S on the in-plane uniaxial magnetic anisotropy and magnetization reversal process in ${\text{Ga}}_{1\ensuremath{-}x}{\text{Mn}}_{x}\text{P}$ as measured by both ferromagnetic resonance (FMR) spectroscopy and superconducting quantum interference device (SQUID) magnetometry. At $T=5\text{ }\text{K}$, raising the S concentration increases the uniaxial magnetic anisotropy between in-plane $⟨011⟩$ directions while decreasing the magnitude of the (negative) cubic anisotropy field. Simulation of the SQUID magnetometry indicates that the energy required for the nucleation and growth of domain walls decreases with increasing $y$. These combined effects have a marked influence on the shape of the field-dependent magnetization curves; while the $[0\overline{1}1]$ direction remains the easy axis in the plane of the film, the field dependence of the magnetization develops double hysteresis loops in the [011] direction as the S concentration increases, similar to those observed for perpendicular magnetization reversal in lightly doped ${\text{Ga}}_{1\ensuremath{-}x}{\text{Mn}}_{x}\text{As}$. The incidence of double hysteresis loops is explained with a simple model whereby magnetization reversal occurs by a combination of coherent spin rotation and noncoherent spin switching, which is consistent with both FMR and magnetometry experiments. The evolution of magnetic properties with S concentration is attributed to compensation of Mn acceptors by S donors, which results in a lowering of the concentration of holes that mediate ferromagnetism.

We present a detailed investigation of the magnetic and magnetotransport properties of thin films of ferromagnetic Ga1-x Mnx As synthesized using ion implantation and pulsed-laser melting (II-PLM). The field and temperature-dependent magnetization, magnetic anisotropy, temperature-dependent resistivity, magnetoresistance, and Hall effect of II-PLM Ga1-x Mnx As films have all of the characteristic signatures of the strong p-d interaction of holes and Mn ions observed in the dilute hole-mediated ferromagnetic phase. The ferromagnetic and electrical transport properties of II-PLM films correspond to the peak substitutional Mn concentration meaning that the nonuniform Mn depth distribution is unimportant in determining the film properties. Good quantitative agreement is found with films grown by low temperature molecular beam epitaxy and having the similar substitutional MnGa composition. Additionally, we demonstrate that II-PLM Ga1-x Mnx As films are free from interstitial MnI because of the high-temperature processing. At high Mn implantation doses, the kinetics of solute redistribution during solidification alone determine the maximum resulting MnGa concentration. Uniaxial anisotropy between in-plane [1- 10] and [110] directions is present in II-PLM Ga1-x Mnx As giving evidence for this being an intrinsic property of the carrier-mediated ferromagnetic phase. © 2008 American Institute of Physics.

We report the observation of ferromagnetic resonance (FMR) and the determination of the magnetocrystalline anisotropy in (100)-oriented single-crystalline thin film samples of ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{P}$ with $x=0.042$. The contributions to the magnetic anisotropy were determined by measuring the angular and the temperature dependencies of the FMR resonance fields and by superconducting quantum interference device magnetometry. The largest contribution to the anisotropy is a uniaxial component perpendicular to the film plane; however, a negative contribution from cubic anisotropy is also found. Additional in-plane uniaxial components are observed at low temperatures, which lift the degeneracy between the in-plane [011] and $[01\overline{1}]$ directions as well as between the in-plane [010] and [001] directions. Near $T=5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the easy magnetization axis is close to the in-plane $[01\overline{1}]$ direction. All anisotropy parameters decrease with increasing temperature and disappear above the Curie temperature ${T}_{C}$. A consistent picture of the magnetic anisotropy of ferromagnetic ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{P}$ emerges from the FMR and magnetometry data. The latter can be successfully modeled when both coherent magnetization rotation and magnetic domain nucleation are considered.

We present measurement and analysis techniques that allow the complete complex magneto-conductivity tensor to be determined from mid-infrared (11-1.6 micron; 100-800 meV) measurements of the complex Faraday (theta_F) and Kerr (theta_K) angles. Since this approach involves measurement of the geometry (orientation axis and ellipticity of the polarization) of transmitted and reflected light, no absolute transmittance or reflectance measurements are required. Thick film transmission and reflection equations are used to convert the complex theta_F and theta_K into the complex longitudinal conductivity sigma_xx and the complex transverse (Hall) conductivity sigma_xy. theta_F and theta_K are measured in a Ga_(1-x)Mn_xAs and SrRuO_3 films. The resulting sigma_xx is compared to the values obtained from conventional transmittance and reflectance measurements, as well as the results from Kramers-Kronig analysis of reflectance measurements on similar films., Comment: LaTeX file 25 pages, 7 figures

Laser processing of polycrystalline CdTe is a promising approach that could potentially increase module manufacturing throughput while reducing capital expenditure costs. For these benefits to be realized, the basic effects of laser irradiation on CdTe must be ascertained. In this study, we utilize surface photovoltage spectroscopy (SPS) to investigate the changes to the electronic properties of the surface of polycrystalline CdTe solar cell stacks induced by continuous-wave laser annealing. The experimental data explained within a model consisting of two space charge regions, one at the CdTe/air interface and one at the CdTe/CdS junction, are used to interpret our SPS results. The frequency dependence and phase spectra of the SPS signal are also discussed. To support the SPS findings, low-temperature spectrally-resolved photoluminescence and time-resolved photoluminescence were also measured. The data show that a modest laser treatment of 250 W/cm2 with a dwell time of 20 s is sufficient to reduce the ef...

We report an energy gap for hole photoexcitation in ferromagnetic Ga{sub 1-x}Mn{sub x}P that is tunable by Mn concentration (x {le} 0.06) and by compensation with Te donors. For x{approx}0.06, electrical transport is dominated by excitation across this gap above the Curie temperature (T{sub c}) of 60 K and by thermally-activated hopping below T{sub c}. Magnetization measurements reveal a moment of 3.9 {+-} 0.4 {micro}{sub B} per substitutional Mn while the large anomalous Hall signal unambiguously demonstrates that the ferromagnetism is carrier-mediated. In aggregate these data indicate that ferromagnetic exchange is mediated by holes localized in a Mn-derived band that is detached from the valence band.

The dilute GaNxAs1-x alloys (with x up to 0.05) have exhibited many unusual properties as compared to the conventional binary and ternary semiconductor alloys. We report on a new effect in the GaNxAs1-x alloy system in which electrically active substitutional group IV donors and isoelectronic N atoms passivate each other's activity. This mutual passivation occurs in dilute GaNxAs1-x doped with group IV donors through the formation of nearest neighbor IVGa- NAs pairs when the samples are annealed under conditions such that the diffusion length of the donors is greater than or equal to the average distance between donor and N atoms. The passivation of the shallow donors and the NAs atoms is manifested in a drastic reduction in the free electron concentration and, simultaneously, an increase in the fundamental bandgap. This mutual passivation effect is demonstrated in both Si and Ge doped GaNxAs1-x alloys. Analytical calculations of the passivation process based on Ga vacancy mediated diffusion show good agreement with the experimental results.

We have investigated the transport and magnetization characteristics of Ga1-xMnxAs intentionally compensated with shallow Te donors. Using ion implantation followed by pulsed-laser melting, we vary the Te compensation and drive the system through a metal-insulator transition (MIT). This MIT is associated with enhanced low-temperature magnetization and an evolution from concave to convex temperature-dependent magnetization., Comment: 2 pages, 2 figures. To appear in the proceedings of the 27th International Conference on the Physics of Semiconductors (ICPS-27, Flagstaff, AZ, July 26-30, 2004)

We report the realization of a new multi-band-gap semiconductor. The highly mismatched alloy Zn1-yMnyOxTe1-x has been synthesized using the combination of oxygen ion implantation and pulsed laser melting. Incorporation of small quantities of isovalent oxygen leads to the formation of a narrow, oxygen-derived band of extended states located within the band gap of the Zn1-yMnyTe host. When only 1.3% of Te atoms is replaced with oxygen in a Zn0.88Mn0.12Te crystal (with band gap of 2.32 eV) the resulting band structure consists of two direct band gaps with interband transitions at ~1.77 eV and 2.7 eV. This remarkable modification of the band structure is well described by the band anticrossing model in which the interactions between the oxygen-derived band and the conduction band are considered. With multiple band gaps that fall within the solar energy spectrum, Zn1-yMnyOxTe1-x is a material perfectly satisfying the conditions for single-junction photovoltaics with the potential for power conversion efficiencies surpassing 50%., Comment: 12 pages, 4 figures

We review prior and on-going works in using laser annealing (LA) techniques in the development of chalcogenide-based [CdTe and Cu(In,Ga)(S,Se)2] solar cells. LA can achieve unique processing regimes as the wavelength and pulse duration can be chosen to selectively heat particular layers of a thin film solar cell or even particular regions within a single layer. Pulsed LA, in particular, can achieve non-steady-state conditions that allow for stoichiometry control by preferential evaporation, which has been utilized in CdTe solar cells to create Ohmic back contacts. Pulsed lasers have also been used with Cu(In,Ga)(S,Se)2 to improve device performance by surface-defect annealing as well as bulk deep-defect annealing. Continuous-wave LA shows promise for use as a replacement for furnace annealing as it almost instantaneously supplies heat to the absorbing film without wasting time or energy to bring the much thicker substrate to temperature. Optimizing and utilizing such a technology would allow production lines to increase throughput and thus manufacturing capacity. Lasers have also been used to create potentially low-cost chalcogenide thin films from precursors, which is also reviewed.

The alloy GaN(x) As(1-x) (with x typically less than 0.05) is a novel semiconductor that has many interesting electronic properties because of the nitrogen-induced dramatic modifications of the conduction band structure of the host material (GaAs). Here we demonstrate the existence of an entirely new effect in the GaN(x) As(1-x) alloy system in which the Si donor in the substitututional Ga site (Si(Ga)) and the isovalent atom N in the As sublattice (N(As)) passivate each other's electronic activity. This mutual passivation occurs in Si-doped GaN(x) As(1-x) through the formation of nearest-neighbour Si(Ga) -N(As) pairs and is thermally stable up to 950 degrees C. Consequently, Si doping in GaN(x) As(1-x) under equilibrium conditions results in a highly resistive GaN(x) As(1-x) layer with the fundamental bandgap governed by a net 'active' N, roughly equal to the total N content minus the Si concentration. Such mutual passivation is expected to be a general phenomenon for electrically active dopants and localized state impurities that can form nearest-neighbour pairs.

The effects of nanosecond pulsed ultraviolet laser annealing on the surface stoichiometry of close-space sublimated polycrystalline thin films are investigated using angle-resolved x-ray photoemission spectroscopy (XPS). The raw data suggest the formation of a Cd-rich surface layer, but this is counter to the expectation based on Cd and Te vapor pressures above CdTe that predicts a Te-rich layer and to direct observation of elemental Te at the surface. In order to explain this apparent discrepancy, we analyze our XPS data in the context of prior reports of lateral segregation of Cd and Te at the surface after pulsed laser treatments with a simple model of angular dependent XPS in the presence of surface roughness. This analysis reveals that a uniform Te layer cannot explain our results. Instead, our analysis suggests that Te enrichment occurs near grain boundaries and that a sub-monolayer Cd layer exists elsewhere. These complex yet repeatable results underscore the challenges in measuring surface stoichiometry to high precision on films relevant for polycrystalline CdTe devices. It also suggests that the Cd and Te vapor pressures above grain boundaries may differ from those above grain interiors and that ohmic contact may be made preferentially at the grain boundaries after pulsed laser annealing.

Cu2ZnSnS4 is a promising low-cost, nontoxic, earth-abundant absorber material for thin-film solar cell applications. In this study, combinatorial coevaporation was used to synthesize individual thin-film samples spanning a wide range of compositions at low (325 °C) and high (475 °C) temperatures. Film composition, grain morphology, crystalline-phase and photo-excitation information have been characterized by x-ray fluorescence, scanning electron microscopy, x-ray diffraction, Raman spectroscopy, and photoluminescence imaging and mapping. Highly textured columnar grain morphology is observed for film compositions along the ZnS-Cu2ZnSnS4-Cu2SnS3 tie line in the quasi-ternary Cu2S-ZnS-SnS2 phase system, and this effect is attributed to structural similarity between the Cu2ZnSnS4, Cu2SnS3, and ZnS crystalline phases. At 475 °C growth temperature, Sn-S phases cannot condense because of their high vapor pressures. As a result, regions that received excess Sn flux during growth produced compositions falling alon...

Cu2ZnSn(S,Se)4 (CZTSSe) is an earth-abundant semiconductor with potential for economical photovoltaic power generation at terawatt scales. In this work, we use Raman scattering to investigate phase coexistence in combinatorial CZTS thin films grown at 325 or 470 °C. The surface of the samples grown at 325 °C is rough except for a prominent specularly reflective band near and along the ZnS-Cu2SnS3 (CTS) tie line in the Cu-Zn-Sn-S quaternary phase diagram. All structurally incoherent secondary phases (SnS2, CuS) exist only as surface phases or are embedded as separate grains, whereas the structurally coherent secondary phase CTS coexists with CZTS in the dense underlying film. In films grown at 325 °C, which are kinetically trapped by the low growth temperature, a change is observed in Cu and Sn site occupancy, evidenced by the shift from cubic-CTS in the Cu-rich region (Cu/Sn > 2) to more tetragonal-CTS in the Sn-rich region (Cu/Sn

We have studied the effect of sodium on the electrical properties of Cu2ZnSnS4 (CZTS) single crystal by using temperature dependence of Hall effect measurement. The sodium substitution on the cation site in CZTS is observed from the increasing of unit-cell size by powder X-ray diffraction. Sodium increases the effective hole concentration and makes the thermal activation energy smaller. The degree of compensation decreases with sodium incorporation, thus the hole mobility is enhanced. We revealed that sodium is important dopant in CZTS to control the electrical properties.

Creating an ohmic back contact has long been a problem for making efficient CdTe solar cells. Current devices utilize some combination of preferential chemical etching, buffer layer, and Cu doping with additional cost, time, and complexity added for each step. In this Letter, these processes are eschewed and replaced with a nanosecond pulsed ultraviolet laser treatment. It is shown that this treatment can eliminate the rollover effect seen in photovoltaic current-voltage (J-V) curves that is indicative of a non-ohmic back contact. Transfer length measurements show that a single UV laser pulse can reduce the specific contact resistivity by a factor of 24 versus untreated samples. X-Ray photoemission spectroscopy shows evidence of increased conductivity and of elemental Te created at the surface by laser pulses. Finally, finite element modeling is used to model the laser-sample interaction, which predicts both the temperature and the amounts of Cd and Te lost during a laser pulse.

CuInSe2 (CISe) is a prototype material for the I–III–VI chalcopyrites such as Cu(In,Ga)(S,Se)2 (CIGSSe) used as absorber layers in thin film photovoltaic cells. These thin film photovoltaic absorber layers are primarily synthesized by vacuum-based techniques in manufacturing. In this work, we investigate non-vacuum film synthesis by electrochemical deposition of CISe from a single bath followed by continuous wave laser annealing (CWLA) using a 1064 nm laser. We find that parameters exist for near-infrared CWLA which result in structural changes without melting and dewetting of the films. While Cu-poor samples show only about 40% reduction in the full width at half maximum (FWHM) of the respective x-ray diffraction (XRD) peaks, identically treated Cu-rich samples indicate a FWHM reduction of more than 70% in the XRD and Raman scattering data for irradiation at 50 W/cm2. This study demonstrates that an entirely solid-phase annealing path driven by intense illumination exists for chalopyrite phase formation and crystallization from electrodeposited CISe thin films.

We elucidate the dominant physical mechanisms for enhanced light absorption in thin film solar cells with embedded dielectric nanoparticles and conformal surface texturing. A prior work reported enhancement in short-circuit current for such a structure and attributed this gain to increased photon absorption due to Mie scattering by the embedded nanoparticles [S. Nunomura, A. Minowa, H. Sai, and M. Kondo, Appl. Phys. Lett. 97(6), 063507 (2010)]. On the contrary, simulations indicate that absorption gain is categorically dominated by the roughened surface texture that resulted from conformal overgrowth of amorphous silicon above the deposited dielectric nanoparticles.

The temperature-dependent conductivity of Cu2ZnSnS4 (CZTS) thin films prepared by sulfurization of different sputtered ZnS/Cu/Sn stacks and also of the same stack annealed for different times was investigated from 30-300 K. Fitting of the through-thickness conductivity requires a model including Mott variable-range hopping (M-VRH), nearest-neighbor hopping (NNH), and thermionic emission over grain boundary (GB) barriers. The GB barrier height varies sensitively from 50–150 (±5) meV with annealing and especially with [Cu]/([Zn] + [Sn]) ratio but is independent of [Zn]/[Sn] ratio. These results are critical for understanding the behavior of solar cells based on polycrystalline CZTS absorber layers.

Wave guidance is an important aspect of light trapping in thin film photovoltaics making it important to properly model the effects of loss on the field profiles. This paper derives the full-field solution for electromagnetic wave propagation in a symmetric dielectric slab with finite absorption. The functional form of the eigenvalue equation is identical to the lossless case except the propagation constants take on complex values. Additional loss-guidance and anti-guidance modes appear in the lossy model which do not normally exist in the analogous lossless case. An approximate solution for the longitudinal attenuation coefficient αz is derived from geometric optics and shows excellent agreement with the exact value. Lossy mode propagation is then explored in the context of photovoltaics by modeling a thin film solar cell made of amorphous silicon.

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Some of the authors thank for the support of the Center for Nanoscale Systems (CNS) at Harvard University is acknowledged. Harvard-CNS is a member of the National Nanotechnology Infrastructure Network (NNIN), which is supported by the National Science Foundation under NSF award No. ECS-0335765. K. M. Yu and J. W. Beeman were supported by the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.

We measured the magnetic anisotropy of nearly fully relaxed ferromagnetic Ga1−xMnxAs formed by Mn ion implantation followed by pulsed-laser melting (II-PLM) using magnetometry and ferromagnetic resonance. In qualitative terms the material formed by II-PLM exhibits all magnetic anisotropy features commonly found in Ga1−xMnxAs films fabricated by low-temperature molecular beam epitaxy (LT-MBE). Quantitatively, however, the magnetic anisotropy of II-PLM Ga1−xMnxAs is dominated by cubic anisotropy terms, which we attribute to the smaller strain in the II-PLM material due to the absence of Mn interstitials. One should note, however, that II-PLM Ga1−xMnxAs also exhibits a weak but finite uniaxial in-plane magnetic anisotropy similar to that observed in LT-MBE Ga1−xMnxAs, which can be ascribed to the small built-in compressive strain. The similarity between II-PLM and LT-MBE Ga1−xMnxAs clearly points to an intrinsic origin of this property, independent of the method of fabrication. At low temperatures the remnan...

We report the passivation of the Mn acceptors in Ga1−xMnxP upon exposure to a hydrogen plasma. The as-grown films are nonmetallic and ferromagnetic with a Curie temperature of TC=55 K. After hydrogenation the sample resistivity increases by approximately three orders of magnitude at room temperature and six orders of magnitude at 25 K. Furthermore, the hydrogenated samples are paramagnetic, which is evidenced by a magnetization curve at 5 K that is best described by a Brillouin function with g=2 and J=5/2 expected for Mn atoms in the 3d5 configuration. Upon annealing, partial depassivation and a recovery of ferromagnetism are observed. These observations unambiguously demonstrate that the ferromagnetism in Ga1−xMnxP is carrier-mediated similar to Ga1−xMnxAs.

The electronic and magnetic effects of intentional compensation with non-magnetic donors are investigated in the ferromagnetic semiconductors Ga1-xMnxAs and Ga1-xMnxP synthesized using ion implantation and pulsed-laser melting (II-PLM). It is demonstrated that compensation with non-magnetic donors and MnI have similarqualitative effects on materials properties. With compensation TC decreases, resistivity increases, and stronger magnetoresistance and anomalous Hall effect attributed to skew scattering are observed. Ga1-xMnxAs can be controllably compensated with Te through a metal-insulator transition through which the magnetic and electrical properties vary continuously. The resistivity of insulating Ga1-xMnxAs:Te can be described by thermal activation to the mobility edge and simply-activated hopping transport. Ga1-xMnxP doped with S is insulating at all compositions but shows decreasing TC with compensation. The existence of a ferromagnetic insulating state in Ga1-xMnxAs:Te and Ga1-xMnxP:S having TCs of the same order as the uncompensated materials demonstrates that localized holes are effective at mediating ferromagnetism in ferromagnetic semiconductors through the percolation of ferromagnetic 'puddles' which at low temperatures.

We report strong near-infrared absorption peaks in epitaxial films of GaAs and AlAs containing approximately 0.5–5% of the semimetal ErAs. The energy of the resonant absorption peak can be changed from 0.62to1.0eV (2.2–1.4μm) by variation of the ErAs volume fraction and the substrate temperature. We interpret the infrared absorption in terms of transitions across an energy gap caused by a confinement-induced semimetal-semiconductor transition. An effective mass model relates the changes in nanoparticle diameter observed in transmission electron microscopy to the energy gap.

We have measured the X-ray absorption (XAS) and X-ray magnetic circular dichroism (XMCD)at the Mn L3,2 edges in ferromagnetic Ga1-xMnxP for 0.018

We have investigated the effect of film thickness on the distribution of Mn atoms at various lattice sites in Ga1−xMnxAs thin films. We find that the growth surface acts as a sink facilitating the outdiffusion of Mn interstitials (MnI), and thus reducing its concentration in the film. The outdiffused MnI accumulate on the surface in a surface oxide layer and do not participate in the ferromagnetism of the film. For thin films less than 15 nm thick, no MnI can be detected. Because of the absence of compensating MnI defects, higher TC can be achieved for such extremely thin Ga1−xMnxAs layers. These results agree with our previously suggested Fermi-level-governed upper limit of the TC of III–Mn–V ferromagnetic semiconductors.

Cu2ZnSnS4 (CZTS) is a promising alternative for Cu(In,Ga)Se2 (CIGS) absorber layers in thin film solar cells and is comprised of commodity elements which will enable scale-up of chalcopyrite panel production unhindered by elemental supplies and costs. Various CZTS synthesis methods, especially sulfurization of stacked metal or metal sulfide layers, are being studied and have led to cell efficiencies up to 6.7% [1]. Here we report our studies of CZTS thin film synthesis via room temperature sputtering from a single CZTS target and co-sputtering from Cu2S, ZnS and SnS2 binary targets, both followed by sulfurization between 500 C - 600 C using either elemental sulfur vapor or in-situ generated H2S. Sputtering from sulfur-containing targets is designed to increase the sulfur content in the precursor films to promote stoichiometry. We report on the effects of processing including deposition on soda-lime and borosilicate glasses and deposition of Na-containing layers on film morphology (AFM/SEM), composition (EDS), phase (XRD), grain size (XRD/EBSD), grain boundary structure (EBSD), optical (spectroscopic ellipsometry) and electrical properties. Processing conditions producing desirable Zn-rich/Cu-poor films are identified [1]. The formation of MoSe2 at Mo/CIGS interface is believed to promote Ohmic contacts, but in CZTS we associate excessive formation of frangible MoS2 with film delamination from Mo/borosilicate glass substrates. Strategies for preventing delamination including adhesion layers are investigated and discussed. P-N junctions are formed with CdS/ZnO using chemical bath deposition and sputtering, and I-V characteristics are reported. Schottky junctions are formed and C-V measurements are used to determine the doping in the CZTS absorber layers.[1] H. Katagiri, et al., MRS Symp. Proc. 1165 1165-M04-01 (2009).