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The open circuit voltage (VOC) deficit of Cu2ZnSn(S,Se)4 (CZTSSe) kesterite solar cells is higher than that of the closely related Cu(InGa)Se2 solar cells. One of the most promising strategies to overcome the large VOC deficit of kesterite solar cells is by reducing the recombination losses through appropriate cation substitution. In fact, replacing totally or partially Zn or Cu by an element with larger covalent radius one can significantly reduce the concentration of I–II antisite defects in the bulk. In this study, an investigation of the impact of partial substitution of Cu by Ag in CZTSSe solid solution monograins is presented. A detailed photoluminescence study is conducted on Ag-incorporated CZTSSe monograins and a radiative recombination model is proposed. The composition and structural quality of the monograins in dependence of the added Ag amount are characterized using Energy Dispersive X-ray Spectroscopy and X-Ray Diffraction method, respectively. The Ag-incorporated CZTSSe monograin solar cells are characterized by temperature dependent current-voltage and electron beam induced current methods. It was found, that low Ag contents (x ≤ 0.02) in CZTSSe lead to higher solar cell device efficiencies.

This research reveals the missing or often undisclosed experimental data on processing conditions of Cu(In,Ga)(S,Se)2 absorbers by the two-step sequential technique. Accordingly, by employing a one-variable-at-a-time approach- where each factor is exclusively changed with respect to a defined center point, we identified a handful of significant parameters which play the most significant role in an absorber's properties and consequently, prospective high-performing solar cells. This was done by analyzing their impact on a few most important metrics. Hence, the vast processing window with numerous factors and levels for development of Cu(In,Ga)(S,Se)2 by this method becomes constrained and feasible to optimize in future endeavours.

The fabrication and properties of a Ge-based Kesterite Cu 2 ZnGeSe 4 (CZGSe) solar cell are discussed. The existence of the quaternary compound has been verified by physical methods such as X Ray Diffraction (XRD) and Energy Dispersive Spectroscopy (EDS). The Cu 2 ZnGeSe 4 solar cell has a power conversion efficiency (PCE) of 5.5% under AM1.5G illumination which is among the highest reported for pure Ge substitution. Detailed low temperature current-voltage and time-resolved photoluminescence measurements show that the Cu 2 ZnGeSe 4 absorber has less bulk defects and less band tailing in contrast to the typical characteristics of Cu 2 ZnSnSe 4 devices. These beneficial opto-electronic properties also resulted in a high open circuit voltage (V oc ) of 744 mV which is amongst the highest values reported for Kesterite materials.

In this contribution, we report on the impact of ammonium sulfide ((NH4)(2)S-x) chemical treatments done at room temperature on the surface properties of Cu2ZnSnSe4 (CZTSe) thin film. The first approach is based on the immersion of the absorber layer in a (NH4)(2)S-x solution (20 wt.%). This method results in the preferential etching of Se, Sn and Zn atoms from the absorber surface. After a treatment time of 1 min, the performances of the solar cells are found to be improved. The second approach consists in the exposure of the CZTSe layer to ammonium sulfide vapors. In this case, it was found that the progressive sulfurization of the surface of the absorber leads to the decomposition of the CZTSe phase into Sn(S,Se)(x) and Se-0 secondary phases. As a consequence, the short circuit current of the corresponding solar cells is reduced. (C) 2016 Elsevier B.V. All rights reserved. This work refers to the patent EP 2 871 683 A1 (date of publication: 13th May 2015). This research is partially funded by the Flemish government, Department Economy, Science and Innovation. AGC is acknowledged for providing Mo-coated soda lime glass substrates. Dr. Carole La (University of Nantes, France) is acknowledged for her technical support for the ICP-AES measurements.

Solution processed CH 3 NH 3 PbI x Cl 3– x based planar heterojunction perovskite solar cells with power conversion efficiency (PCE) above 14% are reported. The devices benefit from a phenyl-C 61 -butyric acid methyl ester (PCBM)/ZnO double electron transport layer (ETL) as well as a short air-aging step. The role of the additional ZnO ETL is studied by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and secondary ions mass spectroscopy (SIMS). Apart from improving the energy level alignment, the ZnO layer blocks the reactions between the metal electrode and perovskite components, increasing the air stability of the device. A crucial step in our processing is a short air-aging step for the device, which significantly increases the device performance by reducing the recombination process. Since the ZnO nanoparticle layer requires no thermal annealing, the maximum temperature to fabricate the device can be kept below 100 °C, making this structure compatible with roll-to-roll processing on plastic films.

We report on the electrical, optical and physical properties of Cu2ZnSnSe4 solar cells using an absorber layer fabricated by selenization of sputtered Cu, Zn and Cu10Sn90 multilayers. A maximum active-area conversion efficiency of 10.4% under AM1.5G was measured with a maximum short circuit current density of 39.7 mA/cm(2), an open circuit voltage of 394 mV and a fill factor of 66.4%. We perform electrical and optical characterization using photoluminescence spectroscopy, external quantum efficiency, current-voltage and admittance versus temperature measurements in order to derive information about possible causes for the low open circuit voltage values observed. The main defects derived from these measurements are strong potential fluctuations in the absorber layer as well as a potential barrier of the order of 133 meV at the back side contact. (C) 2014 Elsevier B.V. All rights reserved.

One of the promising low cost and non-vacuum approaches for the fabrication of semiconductor CuInSe 2 and Cu(In,Ga)(S,Se) 2 thin film absorbers is the printing of precursor materials followed by a sintering/selenization process. The selenization process parameters such as temperature, duration, and selenium vapor pressure strongly influence the morphology and electronic properties of the absorber film. In this study, the effect of pre-annealing in an inert atmosphere and selenization on printed mechanically synthesized CuInSe 0.5 alloy nanopowder precursor films was investigated. 1–2 μm thick CuInSe 0.5 alloy nanopowder layers were deposited on a Mo-sputtered glass substrate by means of doctor blade coating of a nanopowder based precursor suspension. Pre-annealing was performed on a hot plate inside a nitrogen gas filled glove box. Selenization was performed in a home-made rapid thermal processing (RTP) furnace with two RTP heating zones for independent temperature control of the selenium source and the coated substrate. The temperature of the selenium source was fixed at 390–410 °C during the selenization to provide a constant supply of selenium vapor. A two-step process, i.e., a pre-annealing in nitrogen atmosphere at 400 °C for 30 min followed by selenization at 530 °C for 15 min was found to result in better densification and grain growth of the CuInSe 2 phase, compared to a single step selenization at 530 °C for 15 min. The solar cell fabricated by the two-step process had an efficiency of 5.4% and a fill factor of 52%, while the device fabricated by the single step selenization had an efficiency of 1.1% and a fill factor of 31%.

Cu 2 ZnGeSe 4 (CZGeSe) can be considered as a potential alternative for wide band gap thin film devices. In this work, CZGeSe thin films were deposited on Mo-coated soda lime glass substrates by sequential deposition of sputtered Cu, Zn and e-beam evaporated Ge layers from elemental targets followed by annealing at high temperature using H 2 Se gas. We report on the effect of the precursor stack order and composition and the impact of the annealing temperature on the physical properties of CZGeSe thin films. The optimal layer morphology was obtained when using a Mo/Cu/Zn/Ge precursor stack annealed at 460 °C. We have observed that the formation of secondary phases such as ZnSe can be prevented by tuning the initial composition of the stack, the stack order and the annealing conditions. This synthesis process allows synthesizing CZGeSe absorber with an optical band gap of 1.5 eV.

In this paper, we examine photoluminescence spectra (PL) of Cu2ZnSnSe4/CdS/ZnO solar cells, based on an absorber layer fabricated by selenization of sputtered Cu, Zn, Sn multilayers, via temperaturedependent and illumination power-dependent measurements. We observe anomalous emission behavior: the PL peak initially decreases with increasing temperature (red shift) in the temperature range 10– 60 K, followed by a blue shift at higher temperature in the range 60–180 K. A recombination model is proposed that is able to explain both temperature dependent PL as well as power-dependent PL. The important aspect of the proposed model is taking into account the presence of strong potential

We report on the electrical and physical properties of Cu2ZnSnSe4 (CZTSe) solar cells consisting of an absorber layer fabricated by selenization of sputtered Cu, Zn, Sn multilayers. Cross-section scanning electron microscopy images show that the polycrystalline absorber layers are approximately 1 μm thick and that the typical grain size is of the order of 1 μm. Energy-dispersive X-ray spectroscopy measurements show Cu-poor and Zn-rich compositions with Cu/(Zn + Sn) ~ 0.8 and Zn/Sn ~ 1.2. Solar cells are fabricated out of this absorber material using a standard process flow for chalcogenide solar cells. Under AM1.5 G illumination, the best 1 × 1 cm2 CZTSe solar cell shows an efficiency of 6.3% with a maximum short circuit current of 31.3 mA/cm2, an open circuit voltage of 0.39 V and a fill factor of 52%. Doping density of the absorber layers is derived using the drivel level capacitance profiling (DLCP) technique, showing low p-type doping density which seems to increase exponentially with the Zn/Sn ratio. Comparing the values obtained from DLCP to the ones derived from Mott–Schottky plots of the same devices, it is shown that for CZTSe care has to be taken when deriving the doping density. Similar to copper indium gallium selenide junctions, Mott–Schottky plots overestimate the amount of free carriers in the buffer due to the presence of fast defect states inside the bandgap.

The integration of higher carrier mobility materials to increase drive current capability in the next CMOS generations is required for device scaling. But a fundamental issue regarding the introduction of high-mobility III–V in CMOS is the electrical passivation of the interface with the high-κ gate dielectric. In this work, we show that in situ H2S surface treatment on GaAs(001) leads to a stable and reorganized oxide/III–V interface. The exposition of the GaAs surface is monitored in situ by RHEED and the interface is characterized by XPS analyses. Finally, MOS capacitors are fabricated to extract interface state density over the band gap. These results highlight a promising re-interest in chalcogenide passivation of III–V surfaces for CMOS applications.

A fundamental issue regarding the introduction of high-mobility Ge channels in CMOS circuits is the electrical passivation of the interface with the high-k gate dielectric. In this paper, we investigate the passivation of p-Ge(001) using molecular H"2S. The modification of the semiconductor surface is monitored in situ by RHEED and the interface is characterized by XPS analyses. MOS capacitors are fabricated to extract interface state density, and finally we demonstrate the efficiency of the passivation scheme using a combination with an ultra thin Al interlayer.

Si and Se implantations have been systematically investigated in In"0"."5"3Ga"0"."4"7As. Different implant doses and various activation anneals with temperatures up to 700^oC have been examined. Raising Si implant dose from 1x10^1^4 to 1x10^1^5cm^-^2 was found to increase the active doping concentration by about a factor of two. As confirmed by Transmission Electron Microscopy (TEM) and electrical measurements, the rest of the implanted Si ions remain as defects in the crystal and degrade the mobility. It was also confirmed from Secondary Ion Mass Spectrometry (SIMS) that the Si diffusivity in InGaAs is negligible up to 700^oC implant activation anneal making Si a suitable option for the formation of shallow junctions in InGaAs. The activation efficiency, sheet resistance, carrier density and mobility data of 25keV Se and Si implanted InGaAs layers are also presented under various activation anneal temperatures.

In this work, we report the selective area epitaxial growth of high quality InP in shallow trench isolation (STI) structures on Si (0 0 1) substrates 6° miscut toward (1 1 1) using a thin Ge buffer layer. We studied the impact of growth rates and steric hindrance effects on the nano-twin formation at the STI side walls. It was found that a too high growth rate induces more nano-twins in the layer and results in InP crystal distortion. The STI side wall tapering angle and the substrate miscut angle induced streric hindrance between the InP facets and the STI side walls also contribute to defect formation. In the [1 1 0] orientated trenches, when the STI side wall tapering angle is larger than 10°, crystal distortion was observed while the substrate miscut angle has no significant impact on the InP defect formation. In the [1 1 0] trenches, both the increased STI tapering angle and the substrate miscut angle induce high density of defects. With a small STI tapering angle and a thin Ge layer, we obtained extended defect free InP in the top region of the [1 1 0] trenches with aspect ratio larger than 2.

Dichlorosilane (DCS), silane and trisilane have been investigated as Si precursors for low temperature ( 5 A/min). Trisilane permits the growth of Si at lower temperatures below 350 °C due to a specific growth mechanism enhancing H desorption. Layers grown at temperatures lower than 500 °C are defective, irrespective of the carrier gas, pressure and precursor flow used.

Numerous metal oxides have been studied worldwide as possible high-k gate dielectric candidates for MOS devices on alternative semiconductor materials (Ge, III/V compounds). We will discuss thermal and plasma-enhanced atomic layer deposition (ALD) of a few materials, HfO"2 and Al"2O"3. We will spend some attention to characteristic features of the growth process and specific growth precursors as this is known to influence strongly the quality of the layer bulk as well as the interface. Detailed electrical characterization of MOS capacitors build on such dielectric layers, before and after forming gas anneals, shows that these interface modifications can lead to a marked decrease of the smaller interface state peaks close to the edges of the bandgap, whereas the larger mid-gap peaks are barely touched. The results of atomistic modeling of the oxidation of a GaAs surface help to understand the origin of these mid-gap electronic states, which are responsible for the apparent pinning of the Fermi level.

The electron energy band alignment at interfaces of In x Ga 1− x As (0 ⩽ x ⩽ 0.53) with atomic-layer deposited insulators Al 2 O 3 and HfO 2 is characterized using combined measurements of internal photoemission of electrons and photoconductivity. The measured energy of the In x Ga 1− x As valence band top is found to be only marginally influenced by the semiconductor composition. This result suggests that the observed bandgap narrowing from 1.42 to 0.75 eV when the In content increases from 0 to 0.53 occurs mostly through downshift of the semiconductor conduction band bottom. Electron states originating from the interfacial oxidation of In x Ga 1− x As lead to reduction of the electron barrier at the semiconductor/oxide interface.

In this paper we compare the interface trap distributions D"i"t(E) of sulfur treated Al"2O"3/In"0"."5"3Ga"0"."4"7As interfaces, which underwent MOS capacitor and transistor fabrication processes. Lower interface trap densities were found close to the conduction band edge for both cases. The inversion channel MOSFET achieves high device performance despite the fact that its oxide-semiconductor interface quality is a notch below that of the MOS capacitor with optimized process.

Selective epitaxial growth of GaAs on Ge is a prerequisite for the integration of GaAs and Ge in the sub-22 nm CMOS nodes. The problems encountered for epitaxial growth of GaAs on Ge are described and illustrated. Mainly the problem of anti-phase boundary (APB) formation is addressed. Selective epitaxial growth of GaAs on Ge with a SiO 2 mask is discussed and selectively grown layers are characterized by X-ray diffraction, electron microscopy, defect etching and photoluminescence spectroscopy. An optimized growth procedure is presented, which simultaneously reduces loading effects and APB creation. Low temperature photoluminescence measurements show the good quality of the selectively grown GaAs on Ge.

As CMOS is approaching the 22 nm node, the importance of high-mobility materials such as Ge and GaAs is rapidly increasing. For the timely development of these new technologies accurate dopant and carrier-profiling solutions for source-drain extensions with these materials are required. Identical n-type-doped (Si, Se) layers on same and opposite type medium-doped layers on S.I. GaAs substrates will be investigated, with layer thicknesses ranging from 200 down to 50 nm and doping concentration levels up to 1e20 at/cm3. In this work, secondary ion mass spectrometry will be used for dopant profiling. For GaAs carrier profiling, conventional spreading resistance probe, as commonly used in Si-CMOS, fails. Hence, reliable alternatives need to be found for characterizing these high–low structures. Techniques to be discussed range from the more conventional approaches such as Hall or electrochemical capacitance–voltage (performed by different laboratories), over micro-Raman spectroscopy and photo-luminescence along a beveled surface, up to more advanced approaches using scanning spreading resistance microscopy.

Photoluminescence intensity (PLI) measurements of GaAs and InGaAs thin films indicate that InGaAs might be inherently easier to passivate than GaAs. The introduction of just 15% of In leads to a reduction of the surface recombination velocity at native oxide interfaces by an order of magnitude. This is more than the effect expected by a reduced bandgap alone. The PLI method applied to thin films can also be used to determine the surface recombination velocity of other IIIV-oxide interfaces.

We have selectively grown thin epitaxial GaAs films on Ge substrates with the aid of a 200 nm thin SiO2 mask layer. The selectively grown structures have lateral sizes ranging from 1 um width up to large areas of 1 by 1 mm2. The growth with the standard growth procedure for GaAs growth on Ge substrates reveals a limited amount of GaAs nucleation on the mask area and strong loading effects caused by diffusion of group III precursors over the mask area and in the gas phase. Reduction of the growth pressure inhibits GaAs nucleation on the mask area and reduces the loading effects strongly, but favors the creation of anti phase domains in the GaAs. An optimized growth procedure was developed, consisting of a 13 nm thin nucleation layer grown at high pressure, followed by low pressure growth of GaAs. This optimized growth procedure inhibits the nucleation of GaAs on the mask area and is a good compromise between reduction of loading effects and inhibition of anti phase domain growth in the GaAs. X-ray diffraction and photoluminescence measurements demonstrate the good microscopic characteristics of the selectively grown layers., Comment: 14 pages, 8 figures

Due to the slowness of the electron–phonon interaction in small gap STJs currently being developed as the latest generation of photon detectors, during the device operation a broad statistical distribution of interacting quasiparticles and phonons is established. This gives rise to new physical phenomena and also renders the traditional Rothwarf–Taylor model completely inadequate for the analysis of quasiparticle and phonon dynamics for all traditional superconductors except unproximised Nb. We have developed a new kinetic approach replacing the Rothwarf–Taylor scheme. We demonstrate the results of experimental and theoretical studies of the new physical phenomenon of quasiparticle self-generation in a heavily proximised multiple tunneling Ta/Al STJ and discuss the implications of the observed quasiparticle self-generation for photon detection.

We report on the successful fabrication of low leakage aluminium superconducting tunnel junctions with very homogeneous and transparent insulating barriers. The junctions were tested in an adiabatic demagnetisation refrigerator with a base temperature of 35 mK. The normal resistance of the junctions is equal to ~7 uohm cm2 with leakage currents in the bias voltage domain as low as 100 fA/um2. Optical single photon counting experiments show a very high responsivity with charge amplification factors in excess of 100. The total resolving power (including electronic noise) for 500 nm photons is equal to 13 compared to a theoretical tunnel limited value of 34. The current devices are found to be limited spectroscopically by spatial inhomogeneities in the detectors response, 3 pages, 5 figures

The quasiparticle (QP) lifetime in superconducting tunnel junctions (STJs) at sufficiently low temperature is usually found to be governed by loss processes associated with edges, interfaces or contacts. Such losses are closely related to fabrication issues and difficult to control. In our Ta-based STJs we observe variations in pulse decay time up to a factor of 2–3 for nominally the same devices. Nevertheless, experiments with STJs in which the thickness of the Al layers adjacent to the barrier is progressively increased, show a clear trend of increasing QP lifetime. Alternatively, introducing Nb capping layers below and on top of the Ta STJs gives a significant reduction of QP lifetime.

We present the results of a series of X-ray measurements on several prototype TlBr detectors. The devices were fabricated from mono-crystalline material and were typically of size 2.7×2.7×0.8 mm3. The material is extremely pure, having impurity concentrations

We report X-ray measurements on a prototype 3 � 3 TlBr pixel array, produced to assess the technological feasibility of making a Fano limited imager, which can operate near room temperature. The device was fabricated on monocrystalline material of size 2.7 � 2.7 � 1.0 mm 3 . It has a pixel size of 350 � 350mm 2 and pitch of 450mm. Measurements were carried out on all pixels over the energy range 5.9–662 keV using radioactive sources. The leakage currents were found to be low enough to allow room-temperature operation, with typical energy resolutions of B20 keV FWHM at 59.95 keV under full-area illumination. At a reduced detector temperature of –301C, these fell to B4 keV FWHM. Although the spectral performance of the present array is currently impaired by material limitations, its spectral acuity was found to be greatly enhanced by the small pixel effect. Additional photon metrology was carried out at the Hamburger Synchrotron-strahlungslabor radiation facility. Under monochromatic pencil beam illumination, the measured energy resolutions at 20 keV were B3 keV FWHM at � 301C. The spatial uniformity of the array was measured using a 50 � 50mm 2 , 20 keV monoenergetic X-ray beam, raster scanned over the entire active area. The response, in terms of count rate, gain and energy resolution was found to be uniform at the few percent level, consistent with statistics. It was observed during these measurements, that the X-ray response of the pixels was unstable, showing time-dependent gain shifts indicative of polarization effects. The magnitude of the effect was proportional to the total energy deposition per unit time. Lastly, the use of TlBr arrays in nuclear medicine applications is discussed with particular emphasis on radio-guided surgical probes. Recommendations for an optimized design are given. r 2002 Elsevier Science B.V. All rights reserved.

In this, the second part of a detailed study into the X-ray response of InP, we present results of a series of X-ray measurements on a 3.142 mm 2 � 180mm thick semi-insulating InP detector at the BESSY II and HASYLAB synchrotron radiation research facilities. Photon metrology was carried out at energies ranging from 8 to 100 keV. Additional measurements were made using radioactive and fluorescent target sources. At � 601C, under full-area illumination, the FWHM energy resolution was 2.4 keV at 5.9 keV rising to 8.5 keV at 59.54 keV. Under pencil-beam illumination, the measured resolutions were generally less, being 2 keV FWHM at 8 keV rising approximately linearly to 5 keV at 100 keV. Analysis of the energy resolution function indicates that poor charge transport presently limit the performance of InP detectors and specifically hole trapping. This is borne out by the observed low-energy tailing of the pulse height spectra at intermediate and high energies. At very low count rates, it was found that the device was linear to within 1%. However, for count rates above B100 s � 1 and energies above B50 keV, the detector began to display time variable gain shifts indicative of polarization effects. The spatial uniformity of the detector was investigated by raster scanning a 50 � 50mm 2 , 15 keV monoenergetic X-ray beam across the active area. Apart from a few localized areas, the detector response was found to be reasonably uniform at the 10% level, although inconsistent with that expected from counting statistics alone (2%). r 2002 Elsevier Science B.V. All rights reserved. PACS: 07.85n; 29.40Wk; 61.80e

We report X-ray measurements on a prototype 1.1 cm 2 , 32×32 GaAs pixel array with a pixel size of 350×350 μm 2 produced to assess the technological feasibility of making large area, almost Fano-limited arrays, which operate near room temperature. Measurements were carried out on four widely separated pixels both in our laboratories and using monochromatic X-ray pencil beams at the HASYLAB synchrotron research facility in Hamburg, Germany. The pixels were found to be very uniform both in their energy and spatial responses. For example, typical energy resolutions of ∼280 eV at 10.5 keV , rising to ∼560 eV at 60 keV were achieved. The corresponding resolutions measured under full-pixel illumination were found to be the same within statistics, indicating uniform crystallinity and stoichiometry . Likewise, by scanning a 15 keV , 15× 15 μm 2 beam across the entire surface of each of the pixels, the gain uniformity across the pixels (and by implication the entire array) was determined to be statistically flat.

We summarise the results of a number of X-ray measurements on a 7 mm 2 , 0.5 mm thick HgI2 detector carried out both in our laboratory and at two synchrotron radiation facilities in Germany. The detector energy response function was found to be linear over the energy range 2.3– 100 keV with an average rms non-linearity of 0.2%. Using a 50×50 μm 2 15 keV monoenergetic X-ray beam, the spatial uniformity of the detector response was determined by a raster scan technique to be better than 1%. At room temperature, the FWHM energy resolution was 600 eV at 5.9 keV rising to 6 keV at 100 keV with no statistically significant difference between pencil beam (50×50 μm 2 ) and full-area illumination. It was found that the FWHM energy resolution decreased with decreasing temperature reaching a minimum of 400 eV for 5.9 keV X-ray illumination at −19.2°C. Below this temperature, the FWHM begins to rise slowly. By considering the various contributions to the FWHM energy resolution, we estimate the charge collection efficiency to be (95.2±0.7)% at room temperature and (98±0.2)% at −19°C with a Fano factor of 0.30±0.24 at room temperature.

We have developed a theory of the anomalous sub-gap currents in small gap superconducting multiple tunnelling junctions. The sub-gap current at low bath temperatures is predicted to follow a sequence of steps at 2Δ/n, where n is an integer. These steps occur because in small gap multiple tunnelling structures a quasiparticle has the chance to increase its energy successively after each tunnelling event, until eventually its energy exceeds 3Δ. At this point, it relaxes down the edge with the emission of 2Δ phonon which triggers a Cooper pair break resulting in excess sub-gap current.