摘要:

Synchrotron radiation soft x‐ray photoemission spectroscopy was used to investigate the development of the electronic structure at the CdS(In)/CuInSe2heterojunction interface. In‐doped CdS overlayers were deposited in steps on single‐crystaln‐type CuInSe2at 250 °C. Results indicate that the CdS(In) grows in registry with the substrate, initially in a two dimensional growth mode followed by three dimensional island growth as is corroborated by RHEED analysis. Photoemission measurements were acquired after each growth in order to observe changes in the valence band electronic structure as well as changes in the In4d, Se3d, Cd4d, and S2p core lines. The results were used to correlate the interface chemistry with the electronic structure at these interfaces and to directly determine the CdS(In)/CuInSe2heterojunction valence band discontinuity and the consequent heterojunction band diagram as a function of In dopant concentration. We measured a valence band offset &Dgr;Ev=0.3 eV, independent of In doping.

ISSN:0094-243X    

DOI:10.1063/1.42950

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Cu, In, and Se were coevaporated onto unheated Mo‐coated substrates of glass and Al2O3. Cu and In partially segregated in these precursors in a direction normal to the film plane. The precursors were annealed in a rapid thermal processor to form CuInSe2(CIS). The films adhered better to the Al2O3than to the glass upon annealing. Solar cells were made by evaporating CdS and top contacts onto the CIS. The best cell had an efficiency of 3.5% and was obtained after annealing the as‐fabricated device in air.

ISSN:0094-243X    

DOI:10.1063/1.42919

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Efficiency limiting mechanisms in CdTe/CdS solar cells were investigated. It was found that growth of CdTe films under tellurium rich conditions enhanced the interdiffusion between CdTe and CdS and reduced the CdTe bandgap to 1.47 eV, whereas, growth of CdTe films under Cd‐rich conditions retained the CdTe bandgap at 1.5 eV. A CdCl2treatment followed by a 400 °C post‐growth annealing of CdTe improved the cell performance significantly. However, it also produced defects atEv+0.64 andEv+0.17 eV possibly due to chlorine related complexes. An inverse correlation was found between the density of these defects andVoc. Rapid thermal processing (RTP) was investigated as a variation of the conventional furnace anneal post‐growth treatment. Preliminary RTP results look promising with cell efficiency in excess of 8% without any CdCl2treatment. Further improvements are expected by optimizing the CdCl2treatment and the RTP conditions.

ISSN:0094-243X    

DOI:10.1063/1.42920

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Solar Cells, Inc. (SCI) has a program to produce 60 cm×120 cm solar modules based on CdTe films deposited from high temperature vapors. Deposition techniques include close spaced sublimation and chemical vapor deposition using elemental sources. Small area efficiency has been confirmed by NREL at 9.3% on a 0.22 cm2device (825 mV Voc, 18.16 mA/cm2Jsc, and 0.62 FF) deposited on a 100 cm2substrate. Preliminary work has begun on the fabrication of 8 cell, 64 cm2submodules and 60 cm×120 cm modules. Small area devices produced on the larger substrate material have exceeded 8% efficiency.

ISSN:0094-243X    

DOI:10.1063/1.42921

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Laser‐driven physical vapor deposition (LDPVD) and radio‐frequency (rf) sputtering have been used to fabricate thin‐film solar cells on SnO2‐coated glass substrates. The laser‐ablation process readily permits the use of several target materials in the same vacuum chamber and complete solar cell structures have been fabricated on SnO2‐coated glass using LDPVD for the CdS, CdTe, and CdCl2. To date the best devices (∼9% AM1.5) have been obtained after a post‐deposition anneal at 400 °C. In addition, cells have been fabricated with the combination of LDPVD CdS, rf‐sputtered CdTe, and LDPVD CdCl2. The performance of these cells indicates considerable promise for the potential of rf sputtering for CdTe photovoltaic devices. The physical mechanisms of LDPVD have been studied by transient optical spectroscopy on the laser ablation plume. These measurements have shown that, e.g., Cd is predominantly in the neutral atomic state in the plume but with a large fraction which is highly excited internally (≥6 eV) and that the typical neutral Cd translational kinetic energies perpendicular to the target are 20 eV and greater. Quality of as‐grown and annealed films has been analyzed by optical absorption. Raman scattering, photoluminescence, electrical conductivity, Hall effect, x‐ray diffraction, and SEM/EDS.

ISSN:0094-243X    

DOI:10.1063/1.42922

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We report on the deposition of thin cadmium sulfide (CdS) layers from aqueous solutions and their optical properties. CdS layers have been deposited on soda lime glass, tin oxide coated glass and copper indium diselenide (CuInSe2) thin films. A systematic increase in the absorption is found to occur with increasing concentration of the buffer salt used in the bath. CdS/CdTe thin film solar cells have been fabricated by close spaced sublimation of CdTe, yielding 11.3% devices.

ISSN:0094-243X    

DOI:10.1063/1.42923

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

This paper reviews our recent research on ion‐ and photon‐assisted doping and growth of homoepitaxial CdTe thin films. Our earlier work demonstrated doping to 2×1017cm−3with 60 eV P ions during growth by vacuum deposition, but gave low values of minority‐carrier diffusion lengthLd. To increaseLd, we (a) explored photon‐assisted doping, (b) varied the Cd/Te ratio, (c) used lower ion energies, (d) explored co‐evaporation doping from an Cd3As2, and (e) explored electron‐assisted doping. Although 512 nm illumination during growth enhanced crystalline quality, there was no evidence for any increase in doping over that of films not illuminated during growth. Increasing the Cd/Te ratio (1.00<Cd/Te<2.2), both with and without ions and/or light during deposition, had strong effects on In/p‐CdTe Schottky junction transport, but gave little useful alteration of the doping behavior. Using ion‐assisted doping, decreasing the P ion energy to 20 eV, using a Cd/Te ratio=1.002 and adding a low‐energy electron flux has yielded substantially largerLdwith controlled doping up to 1×1017cm−3.

ISSN:0094-243X    

DOI:10.1063/1.42924

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We studied the growth and electronic structure of the ZnTe/CdTe(100) interface with angle‐resolved synchrotron radiation photoemission (ARPES) and reflection high energy electron diffraction (RHEED). RHEED patterns during the growth of ZnTe layers on the CdTe(100) substrate showed that the initial ∼16 A˚ grows in registry. After this pseudomorphic 16 A˚ layer, the next 120 A˚ grows with defects to relieve the 6.6% strain between ZnTe and CdTe. After ∼140 A˚, the ZnTe layers are relaxed. ARPES taken near the Brillouin zone center gave a valance band offset &Dgr;Ev=0.14 eV, with the ZnTe valence band maximum (VBM) higher than the CdTe VBM.

ISSN:0094-243X    

DOI:10.1063/1.42930

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Removed from the deposition region, an upstream hydrogen microwave plasma generates arsenic hydrides by etching the surface of solid arsenic. The hydrides are transported to the deposition region and mixed with trimethylgallium to achieve low temperature (350–400 °C) and low pressure (750 mTorr) homoepitaxial GaAs films. Low precursor V/III ratios are used to achieve homoepitaxial films with high levels of carbon dopants (1019to mid 1020cm−3). No active or afterglow plasma exists in the growth region. The observed homoepitaxial growth activation energies of 54 kcal/mole and 66 kcal/mole for films deposited with V/III ratios of 1/1 and 1/4, respectively, are in the range of those reported for the heterogeneous decomposition of trimethylgallium in the absence of arsine. The majority carriers are holes and have hole concentrations which correlate to the carbon doping, as determined by room temperature Hall effect measurements and secondary ion mass spectroscopy. Carrier mobility versus carbon concentration is also presented.

ISSN:0094-243X    

DOI:10.1063/1.42931

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

This paper summarizes the behavior of a novel inverted reactor, designed to grow large area solar cell material with a high efficiency of chemical utilization. A computer model for this reactor, based on equations for the conservation of mass, momentum, energy, and species, has been used for predicting its operating characteristics. Both the reactor parameters, as well as the properties of doped and undoped GaAs grown in this system, are outlined in this paper.

ISSN:0094-243X    

DOI:10.1063/1.42879

出版商:AIP    

年代:1992

数据来源: AIP