Electronic Properties of Surfaces and Interfaces in Widegap Chalcopyrites

Sadewasser, Sascha

doi:10.1007/3-540-31293-5_10

Cited by 2 publications

(2 citation statements)

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“…The work function is calibrated using highly oriented pyrolytic graphite as a reference. After KCN etching, the sample was transferred through ambient air into the UHV system and sputter cleaned to remove surface contaminations before the KPFM measurement [18]. For Hall measurements the samples are broken into three pieces: two square pieces for the bulk measurement on each side of the grain boundary, measured by the van der Pauw method, and one piece containing the grain boundary with stripe contacts for conductivity measurement across the grain boundary by the four point method.…”

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confidence: 99%

Evidence for a Neutral Grain-Boundary Barrier in Chalcopyrites

et al. 2006

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Single grain boundaries in CuGaSe 2 have been grown epitaxially. Hall measurements indicate a barrier of 30 -40 meV to majority carrier transport. Nevertheless, local surface potential measurements show the absence of space charge around the grain boundary; i.e., it is neutral. Theoretical calculations [Persson and Zunger, Phys. Rev. Lett. 91, 266401 (2003)] have predicted a neutral barrier for the present 3 grain boundary. Thus, we have experimentally shown the existence of a neutral grain-boundary barrier, however, smaller than theoretically predicted. DOI: 10.1103/PhysRevLett.97.146601 PACS numbers: 72.80.Ey, 61.72.Mm, 71.55.Gs, 72.20.ÿi The electronic structure of Cu chalcopyrites shows numerous peculiarities, including, i.e., their grain-boundary properties. The first model [1,2] for the electronic structure of grain boundaries in chalcopyrites was based on the Seto model [3], where charged defects at grain boundaries cause a barrier for majority carriers (holes in the chalcopyrites discussed here). Barriers and space charge regions have been found in polycrystalline films by Hall measurements and Kelvin probe force microscopy (KPFM) (see, e.g., [1,4 -6] ). Theoretically it has been predicted that grain boundaries in chalcopyrites represent a barrier without charged defects [7,8]. In the Cu chalcopyrites, the top of the valence band is formed from antibonding Cu d states, which lifts it to higher energy compared to the corresponding II-VI compounds [9]. Grain boundaries consisting of f112g tet planes in the tetragonal system [10], corresponding to the f111g cub planes in the cubic system, are proposed to be Cu deficient, which results in a lowering of the valence band maximum. This results in a barrier in the valence band without a space charge at the grain boundary. Recently it has been argued that only a specific structure of a f112g tet grain boundary leads to this barrier and that the experimentally observed structures should not show a neutral barrier [11].Grain boundaries along the f112g tet planes can be described as twins. The coincidence site lattice (CSL) of such grain boundaries is characterized by a value of 3, the lowest value possible. Thus, it is expected that grain boundaries along f112g tet planes show a low defect density. A generating function of the CSL for the cubic system has been derived in Ref. [12]. Since the tetragonal distortion of chalcopyrites is small and since the CSL concerns only the two-dimensional plane of the grain boundary we assume the generating function for the cubic system as an approximation for the chalcopyrite system. Then it becomes clear that a polycrystalline film with f220g tet (i.e., f110g cub ) texture and vertical grain boundaries contains predominantly 3 grain boundaries. In fact, it has been shown that polycrystalline absorber films with f220g tet texture result in higher efficiencies of the corresponding solar cells compared to the usual f112g tet texture [13]. Therefore, 3 grain boundaries are the ones appearing in the most successful solar cells ...

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Evidence for a Neutral Grain-Boundary Barrier in Chalcopyrites

et al. 2006

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“…11) Furthermore, a clear correlation exists between energy loss in solar cells and reduced PL decay lifetimes. [12][13][14][15][16] However, the carrier recombination mechanism is still under debate since CIGS has many defect candidates such as impurity phases [e.g., Cu 2Àx Se and Cu(In,Ga) 3 Se 5 ], 17,18) point defects (e.g., vacancies and antisite defects), 19,20) and grain boundaries, [21][22][23] whose role is difficult to specify. Microscopic PL (-PL) analysis seems an effective method to gather the requisite experimental evidence since the composition fluctuation and grain structure of the CIGS thin films are observed at the micrometer scale.…”

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Time-Resolved Microphotoluminescence Study of Cu(In,Ga)Se₂

Sakurai

Taguchi

Islam

et al. 2011

Jpn. J. Appl. Phys.

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The carrier recombination processes in Cu(In 1Àx ,Ga x )Se 2 (CIGS) thin films were investigated by time-resolved microscopic-photoluminescence (-PL) measurement at room temperature. For films with x ¼ 0:45, the spatial distribution of the donor-acceptor pair luminescence is much larger than the grain size. The PL decay lifetime is directly correlated with the -PL intensity, but the spectral shape is identical regardless of the sample position. These results suggest that the nonuniform distribution of nonradiative recombination centers mainly affects the carrier recombination in CIGS thin films. At relatively high Ga concentrations (x ! 0:7), the spatial inhomogeneity in -PL intensity is enhanced and decay accelerated, suggesting an increase in the density of nonradiative recombination centers. Thus, suppression of nonradiative recombination is critical to enhancing the performance of CIGS-based solar cells. #

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Electronic Properties of Surfaces and Interfaces in Widegap Chalcopyrites

Cited by 2 publications

References 38 publications

Evidence for a Neutral Grain-Boundary Barrier in Chalcopyrites

Evidence for a Neutral Grain-Boundary Barrier in Chalcopyrites

Time-Resolved Microphotoluminescence Study of Cu(In,Ga)Se₂

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Electronic Properties of Surfaces and Interfaces in Widegap Chalcopyrites

Cited by 2 publications

References 38 publications

Evidence for a Neutral Grain-Boundary Barrier in Chalcopyrites

Evidence for a Neutral Grain-Boundary Barrier in Chalcopyrites

Time-Resolved Microphotoluminescence Study of Cu(In,Ga)Se2

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Time-Resolved Microphotoluminescence Study of Cu(In,Ga)Se₂