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Band-edge density-of-states and carrier concentrations in intrinsic and p-type CuIn1-xGaxSe2
KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.ORCID-id: 0000-0002-9050-5445
2012 (engelsk)Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 112, nr 10, s. 103708-Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The electronic structures of chalcopyrite CuIn1-xGaxSe2 have recently been reported to have strongly anisotropic and non-parabolic valence bands (VBs) even close to the Gamma-point VB maximum. Also, the lowest conduction band (CB) is non-parabolic for energies 50-100 meV above the CB minimum. The details in the band-edge dispersion govern the material's electrical properties. In this study, we, therefore, analyze the electronic structure of the three uppermost VBs and the lowest CB in CuIn1-xGaxSe2 (x = 0, 0.5, and 1). The parameterized band dispersions are explored, and the density-of-states (DOS) as well as the constant energy surfaces are calculated and analyzed. The carrier concentration and the Fermi energy E-F in the intrinsic alloys as functions of the temperature is determined from the DOS. The carrier concentration in p-type materials is modeled by assuming the presence of Cu vacancies as the acceptor type defect. We demonstrate that the non-parabolicity of the energy bands strongly affects the total DOS. Therefore, it is important to take into account full band dispersion of the VBs and CB when analyzing the free carrier concentration, like for instance, in studies of electronic transport and/or measurements that involve strong excitation conditions.

sted, utgiver, år, opplag, sider
2012. Vol. 112, nr 10, s. 103708-
Emneord [en]
N-Type, Electronic-Properties, Solar-Cells, Thin-Films, Cuinse2, Cugase2, Transport, Germanium, Crystals, Silicon
HSV kategori
Identifikatorer
URN: urn:nbn:se:kth:diva-109640DOI: 10.1063/1.4767120ISI: 000311969800064Scopus ID: 2-s2.0-84870697429OAI: oai:DiVA.org:kth-109640DiVA, id: diva2:585029
Forskningsfinansiär
Swedish Research Council
Merknad

QC 20130109

Tilgjengelig fra: 2013-01-09 Laget: 2013-01-08 Sist oppdatert: 2017-05-23bibliografisk kontrollert
Inngår i avhandling
1. Exploring the Electronic and Optical Properties of Cu(In,Ga) Se2
Åpne denne publikasjonen i ny fane eller vindu >>Exploring the Electronic and Optical Properties of Cu(In,Ga) Se2
2015 (engelsk)Licentiatavhandling, med artikler (Annet vitenskapelig)
sted, utgiver, år, opplag, sider
Stockholm: KTH Royal Institute of Technology, 2015. s. vii, 63
HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-160949 (URN)978-91-7595-453-0 (ISBN)
Presentation
2015-03-06, Sal N111, Brinellvägen 23, KTH, Stockholm, 11:00 (engelsk)
Opponent
Veileder
Merknad

QC 20150305

Tilgjengelig fra: 2015-03-05 Laget: 2015-03-05 Sist oppdatert: 2015-03-09bibliografisk kontrollert
2. First-Principles Study on Electronic and Optical Properties of Copper-Based Chalcogenide Photovoltaic Materials
Åpne denne publikasjonen i ny fane eller vindu >>First-Principles Study on Electronic and Optical Properties of Copper-Based Chalcogenide Photovoltaic Materials
2017 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

To accelerate environmentally friendly thin film photovoltaic (PV) technologies, copper-based chalcogenides are attractive as absorber materials. Chalcopyrite copper indium gallium selenide (CIGS ≡ CuIn1–xGaxSe2) is today a commercially important PV material, and it is also in many aspects a very interesting material from a scientific point of view. Copper zinc tin sulfide selenide (CZTSSe ≡ Cu2ZnSn(S1–xSex)4) is considered as an emerging alternative thin film absorber material. Ternary Cu2SnS3 (CTS) is a potential absorber material, thus its related alloys Cu2Sn1–xGexS3 (CTGS) and Cu2Sn1–xSixS3 (CTSS) are attractive due to the tunable band gap energies. CuSb(Se1–xTex)2 and CuBi(S1–xSex)2 can be potential as ultra-thin (≤ 100 nm) film absorber materials in the future. In the thesis, analyses of these Cu-based chalcogenides are based on first-principles calculations performed by means of the projector augmented wave method and the full-potential linearized augmented plane wave formalisms within the density functional theory as implemented in the VASP and WIEN2k program packages, respectively.

The electronic and optical properties of CIGS (x = 0, 0.5, and 1) are studied, where the lowest conduction band (CB) and the three uppermost valence bands (VBs) are parameterized and analyzed in detail. The parameterization demonstrates that the corresponding energy dispersions of the topmost VBs are strongly anisotropic and non-parabolic even very close to the Γ-point. Moreover, the density-of-states and constant energy surfaces are calculated utilizing the parameterization, and the Fermi energy level and the carrier concentration are modeled for p-type CIGS. We conclude that the parameterization is more accurate than the commonly used parabolic approximation. The calculated dielectric function of CuIn0.5Ga0.5Se2 is also compared with measured dielectric function of CuIn0.7Ga0.3Se2 collaborating with experimentalists. We found that the overall shapes of the calculated and measured dielectric function spectra are in good agreement. The transitions in the Brillouin zone edge from the topmost and the second topmost VBs to the lowest CB are responsible for the main absorption peaks. However, also the energetically lower VBs contribute significantly to the high absorption coefficient.

CTS and its related alloys are explored and investigated. For a perfectly crystalline CTS, reported experimental double absorption onset in dielectric function is for the first time confirmed by our calculations. We also found that the band gap energies of CTGS and CTSS vary almost linearly with composition over the entire range of x. Moreover, those alloys have comparable absorption coefficients with CZTSSe. Cu2XSnS4 (X = Be, Mg, Ca, Mn, Fe, Ni, and Zn) are also studied, revealing rather similar crystalline, electronic, and optical properties. Despite difficulties to avoid high concentration of anti-site pairs disordering in all compounds, the concentration is reduced in Cu2BeSnS4 partly due to larger relaxation effects. CuSb(Se1–xTex)2 and CuBi(S1–xSex)2 are suggested as alternative ultra-thin film absorber materials. Their maximum efficiencies considering the Auger effect are ~25% even when the thicknesses of the materials are between 50 and 300 nm.

sted, utgiver, år, opplag, sider
Stockholm: KTH Royal Institute of Technology, 2017. s. 97
Emneord
density functional theory, electronic structure, dielectric function, absorption coefficient, copper-based chalcogenides, ultra-thin film
HSV kategori
Forskningsprogram
Teknisk materialvetenskap
Identifikatorer
urn:nbn:se:kth:diva-207626 (URN)978-91-7729-396-5 (ISBN)
Disputas
2017-06-12, Sal D3, Lindstedtsvägen 5, Stockholm, 13:15 (engelsk)
Opponent
Veileder
Merknad

QC 20170523

Tilgjengelig fra: 2017-05-23 Laget: 2017-05-22 Sist oppdatert: 2017-05-24bibliografisk kontrollert

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