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Dielectric function spectra at 40 K and critical-point energies for CuIn0.7Ga0.3Se2
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
Visa övriga samt affilieringar
2012 (Engelska)Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 101, nr 26, s. 261903-Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

We report ellipsometrically determined dielectric function ε spectra for CuIn0.7Ga0.3Se2 thin film at 40 and 300 K. The data exhibit numerous spectral features associated with interband critical points (CPs) in the spectral range from 0.74 to 6.43 eV. The second-energy-derivatives of ε further reveal a total of twelve above-bandgap CP features, whose energies are obtained accurately by a standard lineshape analysis. The ε spectra determined by ellipsometry show a good agreement with the results of full-potential linearized augmented plane wave calculations. Probable electronic origins of the CP features observed are discussed.

Ort, förlag, år, upplaga, sidor
2012. Vol. 101, nr 26, s. 261903-
Nyckelord [en]
Interband Critical-Points, Temperature-Dependence, Spectroscopic Ellipsometry, Thin-Films, Electronic-Structure, Cuin1-Xgaxse2, Cuinse2
Nationell ämneskategori
Fysik
Identifikatorer
URN: urn:nbn:se:kth:diva-116662DOI: 10.1063/1.4773362ISI: 000312830700025Scopus ID: 2-s2.0-84871730503OAI: oai:DiVA.org:kth-116662DiVA, id: diva2:600021
Anmärkning

QC 20130123

Tillgänglig från: 2013-01-23 Skapad: 2013-01-22 Senast uppdaterad: 2017-05-23Bibliografiskt granskad
Ingår i avhandling
1. Exploring the Electronic and Optical Properties of Cu(In,Ga) Se2
Öppna denna publikation i ny flik eller fönster >>Exploring the Electronic and Optical Properties of Cu(In,Ga) Se2
2015 (Engelska)Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
Ort, förlag, år, upplaga, sidor
Stockholm: KTH Royal Institute of Technology, 2015. s. vii, 63
Nationell ämneskategori
Materialteknik
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 (Engelska)
Opponent
Handledare
Anmärkning

QC 20150305

Tillgänglig från: 2015-03-05 Skapad: 2015-03-05 Senast uppdaterad: 2015-03-09Bibliografiskt granskad
2. First-Principles Study on Electronic and Optical Properties of Copper-Based Chalcogenide Photovoltaic Materials
Öppna denna publikation i ny flik eller fönster >>First-Principles Study on Electronic and Optical Properties of Copper-Based Chalcogenide Photovoltaic Materials
2017 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Stockholm: KTH Royal Institute of Technology, 2017. s. 97
Nyckelord
density functional theory, electronic structure, dielectric function, absorption coefficient, copper-based chalcogenides, ultra-thin film
Nationell ämneskategori
Materialteknik
Forskningsämne
Teknisk materialvetenskap
Identifikatorer
urn:nbn:se:kth:diva-207626 (URN)978-91-7729-396-5 (ISBN)
Disputation
2017-06-12, Sal D3, Lindstedtsvägen 5, Stockholm, 13:15 (Engelska)
Opponent
Handledare
Anmärkning

QC 20170523

Tillgänglig från: 2017-05-23 Skapad: 2017-05-22 Senast uppdaterad: 2017-05-24Bibliografiskt granskad

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