Direct observation of conduction band plasmons and the related Burstein-Moss shift in highly doped semiconductors: A STEM-EELS study of Ga-doped ZnO

Granerød, Cecilie Skjold; Bilden, Sindre Rannem; Aarholt, Thomas; Yao, Yufeng; Yang, C. C.; Vines, Lasse; Johansen, K. M.; Prytz, Øystein

doi:10.1103/physrevb.98.115301

Cited by 20 publications

(7 citation statements)

References 52 publications

(57 reference statements)

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“…Specifically, (1) small effective mass m * and (2) large dopant levels n (which are target properties of TCs) increase Δ E g BM , corroborating its presence in n-type TCs but not p-type TCs: However, this equation assumes a single, parabolic band configuration, which indicates the magnitude and intrinsic limits of the BM shift depend on (3) the shape and spacing between bands. Because n-type TCs typically exhibit single-valley and degenerate CBMs, this shift can reach up to 0.5 eV in ITO and Ga-doped ZnO. , In contrast, most p-type TCs exhibit multiple, shallow valence bands (VBs), not a single-valley VBM. These three factors compound in the test set’s p-type TCs such that no noticeable Δ E g BM occurs.…”

Section: Resultsmentioning

confidence: 99%

Assessing High-Throughput Descriptors for Prediction of Transparent Conductors

Woods‐Robinson

Broberg²,

Faghaninia

et al. 2018

Chem. Mater.

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The growth of materials databases has yielded significant quantities of data to mine for new energy materials using high-throughput screening methodologies. One application of interest to energy and optoelectronics is the prediction of new high performing p-type transparent conductors (TCs). However, screening methods for such materials have never been validated over the breadth of computed materials properties. In this study, we compile an experimental data set of 74 bulk crystal structures corresponding to known state-of-the-art n-type and p-type TCs, and compute a series of corresponding computational descriptor properties. Our goals are to (1) compare computational descriptors to experimentally demonstrated properties of real materials in the data set, (2) determine the ability of ground state, density functional theory (DFT)-based computational screening methodologies to identify these experimentally realized TCs, and 1 (3) use this understanding to estimate reasonable screening cutoffs for four commonly used descriptors. First, stability calculations demonstrate that most materials in the data set have an energy above the convex hull (E hull) of less than 100 meV/atom, and we also propose a Pourbaix analysis technique to estimate moisture stability. Second, we find a lenient cutoff for the DFT PBE band gap of 0.5 eV is sufficient to include a majority of the wide gap candidates and exclude narrow gap compounds. Next, the effective mass, m * , is found to correlate weakly to conductivity in the p-type materials as compared with n-type materials, which may motivate an increase in the m * cutoff as well. Lastly, we perform an uncertainty analysis and literature comparison for the branch point energy (BPE), a qualitative descriptor for dopability. We find the BPEs of most n-type materials to lie near the conduction band and those of most p-type materials to lie at mid-gap; this is a significant distinction, suggesting BPE to be a more definitive descriptor for n-type TC materials. By assessing the validity of this simple screening methodology via comparing experimental data to computational descriptors, we aim to motivate and strengthen future materials discovery efforts in the field of transparent conductors and beyond.

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Section: Resultsmentioning

confidence: 99%

Assessing High-Throughput Descriptors for Prediction of Transparent Conductors

Woods‐Robinson

Broberg²,

Faghaninia

et al. 2018

Chem. Mater.

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“…As discussed above, the probabilities for change in bandgap for irradiated GZO thin films can be due to; (i) an increase in Zn/O ratio with increasing ion fluence, (ii) activation of Ga dopants sitting at interstitial sites, which contributes to increased carrier concentration, or (iii) formation of defects clusters of Ga Zn -V O . Further, it was reported that in the case of semiconductors, the bandgap increases below Mott's critical concentration and the blue-shift phenomenon in the bandgap is known as Burstein-Moss (BM) effect [43]. Whereas above some critical value of carrier concentration, the narrowing in bandgap was observed and can be understood in the framework of bandgap renormalization (BGN) [44].…”

Section: Optical Propertiesmentioning

confidence: 99%

Signature of strong localization and crossover conduction processes in doped ZnO thin films: synergetic effect of doping fraction and dense electronic excitations

Gupta

Singh

Umapathy

et al. 2021

J. Phys.: Condens. Matter

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Ga x Zn 1−x O thin films with varying Ga fraction within the solubility limit were irradiated with high-energy heavy ions to induce electronic excitations. The films show good transmittance in the visible region and a reduction of about 20% in transmittance was observed for irradiated films at higher ion fluences. The Urbach energy was estimated and showed an augmenting response upon increase in doping fraction and ion irradiation, this divulges an enhancement of localized states in the bandgap or disorder in the films. The evolution of such localized states plays a vital role in charge transport and thus the temperature dependent electrical conductivity of irradiated thin films was studied to elucidate the dominant conduction mechanisms. The detailed analysis unfolds that in the high-temperature regime (180 K < T < 300 K), the charge conduction was dominated by thermally activated band conduction followed by the nearest neighbor hopping (NNH) mechanism. Whereas in the lower temperature regime (25 K < T < 170 K), the conduction mechanism was governed by Mott-VRH (variable range hopping) followed by Efros-Shklovskii (ES)-VRH. A sudden and steep rise in resistivity below 30 K was observed for GZO films with higher doping fraction at higher ion fluence and proclaims the presence of strong localization of carriers.

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“…It shows peaks at excitations' frequencies with spectral weights proportional to the rate at which electrons inelastically scatter by corresponding excitations. The method is regularly used to experimentally determine plasmon frequencies in metals [39][40][41], and it is recently applied to study plasmon dispersions in heavily doped semiconductors [42,43]. The EELS measurements should in principle capture phonon-plasmon coupled excitations as well.…”

Section: Introductionmentioning

confidence: 99%

Phenomenology of phonon-plasmon coupled excitations in three dimensional polar materials

Krsnik,

Barišić

2021

Preprint

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Phonon-plasmon coupled excitations in heavily doped polar materials are addressed by examining bare and integrated electron energy loss spectroscopy (EELS) and phonon spectra. Results are obtained in the zero temperature limit for two semiconductors heavily discussed in the literature, namely GaAs and anatase TiO2, characterized by the weak and the moderate electron-phonon interaction (EPI), respectively. The most prominent spectral features are identified, not only as a function of the electron density that defines the adiabaticity parameter, yet also from the perspective of the EPI strength. In particular, while the adiabaticity parameter undoubtedly governs collective excitations' dispersions, our findings show that the EPI strength profoundly affects the damping of collective excitations within the electron-hole continuum and the distribution of the spectral weight in both the EELS and the phonon spectra. For the weak EPI, the phonon-like excitation is generally well defined and the total EELS spectral weight is redistributed roughly equally among two excitations in the antiadiabatic and the resonant regime. On contrary, in these two regimes, when the EPI is stronger there exist no well-defined collective excitations in a broad range of momenta of the order of magnitude of the Fermi wave vector, with the damping being enhanced by the increasing plasmonic character of excitations. Furthermore, the EELS spectral weight is dominated by the higher frequency excitation, allowing for an experimental estimate of the EPI strength even when the energy resolution is limited. The stronger EPI is accompanied by the large additional phonon spectral weight unambiguously attributed to the lower frequency excitation. In the adiabatic regime, this additional phonon spectra weight is a consequence of the phonon softening effects, while in the antiadiabatic regime it arises due to the virtual cloud of phonons that accompanies the plasma oscillations.

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Direct observation of conduction band plasmons and the related Burstein-Moss shift in highly doped semiconductors: A STEM-EELS study of Ga-doped ZnO

Cited by 20 publications

References 52 publications

Assessing High-Throughput Descriptors for Prediction of Transparent Conductors

Assessing High-Throughput Descriptors for Prediction of Transparent Conductors

Signature of strong localization and crossover conduction processes in doped ZnO thin films: synergetic effect of doping fraction and dense electronic excitations

Phenomenology of phonon-plasmon coupled excitations in three dimensional polar materials

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