Thickness dependence of optical gap and void fraction for sputtered amorphous germanium

Pilione, L. J.; Vedam, K.; Yehoda, J. E.; Messier, R.; McMarr, P.J.

doi:10.1103/physrevb.35.9368

Cited by 45 publications

(20 citation statements)

References 10 publications

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“…There seems to be almost no systematic relation between the mass densities of our Ge films and the process parameters, apart from slightly higher values for the Ge films grown by sputtering with Xe (average density 4.35 g/cm 3 ) than for sputtering with Ar (average density 4.26 g/cm 3 ). Some groups reported that the mass density of amorphous Ge films depends on film thickness or growth rate [15,[20][21][22]. This is not found here, most likely due to the smaller film thickness and growth rates, which are typically lower for ion beam sputter deposition than for evaporation or magnetron sputtering.…”

Section: Resultscontrasting

confidence: 55%

Ion beam sputter deposition of Ge films: Influence of process parameters on film properties

et al. 2015

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Section: Resultscontrasting

confidence: 55%

Ion beam sputter deposition of Ge films: Influence of process parameters on film properties

et al. 2015

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“…Indeed, the reference sample analyzed with Cody plot gives invariably E g lower than 0.8 eV (from 0.6 eV to 0.7 eV), which does not agree with theory and experimental results on a-Ge (E g is around 0.8 eV). 17,33 It should be noted that while Cody plot gave some reliable results for a-Si, 18,21 this is not always true for other semiconductors, especially in a confined system. a-Si film is characterized by large tails in the bandgap, probably weakening the validity of Tauc assumption.…”

Section: Resultsmentioning

confidence: 99%

Optical bandgap of semiconductor nanostructures: Methods for experimental data analysis

Raciti

Bahariqushchi

Summonte³

et al. 2017

Journal of Applied Physics

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Determination of the optical bandgap (Eg) in semiconductor nanostructures is a key issue in understanding the extent of quantum confinement effects (QCE) on electronic properties and it usually involves some analytical approximation in experimental data reduction and modeling of the light absorption processes. Here, we compare some of the analytical procedures frequently used to evaluate the optical bandgap from reflectance (R) and transmittance (T) spectra. Ge quantum wells and quantum dots embedded in SiO2 were produced by plasma enhanced chemical vapor deposition, and light absorption was characterized by UV-Vis/NIR spectrophotometry. R&T elaboration to extract the absorption spectra was conducted by two approximated methods (single or double pass approximation, single pass analysis, and double pass analysis, respectively) followed by Eg evaluation through linear fit of Tauc or Cody plots. Direct fitting of R&T spectra through a Tauc-Lorentz oscillator model is used as comparison. Methods and data are discussed also in terms of the light absorption process in the presence of QCE. The reported data show that, despite the approximation, the DPA approach joined with Tauc plot gives reliable results, with clear advantages in terms of computational efforts and understanding of QCE.

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“…It has been shown that thickness dependence of band gaps of ultrathin amorphous materials can be described by the ODQC effect. 13,16 Figure 4 shows the bandgap energy of the IGZO thin films yielded from the SE modelling. A significant dependence of bandgap on film thickness is observed.…”

Section: Ellipsometric Modelingmentioning

confidence: 99%

Thickness Dependence of Optical Properties of Amorphous Indium Gallium Zinc Oxide Thin Films: Effects of Free-Electrons and Quantum Confinement

Chen

et al. 2015

ECS Solid State Letters

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Dielectric function of amorphous indium gallium zinc oxide (a-IGZO) thin films is found to shift significantly with the film thickness, which is attributed to the changes in both the bandgap and electron concentration of the IGZO thin films with the film thickness. The ultrathin films (film thickness < ∼20 nm) exhibit a bandgap expansion with reducing film thickness due to the quantum confinement effect; while the thicker films (thickness > ∼35 nm) demonstrate the free-electron effect, i.e. the Burstein-Moss shift and increase of free-electrons absorption with increasing electron concentration Amorphous indium gallium zinc oxide (a-IGZO) is a transparent semiconductor material that has promising application in next generation flat panel display due to its high electron mobility and high transparency in visible. 1,2 Although intensive electrical studies have been carried out on the IGZO thin films, 3-6 there is still lack of detailed optical study of the complex dielectric function, one of the fundamental optical properties, of the IGZO thin films. It has been shown in our early work that free-electron concentration of a metal oxide thin film could have a significant impact on the optical properties of the oxide film, in particular, the onset absorption near the band edge. 7 When the electron concentration reaches ∼10 18 -10 19 cm −3 , a semiconductor-to-metal transition occurs, and the conduction band of the oxide semiconductor is partially filled with free electrons, resulting in a bandgap expansion as a result of the Burstein-Moss effect. 8 The dependence of carrier concentration on film thickness could further complicate the situation. 9 On the hand, it has also been shown that when a crystalline oxide film scales down to the nanoscale regime (e.g., the film thickness is less than ∼20 nm), the nanoscale structures exhibit some unique properties different from their bulk counterparts due to quantum confinement effect. 10 Therefore, it is interesting to study the thickness-dependence of the complex dielectric function of a-IGZO thin films as both the free-electron and quantum confinement effects on the optical properties of the oxide films are dependent of the film thickness.In this work, we present a study of the evolution of optical properties of a-IGZO thin films with film thickness. The bandgap and complex dielectric function of the IGZO thin films with various film thicknesses have been determined with spectroscopic ellipsometry (SE) based on the Tauc-Lorentz-Drude (TL-Drude) model. 8 It is observed that the complex dielectric function is strongly dependent of the film thickness. The ultrathin films (thickness < ∼20 nm) show a blueshift of both the real and imaginary parts of the complex dielectric function and an expansion of bandgap with decreasing film thickness due to the quantum confinement effect; in contrast, the thicker films (thickness > ∼35 nm) exhibit both the Burstein-Moss shift and enhancement of free-electrons absorption with increasing film thickness, which are related to the increase of elec...

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Thickness dependence of optical gap and void fraction for sputtered amorphous germanium

Cited by 45 publications

References 10 publications

Ion beam sputter deposition of Ge films: Influence of process parameters on film properties

Ion beam sputter deposition of Ge films: Influence of process parameters on film properties

Optical bandgap of semiconductor nanostructures: Methods for experimental data analysis

Thickness Dependence of Optical Properties of Amorphous Indium Gallium Zinc Oxide Thin Films: Effects of Free-Electrons and Quantum Confinement

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