The optical properties of amorphous and crystalline germanium

Tomlin, S G; Khawaja, E. E.; Thutupalli, G. K. M.

doi:10.1088/0022-3719/9/23/018

Cited by 34 publications

(21 citation statements)

References 20 publications

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“…A broad Raman band at around ϳ270 cm −1 is observed for all samples, and the situation is similar to that of amorphous Ge films. 9,24 The band gap reduction shown in Fig. 22,23 The result of the Raman measurement indicates that all the Ge layers under study are amorphous or at least present a high degree of structural disorder.…”

Section: Modeling and Discussionmentioning

confidence: 97%

Thickness effect on the band gap and optical properties of germanium thin films

Goh¹,

Chen²,

Sun³

et al. 2010

Journal of Applied Physics

125

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The band gap and optical properties ͑dielectric functions and optical constants͒ of Ge thin films with various thicknesses below 50 nm, which were synthesized with electron beam evaporation technique, have been determined using spectroscopic ellipsometry and UV-visible spectrophotometry. The optical properties are well described with the Forouhi-Bloomer model. Both the band gap and optical properties show a strong dependence on the film thickness. For film thickness smaller than ϳ10 nm, a band gap expansion is observed as compared to bulk crystalline Ge, which is attributed to the one-dimensional quantum confinement effect. However, a band gap reduction was observed for thickness larger than ϳ10 nm, which is explained in terms of the amorphous effect in the Ge layers.

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Section: Modeling and Discussionmentioning

confidence: 97%

Thickness effect on the band gap and optical properties of germanium thin films

Goh¹,

Chen²,

Sun³

et al. 2010

Journal of Applied Physics

125

View full text Add to dashboard Cite

show abstract

“…Band gap shows an increment of 0.011-0.013 eV at first-aged stage as compared to as-deposited stage, and 0.119-0.126 eV at annealed stage as compared to aged stage. An increment of 0.119-0.126 eV due to annealing shows good agreements with 0.12 [30] for a-Ge and 0.13 eV [31] for a-Si. It was proposed by Theye [4] that surface resistance increment after deposition was referred to as one phenomenon of SSR.…”

Section: Resultsmentioning

confidence: 67%

“…As shown in figure 4, when MRO is dominant in a-Ge films, some volumes of MRO will transform into CRN, and such a structure change is called MRO-to-CRN SR by us; when CRN is dominant, a-Ge films undergo SSR and AISr In addition, a-Ge films show an increase in band gap after three kinds of Sr This phenomenon due to SR can be interpreted by figure 5. Figure 5 demonstrates the band gap structure of a-Ge (30,31,38,40), which is cited from figure 9 of [30] and figure 8 of [31]. The shaded area represents the region of localized states, and optical band gap is equal to E g1 (E g2 ) [30,31,38,39].…”

Section: Theorymentioning

confidence: 99%

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Structural relaxation probed by resistance drift in amorphous germanium

Dong

Cui

et al. 2020

Mater. Res. Express

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Amorphous germanium films with different thicknesses are deposited by magnetron sputtering (MS) method. Optical band gap and surface resistance are characterized. Our analysis reveals that there are three kinds of structural relaxation (SR) that may occur in amorphous germanium (a-Ge), and they are spontaneous SR (SSR), annealing-induced SR (AISR), and medium range order (MRO)-tocontinuous random network (CRN) Sr Samples all demonstrate a band gap widening after these kinds of Sr The properties and mechanisms of SSR, AISR, and MRO-to-CRN SR are elucidated, respectively, which sheds some light on the controversies about SR in a-Ge films. In addition, some experimental results about SSR and AISR are also provided.

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“…Amorphous Ge has different above-bandgap optical properties than those of its crystalline counterpart 22 . Therefore, to model the 1-D stack, we use the bulk refractive index of amorphous Ge but that of crystalline Cr, Ag, and CaF 2 .…”

Section: Resultsmentioning

confidence: 99%

Semiconductor-based Multilayer Selective Solar Absorber for Unconcentrated Solar Thermal Energy Conversion

Thomas

Chen

Fan

et al. 2017

Sci Rep

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Solar thermal energy conversion has attracted substantial renewed interest due to its applications in industrial heating, air conditioning, and electricity generation. Achieving stagnation temperatures exceeding 200 °C, pertinent to these technologies, with unconcentrated sunlight requires spectrally selective absorbers with exceptionally low emissivity in the thermal wavelength range and high visible absorptivity for the solar spectrum. In this Communication, we report a semiconductor-based multilayer selective absorber that exploits the sharp drop in optical absorption at the bandgap energy to achieve a measured absorptance of 76% at solar wavelengths and a low emittance of approximately 5% at thermal wavelengths. In field tests, we obtain a peak temperature of 225 °C, comparable to that achieved with state-of-the-art selective surfaces. With straightforward optimization to improve solar absorption, our work shows the potential for unconcentrated solar thermal systems to reach stagnation temperatures exceeding 300 °C, thereby eliminating the need for solar concentrators for mid-temperature solar applications such as supplying process heat.

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The optical properties of amorphous and crystalline germanium

Cited by 34 publications

References 20 publications

Thickness effect on the band gap and optical properties of germanium thin films

Thickness effect on the band gap and optical properties of germanium thin films

Structural relaxation probed by resistance drift in amorphous germanium

Semiconductor-based Multilayer Selective Solar Absorber for Unconcentrated Solar Thermal Energy Conversion

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