Nanostructured Germanium with &gt;99% Absorption at 300–1600 nm Wavelengths

Pasanen, Toni P.; Isometsä, Joonas; Garín, M.; Chen, Kexun; Vähänissi, Ville; Savin, Hele

doi:10.1002/adom.202000047

Cited by 23 publications

(18 citation statements)

References 32 publications

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“…However, the former material clearly demonstrates slightly increased VIS reflection with specific silicide related spectral feature at 500 nm (2.5 eV) resulted from first direct interband optical transition in Mg 2 Si 32 . This fact suggests that Mg 2 Si nanoflakes provide enough area for the sur- 2a) and compared to state-of-the-art black surface structures 13,14,16,20,[33][34][35] (Figure 2c). Optical absorption spectra (A) calculated as 1-T-R demonstrate that optical properties of the b-Si changed drastically after Mg 2 Si deposition.…”

Section: Resultsmentioning

confidence: 94%

“…[34] 13,14,16,20,[33][34][35] Significantly, the wide range optical absorption performance of the black silicide is compared with state-of-theart approaches to enhance NIR efficiency of the b-Si as shown in Fig. 2c.…”

Section: Resultsmentioning

confidence: 99%

“…(b) Black silicide morphology reconstruction basing on the STEM HAADF image for modeling normalized squared electric-field amplitude distribution (E 2 /E 2 0 ) at 1300 nm pump wavelength of the Mg 2 Sicovered and bare b-Si structures. (c) Survey of operating wavelength range and averaged optical absorption of the produced black silicide and several representative b-Si structures reported in13,14,16,20,[33][34][35] .…”

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confidence: 99%

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Mg$_2$Si is the new black: introducing a black silicide with $>$95% average absorption at 200-1800 nm wavelengths

Shevlyagin,

Il'yaschenko,

Kuchmizhak

et al. 2022

Preprint

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Textured silicon surface structures, in particular black silicon (b-Si), open up possibilities for Si-based solar cells and photodetectors to be extremely thin and highly sensitive owing to perfect light-trapping and anti-reflection properties. However, near-infrared (NIR) performance of bare b-Si is limited by Si band gap of 1.12 eV or 1100 nm. This work reports a simple method to increase NIR absorption of b-Si by in vacuo silicidation with magnesium. Obtained Mg 2 Si/b-Si heterostructure has a complex geometry where b-Si nanocones are covered by Mg 2 Si shells and crowned with flake-like Mg 2 Si hexagons. Mg 2 Si formation atop b-Si resulted in 5-fold lower reflectivity and optical absorption to be no lower than 88% over 200-1800 nm spectral range. More importantly, Mg 2 Si/b-Si heterostructure is more adjusted to match AM-1.5 solar spectrum with theoretically higher photogenerated current density. The maximal advantage is demonstrated in the NIR region compared to bare b-Si in full accordance with one's expectations about NIR sensitive narrow band gap ( ∼ 0.75 eV) semiconductor with high absorption coefficient, which is Mg 2 Si. Results of optical simulation confirmed the superiority of Mg 2 Si/b-Si NIR performance. Therefore, this new wide-band optical absorber called black silicide proved rather competitive alongside stateof-the-art approaches to extend b-Si spectral blackness.

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Section: Resultsmentioning

confidence: 94%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

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Mg$_2$Si is the new black: introducing a black silicide with $>$95% average absorption at 200-1800 nm wavelengths

Shevlyagin,

Il'yaschenko,

Kuchmizhak

et al. 2022

Preprint

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“…Reflectance of Ge surfaces has also been efficiently reduced by various different means, including growth of nanoneedles by metal-catalyzed synthesis 42 and nanostructure fabrication on the surface by, e.g., dry etching 43,44 or metal-assisted chemical etching. 45,46 In many of optical devices, specular reflection modulation has been a critical scientific problem for the past few years.…”

Section: ■ Introductionmentioning

confidence: 99%

Strong Reduction in Ge Film Reflectivity by an Overlayer of 3 nm Si Nanoparticles: Implications for Photovoltaics

Rezk

Hadi

Ashraf

et al. 2021

ACS Appl. Nano Mater.

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We examine the effect of a top nanofilm of 3 nm silicon nanoparticles (Si-NPs) on the spectral features of the reflectivity of germanium (Ge). We use a 450 nm Ge layer grown by low temperature plasma enhanced chemical vapor deposition on a crystalline Si substrate. The Si-NPs are drop casted incrementally on the Ge/Si structure from a particle colloid, forming a nanofilm of increasing thickness up to 30 nm. The stack is characterized using luminescence microscopy, atomic force microscopy, transmission electron microscopy, and reflectivity spectroscopy. The reflectance of the stack is measured over UV/ visible and infrared range 4.8−0.8 eV. With the increasing thickness of the Si nanocoating, the results show a strong reduction in the reflectivity of Ge in the visible and blue-UV region of the spectrum with less effect in the infrared, as well as a difference in reflectance at the adjacent lying complex of Λ and L transitions of Ge. The strong reduction in the visible/UV range is understood in terms of a near overlap of the band to band transitions of Si-NPs and Ge. The diminished response in the infrared contributes to shifting of the bandgap of Si-NPs from the infrared to the visible due to quantum confinement. Furthermore, optical properties of Si-NP are estimated and samples are analyzed using Modified Transfer Matrix Method model. The strong reduction of reflectivity of Ge in the visible-UV region is very useful in photovoltaics, with special emphasis on Ge-based multijunction solar cells.

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“…There have been intensive research efforts to fabricate black Ge by using the standard dry etching technique based on sulfur hexafluoride (SF 6 ) and chlorine (Cl 2 ) gases. [17,18] Although Pasanen et al fabricated black Ge surface by SF 6 -based inductively coupled plasma reactive ion etching (ICP-RIE), [19] the etching process was carried out at −120 °C, resulting in substantial challenges for processing. Steglich et al realized black Ge by using Cl 2 -based RIE at room temperature, but the process requires a longer etching time of 45 min.…”

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confidence: 99%

Black Germanium Photodetector Exceeds External Quantum Efficiency of 160%

Liao

Shin

et al. 2021

Adv Materials Technologies

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Inspired by the formation of black Si, [14,15] black Ge with nanospiked structures was achieved by femtosecond laser irradiation in SF 6 environment. [16] However, optical properties of the structure were not characterized. There have been intensive research efforts to fabricate black Ge by using the standard dry etching technique based on sulfur hexafluoride (SF 6 ) and chlorine (Cl 2 ) gases. [17,18] Although Pasanen et al. fabricated black Ge surface by SF 6 -based inductively coupled plasma reactive ion etching (ICP-RIE), [19] the etching process was carried out at −120 °C, resulting in substantial challenges for processing. Steglich et al. realized black Ge by using Cl 2 -based RIE at room temperature, but the process requires a longer etching time of 45 min. [18] The extremely high absorbance of black Ge reaching 99% was experimentally obtained in the 300-1600 nm wavelength range. However, more importantly, the excellent light absorption property of black Ge has not translated into optoelectronic performance of any functional devices.In this paper, we report the demonstration and comprehensive performance characterization of black Ge-based metal-semiconductor-metal (MSM) PDs. Spike-like Ge nanostructures with optimized dimension and uniformity are formed by Cl 2 -based room-temperature standard RIE process in 2 min. Black Ge surface exhibits an optical reflection as low as 1% at a wavelength range of 1000-2000 nm. The surface is covered with aluminum oxide (Al 2 O 3 ) to reduce dark current via an atomic layer deposition (ALD). The optoelectrical properties of black Ge PDs are compared to those of the Ge PDs made on planar surface to evaluate the applicability of black Ge toward light trapping at a device level. Responsivity of black Ge MSM PDs is enhanced significantly in the NIR range of 1.5-2 µm with a slight degradation of dark current. In addition, EQE of black Ge PDs not covered with Al 2 O 3 layer is as high as 161% at 1550 nm. Therefore, our black Ge fabricated by the simple RIE process exhibits outstanding potential for efficient NIR photodetection. Results and DiscussionFigure 1 illustrates the schematic fabrication process of black Ge PDs. Detailed process is provided in Method. In short, undoped Ge substrate (n-type, resistivity > 50 Ω cm) was thoroughly cleaned by acetone, isopropyl alcohol (IPA), and DI water. The dry etching was performed in Cl 2 environment for 2 min to In this work, a viable method is demonstrated to realize high-performance germanium (Ge) photodetectors (PDs) on the nanostructured Ge surface, namely black Ge, formed by chlorine (Cl 2 ) gas-based reactive ion etching at room temperature. Black Ge surface has spike-like pyramidal structures with a width and height up to 150 and 570 nm, respectively. Average reflection of black Ge is reduced to 2% at a wavelength range from 1 to 2 µm, while that of planar Ge is ≈37%. Light absorption is strongly enhanced by the significantly reduced reflection, thereby leading to an increase in responsivity of black Ge PDs. Moreover, external...

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Nanostructured Germanium with >99% Absorption at 300–1600 nm Wavelengths

Cited by 23 publications

References 32 publications

Mg$_2$Si is the new black: introducing a black silicide with $>$95% average absorption at 200-1800 nm wavelengths

Mg$_2$Si is the new black: introducing a black silicide with $>$95% average absorption at 200-1800 nm wavelengths

Strong Reduction in Ge Film Reflectivity by an Overlayer of 3 nm Si Nanoparticles: Implications for Photovoltaics

Black Germanium Photodetector Exceeds External Quantum Efficiency of 160%

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