Mesoporous Germanium formed by bipolar electrochemical etching

Tutashkonko, Sergii; Boucherif, Abderraouf; Nychyporuk, T.; Kaminski‐Cachopo, Anne; Arès, Richard; Lemiti, M.; Aimez, Vincent

doi:10.1016/j.electacta.2012.10.031

Cited by 38 publications

(24 citation statements)

References 29 publications

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“…Recently, we have reported mesoporous Ge formation by an optimized bipolar electrochemical etching of p-type Ge wafers with dimensions between 4 and 10 nm. 40,41 This substantial reduction in dimensions compared to the bulk is expected to create light emitting structures with longer wavelengths than those previously reported by Armatas. 5 In this work, we show for the first time, tunable near-infrared photoluminescence emission from mesoporous Ge, with strong direct and indirect evidences of quantum confinement effects.…”

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confidence: 90%

“…A platinum wire shaped as a spiral is used as a counter electrode. Contrary to porous Si which can be formed by DC current, the formation mesoporous Ge layers requires the use of bipolar electrochemical etching (BEE), 28,40 which means that the current should be switched from anodic to cathodic in a periodic manner. The anodic sequence induces localised etching (i.e mesopores formation), while the cathodic sequence insures the passivation of the pore walls to avoid pure chemical dissolution of the crystallites.…”

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Near-infrared emission from mesoporous crystalline germanium

et al. 2014

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Mesoporous crystalline germanium was fabricated by bipolar electrochemical etching of Ge wafer in HF-based electrolyte. It yields uniform mesoporous germanium layers composed of high density of crystallites with an average size 5-7 nm. Subsequent extended chemical etching allows tuning of crystallites size while preserving the same chemical composition. This highly controllable nanostructure exhibits photoluminescence emission above the bulk Ge bandgap, in the near-infrared range (1095-1360nm) with strong evidence of quantum confinement within the crystallites.

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Near-infrared emission from mesoporous crystalline germanium

et al. 2014

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“…Therefore crystallographic defects and surface impurities which affect the state of the surface are responsible for the resulting porous structures after etching. This technique has been applied to a broad range of materials such as silicon [104], germanium [105], gallium phosphide [103] , gallium arsenide [106] , and gallium nitride [107] and has been further developed by using light sources (especially UV light) with a technique called photo-assisted electrochemical etching [108]. The reported PL power of the porous InP is approximately 70 percent of the unetched InP prior to etching which indicates that the surface damage is not significant [109].…”

Section: Techniques Based On Wet Etchingmentioning

confidence: 99%

Efficient luminescence extraction strategies and anti-reflective coatings to enhance optical refrigeration of semiconductors

Nia

Rezaei

Brown

et al. 2016

Journal of Luminescence

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Laser refrigeration of solids has emerged as a viable solution for vibration-free and compact cooling that does not require any moving parts or cryogenic liquid. So far, rare-earth doped glasses are the only bulk materials that have provided efficient laser cooling based on the anti-Stokes process. These materials have low indices of refraction and are suitable for efficient luminescence extraction. However, up until this date, laser cooling of bulk semiconductors has not been achieved. One major challenge that needs to be addressed is the photoluminescence trapping and the consequent photon recycling. In this paper, we explain various methods to enhance light extraction for the purpose of laser cooling. We specifically provide guidelines for design and fabrication of graded index and subwavelength structures to maximize the extraction efficiency. Furthermore we present novel techniques for increasing the external quantum efficiency and enhancing the overall laser cooling efficiency. * . These include Coulomb assisted laser cooling in piezoelectric materials[8], luminescence-up conversion (known as anti-Stokes optical refrigeration[9]) , frequency down-conversion[10] and superradiance[11] to name a few. However, anti-Stokes has been the dominant mechanism used for laser cooling of condensed matter [9,[12][13][14][15][16][17][18] .Although anti-Stokes optical refrigeration is the subject of this study, efficient luminescence extraction is required to increase the cooling efficiency of all of the aforementioned laser cooling methods. The anti-Stokes mechanism is schematically shown in Fig. 1. The laser source, which is tuned slightly below the bandgap, produces electrons at the bottom of conduction band and holes at the top of the valence band. These carriers interact with the phonons and scatter to the empty energy states. After reaching equilibrium, i.e. once they thermalize with the phonons, the average electron energy increases by kT where k is the Boltzmann Constant and T is the temperature. Therefore, at equilibrium the average energy of the emitted photons by radiative recombination is higher than the absorbed laser photons. In this process, if all of the photogenerated carriers undergo radiative recombination and all the luminescence energy transfers out of the material, there will always be a net energy extraction (i.e. net cooling). The energy extraction results in the temperature drop and continues up to point where kT becomes so small that laser cooling power gets balanced by the heating produced due to parasitic absorption of the laser. The first observation of such a phenomenon was not realized experimentally until 1995, in trivalent ytterbium ion doped heavy-metal-fluoride glass [19]. In rare earth ions, the electronic 4f levels are shielded from the surrounding by the filled 5s and 5p shells, leading to suppression of multi-phonon relaxation[20] and a high radiative recombination rate favorable for optical refrigeration. In addition, the refractive index of the host material is close to the refracti...

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“…11 This late experimental exploration is mainly due to the difficulty related to fabrication of sufficiently thick homogeneous meso-PGe layers with clearly defined morphologies and it was a big technological challenge for a long time. 12 Only recently, this barrier has been overcome 13 and this breakthrough opens new possibilities for deep scientific studies of physicochemical properties and for design of various applications of the meso-PGe layers. [14][15][16] In this Letter, thermal conductivity measurements performed by photoacoustic (PA) technique on sponge-like meso-PGe layers fabricated by electro-chemical etching are reported.…”

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“…[17][18][19][20] A phenomenological phonon-confinement model initially developed for nano-Si 16 allows estimation of a mean diameter of the Ge nanocrystallites from the spectral position and the asymmetric shape of the Raman spectrum. The Raman profile calculated from the phonon-confinement model 13 is presented as a hatched blue area in Figure 1(d). The mean crystallite diameter of 3.1 nm with standard deviation of 0.68 nm was found from the model to ensure the best fitting of the high energy tail and position of the peak maximum.…”

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Thermal conductivity of meso-porous germanium

Isaiev

Tutashkonko

Jean

et al. 2014

Applied Physics Letters

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Thermal conductivity value of sponge-like meso-porous germanium (meso-PGe) layers measured by means of photoacoustic technique is reported. The room temperature thermal conductivity value is found to be equal to 0.6 W/(m K). The experimental results are in excellent agreement with molecular dynamic and Monte Carlo simulations. Both experiments and simulations show an important thermal conductivity reduction of the meso-PGe layers compared to the bulk Ge. The obtained results reveal meso-PGe as an interesting candidate for both thermoelectric and photovoltaic applications in which thermal transport is a really crucial issue.

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Mesoporous Germanium formed by bipolar electrochemical etching

Cited by 38 publications

References 29 publications

Near-infrared emission from mesoporous crystalline germanium

Near-infrared emission from mesoporous crystalline germanium

Efficient luminescence extraction strategies and anti-reflective coatings to enhance optical refrigeration of semiconductors

Thermal conductivity of meso-porous germanium

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