Numerical evaluation of Auger recombination coefficients in relaxed and strained germanium

Dominici, Stefano; Wen, Hanqing; Bertazzi, Francesco; Goano, Michele; Bellotti, E.

doi:10.1063/1.4952720

Cited by 17 publications

(14 citation statements)

References 23 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Hereby, we provide experimental data that complement and enhance numerical simulation techniques. 20,21 As a result, we underline the dominating influence of SRH processes over Auger recombination in heavily doped Ge epilayers even in the limit of large Auger coefficients as reported in the literature. 19,20 Highly n-doped Ge/Si(001) films, featuring different phosphorous donor concentrations in the 1 Â 10 19 cm À3 range and a film thickness of approximately 800 nm, were grown by reduced pressure chemical vapor deposition 22 on 8-inch Si wafers.…”

supporting

confidence: 74%

“…While it is generally accepted that Auger recombination is the dominant mechanism in moderately doped Ge (<1 Â 10 18 cm À3 ), 16,17 its relative contribution to the total nonradiative recombination rate in the limit of high-or even ultrahigh donor densities is still in debate. [18][19][20] In fact, recent studies suggest that high doping triggers a drastic reduction of the Shockley-Read-Hall (SRH) nonradiative recombination time s SRH in Ge/Si heterostructures, making this mechanism the one responsible for a reduced excess carrier density and, consequently, for an overall decrease in the photon emission rate. [21][22][23] Nevertheless, other studies concluded that the presence of dopants in epitaxial Ge on Si has a negligible effect only on s SRH .…”

mentioning

confidence: 99%

See 1 more Smart Citation

Ultrafast carrier recombination in highly n-doped Ge-on-Si films

Allerbeck

Herbst

Yamamoto

et al. 2019

Applied Physics Letters

View full text Add to dashboard Cite

We study the femtosecond carrier dynamics of n-type doped and biaxially strained Ge-on-Si films which occurs upon impulsive photoexcitation by means of broadband near-IR transient absorption spectroscopy. The modeling of the experimental data takes into account the static donor density in a modified rate equation for the description of the temporal recombination dynamics. The measurements confirm the negligible contribution at a high n-type doping concentration, in the 10 19 cm À3 range, of Auger processes as compared to defect-related Shockley-Read-Hall recombination. Energy resolved dynamics reveal further insights into the doping-related band structure changes and suggest a reshaping of direct and indirect conduction band valleys to a single effective valley along with a significant spectral broadening of the optical transitions.

show abstract

supporting

confidence: 74%

mentioning

confidence: 99%

Ultrafast carrier recombination in highly n-doped Ge-on-Si films

Allerbeck

Herbst

Yamamoto

et al. 2019

Applied Physics Letters

View full text Add to dashboard Cite

show abstract

“…This coefficient is rather independent of material (typically 10 −32 -10 −30 cm 6 /s and it is in the order of 10 −31 for indirect transition in Si and Ge and GaAs [32][33][34][35]. We want to estimate the Auger effect using an approximate model that is material independent, and we therefore set C a = 10 −31 cm 6 /s for all considered materials.…”

Section: Resultsmentioning

confidence: 99%

High absorption coefficients of the CuSb(Se,Te)₂ and CuBi(S,Se)₂ alloys enable high-efficient 100 nm thin-film photovoltaics

Chen

Persson

2017

EPJ Photovolt.

View full text Add to dashboard Cite

We demonstrate that the band-gap energies Eg of CuSb(Se,Te)2 and CuBi(S,Se)2 can be optimized for high energy conversion in very thin photovoltaic devices, and that the alloys then exhibit excellent optical properties, especially for tellurium rich CuSb(Se1−xTex)2. This is explained by multivalley band structure with flat energy dispersions, mainly due to the localized character of the Sb/Bi p-like conduction band states. Still the effective electron mass is reasonable small: mc ≈ 0.25m0 for CuSbTe2. The absorption coefficient α(ω) for CuSb(Se1−xTex)2 is at ω = Eg + 1 eV as much as 5-7 times larger than α(ω) for traditional thin-film absorber materials. Auger recombination does limit the efficiency if the carrier concentration becomes too high, and this effect needs to be suppressed. However with high absorptivity, the alloys can be utilized for extremely thin inorganic solar cells with the maximum efficiency ηmax ≈ 25% even for film thicknesses d ≈ 50−150 nm, and the efficiency increases to ∼30% if the Auger effect is diminished.

show abstract

“…Ca is the total ambipolar Auger coefficient, which is rather independent of material (typically 10 -32 -10 -30 cm 6 /s and it is in the order of 10 -31 for indirect transition in Si and Ge and GaAs [76][77][78][79]. We want to estimate the Auger effect using an approximate model that is material independent, and we therefore set Ca = 10 -31 cm 6 /s for all considered materials.…”

Section: Modelling the Maximum Efficiencymentioning

confidence: 99%

Solar Energy Capture Materials

2019

View full text Add to dashboard Cite

Herein we investigate the structural, electronic, and optical properties of emerging copper-based chalcogenides, employing atomistic first-principles computational method within the density functional theory. The fundamental material characteristics of the compounds are analysed, and the optoelectronic performances are improved by alloying with isovalent elements. In order to develop inorganic photovoltaics based on ultrathin photon-absorbing film (i. e., with thicknesses d < 100 nm), the material shall exhibit optimized band-gap energy Eg as well as having a very high absorption coefficient α(ω), especially for photons energies in the lower spectrum: Eg ≤ E < (Eg + 2 eV). To develop high-efficient solar cells we therefore suggest to tailor-make the materials to form direct gap multi-valley band edges, and energy bands with rather flat dispersions. That can typically be achieved by considering alloys with heavy elements that have relatively localized sp-like orbitals. With such tailored materials, we demonstrate that it is possible to reach a theoretical maximum efficiency as high as ηmax ≈ 30% for film thicknesses of d ≈ 50-100 nm. 4.1 Introduction In this work, we theoretically investigate inorganic solar cell materials by means of first-principles atomistic methods within the framework of the density functional theory (DFT). The aim is to further accelerate the progress of developing environmentally friendly p-n junction photovoltaics (PV), especially towards technologies with high-efficient and inexpensive ultrathin films. Crystalline silicon (c-Si) is today by far the most commercialized materials in PV modules with above 90% of the market [1], despite having indirect gap with band-gap energy Eg ≈ 1.2 eV. For laboratory solar cell, the energy conversion efficiency for single crystal c-Si without concentrator is ηmax = 25.8% (Rev. 10-30-2017 [2]), but the active absorber material is rather thick, often 100-200 μm due to insufficient absorption. Thin-film PV technologies rely on 100 times thinner layer (typically around 1 μm), and the absorbers must therefore have higher capacity to absorb the sunlight in the energy region from ~1 to ~3 eV. The most traditional inorganic solar cells [2] are based on either amorphous silicon (a-Si or its hydrogenated compound a-Si:H with Eg = 1.7 eV and ηmax = 14.0%), cadmium telluride (CdTe; Eg = 1.5 eV and ηmax = 22.1%), thin-film gallium arsenide (GaAs; Eg = 1.5 eV and ηmax = 28.8%), or copper indium gallium selenide (CuIn1-xGaxSe2; Eg ≈ 1.2 eV for x = 0.3 and ηmax = 22.6%), and these materials have their "pros and cons" in terms of prospective large-scale production. Developments of even thinner absorber materials, i.e., for ultrathin inorganic solar cells, is an emerging concept to produce competitive PV cells or to complement the c-Si technologies with a proper top-cell in tandem structures. Here, ultrathin implies absorber layers with thicknesses less than 100 nm (perhaps as thin as 10-30 nm), which is then at least more than 10 times thinner than in the traditional thin...

show abstract

Numerical evaluation of Auger recombination coefficients in relaxed and strained germanium

Cited by 17 publications

References 23 publications

Ultrafast carrier recombination in highly n-doped Ge-on-Si films

Ultrafast carrier recombination in highly n-doped Ge-on-Si films

High absorption coefficients of the CuSb(Se,Te)₂ and CuBi(S,Se)₂ alloys enable high-efficient 100 nm thin-film photovoltaics

Solar Energy Capture Materials

Contact Info

Product

Resources

About

Numerical evaluation of Auger recombination coefficients in relaxed and strained germanium

Cited by 17 publications

References 23 publications

Ultrafast carrier recombination in highly n-doped Ge-on-Si films

Ultrafast carrier recombination in highly n-doped Ge-on-Si films

High absorption coefficients of the CuSb(Se,Te)2 and CuBi(S,Se)2 alloys enable high-efficient 100 nm thin-film photovoltaics

Solar Energy Capture Materials

Contact Info

Product

Resources

About

High absorption coefficients of the CuSb(Se,Te)₂ and CuBi(S,Se)₂ alloys enable high-efficient 100 nm thin-film photovoltaics