Intrinsic Optical Absorption in Single-Crystal Germanium and Silicon at 77°K and 300°K

Dash, W. C.; Newman, Roger H.

doi:10.1103/physrev.99.1151

Cited by 1,021 publications

(258 citation statements)

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“…Figure 3(b) reports the measured values of λ L and the calculated values of P S versus photon energy, taken from Refs. [19] and [13] respectively. In the same figure, the l SF values for holes and electrons, from our previous work on slightly doped n-Ge considering excitation close to the direct gap [9], are marked with circles on the λ L curve (1 μm for electrons and 150-220 nm for holes).…”

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Wide-range optical spin orientation in Ge from near-infrared to visible light

et al. 2014

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Ge-based spin-photodiodes have been employed to investigate the spectral dependence of optical spin orientation in germanium, in the range 400-1550 nm. We found the expected maximum in the spin polarization of photocarriers for excitation at the direct gap in (1550 nm) and a second sizable peak due to photogeneration in the L valleys (530 nm). Data suggest distinct spin depolarization mechanisms for excitation at and L, with shorter spin relaxation times whether the X point is involved. These devices can be used as integrated photon-helicity detectors over a wide spectral range. Spin-optoelectronics is a novel branch of semiconductor spintronics, aiming at adding a new degree of freedom to optoelectronics: the photon helicity. Exploiting the interplay between the photon angular momentum and the spin of electrons, integrated emitters (spin-LEDs) and detectors (spin photodiodes) of circularly polarized light have been proposed. Although GaAs is traditionally the material of choice for spin optoelectronics, because of its direct gap allowing for efficient conversion between light and spin polarization, recently Ge has attracted a considerable attention. In fact, thanks to the inversion symmetry of the crystal and the related absence of the D Yakonov-Perel spin scattering mechanism, Ge presents a longer spin coherence time than the one of GaAs. Spin manipulation [1], spin transport [2], spin optical pumping in the infrared [3][4][5][6][7], and electrical spin injection [8] in Ge have been reported. In our previous works [9,10], we demonstrated the room temperature operation of spin-PDs based on fully epitaxial Fe/MgO/Ge(001) heterostructures, working at 0.95 eV [11,12]. However, there is still a poor understanding of electrons and holes optical spin orientation in Ge, especially at photon energies much higher than the direct gap (0.8 eV). The optical spin orientation in Ge over a wide spectral range has been theoretically investigated by Rioux and Sipe [13]. However, no experimental data for excitation far from the point of the Brillouin zone (BZ) have been reported so far. Even for GaAs, only very recently the photon energy dependence of optical spin orientation well above the absorption edge has been reported [14].In this Rapid Communication, we report on the spectral dependence of the optical spin orientation in Ge at room temperature and over a wide spectral range (400-1550 nm, corresponding to 3.1-0.8 eV), via measurements of the helicitydependent photocurrent on Ge-based spin PDs. Surprisingly enough, the maximum sensitivity to photon helicity is observed far away from the direct gap (0.8 eV), where optical pumping is supposed to produce the highest initial spin polarization. Indeed, the helicity-dependent photocurrent variation indicates a first peak around 1500 nm (0.8 eV) and then an absolute maximum of about 10% at ∼530 nm (∼2.3 eV), corresponding to optical pumping in the L valley of the Ge band structure, * christian.rinaldi@polimi.it as shown in Fig. 1(a). Fitting of our data within a simple diffusive m...

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“…[13]. The light absorption length λ L [19] is compared with the spin-diffusion length l SF values for carriers [9] excited around (open circles on the λ L curve). energy range, confirming our previous suggestion [9] of a sizable equivalent spin diffusion length for holes.…”

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Wide-range optical spin orientation in Ge from near-infrared to visible light

et al. 2014

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“…5(a) and (b)) with 625 mm thick wafer, since the nonlinear diffusion of the holes was enhanced with longer diffusion length. In the case of thinner wafer with 200 mm thick, on the contrary, non-uniform formation of the pores were also observed, which could be due to the penetration of light through the Si wafer to generate the holes at near surface region [33]. Therefore, in order to decrease hole diffusion ARTICLE IN PRESS length and inhibit the light penetration, 400 mm thick wafer was used, and as a result, uniform pores were formed, as shown in Figs.…”

Section: Article In Pressmentioning

confidence: 99%

“…The key processes to fabricate these high-aspect-ratio structures are deep etching to form pores and uniform coating or filling to modify the pores. For the deep etching, dry processes such as reactive ion etching (RIE) have been widely used [20][21][22], which require relatively high initial and running costs and have limitation for fabricating the structure with maximum aspect ratio up to [30][31][32][33][34][35][36][37][38][39][40]. On the other hand, electrochemical or wet processes, which are applicable to wide surface area with relatively low cost, have capability for precise etching to fabricate high-aspect-ratio pores.…”

Section: Introductionmentioning

confidence: 99%

Fabrication of high-aspect-ratio arrayed structures using Si electrochemical etching

Sato

Homma

2006

Science and Technology of Advanced Materials

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This paper reviews microscale processes to fabricate three-dimensional structures, in particular, high-aspect-ratio arrayed structures, using precise electrochemical etching process. Array of sharp micropits were pre-formed on the front side surface of Si wafer and the electrochemical etching was carried out using aqueous HF solution, with the back side illumination to generate holes, which diffused to the edge of the micropits to proceed the dissolution of Si with fluoride species. In order to form high-aspect-ratio pores at selected areas, a shade mask pattern was fabricated on the back side surface to align the illumination to the pre-patterned area on the front side surface. The parameters, such as HF concentration, current density and hole diffusion length, were optimized and uniform array of straight pores was formed into the designed area of Si wafer.Subsequently the surface of the pores was thermally oxidized to form SiO 2 layers, and arrayed glass tubes with picoliter volume were fabricated. On the other hand, the pore filling with metal was attempted using electrodeposition to obtain array of the metal needles. For this, the ''single batch'' process was developed to form the pore array and metal filling with single electrolyte, and array of metal micro needles was successfully formed. These processes demonstrated capability and possibility of the electrochemical processes for microscale fabrication, and further precise processes can be developed using these approaches. r

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“…A subset of these studies is particularly relevant to the optical and near-IR response of a CCD [6,7,[19][20][21][22][23][24][25][26][27][28]. Two of these are relevant to our studies:…”

Section: A Index Of Siliconmentioning

confidence: 99%

Quantum efficiency modeling for a thick back-illuminated astronomical CCD

Groom

Haque

Holland

et al. 2017

Journal of Applied Physics

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The quantum efficiency and reflectivity of thick, back-illuminated CCD's being fabricated at LBNL for astronomical applications are modeled and compared with experiment. The treatment differs from standard thin-film optics in that (a) absorption is permitted in any film, (b) the 200-500 µm thick silicon substrate is considered as a thin film in order to observe the fringing behavior at long wavelengths, and (c) by using approximate boundary conditions, absorption in the surface films is separated from absorption in the substrate. For the quantum efficiency measurements the CCD's are normally operated as CCD's, usually at T = −140• C, and at higher temperatures as photodiodes. They are mounted on mechanical substrates. Reflectivity is measured on air-backed wafer samples at room temperature. The agreement between model expectation and quantum efficiency measurement is in general satisfactory. * degroom@lbl.gov 2

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Intrinsic Optical Absorption in Single-Crystal Germanium and Silicon at 77°K and 300°K

Cited by 1,021 publications

References 17 publications

Wide-range optical spin orientation in Ge from near-infrared to visible light

Wide-range optical spin orientation in Ge from near-infrared to visible light

Fabrication of high-aspect-ratio arrayed structures using Si electrochemical etching

Quantum efficiency modeling for a thick back-illuminated astronomical CCD

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