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Fabrication and characterization of sensitive vertical P-i-N germanium photodiodes as infrared detectors
摘要： Germanium on silicon P-i-N photodetectors fabricated using standard CMOS tools are now successfully used as uncooled detectors in the near-infrared (NIR), which extends from 0.75 to 1.4 μm and in the short-wave infrared (SWIR), which extends from 1.4 to 3 μm. They feature a remarkably high responsivity up to 1550 nm and a low dark current when they are operated at reverse biases. The aim is to achieve a very low dark current density and a high responsivity with a small Germanium photodiode pitch. In this paper we discuss the fabrication and the characterization of vertical P-i-N photodiodes with the epitaxy of Germanium on Silicon. The Germanium epilayer is a 1.3 μm thick Ge ?lm with a bottom Ge layer P-type doped with boron at 1019 cm?3 and a top Ge layer N-type doped with phosphorus at 1020 cm?3. Secondary ion mass spectroscopy was used to assess the doping level of the Phosphorus doped N?+?region. The strain in the Germanium epilayer on Silicon substrate was investigated. It was tensile, with a value around +0.15% from x-ray diffraction (XRD), in good agreement with a +0.12% value from Raman spectroscopy. In this paper, we focus on P-i-N photodiodes with a circular shape and a diameter of 10 μm. Electrical characterizations were performed in dark and under NIR-SWIR radiation (1310 nm, 1550 nm), with very low dark current of 0.45 nA and enhanced photocurrent at ?1 V. The external responsivities were measured at 0.275 and 0.133 A W?1 for 1310 nm and 1550 nm, respectively. Finally, internal quantum ef?ciencies of the fabricated vertical P-i-N photodiodes were extracted at 66% and 52% at 1310 nm and 1550 nm, respectively, in good agreement with TCAD simulations. Finally, a measurement of the noise in dark conditions is presented.
关键词： infrared detectors,photodiodes,strain,germanium
更新于2025-09-23 15:19:57
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Interface Engineering Assisted 3D-Graphene/Germanium Heterojunction for High-Performance Photodetectors
摘要： Three-dimensional graphene (3D-Gr) with excellent light absorption properties has received enormous interest but in conventional processes to prepare 3D-Gr, amorphous carbon layers are inevitably introduced as buffer layers which may degrade the performance of graphene-based devices. Herein, 3D-Gr is prepared on germanium (Ge) using two-dimensional graphene (2D-Gr) as the buffer layer. 2D-Gr as the buffer layer facilitates in-situ synthesis of 3D-Gr on Ge by plasma-enhanced chemical vapor deposition (PECVD) by promoting 2D-Gr nucleation and reducing the barrier height. The growth mechanism is investigated and described. The enhanced light absorption as confirmed by theoretical calculation and 3D-Gr/2D-Gr/Ge with a Schottky junction improves the performance of optoelectronic devices without requiring pre- and post-transfer processes. The photodetector constructed with 3D-Gr/2D-Gr/Ge shows an excellent responsivity of 1.7 AW-1 and detectivity 3.42 × 1014 cmHz1/2W?1 at a wavelength of 1,550 nm. This novel hybrid structure which incorporates 3D- and 2D-Gr into Ge-based integrated circuits and photodetectors deliver excellent performance and has large commercial potential.
关键词： Buffer layer,Germanium,Photodetectors,Built-in potential,3D/2D-graphene
更新于2025-09-23 15:19:57
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Switchable Photocurrent Generation in an Ultra-thin Resonant Cavity Solar Cell
摘要： Fabry-Perot type resonant nanocavities allow for broadband enhancement of light absorption in ultra-thin absorber layers. By introducing a switchable mirror, these thin film structures can be used as unique optical devices enabling interesting applications with switchable absorption. We use a thin film photovoltaic layer stack based on an amorphous germanium absorber layer and combine it with a thin Mg/Pd mirror to create a switchable solar cell. In this work we demonstrate, how we can switch the light absorption and hence the photocurrent generation of the thin film solar cell by changing the refractive index of Mg, due to hydrogen absorption. Our results show, how optical resonances in the absorber can be switched “on / off” by the change of optical properties of the magnesium reflector. The multi-layer system can be switched from a light absorbing and photocurrent generating state to a transparent window state with excellent color neutrality. We emphasize our study as an important step towards the realization of switchable photovoltaic windows, which paves the way for larger scale building integrated photovoltaic applications.
关键词： Ultra-thin absorber,light trapping,photovoltaic,amorphous germanium,switchable magnesium mirror,smart window
更新于2025-09-23 15:19:57
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Electron and proton irradiation effect on the minority carrier lifetime in SiC passivated p-doped Ge wafers for space photovoltaics
摘要： We report on the effect of electron and proton irradiation on effective minority carrier lifetimes (τeff) in p-type Ge wafers. Minority carrier lifetimes are assessed using the microwave-detected photoconductance decay (μW-PCD) method. We examine the dependence of τeff on the p-type doping level and on electron and proton radiation fluences at 1 MeV. The measured τeff before and after irradiation are used to estimate the minority carriers’ diffusion lengths, which is an important parameter for solar cell operation. We observe τeff ranging from ~50 to 230 μs for Ge doping levels between 1 × 1017 and 1 × 1016 at.cm-3, corresponding to diffusion lengths of ~500–1400 μm. A separation of τeff in Ge bulk lifetime and surface recombination velocity is conducted by irradiating Ge lifetime samples of different thicknesses. The possible radiation-induced defects are discussed on the basis of literature.
关键词： Space photovoltaics,Minority carrier lifetime,Germanium,Surface passivation,Irradiation
更新于2025-09-23 15:19:57
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High-Performance Germanium Waveguide Photodetectors on Silicon
摘要： Germanium waveguide photodetectors with 4 ??m widths and various lengths are fabricated on silicon-on-insulator substrates by selective epitaxial growth. The dependence of the germanium layer length on the responsivity and bandwidth of the photodetectors is studied. The optimal length of the germanium layer to achieve high bandwidth is found to be approximately 8 ??m. For the 4 × 8 ??m2 photodetector, the dark current density is as low as 5 mA/cm2 at ?1 V. At a bias of ?1 V, the 1550 nm optical responsivity is as high as 0.82 A/W. Bandwidth as high as 29 GHz is obtained at ?4 V. Clear opened eye diagrams at 50 Gbits/s are demonstrated at 1550 nm.
关键词： responsivity,Germanium waveguide photodetectors,silicon-on-insulator substrates,selective epitaxial growth,bandwidth
更新于2025-09-23 15:19:57
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Intersubband Transition Engineering in the Conduction Band of Asymmetric Coupled Ge/SiGe Quantum Wells
摘要： n-type Ge/SiGe asymmetric coupled quantum wells represent the building block of a variety of nanoscale quantum devices, including recently proposed designs for a silicon-based THz quantum cascade laser. In this paper, we combine structural and spectroscopic experiments on 20-module superstructures, each featuring two Ge wells coupled through a Ge-rich SiGe tunnel barrier, as a function of the geometry parameters of the design and the P dopant concentration. Through a comparison of THz spectroscopic data with numerical calculations of intersubband optical absorption resonances, we demonstrated that it is possible to tune, by design, the energy and the spatial overlap of quantum confined subbands in the conduction band of the heterostructures. The high structural/interface quality of the samples and the control achieved on subband hybridization are promising starting points towards a working electrically pumped light-emitting device.
关键词： quantum wells,THz spectroscopy,group IV epitaxy,intersubband transitions,silicon–germanium heterostructures
更新于2025-09-23 15:19:57
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Hole spin in tunable Ge hut wire double quantum dot
摘要： Holes in germanium (Ge) exhibit strong spin-orbit interaction, which can be exploited for fast and all-electrical manipulation of spin states. Here, we report transport experiments in a tunable Ge hut wire hole double quantum dot. We observe the signatures of Pauli spin blockade (PSB) with a large singlet-triplet energy splitting of ~1.1 meV and extract the g factor. By analyzing the the PSB leakage current, we obtain a spin-orbit length ?????? of ~ 40–100 nm. Furthermore, we demonstrate the electric dipole spin resonance. These results lay a solid foundation for implementing high quality tunable hole spin-orbit qubits.
关键词： Pauli spin blockade,electric dipole spin resonance,germanium,spin-orbit interaction,quantum dots
更新于2025-09-23 15:19:57
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Editors' Choice—Optical Emission from Germanium Nanocrystals
摘要： We analyze the intense photoluminescence (PL) observed at energies from 600 to 1100 meV for a large number of Si1-xGex epitaxial layers grown by molecular beam epitaxy. In the present work we show that this previously unexplained broad PL peak can be assigned to Ge nanocrystals (NCs) self-assembled within the SiGe layers. These NCs are assumed to be lattice matched to the SiGe in the vertical, growth direction. A consequence of this assignment is that as the Ge-fraction in the SiGe layer increases the vertical strain in the NCs changes from compressive to tensile at x ～ 0.36, lowering the NC bandgap (BG) below that of bulk Ge. We examine the PL results for more than 60 samples exhibiting this broad PL peak by examining how it follows the strained Ge BG for x from 0.05 to 0.53. The PL is resolvable as two narrower peaks separated by the momentum conserving phonon energy for Ge. Strain and con?nement shifted NC bound exciton energies calculated numerically agree well with the measured ones. When Raman scattering results were examined for some of the same samples, the phonon mode frequencies obtained provided valuable corroborative evidence for the presence of the Ge NCs.
关键词： molecular beam epitaxy,SiGe epitaxial layers,Raman spectroscopy,Germanium nanocrystals,photoluminescence
更新于2025-09-23 15:19:57
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Comparison study of temperature dependent direct/indirect bandgap emissions of Ge1-x-ySixSny and Ge1-ySny grown on Ge buffered Si
摘要： Temperature-dependent photoluminescence (PL) of two sets of ternary samples with fixed tin concentrations of ~5.2% (Ge0.924Si0.024Sn0.052, and Ge0.911Si0.036Sn0.053) and ~7.3% (Ge0.90Si0.027Sn0.073, and Ge0.888Si0.04Sn0.072) were measured along with their binary counterparts (Ge0.948Sn0.052 and Ge0.925Sn0.075). The variations of direct bandgap emission (ED) and indirect bandgap emission (EID) with temperature were studied for both ternary and binary alloys by means of Gaussian curve fitting, and the results are compared. The bandgap widths of ternaries clearly increase after Si incorporation into the GeSn with similar Sn concentrations. It is found that for the ternaries both ED and EID peak energies are blue shifted, and the energy separation of ED and EID peaks becomes larger than that of binaries for similar Sn concentrations. Moreover, both ED and EID peaks appear at room temperature (RT) in the GeSiSn spectra, but the ED peak position is greater than EID, indicating these ternaries are indirect bandgap materials. Low temperature PL validates the existence of indirect PL emission in Ge0.90Si0.027Sn0.073 and direct gap behavior in Ge0.925Sn0.075, indicating GeSn becomes a direct bandgap material at lower Sn concentration than GeSiSn. The PL intensities of these ternaries are generally weaker and the spectra become more complicated than those of binaries, probably due to increased strain and defects in the ternaries. Finally, it is found that the effect of large differences in strain of ternary samples on PL peak positions can be greater than that of small Si composition differences in ternaries. A large compressive strain in ternaries can also make splitting of the ED into ED,HH (conduction band minimum-Γ valley to heavy hole maximum) and ED,LH (conduction band minimum-Γ valley to light hole maximum) transitions more observable in the PL spectra.
关键词： strain,germanium tin,photoluminescence,direct/indirect bandgap emissions,valence band splitting,germanium silicon tin
更新于2025-09-19 17:15:36
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Hall Effect in Germanium Doped with Different Impurities
摘要： The influence of different impurities on the kinetics of electronic processes in n-Ge?Sb? single crystals is investigated. A substantial decrease in the charge carrier mobility in the region of predominantly impurity scattering (at 77 K) in n-Ge?Sb + Si? crystals, as well as in germanium crystals doped with the rare-earth elements, is detected, and this effect is explained.
关键词： Hall effect,charge carrier mobility,germanium,Hall coefficient,impurities
更新于2025-09-19 17:15:36