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Driving chemical interactions at graphene-germanium van der Waals interfaces via thermal annealing
摘要： Despite its extraordinary charge carrier mobility, the lack of an electronic bandgap in graphene limits its utilization in electronic devices. To overcome this issue, researchers have attempted to chemically modify the pristine graphene lattice in order to engineer its electronic bandstructure. While significant progress has been achieved, aggressive chemistries are often employed which are difficult to pattern and control. In an effort to overcome this issue, here we utilize the well-defined van der Waals interface between crystalline Ge(110) and epitaxial graphene to template covalent chemistry. In particular, by annealing atomically pristine graphene-germanium interfaces synthesized by chemical vapor deposition under ultra-high vacuum conditions, chemical bonding is driven between the germanium surface and the graphene lattice. The resulting bonds act as charge scattering centers that are identified by scanning tunneling microscopy. The generation of atomic-scale defects is independently confirmed by Raman spectroscopy, revealing significant densities within the graphene lattice. The resulting chemically modified graphene has the potential to impact next-generation nanoelectronic applications.
关键词： graphene,van der Waals interfaces,germanium,Raman spectroscopy,chemical bonding,scanning tunneling microscopy,thermal annealing
更新于2025-09-10 09:29:36
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Monolithic axial and radial metal-semiconductor nanowire heterostructures
摘要： The electrical and optical properties of low dimensional nanostructures depend critically on size and geometry and may differ distinctly from those of their bulk counterparts. In particular, ultra-thin semiconducting layers as well as nanowires have already proven the feasibility to realize and study quantum size effects enabling novel ultra-scaled devices. Further, plasmonic metal nanostructures attracted recently a lot of attention because of appealing near-field mediated enhancement effects. Thus, combining metal and semiconducting constituents in quasi 1D heterostructures will pave the way for ultra-scaled systems and high-performance devices with exceptional electrical, optical and plasmonic functionality. This paper reports on the sophisticated fabrication and structural properties of axial and radial, Al-Ge and Al-Si nanowire heterostructures, synthesized by a thermally induced exchange reaction of single-crystalline Ge-Si core-shell nanowires and Al pads. This enables a self-aligned metallic contact formation to Ge segments beyond lithographic limitations as well as ultra-thin semiconducting layers wrapped around monocrystalline Al core nanowires. High-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy and μ-Raman measurements proved the composition and perfect crystallinity of these metal-semiconductor nanowire heterostructures. This exemplary selective replacement of Ge by Al represents a general approach for the elaboration of radial and axial metal-semiconductor heterostructures in various Ge-semiconductor heterostructures.
关键词： metal-semiconductor heterostructure,germanium,aluminum,transmission electron microscopy,nanowire
更新于2025-09-10 09:29:36
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Defects and their reduction in Ge selective epitaxy and coalescence layer on Si with semicylindrical voids on SiO<formula><tex>$_{2}$</tex></formula> masks
摘要： Formation of semicylindrical voids on SiO2 masks in Ge layers selectively grown on Si has positive impacts for reduction of threading dislocation density (TDD). Semicylindrical voids are formed through selective epitaxial growth (SEG) and coalescence of SEG Ge layers. A cross-sectional transmission electron microscope (TEM) observation reveals that a threading dislocation (TD) is terminated at a semicylindrical void, resulting in the reduction of TDD. The semicylindrical voids also contribute to the suppression of two-dimensional defects generated at the coalesced interfaces between the SEG Ge layers, which were widely observed in previous reports. Plan-view TEM observations reveal that there are TDs inclined to be parallel to the semicylindrical voids, and plan-view TEM observations show a large (4 μm × 4 μm) TD-free area in the Ge layer with the semicylindrical voids.
关键词： silicon photonics,threading dislocation density,germanium (Ge),semiconductor epitaxial layers,Epitaxial growth
更新于2025-09-10 09:29:36
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First Experimental Demonstration and Mechanism of Abnormal Palladium Diffusion Induced by Excess Interstitial Ge
摘要： This letter represents the ?rst direct experimental demonstrations and mechanism proposal regarding abnormal palladium diffusion into germanium (Ge). Our experiments indicated that excess Ge atoms among palladium germanide alloy formation indirectly induce the abnormal out-diffusion of mass palladium atoms into Ge. Consequently, palladium germanide alloy on both n-type and p-type Ge form ohmic-like Schottky junctions. To identify this phenomenon, ?rst-principle calculations and technology computer-aided design simulation were used to evaluate the electrical in?uence of palladium atoms in Ge. We discovered that the activated palladium atoms in Ge induce large midgap bulk-trap states, which contribute to a severe increment of trap-assisted tunneling current at the palladium germanide/Ge junction.
关键词： Schottky junction,First-principles calculations,palladium germanide,technology computer-aided design,germanium,trap-assisted tunneling,fermi-level pinning effect
更新于2025-09-10 09:29:36
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Front-end ASIC for germanium strip detectors
摘要： The characteristics of a recently developed front-end application specific integrated circuit (ASIC) designed for high-purity germanium (HPGe) strip detectors are detailed. The ASIC contains 32 channels, and can instrument either cathode or anode signals from the HPGe detector. The channels provide low-noise charge amplification, four shaping times, four gain ranges, trimmable discrimination for each channel, time to analog output, and peak detectors with analog memory. The channels process events in parallel, and the ASIC emits a logical-OR of the internal discriminators for external control. Each channel contains a time-to-analog circuit to allow the depth of interaction in a detector to be determined. The ASIC has a small noise slope, allowing it to maintain germanium energy resolution at the large, 30 pF, input capacitance of a germanium strip detector connected through the cryostat by a kapton flex cable. The ASIC sparsifies the triggered channels for low deadtime readout. Each channel dissipates 6.2 mW and covers an energy range up to 4 MeV in HPGe. Measurements demonstrate an equivalent noise charge (ENC) of 260 electrons at an input capacitance of 32.5 pF with a slope of 6.4 electrons/pF for a peaking time of 2 μs.
关键词： Gamma ray,Compton,Germanium,HPGe,ASIC
更新于2025-09-10 09:29:36
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Optoelectronic properties of high-Si-content-Ge <sub/> 1 <i>?x</i> – <i>y</i> </sub> Si <sub/><i>x</i> </sub> Sn <i> <sub/>y</sub></i> /Ge <sub/> 1? <i>x</i> </sub> Sn <sub/><i>x</i> </sub> /Ge <sub/> 1? <i>x–y</i> </sub> Si <sub/><i>x</i> </sub> Sn <sub/><i>y</i> </sub> double heterostructure
摘要： The optoelectronic properties of Ge1?x?ySixSny/Ge1?xSnx/Ge1?x?ySixSny double heterostructures pseudomorphically grown on a Ge substrate were investigated. The photoluminescence (PL) intensity of the sample with Ge0.66Si0.23Sn0.11 cladding layers is three times larger compared to PL from structure with a Ge cladding layer, which can be attributed to higher energy band offsets at both conduction and valence band edges at the Ge0.91Sn0.09/Ge0.66Si0.23Sn0.11 interface. The PL spectrum of the sample with the Ge0.66Si0.23Sn0.11 cladding layer at room temperature can be deconvoluted into four components, and the origins of these components can be assigned to direct and indirect transitions by measuring the temperature dependence of each component’s intensity. In addition, we examined the formation and characterization of strain-relaxed Ge1?x?ySixSny/Ge1?xSnx/Ge1?x?ySixSny double heterostructures to relieve the compressive strain in the Ge1?xSnx layer. Stacking faults were observed in the Ge1?xSnx and Ge1?x?ySixSny layers. The PL peak intensity of the strain-relaxed Ge1?xSnx layer decreases by a factor of 1/20 compared to the PL peak intensity of the double heterostructure pseudomorphically grown on a Ge(001) substrate. In addition, PL intensity can be increased by post-deposition annealing owing to decreasing defects.
关键词： silicon,germanium,photoluminescence,heterostructure,tin
更新于2025-09-10 09:29:36
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Study on Al <sub/>2</sub> O <sub/>3</sub> /Ge interface formed by ALD directly on epitaxial Ge
摘要： Germanium (Ge) has been attracting considerable attention as a high mobility channel material to enhance the performance of CMOS circuits. One of the most important issues for realization of practical Ge-MOSFET devices with superior performances is requirement to improve qualities of gate dielectric/Ge interfaces. In this work, Al2O3/Ge structures are fabricated by direct atomic layer deposition (ALD) on epitaxialy grown Ge. We indicate that ALD incubation time is fully suppressed by the ALD on a completely clean Ge surface created by Ge epitaxy on a Ge substrate. Moreover, x-ray photoelectron spectroscopy analyses reveal that unintentional formation of a GeO2 at the Al2O3/Ge interface can be almost avoided by the ALD on the epitaxial Ge whereas the interfacial GeO2 layer is present for samples exposed to the air before ALD. These results clearly indicate that direct ALD on epitaxial Ge is a very promising method to signi?cantly improve Ge MOSFET performances.
关键词： Germanium,XPS,Al2O3,ALD,MBE
更新于2025-09-09 09:28:46
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Aerosol synthesis of germanium nanoparticles supported by external seeding: Theoretical and experimental analysis
摘要： In this work we present a detailed study of the effect of heterogeneous nucleation on the formation of germanium nanoparticles (Ge NPs) produced from monogermane (GeH4) in a hot wall reactor gas phase synthesis. As external seeding unit we use a hot wire generator (HWG) which produces a stable concentration of aerosol particles. The particle concentration and size of the seeds is easily controllable via the applied voltage and used metal. We demonstrate the importance of seed particles for the production of narrowly distributed Ge NPs with geometrical standard deviations (GSD) < 1.1 in our setup. Thereby, molybdenum and tungsten as wire metal show the best seeding results. The size of the final Ge NPs can be precisely controlled in the range of 20 to 60 nm. The expansion of Ge lattice seen in XRD and tiny amount of Mo probed by high-resolution STEM-EDXS analysis indicate that the Mo seed particles are most likely dissolved and incorporated in the Ge lattice during growth. Furthermore, we demonstrate an approach to investigate the effect of heterogeneous nucleation on the particle formation by population balance modeling. The results are in good agreement with experimental data. The seed concentration is the key parameter and has a major influence on the nucleation rate.
关键词： Germanium,Nanoparticles,Simulation,Hot wire generator,Gas phase synthesis,Heterogeneous nucleation
更新于2025-09-09 09:28:46
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Lead‐Free Semiconductors: Soft Chemistry, Dimensionality Control, and Manganese‐Doping of Germanium Halide Perovskites
摘要： Lead halide perovskites have drawn enormous interest due to their exceptional photovoltaic and optoelectronic properties. However, the toxic heavy metal lead is harmful to humans and the environment resulting in a need for strategies to replace this toxic element. Herein, we report a facile aqueous synthesis of CsGeX3 (X = I, Br) perovskite nanocrystals with size control achieved by varying the cysteammonium halide ligand concentration. We observe a variety of morphologies including pyramidal, hexagonal, and spheroidal. CsGeX3 nanocrystals undergo a lattice expansion due to partial replacement of Cs+ with larger cysteNH3+ cations into the lattice. We successfully dope Mn2+ into the CsGeX3 lattice for the first time with incorporation up to 29% in bulk and 16% in nano samples. XRD peak shifts and EPR hyperfine splitting strongly indicate that Mn2+ is doped into the lattice. Our results introduce a new member to the lead-free halide perovskite family and set the fundamental stage for their use in optoelectronic devices.
关键词： Germanium Halide Perovskites,Manganese(II) Doping,Perovskite Phases,Lead Substitution,Perovskite Nanocrystals
更新于2025-09-09 09:28:46
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Direct writing of single germanium vacancy center arrays in diamond
摘要： Single photon emitters in solid-state systems with superior optical properties are of fundamental importance for they are building block candidates of many quantum optics applications. The ideal qubit will have a bright narrow band emission (i.e. high Debye Waller (DW) factor) and an access to optically read out and manipulate its spin states. Numerous candidates have been studied in diamond including the nitrogen vacancy (NV) center and more recently the silicon vacancy (SiV) center. The advantage of the SiV is its high DW factor, with nearly 80% of its emission is within its zero phonon line (ZPL). But its coherence time is limited by the narrow ground state splitting (~40 GHz) which favors single-phonon absorption from the lower branch to the upper one. This necessitates the search for an alternative system with a larger ground state splitting to suppress the phonon-mediated processes. Color centers in diamond are promising solid-state qubits for scalable quantum photonics applications. Amongst many defects, those with inversion symmetry are of an interest due to their promising optical properties. In this work, we demonstrate a maskless implantation of an array of bright, single germanium-vacancy (GeV) centers in diamond. Employing the direct focused ion beam technique, single GeV emitters are engineered with the spatial accuracy of tens of nanometers. The single GeV creation ratio reaches as high as 53% with the dose of 200 Ge+ ions per spot. The presented fabrication method is promising for future nanofabrication of integrated photonic structures with GeV emitters as a leading platform for spin-spin interactions.
关键词： diamond,germanium-vacancy centers,single photon emitters,quantum photonics,focused ion beam
更新于2025-09-09 09:28:46