Ge Crystals Research Articles

(Invited) Three-Dimensional Epitaxial Si1-XGex, Ge and SiC Crystals on Deeply Patterned Si Substrates

We show that geometric shielding of the reactive flux in chemical vapor deposition by tall neighboring structures obtained by deep substrate patterning, along with short surface diffusion lengths, can provide nearly space filling arrays of high-quality epitaxial crystals despite large mismatches of lattice parameters and thermal expansion coefficients. The density of extended defects is strongly reduced by the method, and wafer bowing and crack formation largely inhibited. The concept is shown to be valid for SiGe/Si heterostructures ranging from pure Si to pure Ge both on Si(001) and Si(111) substrates. Here, dislocations are efficiently eliminated from three-dimensional faceted crystals with high-aspect ratios on top of micron-sized Si pillars. The application to 3C-SiC/Si(001) ridges, characterized by a lattice mismatch of nearly 20%, provides significantly lower stacking fault densities compared with layers grown on planar substrates.

Temperature Dependent Internal Friction Behavior of Single Crystal Germanium Studied by the Impulse Excitation Technique

The anelastic relaxation process in crystalline solids is influenced by various mechanisms including a.o. diffusion of point defects, dislocation formation, movement and multiplication. To analyze the type and concentration of relaxing units participating in a particular thermally activated process, measuring the temperature dependent internal friction is a well-known approach. In the present study, the impulse excitation technique was used to analyze the internal friction in single crystal Ge in the <111>-, <110>- and <100>- directions between room and melting temperature. The internal friction spectra reveal up to three internal friction peaks. To interpret the observed internal friction peaks, various aspects of the peaks such as activation energy, position and relaxation time will be discussed.

Liquid Phase Epitaxy (LPE) Formation of Localized High Quality and Mobility Ge & SiGe by High Dose Ge-Implantation with Laser Melt Annealing for 10nm and 7nm Node CMOS Technology

We investigated using high dose (5E16/cm2) Ge beam-line ion implantation in combination with laser melt annealing as an alternative to Ge-epi by CVD to form high quality single crystal Ge-epilayer by LPE (liquid phase epitaxy) that is very uniform, thin 10-25nm and localized for high mobility Ge-channels. The implant resulted in 7nm amorphous Ge deposition by a method called dose controlled deposition (DCD). A 515nm laser was used to vary the melt depth from 9nm to 500nm based on laser anneal pulse duration and power level. Ellipsometer was used to measure the surface amorphous layer thickness while therma-wave (TW) analysis was used to monitor Ge implant damage recovery after LPE. SIMS depth profiles showed Ge surface concentration varied from 100% down to 2% based on the laser melt depth. X-TEM analysis showed the transformation of deposited amorphous Ge surface layer to single crystal Ge after laser melt and LPE. Sb implantation at two dose levels of 3E15/cm2 and 3E13/cm2 was used to examine laser melt annealing effects on n-type dopant activation and electron mobility in Ge. Special Hx-probe tips on the 4PP system was required to measure sheet resistance and CAOT/DHE method was used for Differential Hall Effect measurements.

Determination of the single crystal Ge Young’s modulus between room temperature and melting temperature using the impulse excitation technique

AbstractIn the present study, the vibrational properties of single crystal Ge samples are studied between room and melt‐ing temperature using the impulse excitation technique (IET). From the IET measurements, the temperature dependent Young's moduli Eijk of single crystal Ge are extracted in the (100), (110) and (111) crystallographic directions in inert atmosphere.The results show an anomalous softening of an elastic constant around 890 °C temperature during the measure‐ment. The Young's moduli values between 88 to 132 GPa are obtained close to the melting temperature, depending on the crystallographic direction. Empiric expressions are derived for the temperature dependence of E(100), E(110) and E(111). (© 2014 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Temperature Dependent Young's Modulus of Si and Ge

The vibrational properties of single crystal Si and Ge are studied between room and melting temperature T m using the impulse excitation technique. From the measurements, the temperature dependent Young’s moduli E <ijk> are extracted in the <100>-, <110>- and <111>- directions. For both semiconductors, the Young’s moduli decrease smoothly with increasing temperature and retain high values up to T m . Using the semi-empiric Wachtman's equation allows an excellent fit to the experimental data for the temperature dependence of E <100> , E <110> and E <111> between room temperature and 0.6T m ,. For higher temperatures, the Young's moduli decrease faster than predicted by Wachtman's equation. In the case of Ge, an apparent enhanced softening is observed starting from about 850 ºC which is due to a loss of Ge material, leading to a decrease of sample dimensions and weight.

(Invited) Three-Dimensional Epitaxial Si1-XGex, Ge and SiC Crystals on Deeply Patterned Si Substrates

The heteroepitaxial growth of layers onto substrates differing substantially in lattice parameter and thermal expansion coefficients continues to be a challenge because of the formation of crystal defects, wafer bowing or layer cracking. We have recently demonstrated for the example of Ge/Si(001) that these deficiencies can be avoided by combining deep substrate patterning with appropriately tuned surface diffusion lengths, resulting in dense arrays of highly perfect three-dimensional epitaxial crystals [1]. Here we discuss the extension of the method to layer/substrate combinations with lattice misfits ranging from zero for pure Si/Si(001) up to 20% for 3C-SiC/Si(001).As an example we show in Fig. 1 scanning electron microscopy images obtained on space-filling arrays of Si, Si0.6Ge0.4 and Ge crystals grown to a height of 8 µm onto 2 µm wide pillars separated by 2 µm wide trenches etched to a depth of 8 µm into Si(001). The surface diffusion lengths were kept approximately the same for the three arrays by keeping the deposition rate constant while lowering the substrate temperature from 810° C for Si, to 660° C for the alloy and finally to 485° C for Ge. This is reflected in the remarkably similar crystal morphology for the three cases, characterized by narrow gaps between neighboring crystals and closely similar facet structures. The unusual growth mode of Fig. 1 results mainly from the combination of short surface diffusion lengths below typical facet sizes and reactive flux shielding by neighboring substrate pillars or crystals. While the latter is essentially given by the substrate geometry, tuning of the diffusion lengths by means of substrate temperature may affect the deposition rate. Indeed, the structures of Fig. 1 have been obtained by low-energy plasma-enhanced chemical deposition [2], providing fast, nearly temperature independent deposition rates. The approach is applicable also to off-cut substrates and to other substrate orientations. Figure 2 shows an example of an array of 8 µm tall Ge0.9Si0.1crystals on Si(111) pillars.High-resolution X-ray diffraction with laboratory sources and scanning nano-diffraction by a focused synchrotron X-ray beam proves that the structures of Figs. 1 and 2 are entirely free from misfit and thermal strain [3]. Wafer bowing is virtually eliminated and layer cracks cannot arise.The short surface diffusion lengths required for the growth of 3D crystal arrays can more easily be attained for compound semiconductors. Here the ratio of anion and cation radical fluxes provides an additional control parameter such that molecular beam epitaxy and even chemical vapor deposition (CVD) can be used as deposition tools.We have applied the method outlined above to the growth of 3C-SiC on deeply patterned Si(001) by low pressure CVD. As an example we show in Fig. 3 a cross-section SEM image through 3C-SiC ridges which clearly exhibit the kind of self-limited lateral expansion visible also in Figs. 2 and 3. For high SiC ridges all stacking faults on {111} planes parallel to the ridges escape through the ridge sidewalls.Financial support by the Swiss federal program Nano-Tera through project NEXRAY, by Fondazione Cariplo through the MANDIS project, and by PileGrowth Tech is gratefully acknowledged.[1] C.V. Falub et al., Science 335, 1330 (2012).[2] C. Rosenblad et al., J. Vac. Sci. Technol. A 16, 2785 (1998).[3] C.V. Falub et al., Sci. Rep. 3, 2276 (2013).

Liquid Phase Epitaxy (LPE) Formation of Localized High Quality and Mobility Ge & SiGe by High Dose Ge-Implantation with Laser Melt Annealing for 10nm and 7nm Node CMOS Technology

Localized Ge and SiGe high quality/mobility device surface material region on bulk-Si and SOI wafers are needed for 10nm and 7nm node CMOS technology. Traditionally SiGe and Ge device surface material on bulk-Si or SOI wafers are realized by CVD epitaxial growth or Vapor Phase Epi (VPE) at elevated temperatures. Selective deposition can be achieved with hard mask. To reduce defects strain relaxed buffer (SRB) or aspect ratio trapping (ART) have been employed with bulk-Si or layer transfer wafer bonding for SiGeOI or GeOI. An alternative to VPE is to use either SPE (solid phase epitaxy) or LPE (liquid phase epitaxy) to form SiGe or Ge epitaxial surface layers. Using high dose Ge implantation >E16/cm2 with photoresist soft mask as proposed in 2004 by Borland et al [1,2]. Localized amorphous Ge surface regions can be formed after Ge-infusion doping by Gas Cluster Ion Beam (GCIB) technique followed by low temperature SPE to form single crystal thin surface Ge epitaxial layers but residual end-of-range (EOR) damage remained. Today, laser melt annealing of implanted junctions are currently being used in production for high quality back-side illuminated CMOS image sensors used in smart phone cameras by several IC and foundry semiconductor manufacturers to completely eliminate any residual implant damage/defects with 100% dopant activation provided the melt depth exceeds the implant damage depth [3]. Last year at IWJT-2013 Borland et al [4] reported using Ge-plasma ion implantation at 1E16/cm2 and 1E17/cm2 doses with laser melt annealing to realize up to 55% SiGe by LPE with >4x higher mobility at 160cm2/Vs. One limitation they noted with plasma implantation was poor retained dose due to surface sputtering at low energies which limited the Ge content to <55% for 1E17/cm2 dose. Therefore to overcome this retained dose problem we investigated Ge beamline ion implantation in this paper which should give 100% retained dose. The Ge surface amorphous layer thickness measured by elipsometry was 15nm while the Ge-SIMS depth profile measures 7nm Ge at 100%. Therma-wave analysis was used to monitor the Ge-implant damage recovery and Ge or SiGe recrystallized epitaxial surface layer after various laser melt annealing conditions of varying power level and pulse duration. The Ge-SIMS depth profiles shows we could vary the melt depth for LPE Ge layer from 10nm to >400nm and the Ge layer content from 97% down to 2% respectively. We will also show X-TEM of the Ge-LPE regions. Sb implantation was used to investigate n-type dopant activation in Ge at low and high doses of 3E13/cm2 and 3E15/cm2. Rs measurements were done using a special Hx 4 point probe and SRP (spreading resistance profile) depth profiles. In summary, using high dose beam-line Ge-implantation we realized >7nm amorphous Ge deposition. Epitaxial growth of Ge was achieved by liquid phase epitaxy using shallow laser melt annealing between 10nm and >400nm melt depths.

Lateral Gemanium Growth for Local GeOI Fabrication

Ge is a very attractive material for optoelectronic applications and for future CMOS technologies. Therefore the creation of Ge on Si with low defect density is of great interest. Several techniques to grow high quality Ge on Si are reported e. g. in combination with cyclic annealing and etching (1, 2) or using the aspect ratio trapping technique (3). In this study, the fabrication of local GeOI structures is demonstrated by filling a lateral cavity which was formed by selective sidewall etching (4) of a mesa-patterned SiO2 / Si layer on a SOI wafer. Lateral Ge growth is carried out by using a single wafer reduced pressure CVD system. For sample preparation, epitaxial Si is deposited. The thickness of the Si on buried oxide (BOX) is targeted to 430 nm. Then wet oxidation for 300 nm is performed to produce a 300 nm thick SiO2 cap on top of 300 nm thick Si on the BOX. Top SiO2 and Si on BOX are removed by RIE dry etching to form lateral Si (010) or Si (110) surfaces at the sidewall of a mesa structure. After that, the wafer is cleaned by standard HF-last RCA cleaning. The wafer is loaded into the epi. chamber and baked at 850oC in H2 to remove residual oxide on the Si sidewalls. Then selective etching of Si by HCl is performed to form a cavity in the SiO2. After the HCl etching, Ge is deposited selectively using a H2-GeH4-HCl gas mixture. SEM is used for characterization of the deposited Ge and TEM is applied for dislocation analysis. The strain distribution is analyzed by micro Raman spectroscopy at 514 nm laser wavelength. An angle view SEM image of the sample after HCl etching is shown in Fig. 1. By HCl etching Si between the BOX and the SiO2 cap is laterally removed. The thickness loss of the BOX and the SiO2 cap are negligible indicating that the Si etching process is highly selective to SiO2. No bending is observed at the floating part of the SiO2 cap layer. At the etchfront a Si (111) facet is formed by the lateral HCl etching. A cross section TEM image of the sample after HCl etching and selective Ge growth is shown in Fig. 2. The Ge layer is selectively grown laterally on the Si surface in the cavity formed by the HCl etching. Dislocations are densely located near the interface between Si and Ge. Aspect ratio trapping (3) also works for the lateral direction, resulting in a high crystal quality Ge layer growth after ~200 nm. In Figure 3, an AFM amplitude image of a 5 µm square mesa structure with [010] sidewall direction is shown after HCl etching and lateral Ge growth followed by the removal of the SiO2 cap by HF dip. The interface between Si and Ge is visible. The root mean square of the Ge surface roughness is ~0.4 nm. It is defined by the interface roughness between Si and the SiO2cap layer. In Figure 4, a plan-view TEM image of a 5 µm square mesa structure after HCl etching and lateral Ge growth is shown. A (113) facet is observed at the growthfront of Ge. Dislocation networks are located near the Si interface. Stacking faults run only parallel or perpendicular to the [110] direction. Between them a wide area without any dislocations toward the [010] direction is observed. These results demonstrate the feasibility of the fabrication of local GeOI with high crystal quality by an additional lithography and an etching process. References 1) Y. Yamamoto et al., Solid-State Electronics 60 (2011) 22) Y. Yamamoto et al., Thin Solid Films 520 (2012) 32163) J. S. Park et al., Appl. Phys. Lett. 90 (2007) 0521134) Y. Yamamoto et al. Thin Solid Films 517 (2008) 90

Temperature Dependent Internal Friction Behavior of Single Crystal Germanium Studied by the Impulse Excitation Technique

The anelastic relaxation process in crystalline solids is influenced by various mechanisms including diffusion of atoms and point defects, grain boundary viscosity, dislocation, phase transformation, etc. To analyze the type and concentration of relaxing units participating in a particular activated process, measuring the internal friction is a well-known approach. A fundamental measure of internal friction can be defined as the ratio between the mechanical energy dissipated during one cycle in a unit volume and the maximum stored elastic energy per unit volume during that cycle [1]. The impulse excitation technique (IET) is a well-established mechanical spectroscopic technique analyzing the internal friction and Young’s modulus behaviour of materials as function of temperature [2]. IET measures the resonant frequency of a specimen by exciting it mechanically with an impulse tool. The resonance frequencies are characteristic for the sample material and are related to its stiffness, mass and geometry. The amplitude decay of a free vibration can be related to the internal friction, i.e. the dissipation of the vibration energy or damping. Measurement of the resonance frequency allows the calculation of Young's modulus E. This technique has been previously applied to determine the temperature dependent Young's modulus of single crystal silicon and germanium in the <100>, <110> and <111> crystallographic directions [3,4,5]. More and more, single crystal germanium and silicon layers and substrates are used together to process advanced nano-eletronic devices. The thermal stresses during crystal growth and device processing have an important impact on generation and diffusion of point defects and in the worst case also can lead to dislocation generation. Although the temperature dependent mechanical properties of silicon are well known, this is much less the case for germanium.In the present study, the impulse excitation technique was used to analyze the temperature dependence of the internal friction in single crystal Ge in the <111>, <100> and <110> directions between room and melting temperatures. A similar set-up was used as in [6] but equipped with a specimen chamber and specimen suspension system allowing heating the samples in an inert atmosphere up to the Ge melt temperature. Between room temperature and melt temperature, three internal friction peaks were observed for each crystallographic orientation after internal friction spectrum analysis, a typical spectrum is shown in the figure. The mechanism leading to these peaks is thermally activated. To interpret the observed internal friction peaks, various aspects such as activation energy of peaks, peak positions and relaxation time will be discussed. The origin of the relaxation peaks is associated with intrinsic point defect processes and/or extended defect formation.

(Invited) Light Emission from Highly-Strained Germanium for On-Chip Optical Interconnects

The relentless device scaling paradigm is being threatened by the limits of Cu-based interconnects including excessive power dissipation, insufficient communication bandwidth, and signal latency. Many of these limitations are caused by the increase in Cu resistivity as wire dimensions are scaled down [1]. To alleviate this performance bottleneck in integrated circuits (ICs), optical interconnects, which have already revolutionized long-haul communications, have recently gained much attention for on-chip applications.Ge has emerged as a viable candidate to augment Si for CMOS and optoelectronics. First, the lower effective mass and lower valley degeneracy of Ge could alleviate the problem by providing a higher source injection velocity, rendering higher drive current and smaller gate delay in MOSFETs [2]. Second, Ge has a larger absorption coefficient than Si in the telecommunications wavelength range (1.3-1.55 µm), which makes it attractive for integration of monolithic optical components for the use in optical interconnects. Third, lower processing temperatures allow 3-D integration of Ge on Si.Over the past decade many of the key Ge-based constituents of an on-chip optical interconnect system, such as high-performance photodetectors and modulators, have been demonstrated on a silicon-compatible platform. We have demonstrated p-i-n [3] and metal–semiconductor–metal (MSM) photodetectors [4] in Ge grown on Si with excellent quantum efficiency and responsivities at a wavelength of 1.55 µm. Dark current, a concern for Ge photodetectors due to its small bandgap, has been mitigated by using electrodes with asymmetric work functions in MSM detectors [4]. Researchers have also observed quantum-confined Stark effect electro-absorption in Ge quantum wells with SiGe barriers grown on Si substrates, and a Ge modulator based on this effect has been demonstrated on a Si substrate [5]. This effect is very promising for high-speed, low-power modulators fabricated compatibly with mainstream Si ICs [5].An efficient light source, on the other hand, remains particularly challenging: Si and Si-compatible materials such as Ge are not readily suitable for light emission because their band gaps are indirect. In Ge, however, the energy difference between the direct Γ valley and the indirect L valley is only 136 meV and this difference can be reduced further by introducing tensile strain [6]. It has been proposed to use tensile strain to make Ge’s band gap direct and thus suitable for light emission [7,8], however highly-strained Ge experimental device realization has thus far been limited to LEDs [9] rather than lasers.In this presentation, we focus on developing an efficient Si-compatible light emitter based on highly-strained Ge technology. Starting from theoretical calculations showing how tensile strain can improve the light emission efficiency of Ge [7,8], we present several approaches for enhancing light emission from highly strained Ge on a CMOS-compatible platform. We have developed methods to grow single crystal Ge films with low defect densities on Si [10]. First, we describe a thin film membrane technique in which a large residual stress in a tungsten layer as a stressor is used to induce a biaxial tensile strain in a Ge membrane, upon which we have fabricated optoelectronic devices [11]. Second, we introduce an approach to induce sufficiently large uniaxial strain to create a direct band gap in Ge wire using geometrical amplification of a small pre-existing strain induced during the heteroepitaxial growth of Ge on Si [12]. Lastly, we present a novel way to mimic double-heterostructure behavior within a single material, further enhancing light emission from Ge by capturing photo-generated carriers within a strain-induced potential well [13]. In summary we have demonstrated integration of Ge on Si for optoelectronic applications. This should alleviate a critical performance bottleneck in the continued scaling of integrated circuits to future technology nodes.

X-Ray Nano-Diffraction on Epitaxial Crystals

The concept of growing epitaxial Ge and SiGe crystals onto tall Si pillars may provide a means for solving the problems associated with lattice parameter and thermal expansion coefficient mismatch, i.e., dislocations, wafer bowing and cracks. For carefully tuned epitaxial growth conditions the lateral expansion of crystals stops once nearest neighbors get sufficiently close. We have carried out scanning nano-diffraction experiments at the ID01 beam-line of the European Synchrotron Radiation Facility (ESRF) in Grenoble on the resulting space-filling arrays of micron-sized crystals to assess their structural properties and crystal quality. Elastic relaxation of the thermal strain causes lattice bending close to the Si interface, while the dislocation network is responsible for minute tilts of the crystals as a whole. To exclude any interference from nearest neighbors, individual Ge crystals were isolated first by chemical etching followed by micro-manipulation inside a scanning electron microscope. This permitted us to scan an X-ray beam, focused to a spot a few hundreds of nm in size, along the height of a single crystal and to record three-dimensional reciprocal space maps at chosen heights. The resolution limited width of the scattered X-ray beams reveals that the epitaxial structures evolve into perfect single crystals sufficiently far away from the heavily dislocated interface.

NiGe Thin Films for Write-Once Blue Laser Media

In this paper, Ni 41 Ge 59 , Ni 46 Ge 54 , Ni 50 Ge 50 , Ni 58 Ge 42 thin films with the thickness of 16 nm were deposited at room temperature by cosputtering using Ni and Ge targets. From the result of reflectivity-temperature measurement, it was found the NiGe layers possessed two temperature ranges of reflectivity change, i.e, 180°C-230°C and 360°C-400°C. By measuring the optical reflectivity at a wavelength of 405 nm, the optical contrasts of these films before and after annealing for 400°C were determined to be 35.1%, 39.4%, 40.3%, and 42.5% with the Ni contents of 41, 46, 50, and 58 at%, respectively. Microstructural analysis indicated that the NiGe nanocrystalline phase was formed in the as-deposited state. After annealing at 270°C and 400°C, the crystallinity of NiGe phase was enhanced and the Ge crystallization was formed, respectively. The optimum jitter values of Ni 58 Ge 42 Blu-ray disk were 6.6% at 7 mW and 7.2% at 8.4 mW, respectively, for 1× and 2× recording speeds. It reveals that the NiGe films have high potential in the application of blue laser recording media.

Direct synthesis of highly textured Ge on flexible polyimide films by metal-induced crystallization

The highly (111)-textured Ge thin film (50-nm thickness) is demonstrated on a flexible polyimide film via the low-temperature crystallization (325 °C) of amorphous Ge using Al as a catalyst. Covering the polyimide with insulators significantly improved the crystal quality of the resulting Ge layer. In particular, SiN covering led to 97% (111)-oriented Ge with grains 200 μm in size, two orders larger than the grain size of polycrystalline Ge directly formed on the polyimide film. This achievement will give a way to realize advanced electronic and optical devices simultaneously allowing for high performance, inexpensiveness, and flexibility.

High carrier mobility in orientation-controlled large-grain (≥50 μm) Ge directly formed on flexible plastic by nucleation-controlled gold-induced-crystallization

High-carrier-mobility semiconductors on flexible-plastic are essential to realize flexible electronics. For this purpose, electrical properties of orientation-controlled large-grain Ge crystals on flexible-plastic directly formed by nucleation-controlled gold-induced-crystallization (GIC) are examined, and compared with those obtained by aluminum-induced-crystallization (AIC). The Ge crystals show p-type conductions. Here, hole concentrations are 2.2 × 1017 and 5.8 × 1020 cm−3 for GIC-Ge and AIC-Ge, respectively, which are explained on the basis of the solubility of Au and Al in Ge. Thanks to the low hole concentration, GIC-Ge shows high hole mobility (160 cm2 V−1 s−1) compared with AIC-Ge (37 cm2 V−1 s−1). These demonstrate significant advantage of GIC to realize high-performance flexible-electronics.

A new possible way to explain the DAMA results

At present there is an effort to reconcile the results of the DAMA experiment with those from other Dark Matter experiments such as CoGeNT, CRESST, CDMS, and all LXe experiments. The author suggests a new model describing the Dark Matter signal as the result of collisions of very light (1-to-few GeV/c2) WIMPs with hydrogen, and compares it with currently accepted models of collisions with heavy nuclei (Na, Ge or Xe). The hydrogen target would come from H-contamination of NaI(Tl), Ge and CaWO4 crystals. Initial tuning indicates that one can explain the modulation amplitude of DAMA and CoGeNT with this model, assuming a WIMP-proton cross section between 10−33 and 10−32 cm2. This paper should be considered to be a new idea which will need substantial new experimental input from all involved experiments.

Photoluminescence study of γ‐irradiation effect on the defect structure in Ge‐doped CdTe single crystals

AbstractAn effect of γ‐irradiation in the dose range 10‐500 kGy on the defect structure of Ge‐doped CdTe single crystals (CdTe:Ge) was investigated via the method of low‐temperature photoluminescence. It was obtained that γ‐irradiation in mentioned above dose range leads to the substantial decreasing of intensities of excitonic emission bands – D0X, A0X, VDX and increase in the intensities of impurity‐related emission bands – eA1,eA2, DA. It was shown that such changes in the luminescence can be explained by radiation‐stimulated redistribution of luminescence centers between recombination channels. The latter includes vacancy‐type defects filling by Ge dopant atoms which leads to the improving of the crystalline perfection of irradiated CdTe:Ge crystals. Mentioned material quality increasing was confirmed analysing the electron‐LO‐phonon coupling in irradiated crystals which was characterized via the Huang‐Rhys factor for corresponding luminescence bands. For the verification of the assumption about radiation‐stimulated compensation of native defects the resonant Raman measurements also were carried out. (© 2014 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Flat single crystal Ge membranes for sensors and opto-electronic integrated circuitry

A thin, flat and single crystal membrane on which to mount sensors is generally required for integration with electronics through standard silicon processing technology. We present an approach to producing single crystal membranes of germanium with in-built tensile strain, which serves to keep the membrane flat and ripple free, and demonstrate a 600nm thick, free-standing 1mm2 Ge membrane. We convert the fabrication technique into an integrated-circuit compatible wafer scale process to produce 60nm thin membranes with large areas of 3.5mm2. The single crystal Ge membrane provides an excellent platform for further epitaxial growth or deposition of materials.

Resonant Coherent Excitation of Hydrogenlike Fe25+ in a Ge crystal

An extremely-thin Germanium crystal (0.8 μm-thick) has been firstly exploited in the resonant coherent excitation (RCE) experiment. The 460 MeV/u H-like Fe25+ ions were incident on the Ge crystal under the (220) planar channeling as well as non-channeling conditions. The RCE from 1s to 2p1/2 and 2p3/2 states were successfully observed as an enhancement of the x-ray fluorescence.

High quality single crystal Ge nano-membranes for opto-electronic integrated circuitry

A thin, flat, and single crystal germanium membrane would be an ideal platform on which to mount sensors or integrate photonic and electronic devices, using standard silicon processing technology. We present a fabrication technique compatible with integrated-circuit wafer scale processing to produce membranes of thickness between 60 nm and 800 nm, with large areas of up to 3.5 mm2. We show how the optical properties change with thickness, including appearance of Fabry-Pérot type interference in thin membranes. The membranes have low Q-factors, which allow the platforms to counteract distortion during agitation and movement. Finally, we report on the physical characteristics showing sub-nm roughness and a homogenous strain profile throughout the freestanding layer, making the single crystal Ge membrane an excellent platform for further epitaxial growth or deposition of materials.

Determination of trace concentrations of transmuted stable nuclides in TMD detectors using PGAA

The capability of prompt gamma-ray activation analysis (PGAA) for neutron fluence dosimetry by means of transmutation detectors is reported. The metallic foils of Ni, Au, Cu and Nb and the small piece of Ge crystal, which were irradiated at the LVR-15 reactor at Řež for several days, were selected for analysis by PGAA technique. Concentrations of transmuted stable nuclides in these foils were measured using the PGAA facility installed at the research reactor FRM II in Garching.