Purity Germanium Research Articles

Scintillating bolometers for ββ Decay search

We present the results achieved in the development of scintillating bolometers for double beta decay searches. A bolometric light detector was developed using an extremely pure germanium crystal. The excellent results represent the first proof of the feasibility of this kind of technique.

Surface Dangling Bond-Mediated Molecules Doping of Germanium Nanowires

We report on the controllable doping of germanium nanowires (GeNWs) via selective molecule adsorption on the surface dangling bond. The GeNWs investigated are fabricated by evaporating pure germanium powder. Electron spin resonance analysis shows the presence of a surface dangling bond with g value of 2.023 and a spin density of Cspin = 2.47 × 1013 mg–1. The as-prepared undoped GeNW exhibits typical p-type conduction behavior in air but n-type electrical characteristics in ammonia atmosphere. Significantly, the conductance, carrier mobility, and concentrations are found to be highly dependent on vacuum and ammonia gas pressures. Such an ambient effect could be explained by a surface dangling bond-mediated molecule doping model, according to which an acceptor or donor level is formed by water or ammonia adsorption, respectively. The generality of the above results suggests that surface dangling bond-mediated molecule doping may be applicable to modulation of the electrical characteristics of other semicond...

Synchrotron Radiation Photoemission Study of Ge3N4/Ge Structures Formed by Plasma Nitridation

Chemical bonding states and energy band alignment of pure germanium nitride (Ge3N4) layers formed on Ge(100) surfaces by high-density plasma nitridation were characterized by synchrotron radiation photoemission spectroscopy (SR-PES). The core-level shift of 2.31 eV originating from Ge–N bonds (Ge4+) with respect to the bulk Ge 3d5/2 peak position (Ge0+) was determined by peak deconvolution of Ge 3d core-level spectra. In situ SR-PES study on changes in Ge 3d, N 1s, and O 1s core-level spectra during thermal annealing under ultrahigh vacuum (UHV) conditions revealed that oxidized surface layer on Ge3N4 film could be selectively removed at around 500 °C, which was 50 °C lower than the decomposition temperature of Ge3N4. Ge3+ component was found to increase with decreasing Ge4+ component during thermal decomposition of Ge3N4 while no significant change in Ge1+ and Ge2+ components. The Ge3N4 energy bandgap of 3.68 eV was experimentally determined from energy loss spectra of N 1s photoelectrons. The valence band offset at Ge3N4/Ge(100) interfaces were also estimated to be 1.65 eV from valence band spectra, and thus, the energy band alignment between Ge3N4 dielectrics and Ge substrate was determined.

Structural analysis and electrical properties of pure Ge3N4 dielectric layers formed by an atmospheric-pressure nitrogen plasma

Pure germanium nitride (Ge3N4) thin films were successfully formed on n-type Ge (111) substrate using an atmospheric-pressure (AP) nitrogen plasma. Their film structures and electrical properties were then examined in detail. Synchrotron radiation photoelectron spectroscopy clearly revealed that the Ge3N4 thin films formed by AP plasma had superior oxidative resistance compared to those made using conventional plasma techniques. Films fabricated at 500 °C showed only minor post-oxidation, even after exposure to air, which is a potentially very useful feature for passivation layers at high-permittivity (high-k) dielectric film–Ge interfaces. The films also showed excellent electrical properties. Capacitance-voltage measurements revealed no hysteresis or kinks, indicating that the trap-state density was low at the Ge3N4–Ge interface. The leakage current density is also lower than in films fabricated using other plasma systems. Direct-tunneling current simulations revealed that the effective tunneling mass increased due to the formation of high-quality Ge3N4 thin films, resulting in superior leakage current. These results suggest that our nitridation technique would show major benefits in Ge field-effect transistors.

Distribution of Natural Radioactivity in Oil-Derived Lubricants

Oil and gas production processing operations have been known to cause naturally occurring radioactive materials that could lead to internal and external radiation hazards and then a significant radiation dose to the workers. So, in this work, nine oil lubricants samples used on a daily basis were collected from local suppliers in Egypt in order to determine their natural radioactivity. The activity concentrations of the radionuclides were measured using coaxial hyper pure germanium (HPGe) detector system, and the derived doses were evaluated. The average activity concentrations obtained were 0.57 ± 0.04, 2.33 ± 0.39 and 5.44 ± 0.27 Bq·kg−1 for 238U,232Th and 40K, respectively. The absorbed doses were very low ranging from 0.57 to 4.20 nGyh−1.

Growth of axial SiGe heterostructures in nanowires using pulsed laser deposition

Axial heterojunctions between pure silicon and pure germanium in nanowires havebeen realized combining pulsed laser deposition, chemical vapor deposition andelectron beam evaporation in a vapor–liquid–solid nanowire growth experiment usinggold nanoparticles as catalyst for the 1D wire growth. Energy dispersive x-raymappings and line scans show a compositional transition from pure silicon topure germanium and vice versa with exponential and thus comparably sharptransition slopes. Based on these results not only Si–Ge heterojunctions seem to bepossible using the vapor–liquid–solid growth process but also heterojunctionsin optoelectronic III–V compounds such as InGaAs/GaAs or group III nitridecompounds such as InGaN/GaN as well as axial p–n junctions in Si nanowires.

Evaluation of natural radioactivity in soil, sediment and water samples of Niger Delta (Biseni) flood plain lakes, Nigeria

This paper presents the findings of a baseline study undertaken to evaluate the natural radioactivity levels in soil, sediment and water samples in four flood plain lakes of the Niger Delta using a hyper pure germanium (HPGe) detector. The activity profile of radionuclides shows low activity across the study area. The mean activity level of the natural radionuclides 226Ra, 232Th and 40K is 20 ± 3, 20 ± 3 and 180 ± 50 Bq kg −1, respectively. These values are well within values reported elsewhere in the country and in other countries with similar environments. The study also examined some radiation hazard indices. The mean values obtained are, 76 ± 14 Bq kg −1, 30 ± 5.5 ηGy h −1, 37 ± 6.8 μSv y −1, 0.17 and 0.23 for Radium Equivalent Activity (Ra eq), Absorbed Dose Rates (D), Annual Effective Dose Rates (E ff Dose), External Hazard Index (H ex) and Internal Hazard Index (H in) respectively. All the health hazard indices are well below their recommended limits. The soil and sediments from the study area provide no excessive exposures for inhabitants and can be used as construction materials without posing any significant radiological threat to the population. The water is radiologically safe for domestic and industrial use. The paper recommends further studies to estimate internal and external doses from other suspected radiological sources to the population of the Biseni kingdom.

Germanium vertical Tunneling Field-Effect Transistor

The first realization of a pure Germanium bulk vertical Tunneling Field-Effect Transistor (vTFET) and a high I on/ I off ratio for a pure Silicon bulk vTFET are both reported. The manufacturing process, the electrical characteristics and key features and the differences of the two varieties of vTFET devices (pure Germanium bulk vTFET and pure Silicon bulk vTFET) will be discussed in detail.

Electrical Characteristics of Ge-Based Metal-Insulator-Semiconductor Devices with Ge<SUB>3</SUB>N<SUB>4</SUB> Dielectrics Formed by Plasma Nitridation

We have fabricated pure germanium nitrides (Ge3N4) using high-density plasma nitridation and investigated electrical properties of Au/Ge3N4/Ge capacitors. We achieved equivalent oxide thickness (EOT) of 1.4 nm, and dielectric constant of Ge3N4 was estimated to be 9.7. The gate leakage current density of 4.3 A/cm2 in the accumulation condition at V(fb)-1 V, where V(fb) is the flatband voltage, was one order of magnitude lower than that of conventional poly-Si/SiO2/Si stacks. The interface state density (D(it)) of Ge3N4/Ge interfaces evaluated by a low-temperature conductance method exhibited a minimum value of 9.4 x 10(11) cm(-2)eV(-1) at E - E(v) = 0.27 eV. Furthermore, the insulating property and interface quality of Ge3N4/Ge system was found to be thermally stable up to 650 degrees C. These results indicate that Ge3N4 is a promising candidate for either a gate insulator or an interfacial layer under high-k dielectrics for Ge-MIS devices.

실리콘-게르마늄 합금의 전자 소자 응용

실리콘(Si)에 비해 상대적으로 밴드 갭이 작고, 열전도도가 낮으며, 기존의 Si 반도체 공정 기술과 호환이 가능한 실리콘-게르마늄(SiGe) 합금은 트랜지스터, 광수신 소자, 태양전지, 열전 소자 등 다양한 전자 소자에서 사용되고 있다. 본 논문에서는 SiGe 합금이 전자소자에 응용되는 원리 및 응용과 관련된 기술적인 논제들을 고찰한다. Si에 비해 밴드 갭이 작은 게르마늄(Ge)이 그 구성 원소인 SiGe 합금의 밴드 갭은 Si과 Ge의 분률과 상관없이 항상 Si의 밴드 갭 보다 작다. 이러한 SiGe의 작은 밴드 갭은 전류 이득의 손실 없이 베이스 두께를 감소시키는 것을 가능하게 하여 바이폴라 트랜지스터의 동작속도를 향상시킨다. 또한, Si이 흡수하지 못하는 장파장 대의 빛을 SiGe이 흡수하여 광전류를 생성하게 함으로써 태양전지의 변환효율을 증가시킨다. 질량이 서로 다른 Si 및 Ge 원소의 불규칙적인 분포에 의해 발생하는 포논 산란 효과 때문에 SiGe 합금은 순수한 Si 및 Ge과 비교할 때 낮은 열전도도를 갖는다. 낮은 열전도도 특성의 SiGe 합금은 전자 소자 구조 내에서의 열 손실을 억제하는데 효과가 있으므로 Si 반도체 공정 기반의 열전 소자의 구성 물질로서 활용이 기대된다. The silicon-germanium (SiGe) alloy, which is compatible with silicon semiconductor technology and has a smaller band gap and a lower thermal conductivity than silicon, has been used to fabricate electronic devices such as transistors, photodetectors, solar cells, and thermoelectric devices. This paper reviews the application of SiGe alloys to electronic devices and related technical issues. Since the SiGe alloy comprises germanium whose band gap is smaller than silicon, its band gap is also smaller than that of silicon irrespective of the ratio of silicon to germanium. This narrow band gap of SiGe enables the base thickness of bipolar transistors to decrease without a loss in current gain so that it is possible to improve the speed of bipolar transistors by adopting the SiGe-base. In addition, the conversion efficiency of solar cells is enhanced by the absorption of long-wavelength light in the SiGe absorption layer. Phonon scattering caused by the irregular distribution of alloying elements induces the lower thermal conductivity of SiGe than those of pure silicon and germanium. Because a thin film layer with a low thermal conductivity suppresses thermal conduction through a thermal sink, the SiGe alloy is considered to be a promising material for silicon-based thermoelectric systems.

Low natural terrestrial radioactivity in oil-derived lubricants

Oil and gas production processing operations have been known to involve naturally occurring radioactive materials that lead to internal and external radiation hazards and thus a significant radiation dose to the workers. In this work, samples of nine oil lubricants used on a daily basis were collected from local suppliers in Egypt and analysed to determine their natural radioactivity. The activity concentrations of the radionuclides were measured using a coaxial Hyper Pure Germanium (HPGe) detector system, and derived doses were evaluated. The average activity concentrations obtained were 0.57 ± 0.04, 2.33 ± 0.39 and 5.44 ± 0.27 Bq kg –1 for 238 U, 232 Th and 40 K, respectively. The absorbed doses were very low ranging from 0.57 to 4.20 nGy h –1 .

Radiation dose estimation of sand samples collected from different Egyptian beaches

A high pure germanium detector-based gamma-ray spectroscopy low-background counting system was used to determine the levels of natural radioactivity from beach sand samples on the Egyptian coast along the Mediterranean and Red Seas. The activity concentrations of (226)Ra, (232)Th and (40)K were found to lie in the range of 30±11 to 60±14 Bq kg(-1) with a mean of 39±15 Bq kg(-1), 12±3 to 30±14 Bq kg(-1) with a mean of 21±13 Bq kg(-1) and 392±22 to 413±22 Bq kg(-1) with a mean of 402±23 Bq kg(-1), respectively. Radiation hazard indices and annual effective doses were evaluated and compared with the international data. The results indicate that the values obtained fall below the internationally accepted maximum limits and do not pose any significant radiation hazard to individuals in the study area. From these results, a radiological baseline map of Egyptian beaches can be drawn and used as reference information to assess any future alterations in the radioactivity of beach sands due to any changes in the sea sediments.

Formation of Si<sub>0.80</sub>Ge<sub>0.20</sub> Solid Solution by Mechanical Alloying

In general, semiconductor materials for thermoelectric generation prepared by vacuum metallurgy shows a relatively high value of figure-of-merit. However, differences in some properties of alloys elemental constituents can cause processing problems. Recently, Mechanical Alloying (MA) has been used to produce polycrystalline thermoelectric materials, such as (Bi,Sb)2 and (Te,Se)3(1). The industry is using this process since early 70’s to produce oxide dispersion strengthened alloys and those with widely different melting temperatures (2) In the present work, Si0.80Ge0.20 alloys were prepared via Mechanical Alloying (MA), using 99.9 % pure silicon and germanium powders, with a sieve size of 100 mesh. The MA has been performed, for several balls - to - powder ratio, in a SPEX 8000 vibratory high energy milling with tungsten carbide balls. Time for alloy formation was in a range from 3 to 9 hours, corresponding to charge ratio of 12:1 and 4:1, respectively. After two hours of processing time, the grinding temperature reached 80 0 C, and remained at this level until the end of the process. It was possible to follow the SiGe alloy formation by x-ray diffractometry, as the peak lines positions of elemental Si and Ge were continuously shifted, and end up to merge into a single broad peak. There was a convergence of the individual lattice parameters of Si and Ge to a single value of 5.470 A, measured within the limit of  0.005 A. For the Si0.80Ge0.20 system evaluated in this work, the alloying progress occurred continuously, and changed inversely with charge ratio.

Raman efficiency in SiGe alloys

Raman spectroscopy is commonly used for the optical characterization of structural properties of SiGe alloys but a measurement of the Raman efficiency as a function of excitation wavelength and concentration is still lacking. This information is nevertheless important for the interpretation of data, especially for the analysis of inhomogeneous samples. In this work, the relative Raman efficiency of ${\text{Si}}_{1\ensuremath{-}x}{\text{Ge}}_{x}$ alloys has been obtained for several excitation energies as a function of the composition $x$ with steps of $\ensuremath{\Delta}x\ensuremath{\sim}0.02$ across the whole composition range. We observed resonances in correspondence of the ${E}_{1}/{E}_{1}+{\ensuremath{\Delta}}_{1}$ and ${E}_{0}/{E}_{0}+{\ensuremath{\Delta}}_{0}$ transitions. For a fixed excitation energy the efficiency varies of about 2 orders of magnitude vs the composition of the alloy, while, for a fixed composition, we observed a change in efficiency of up to 3 orders of magnitude depending on the excitation energy. The maximum scattering efficiency at resonance decreases by an order of magnitude when moving from silicon-rich to germanium-rich alloys. The data are discussed in terms of the polarizability and compared to the literature relative to pure silicon and germanium. The data reported in this paper can be used to design experiments under resonant conditions to selectively probe different regions in inhomogeneous samples.

Radioactivity levels and radiological hazard indices at the Saudi coastline of the Gulf of Aqaba

The coast of the Gulf of Aqaba is subjected to several sources of pollution due to several activities occurring at the coastal area. The activities vary between industrial, tourist and other development aspects at the Jordanian coastline of the Gulf of Aqaba. Phosphate industry has been considered a major source polluting the marine environment. According to official reports, 4–7 million tons of raw phosphate is exported through the Gulf of Aqaba. During transportation and loading, a small proportion of this enters the waters of the Gulf. Phosphate dust has also been considered another source of nutrients loading to the Gulf. 19 sediment samples were collected along the Saudi Gulf coastline, from the Saudi-Jordan border down to the end of the Gulf at Tiran Strait. Measurements of the activity concentrations of 226Ra, 232Th, 40K and 137Cs in Bq/kg (in dry weight) of the collected samples were carried out using gamma-ray spectrometry based on a highly pure germanium coaxial detector (HPGe). The concentrations of 238U and 232Th were also determined using ICP-MS technique. The average specific activities for 226Ra, 232Th, 40K and 137Cs were found to be 11.4±1.5, 22.5±3.7, 641.1±61.3 and 3.5±0.7 Bq/kg, respectively. The results show that the mean activity of 226Ra and 232Th is lower than the world average of 25 Bq/kg for both of them, whereas the mean value for 40K is about double the world average of 370 Bq/kg. The presence of 137Cs in the analyzed samples is low in most locations. The mean concentrations of 238U and 232Th in the study area are 1.2 and 5.4 mg/kg, respectively, and the ratio 238U/ 232Th is 0.2, which is lower than the global ratio of 0.3. The ratio of 226Ra/ 228Ra was found to decrease southwards in the direction of Tiran Strait, away from the phosphate industry in Jordan. Mean values for radium equivalent, absorbed dose, annual effective dose, external and internal hazard index and representative level index were determined as: 92.9 Bq/kg, 45.6 nGy/h, 56.0 μSv/y, 0.13, 0.28 and 0.73, respectively.

High temperature, high density opacity measurements using short pulse lasers

Heating of thin foil targets by a high power laser at intensities of 1017 -1019W/cm2 has been studied as a method for producing high temperature, high density samples to investigate X-ray opacity and equation of state. The targets were plastic (parylene N) foils with a buried microdot of a sample material, which was either aluminium, germanium or a mixture of germanium and titanium mixture of germanium and titanium. L-shell and K-shell spectra were taken using crystal spectrometers recording onto film and an ultrafast X-ray streak camera coupled to a conical focussing crystal with a time resolution of 1ps. The conditions in the microdot were inferred by comparing the measured spectra to synthetic spectra produced by the time-dependent collisional-radiative (CR) models FLY and FLYCHK. The data were also compared to simulated spectra from a number of opacity codes assuming local thermodynamic equilibrium (LTE). Temperature and density gradients were taken into account in the comparisons. The sample conditions, inferred from the CR modelling using FLYCHK, were 800±100eV and 1.5±0.5g/cc, in the germanium/titanium samples and 600+50/-150eV, 3–4g/cc in the pure germanium or aluminium samples. The higher densities were achieved by using a combination of long and short pulses to compress and heat the foils respectively. The experimental results and comparisons to predicted spectra are presented and discussed.

Radiation hazard assessment in Egyptian painting oxides. A comparative study

Building materials are potential sources of radiation, which represents a risk factor for human disease including cancer. In this work, the natural radioactivity due to the presence of (238)U, (226)Ra, (232)Th and (40)K in different painting oxides has been measured using gamma spectrometry with a Hyper Pure germanium detector. The concentrations of the heavy metals (Cd, Co, Mn, Pb, Ni, Sr, Rb, Cr, Cu and Zn) were determined by atomic absorption spectrometry in order to investigate their possible correlation with radioactive elements. The activity concentrations of (238)U, (226)Ra, (232)Th and (40)K ranged from 15 ± 0.75 to 126 ± 14, 2.35 ± 0.09 to 72.96 ± 1.96, 1.76 ± 0.31 to 12.88 ± 0.7 and 2.26 ± 0.09 to 200 ± 3.34 Bq kg(-1), respectively. The calculated radium-equivalents were lower than values recommended for construction materials (370 Bq kg(-1)). The absorbed dose rates due to the natural radioactivity of the investigated samples ranged from 8.11 ± 0.24 to 68.46 ± 4.20 nGy/h. Also, the results revealed that some heavy metals (Cd, Co, Mn and Rb) were correlated with (238)U, (226)Ra, (232)Th or (40)K.

Direct and indirect band gap room temperature electroluminescence of Ge diodes

Germanium is a promising material for electrically pumped light emitters integrated on silicon. In this work, we have investigated the room temperature electroluminescence of pure germanium diodes grown by metal organic chemical vapor deposition. The dependence of the optical response of the p-n diodes is studied as a function of the injected current. Both direct and indirect band gap recombinations are observed at room temperature around 1.6 and 1.8 μm. The amplitude of the direct band gap recombination is equivalent to the one of the indirect band gap.

Conduction band discontinuity and electron confinement at the SixGe1−x/Ge interface

Germanium rich heterostructures can constitute a valid alternative to Silicon for the confinement of single electron spins. The conduction band discontinuity in SiGe/Ge heterostructures grown on pure germanium substrate is predicted to allow the confinement of electrons in the germanium, and the conduction band profile of germanium rich heterostructures allow the implementation of g-factor modulation devices not possible in Silicon. We here prove that electrons can indeed be trapped at the Si0.1Ge0.9/Ge interface and we measure the height of the energy barrier to 0.55±0.05 eV by measuring the tunneling time of electrons as a function of the electric field.

Normal incidence p–i–n Ge heterojunction photodiodes on Si substrate grown by ultrahigh vacuum chemical vapor deposition

We report on normal incidence p–i–n heterojunction photodiodes operating in the near-infrared region and realized in pure germanium on planar silicon substrate. The diodes were fabricated by ultrahigh vacuum chemical vapor deposition at 600 °C without thermal annealing and allowing the integration with standard silicon processes. Due to the 0.14% residual tensile strain generated by the thermal expansion mismatch between Ge and Si, an efficiency enhancement of nearly 3-fold at 1.55 μm and the absorption edge shifting to longer wavelength of about 40 nm are achieved in the epitaxial Ge films. The diode with a responsivity of 0.23 A/W at 1.55 μm wavelength and a bulk dark current density of 10 mA/cm 2 is demonstrated. These diodes with high performances and full compatibility with the CMOS processes enable monolithically integrating microphotonics and microelectronics on the same chip.