N-type Germanium Research Articles

A plant based electrochemical device with transistor like behavior

Since its invention, transistor has become the fundamental building block of virtually all of today’s integrated circuits which constitute the electronics technology. In the present letter, we report the vegetal version of a self-powered electrochemical transistor, i.e., a device with an inherent energy source which exhibits energy-converting and amplifying-modulating properties. Surprisingly, at the interface constituted by the surface of an n-type germanium sample and a vegetal slice it become apparent that the surface of the n-type germanium passing anodic current acts as a multiplying collector for holes. Experimental transconductance characteristics show well-defined the cut-off, active and saturation regions. Likewise, since the collector is itself part of an electrolytic cell, device incorporates its own power supply. Thereby, it is able to reproduce an analogical AC signal via the DC electrolytic cell voltage. Furthermore, one of the most outstanding properties of the transistors is their DC current gain (hFE), which for commercially available small-signal transistors typically ranges 50–350, and for medium power transistors 15–70. The proposed device presents an hFE of 70 and 40 for the potato and apple based transistors respectively. Genuinely, this approach opens an alternative route for the development of a novel green electronics based on self-powered vegetative devices. Genuinely, this approach opens an alternative route for the development of a novel green electronics based on self-powered vegetative devices which could works as sensing devices for monitoring living plants during sow and harvest.

Calibration and performance evaluation of an N-type HPGe detector for a collimated and focused PGNAA system by experimental and Monte Carlo methods

The MCNP code was utilized to assess the operational status of an N-type high-purity germanium (HPGe) detector and to evaluate its potential for a collimated and focused Prompt Gamma Neutron Activation Analysis (PGNAA) detection system. In order to calibrate the detector, a narrow beam γ collimator was designed to scan the detector in both axial and radial directions. The curvature of the crystal front edge and the non-uniform description of the detector dead layer (DL) were taken into account when adjusting the effective crystal size. A collimated 137Cs γ source was used to assess the detection efficiency in the scanning experiments. Monte Carlo studies were performed using 0.662 MeV γ rays, and separately, a uniform γ-ray energy distribution from 0 to 1.6 MeV. Lastly, the effects of a collimation aperture with different sizes and different incident directions were considered to discuss the relationship between the spatial resolution and suitable measurement scenarios. Therefore, a detailed calibration method for non-uniform dead layers was introduced through a comparison between experiments and Monte Carlo simulations. This work reevaluates the performance of HPGe detectors and provides valuable data support for a detailed system design and γ spectroscopy analysis in future.

Modeling of N and P-Type of Coaxial Ge Detectors Using MCNPX and the Effect of Dead Layer Variation on Its Response Function

Abstract This study assessed the response function of a p-type and n-type coaxial high-purity germanium (HPGe) detector via Monte Carlo N-Particle eXtended (MCNPX). MCNPX was employed to model the Coaxial Ge detectors, and for a precise simulation, the dimensions of the dead layer of germanium crystals were added. The dead layer was separated into front and lateral surfaces, and the thickness of each dead layer was modeled. In this work, the simulated detectors have been performed at different energy lines using a radioactive source Eu-152 to study the response function of each with dead layer variations for the front dead layer and study the range of relative deviation of the Monte Carlo simulation outputs from the manufactured declared data. The results proved that the n-type coaxial HPGe detector is more sensitive to the dead layer change than the p-type with a thick change of 0.01 mm. This research has significant effects on the efficiencies of the radiation detection systems in the energy range ∼ (120–1410) keV.

Strain-dependent grain boundary properties of n-type germanium layers

Polycrystalline Ge thin films have attracted considerable attention as potential materials for use in various electronic and optical devices. We recently developed a low-temperature solid-phase crystallization technology for a doped Ge layer and achieved the highest electron mobility in a polycrystalline Ge thin film. In this study, we investigated the effects of strain on the crystalline and electrical properties of n-type polycrystalline Ge layers. By inserting a GeOx interlayer directly under Ge and selecting substrates with different coefficients of thermal expansion, we modulated the strain in the polycrystalline Ge layer, ranging from approximately 0.6% (tensile) to − 0.8% (compressive). Compressive strain enlarged the grain size to 12 µm, but decreased the electron mobility. The temperature dependence of the electron mobility clarified that changes in the potential barrier height of the grain boundary caused this behavior. Furthermore, we revealed that the behavior of the grain boundary barrier height with respect to strain is opposite for the n- and p-types. This result strongly suggests that this phenomenon is due to the piezoelectric effect. These discoveries will provide guidelines for improving the performance of Ge devices and useful physical knowledge of various polycrystalline semiconductor thin films.

Germanium-OLED short-wave infrared-to-visible upconverters

Infrared-to-visible upconverters consisting of infrared photodetectors (PDs) with visible light-emitting diodes (LEDs) to directly visualize infrared images without intermediate electronics have stimulated research interest. However, existing upconverters mostly detect infrared only in the near-infrared region, preventing the extensive short-wave infrared (SWIR) application. Here, we innovatively integrate strong-SWIR-response n-type germanium (Ge)/indium tin oxide (ITO) PDs with phosphorescence organic LEDs (OLEDs) to realize the efficient upconversion of SWIR to green light through a simple fabrication process. The ITO layers not only construct Schottky heterojunction with the Ge to improve SWIR detection ability but also provide the photogenerated carriers transport channel from PDs to OLEDs. As a result, the Ge-OLED upconverters exhibit the efficient upconversion of SWIR and high p–p efficiency of 7%.

Temperature dependence of the electron-drift anisotropy and implications for the electron-drift model

The electron drift in germanium detectors is modeled making many assumptions. Confronted with data, these assumptions have to be revisited. The temperature dependence of the drift of electrons was studied in detail for an n-type segmented point-contact germanium detector. The detector was mounted in a temperature controlled, electrically cooled cryostat. Surface events were induced with collimated 81 keV photons from a 133Ba source. A detailed analysis of the rise time of pulses collected in surface scans, performed at different temperatures, is presented. The longitudinal anisotropy of the electron drift decreases with rising temperature. A new approach, making use of designated rise-time windows determined by simulations using SolidStateDetectors.jl, was used to isolate the longitudinal drift of electrons along different axes to quantify this observation. The measured temperature dependence of the longitudinal drift velocities combined with the standard electron-drift model as widely used in relevant simulation packages results in unphysical predictions. A modification of the electron-drift model based on assuming phonons to be the dominating scattering centers for electrons is motivated and described. The results of a first implementation of the modified model in SolidStateDetectors.jl are shown. They describe the temperature dependence of the data reasonably well. A general review of the model and the standard input values for mobilities is suggested.

3D printing of bulk thermoelectric materials: Laser powder bed fusion of N-type silicon germanium

Among Additive Manufacturing (AM) methods, Laser Powder Bed Fusion (L-PBF), also called Selective Laser Melting (SLM), is prevalent to printing complex metal parts in small and medium series. Recent studies in L-PBF processing develops the manufacturing of new materials, including thermoelectric (TE) materials. This study presents manufacturing of an N type Si80Ge20 powder by L-PBF. Silicon germanium alloy is a TE material intended for high temperature applications. It is the first time that this semiconductor material is studied by AM technology. Dense samples of various shapes and sizes were produced, and a first process window was identified. Structural analyses have been performed, highlighting good densification. Unfortunately, mechanical cracking occurs in all samples. TE properties were investigated on as built samples, displaying low values (ZT = 0.11 at 600 °C), due to poor electrical conductivity. Overall, these results show that L-PBF of silicon germanium is possible, which could open up its scope of applications.© 2023 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Materials science in semiconductor processing.

Excellent passivation of germanium surfaces by POx/Al2O3 stacks

Passivation of germanium surfaces is vital for the application of germanium in next-generation electronic and photonic devices. In this work, it is demonstrated that stacks of phosphorous oxide and aluminum oxide (POx/Al2O3) provide excellent and stable passivation of germanium surfaces, with state-of-the-art surface recombination velocities down to 8.9 cm/s. The POx/Al2O3 stack also exhibits positive fixed charge on germanium, which makes it especially suited for passivation of highly doped n-type germanium surfaces. The chemical passivation mechanism is found to be related to the passivation of defects by hydrogen, which is mobilized by the formation of AlPO4 upon annealing. Furthermore, the GeOx interlayer is removed due to a kind of “self-cleaning” process during the deposition of POx/Al2O3 stacks on germanium, which may in part explain the excellent passivation quality. This self-cleaning of the interface may also allow simplified device fabrication workflows, as pretreatments may be omitted.

Novel process integration flow of germanium-on-silicon FinFETs for low-power technologies

Germanium channel FinFET transistors process integration on a silicon substrate is a promising candidate to extend the complementary metal–oxide–semiconductor semiconductor roadmap. This process has utilized the legacy of state-of-art silicon fabrication process technology and can be an immediate solution to integrate beyond Si channel materials over standard Si wafers. The fabrication of such devices involves several complicated technological steps, such as strain-free epi layers over the Si substrate to limit the substrate leakage and patterning of narrow and sharp fins over germanium (Ge). To overcome these issues, the active p-type germanium layers were grown over n-type germanium and virtual substrates. The poly ((4-(methacryloyloxy) phenyl) dimethyl sulfoniumtriflate) was utilized as a polymeric negative tone e-beam resist for sub-20 nm critical dimensions with low line edge roughness, line width roughness, and high etch resistance to pattern p-Ge fins to meet these concerns. Here, the devices use the mesa architecture that will allow low bandgap materials only at the active regions and raised fins to reduce the active area interaction with the substrate to suppress leakage currents. This paper discusses the simple five-layer process flow to fabricate FinFET devices with critical optimizations like resist prerequisite optimization conditions before exposure, alignment of various layers by electron beam alignment, pattern transfer optimizations using reactive ion etching, and bilayer resist for desired lift-off. The Ge-on-Si FinFET devices are fabricated with a width and gate length of 15/90 nm, respectively. The devices exhibit the improved ION/IOFF in order of ∼105, transconductance Gm ∼86 μS/μm, and subthreshold slope close to ∼90 mV/dec.

Reducing specific contact resistivity for n-type germanium using laser activation process and nano-island formation

This study presents a laser activation process (LAP) for germanium (Ge) to improve the electrical performance of n-type Ge devices. The LAP highly activated the dopant and created a shallow junction in Ge. We also investigated a triple contact of titanium (Ti)/nickel (Ni) nano-island/Ge to reduce contact resistivity and enhance the tunneling current. The results showed that the LAP with a fluence of 140 mJ/cm2 effectively activated the dopant, resulting in a high forward current density and a low ideality factor of the n+-p junction diode. The triple contact of Ti/Ni nano-island/Ge showed the lowest specific contact resistivity, indicating an increase in the tunneling current. The Ni nano-island contact showed the best overall electrical performance, attributed to the boosted electric field and the lower density of states at the interface. The results show that combining multiple approaches, including the optimized laser activation process and triple contact formation, can significantly reduce the contact resistance on n-type Ge, providing a promising approach for improving performance.

Photo-Seebeck measurement of Bi-doped amorphous germanium telluride oxide film

Seebeck measurements of n-type amorphous germanium telluride thin films (100 nm) containing oxygen and implanted with Bismuth (Bi) have been studied under dark and monochromatic light conditions from 1800 to 400 nm. The Bi-doped film has a negative Seebeck coefficient indicating its n-type nature that results from the implantation compared to the p-type undoped films. Upon illumination with monochromatic light across the near-infrared and visible region the magnitude of the measured Seebeck voltage increases (becomes more negative). This increase in Seebeck coefficient displays distinctive behaviours in different spectral regions and is caused by the inclusion of Bi ions as foreign impurities. Furthermore, the Seebeck coefficients are used to determine the film electrical properties and enable, along with complementary characterisation including X-ray photoelectron spectroscopy, electronic band diagrams to be proposed for before and after Bi ion implantation. The photo-Seebeck technique is utilised for the first time to probe the trap states created due to the implantation, providing an understanding of the mechanisms behind non-equilibrium carrier-type reversal in an amorphous system, including the modification of electronic and optoelectronic properties such as the optical bandgap.

Identification and simulation of surface alpha events on passivated surfaces of germanium detectors and the influence of metalisation

Events from alpha interactions on the surfaces of germanium detectors are a major contribution to the background in germanium-based searches for neutrinoless double-beta decay. Surface events are subject to charge trapping, affecting their pulse shape and reconstructed energy. A study of alpha events on the passivated end-plate of a segmented true-coaxial n-type high-purity germanium detector is presented. Charge trapping is analysed in detail and an existing pulse-shape analysis technique to identify alpha events is verified with mirror pulses observed in the non-collecting channels of the segmented test detector. The observed radial dependence of charge trapping confirms previous results. A dependence of the probability of charge trapping on the crystal axes is observed for the first time. A first model to describe charge trapping effects within the framework of the simulation software SolidStateDetectors.jl is introduced. The influence of metalisation on events from low-energy gamma interactions close to the passivated surface is also presented.

A novel wide-angle Compton Scanner setup to study bulk events in germanium detectors

A novel Compton Scanner setup has been built, commissioned and operated at the Max-Planck-Institute for Physics in Munich to collect pulses from bulk events in high-purity germanium detectors for pulse shape studies. In this fully automated setup, the detector under test is irradiated from the top with 661.660 keV gammas, some of which Compton scatter inside the detector. The interaction points in the detector can be reconstructed when the scattered gammas are detected with a pixelated camera placed at the side of the detector. The wide range of accepted Compton angles results in shorter measurement times in comparison to similar setups where only perpendicularly scattered gammas are selected by slit collimators. In this paper, the construction of the Compton Scanner, its alignment and the procedure to reconstruct interaction points in the germanium detector are described in detail. The creation of a first pulse shape library for an n-type segmented point-contact germanium detector is described. The spatial reconstruction along the beam axis is validated by a comparison to measured surface pulses. A first comparison of Compton Scanner pulses to simulated pulses is presented to demonstrate the power of the Compton Scanner to test simulation inputs and models.

Simulation of semiconductor detectors in 3D with SolidStateDetectors.jl

The open-source software package SolidStateDetectors.jl to calculate the fields and simulate the drifts of charge carriers in solid state detectors, especially in large volume high-purity germanium detectors, together with the corresponding pulses, is introduced. The package can perform all calculations in full 3D while it can also make use of detector symmetries. The effect of the surroundings of a detector can also be studied. The package is programmed in the user friendly and performance oriented language julia, such that 3D field calculations and drift simulations can be executed efficiently and in parallel. The package was developed for high-purity germanium detectors, but it can be adjusted by the user to other types of semiconductors. The verification of the package is shown for an n-type segmented point-contact germanium detector. Additional features of SolidStateDetectors.jl, which are under development are listed.

Curie–Weiss behavior of the low-temperature paramagnetic susceptibility of semiconductors doped and compensated with hydrogen-like impurities

For the first time, a quantitative model of the Curie–Weiss behavior of a low-temperature paramagnetic susceptibility of electrically neutral donors in n-type diamagnetic covalent semiconductors is proposed. The exchange interaction between nearest two neutral donors was calculated with the use of the Heitler–London model. In this model, we take into account the change in the thermal ionization energy of donors due to the shift of the bottom of the conduction band to the bandgap with doping and compensation. The energy of the exchange spin–spin interaction between electrons localized on donors is calculated as a function of the donor concentration and the degree of their compensation by acceptors. The broadening of the donor band due to the Coulomb interaction of the nearest impurity ions was taken into account. We considered crystals of n-type germanium doped with arsenic up to the concentration close to the insulator–metal phase transition (Mott transition) and compensated with gallium. The compensation ratio K is the ratio of the concentration of compensating acceptors KN to the concentration of doping donors N. The model predicts a change in the sign of the Curie–Weiss temperature from minus to plus (a transition from the antiferromagnetic to ferromagnetic local ordering of electron spins on donors) for K ≈ 0.15–0.3, reaching its maximum positive values of ≈1.3 K for K ≈ 0.5 with the following decrease (a transition to paramagnetism) for K > 0.85. The calculated behavior of the paramagnetic susceptibility of donors is consistent with the experimental data for compensated n-Ge:As,Ga samples close to the Mott transition.

Automated method for offline correction of spectrometry data affected by time instability

A new automated method has been developed with the aim to correct measured spectra for sudden gain and offset drifts due to temporal instrumentation instabilities. It is based on discrete cross-correlation that alleviates the need for Gaussian-shaped peaks and is capable of correcting spectra that change their shape in time. Potential of this method has been tested on decay and in-beam γ-ray spectroscopy data measured with an array of three n-type coaxial High-Purity Germanium detectors albeit its use is not limited only for γ-ray spectroscopy.

Towards the Modeling of Impurity-Related Defects in Irradiated n-Type Germanium: a Challenge to Theory

Electrical measurements on heavily doped n-type germanium subjected to gamma-irradiation show that the features of impurity-related defect formation before n–p conversion of conductivity type are the same as those previously observed in lightly and moderately doped materials, thus extending the range of doping from ≈1014 to ≈1016 cm–3. It is clear now that the presently adopted model of the dominant impurity-related defects as simple vacancy-impurity pairs in irradiated n-Ge, in analogy to such defects reliably identified in irradiated n-Si, appears to be inconsistent with the experimental information collected so far. As a consequence, the impurity diffusion simulations in heavily doped Ge based on this model need to be reconsidered. The requirements to be met while modeling impurity-related defects in irradiated n-Ge in accordance with the reliable experimental data are established.

Atomic Layer Densification of AlN Passivation Layer on Epitaxial Ge for Enhancement of Reliability and Electrical Performance of High-K Gate Stacks

The impact of atomic layer bombardment (ALB) on the aluminum nitride (AlN) passivation layer between the HfO2 gate dielectric and the n-type epitaxial germanium (Ge) was investigated. The ALB technique was performed with the layer-by-layer, in situ helium/argon plasma bombardment in each cycle of atomic layer deposition (ALD) of AlN. An increase in the film density and a decrease in nitrogen vacancies, as manifested by the X-ray reflection and X-ray spectroscopy, were observed in the AlN layer treated by the ALB process. The improvements in the AlN quality contribute to a reduction of the equivalent oxide thickness from 1.36 to 1.19 nm of the AlN/HfO2 gate stack, together with the suppression of the gate leakage current, the interfacial state density, and the slow trap density. The reliability tests reveal promising reliability of the AlN/HfO2 gate stack with a small flat-band voltage shift under the constant voltage stress and a high operation voltage of ∼2.4 V projected for a 10 years time-dependent-dielectric-breakdown lifetime. All of the results point that the ALB technique can effectively enhance the material/interface properties, electrical characteristics, and reliability of nanoscale devices, which is critical and beneficial to the next-generation high-speed and low-power nanoelectronics.

Spin transport in antimony-doped germanium detected using vertical spin-valve structures

Using a vertical spin-valve structure, we observe spin-dependent transport through antimony (Sb)-doped n-type germanium (n-Ge). Epitaxial intermediate Sb-doped Ge layers can be formed between ferromagnetic CoFe and Fe3Si epilayers on Si(111), where the doping concentration of Sb is estimated to be ∼3 × 1019 cm−3. From the measurement of the current perpendicular to the plane magnetoresistance, we can evidently detect the spin-valve signals from low temperatures up to room temperature. The room-temperature spin diffusion length in the Sb-doped Ge layer can roughly be estimated to be 150–290 nm. By comparing this result and the previous ones, we can clarify the influence of the dopant species on the spin transport even at room temperature in Ge.

Optimization of HPGe detector response using fast and reliable method

Safeguards system with high effectiveness and efficiency must comprise a set of measurements with capabilities satisfactory for the verification of nuclear materials. In this paper, we present key parameter measurements of detector modeling in a commercial n-type low energy germanium detector of a planar crystal with a relative efficiency of nearly 15 %. The detector optimization will hold a significant function in measuring nuclear materials for safeguards application. Standard nuclear materials with diverse enrichment (depleted and low enriched) of uranium and point-like sources (137Cs, 60Co) and mixed radioactive source for Eu isotopes (152Eu, 154Eu, and 155Eu) were benefited to explore the energy resolution and detector efficiency. The energy resolution is measured over a wide range of rise time and flattop. In addition to the experimental work, the Monte Carlo simulation code is used for modeling the setup configuration to obtain the absolute efficiency at different energies. A fast and reliable method was applied in detector efficiency measurements. The data are discussed and interpreted.