Donors In Ge Research Articles

Diffusion of Ge Donors in β‐Ga2O3

Diffusion of Ge donors in β‐Ga2O3 is studied using a combination of secondary‐ion mass spectrometry, diffusion simulations, and first‐principles calculations, and compared to previous studies on Sn diffusion. Ge is implanted into (01)‐oriented samples and annealed at temperatures from 900 to 1050 °C for a total of 8 h. From previous first‐principles calculations, Sn is predicted to diffuse via the formation of a mobile complex with VGa that migrates through a sequence of exchange and rotation jumps. Herein, it is similarly predicted that Ge diffusion is mediated by VGa. However, the microscopic mechanism differs, as Ge can diffuse more easily through exchange combined with complex dissociation, rather than rotational jumps. This is explained by the difference in Ga‐site preference of Ge compared to Sn, and the three‐split mechanism that enables low migration barriers for VGa. The dissociation mechanism leads to a considerably faster transport for Ge as compared to Sn. The experimentally obtained Ge diffusion profiles are successfully fitted using a reaction–diffusion model based on the predicted diffusion mechanism, yielding a migration barrier of 2.5 ± 0.2 eV for the complex. The 2.72 eV obtained from first‐principles calculations is in good agreement with this value.

Central-cell corrections for hydrogenic, silicon (Si), selenium (Se), sulfur (S), and germanium (Ge) donor impurities and pressure–temperature effects on the optical properties of the GaAs/GaAlAs multi-layer quantum disk

GaAs/GaAlAs quantum dots can be doped with various impurities to modify their optoelectronic properties. Common impurities used for doping include: Hydrogenic impurity (HI), Silicon (Si), Selenium (Se), Germanium (Ge), and Sulfur (S) are common n-type dopant in GaAs-based materials. This work has investigated the effects of temperature and pressure on the refractive index changes (RICs) and optical absorption coefficients (OACs) in the multi-layer quantum disk, accounting for central cell correction. We have used the finite element method to calculate the eigenvalues and their corresponding wave-functions. These values are utilized in the computation of the OACs and RICs. Our outcomes can be summarized as follows: (i) The applied pressure induces a red-shift of the OACs peaks, and their magnitude is reduced. Similarly, temperature causes a blue-shift of the OACs peaks, and their magnitude is enhanced. (ii) The presence and type of impurity lead to significant changes in both OACs and RICs.

Enhancement of excitonic and defect-related luminescence in neutron transmutation doped β−Ga2O3

Neutron irradiation analysis, inductively coupled plasma mass spectrometry (ICPMS), and cathodoluminescence (CL) spectroscopy are used to investigate the influence of transmuted Ge incorporation on the luminescence properties of $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ single crystals. Calculations based on ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$-neutron interaction reveal temporal variations of both Ge and Zn concentrations as a function of time during and after neutron irradiation. To produce a concentration of $5\ifmmode\times\else\texttimes\fi{}{10}^{18}\phantom{\rule{0.16em}{0ex}}\mathrm{Ge}\phantom{\rule{0.16em}{0ex}}\mathrm{donors}/\mathrm{c}{\mathrm{m}}^{3}$ from the neutron transmutation of Ga, the $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ crystal was irradiated for 27 h, which was accompanied by the incorporation of ${10}^{16}\phantom{\rule{0.16em}{0ex}}\mathrm{Zn}\phantom{\rule{0.16em}{0ex}}\mathrm{acceptors}/\mathrm{c}{\mathrm{m}}^{3}$. These calculated dopant concentrations are confirmed by ICPMS. The $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ crystals exhibit a UV band at 3.40 eV due to self-trapped holes (STHs) and two blue donor-acceptor pair (DAP) peaks at 3.14 eV (BL1) and 2.92 eV (BL2). In addition to the neutron-induced incorporation of substitutional Ge donors and Zn acceptors on Ga sites, Ga vacancies (${V}_{\mathrm{Ga}}$) were created by high-energy neutrons in the flux, which strongly enhanced the BL1 peak. The ${V}_{\mathrm{Ga}}$ acceptors compensate the neutron-induced Ge donors, making the ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ crystal highly resistive. Concurrent temperature-resolved CL measurements of the $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ before and after neutron irradiation reveal a twofold increase in both the STH and BL1 peaks. This result suggests that STHs are preferentially localized at an O site adjacent to ${V}_{\mathrm{Ga}}$, as theoretically predicted by Kananen et al. [Appl. Phys. Lett. 110, 202104 (2017).]. Analysis of the ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ CL temperature dependence reveals that the UV and BL1 bands after the neutron irradiation exhibit an equivalent activation energy of $100\ifmmode\pm\else\textpm\fi{}10\phantom{\rule{0.16em}{0ex}}\mathrm{meV}$ due to the presence of a neutron-induced defect that acts as an efficient competitive nonradiative recombination channel. The results also provide evidence that the BL1 and BL2 bands arise from different DAP pairs.

Activation of implanted Si, Ge, and Sn donors in high-resistivity halide vapor phase epitaxial β-Ga2O3:N with high mobility

Activation of implanted donors into a highly-resistive, nitrogen-doped homoepitaxial β-Ga2O3 has been investigated. Nitrogen acceptors with the concentration of ∼1017 cm−3 were incorporated during epitaxial growth yielding low-doped (net donor concentration <1014 cm−3) films subsequently implanted with Si, Ge, and Sn. Upon Ohmic contact formation to the implanted regions, sheet resistance values of 314, 926, and 1676 Ω/sq were measured at room temperature for the Si-, Ge-, and Sn-implanted samples, respectively. Room temperature Hall measurements resulted in sheet carrier concentrations and Hall mobilities of 2.13 × 1014 /93, 8.58 × 1013/78, and 5.87 × 1013/63 cm2/(V s), respectively, for these three donor species. Secondary ion mass spectroscopy showed a volumetric dopant concentration of approximately 2 × 1019 cm−3 for the three species, resulting in carrier activation efficiencies of 64.7%, 40.3%, and 28.2% for Si, Ge, and Sn, respectively. Temperature-dependent Hall effect measurements ranging from 15 to 300 K showed a nearly constant carrier concentration in the Si-implanted sample, suggesting the formation of an impurity band indicative of degenerate doping. With a bulk carrier concentration of 1.3 × 1019 cm−3 for the Si implanted sample, a room temperature mobility of 93 cm2/(V s) is among the highest reported in Ga2O3 with a similar carrier concentration. The unimplanted Ga2O3:N regions remained highly resistive after the surrounding areas received implant and activation anneal. These results open the pathway for fabricating Ga2O3 devices through the selective n-type doping in highly resistive epitaxial Ga2O3.

(Digital Presentation) Ge-on-insulator Platform for Mid-infrared Photonic Integrated Circuits

Since mid-infrared (MIR) wavelengths have a great potential for optical communication, sensing, and quantum information, Si-based MIR photonic integrated circuits (PICs) have been developed by leveraging Si photonics technology for near-infrared wavelengths. However, the transparency wavelength window of Si is from 1.2 µm to 8 µm, limiting the available wavelengths in the MIR spectrum. Ge is emerging as a waveguide material to overcome this difficulty because Ge is transparent in the entire MIR spectrum. A Ge-on-Si waveguide is one of the promising platform for a MIR PICs. We have also proposed a Ge-on-insulator (GeOI) platform for MIR integrated photonics [1]. The strong optical confinement in a GeOI waveguide enables an ultracompact MIR PIC. Using wafer bonding and smart-cut, a GeOI wafer was successfully fabricated [2]. As a result, we have demonstrated various Ge passive devices, thermo-optic phase shifters, and modulators on a GeOI platform [3][4].The propagation loss of a GeOI waveguide is one of the issues. The crystal defects induced by hydrogen implantation for smart-cut generates holes in a Ge film. As a result, evening using an n-type Ge donor wafer for smart-cut, a final Ge layer tends to be p-type. Since free-hole absorption in Ge is significant, the propagation loss of a p-type GeOI becomes large. To suppress hole generation, the optimization of the hydrogen implantation conditions was conducted. We found that the higher the implantation energy was, the deeper the center of the defect position was from a Ge surface [5]. When the implantation energy increases from 80 keV to 160 keV, the defects can be removed from a 300-nm-thick Ge device layer, enabling an n-type GeOI wafer. As a result, a low-loss GeOI waveguide with a propagation loss of 2.3 dB/cm was demonstrated.The monolithic integration of Ge passive waveguides and photodetectors (PDs) is also essential for a MIR PIC. We examined the defect-assist photodetection mechanism in a GeOI waveguide with a lateral PIN junction. When a reverse voltage was applied to the PIN junction, the substantial photocurrent was observed at a wavelength of 2 µm for which Ge is transparent. The defect-assist photodetection is expected to be enhanced due to the large intrinsic carrier density in Ge. As a result, the responsivity of 0.25 A/W was obtained at -5 V.In conclusion, we have developed a GeOI photonics platform for MIR wavelengths. We have achieved a low-loss Ge waveguide, PDs, and optical modulators, the indispensable building blocks for large-scale MIR PICs. The functionality of a GeOI platform can be extended with emerging materials including graphene and phase change materials.This work was partly based on the results from the project JPNP13004, commissioned by the New Energy and Industrial Technology Development Organization (NEDO) and supported by JST-Mirai Program Grant Number JPMJMI20A1, JSPS KAKENHI Grant Number JP20H02198, and the Canon Foundation.Reference[1] Z. Zhao, C.-M. Lim, C. Ho, K. Sumita, Y. Miyatake, K. Toprasertpong, S. Takagi, and M. Takenaka, “Low-loss Ge waveguide at the 2-µm band on an n-type Ge-on-insulator wafer,” Opt. Mater. Express, vol. 11, no. 12, pp. 4097–4106, 2021.[2] J. Kang, X. Yu, M. Takenaka and S. Takagi, “Impact of thermal annealing on Ge-on-Insulator substrate fabricated by wafer bonding,” Materials Science in Semiconductor Processing, vol. 42, Part 2, pp. 259-263, 2016.[3] M. Takenaka et al., “Heterogeneous CMOS Photonics Based on SiGe/Ge and III–V Semiconductors Integrated on Si Platform,” IEEE J. Sel. Top. Quantum Electron., vol. 23, no. 3, pp. 64–76, May 2017.[4] T. Fujigaki, S. Takagi, and M. Takenaka, “High-efficiency Ge thermo-optic phase shifter on Ge-on-insulator platform,” Opt. Express, vol. 27, no. 5, p. 6451, Mar. 2019.[5] Z. Zhao et al., “Low-loss Ge waveguide at the 2-µm band on an n-type Ge-on-insulator wafer,” Opt. Mater. Express, OME, vol. 11, no. 12, pp. 4097–4106, Dec. 2021.[6] Z. Zhao, C.-P. Ho, K. Toprasertpong, S. Takagi, and M. Takenaka, “Monolithic Germanium PIN Waveguide Photodetector Operating at 2 μm Wavelengths,” Optical Fiber Communication Conference (OFC2020), W4G.3, San Diego, 8–12 March 2020.

Towards n-type conductivity in hexagonal boron nitride

Asymmetric transport characteristic in n- and p-type conductivity has long been a fundamental difficulty in wide bandgap semiconductors. Hexagonal boron nitride (h-BN) can achieve p-type conduction, however, the n-type conductivity still remains unavailable. Here, we demonstrate a concept of orbital split induced level engineering through sacrificial impurity coupling and the realization of efficient n-type transport in 2D h-BN monolayer. We find that the O 2pz orbital has both symmetry and energy matching to the Ge 4pz orbital, which promises a strong coupling. The introduction of side-by-side O to Ge donor can effectively push up the donor level by the formation of another sacrificial deep level. We discover that a Ge-O2 trimer brings the extremely shallow donor level and very low ionization energy. By low-pressure chemical vapor deposition method, we obtain the in-situ Ge-O doping in h-BN monolayer and successfully achieve both through-plane (~100 nA) and in-plane (~20 nA) n-type conduction. We fabricate a vertically-stacked n-hBN/p-GaN heterojunction and show distinct rectification characteristics. The sacrificial impurity coupling method provides a highly viable route to overcome the n-type limitation of h-BN and paves the way for the future 2D optoelectronic devices.

Low-resistivity vertical current transport across AlInN/GaN interfaces

Effects of n-type doping of Al0.82In0.18N/GaN heterostructures on the conduction band (CB) profile have been investigated. Doping concentrations well above 1019 cm−3 are required to reduce the large barriers in the CB. Experimentally, Si- and Ge donor species are compared for n-type doping during metalorganic vapor phase epitaxy. For Si doping, we find substantial interface resistivity that will strongly contribute to total device resistivity. Doping of AlInN is limited by either the onset of a self-compensation mechanism (Si) or structural degradation of the AlInN (Ge). Only by Ge doping, purely ohmic behavior of periodic AlInN/GaN layer stacks could be realized.

Manufacturing of Optimized Ge Substrates Using a Covalent Bonding Process

Germanium is an interesting material for applications ranging from nanoelectronics to solar cells, near infrared detectors, gamma spectroscopy detectors or optical components [1]. Previous studies demonstrated the interest of thick germanium-on-insulator (GeOI) substrates for the manufacturing of advanced photonics devices [2].Two methods are commonly used to manufacture GeOI substrates for photonic applications. First, a rather thick, slightly tensily strained Germanium layer can be grown on top of a 200mm Si(001) wafer and the top part transferred, thanks to the Smart CutTM approach, onto oxidized Si. The threading dislocation density in that Ge layer will be of the order of a few 106 cm-2, then, which could be a drawback for future applications. To manufacture GeOI with, on top, a higher quality Ge film, another approach is to start from bulk Ge, which has a much better crystalline quality [3, 4]. The drawback of this approach is that the thin Ge film on top of the GeOI substrate does not have any internal strain, then. In order to fabricate high quality strained GeOI substrates, in the end, one could start from Ge films coming from bulk Ge donors and strain while bonding them on top of 200mm Si(001) substrates.Covalent bonding is an interesting candidate in order to obtain high quality Ge films on Si while managing, at the same time, the internal stress. Indeed, stress can be tailored with the proper temperature control during the bonding process itself. The EVG®Combond® equipment used in this study enables to bond at “high” temperature Si/Ge heterostructures with a very high bond strength. In this paper, the bonding process performed will be described and characterized.A bonding at temperatures higher than Room Temperature is adopted to generate tensily strained Ge films. The choice of the right temperature depends on two criteria, however: (i) have the highest stress possible in the future Ge film and (ii) allow the Si/Ge heterostructure with thick substrates to withstand the stress without breaking at room temperature just after bonding. Point (i) requires high temperatures, while low temperatures are better for point (ii); a tradeoff will thus have to be identified. Simulations were performed in order to evaluate the bow of the structure after bonding and will be presented in the paper.Si/Ge heterostructures were fabricated at 100°C. A very high bond strength (> 5 j/m2) was measured using the classical double cantilever beam (DCB) technique on an equivalent Si/Ge/Si structure. Indeed, the bow with a Si/Ge heterostructure was too important to allow a correct bond strength measurement. Thus, an epitaxy of a few µm of Ge was performed on top of a Si wafer and the Si/Ge stack bonded to another Si wafer with the same covalent bonding process prior to measurements of the bonding interface strength. Bow in temperature of the Si/Ge heterostructure was also measured. A heating ramp and then a cool down phase were applied to the bonded pair in an atmospheric pressure chamber with a curvature radius measurement done with a laser beam. The bonded pair reached an equilibrium point with a bow of 0 µm for a temperature close to 100°C, in line with the bonding temperature adopted (figure 1).Using this newly qualified bonding process, a strained Ge film was transferred onto an Si wafer. The process flow will be described in the paper, as well as the characterization of the thin Ge film transferred at the end of the process. The quality of the Ge film will be characterized using a SP2 equipment in haze mode. Transmission Electron Microscopy will be performed to observe the amorphous zones at the bonding interface, and Focused-Ion-Beam Scanning Electron Microscopy will yield the thickness of the Ge film transferred. Figure 1: Bow measurement in temperature of a Si/Ge heterostructure, bonded using a covalent bonding process at 100°C [1] R. King et al., ‘Pathways to 40% efficient concentrator photovoltaics’. 20th European Photovoltaic Solar Energy Conf., Barcelona, Spain, 2005, p. 118[2] V. Reboud et al., “Structural and optical properties of 200 mm germanium-on- insulator (GeOI) substrates for silicon photonics applications,” Proc. SPIE 936714, 1–6 (2015). [3] F. Letertre et al., ‘Germanium-on-insulator (GEOI) structure realised by the Smart CutTM technology’, Mater. Res. Soc. Proc., 2004, 809, (B4.4), p. 153[4] C. Deguet et al., ‘200 mm germanium-on-insulator (GEOI) structures realized from epitaxial wafers using the smart cut technology’, Electrochem. Soc. Proc., 2005, 2005-06, p. 78 Figure 1

LACK OF HUMAN THROMBOMODULIN GENE EXPRESSION IN LIFE SUPPORTING PIG-TO-BABOON CARDIAC XENOTRANSPLANTATION MODELS ACCELERATE ANTIBODY MEDIATED REJECTION

Introduction: Transplantation of organs from animals to humans (xenotransplantation) has been proposed to address the critical shortage of organs for transplantation. The use of genetically engineered organ xenografts, including knock-out (KO) of alpha 1-3 galactosyltransferase (GTKO) along with insertion of a human complement regulator genes (hCD46-human CD46, hDAF-human decay accelerating factor) and other cell surface carbohydrate KOs, has been helpful in circumventing acute and subacute rejection. However, thrombotic complications still remain. Xenografts with additional human transgenes, including human thrombomodulin (hTBM), have been generated to address this barrier. Here, we studied the importance of hTBM in preventing microvascular and intramural thrombosis and rejection by comparing two transplanted groups utilizing GE donors with or without hTBM. Methods: Specific pathogen-free baboons of either sex weighing 15-30 kg (2-3 years of age) were used as recipients. 6 to 8-week-old genetically modified pigs with hTBM (GTKO.hCD46.hTBM) or without hTBM (triple knock out-GTKO.B4KO.CMAHKO, with or without hCD46 and hDAF) were used as donors. Expression of transgenes were consistent and high level across all pigs. All animals were used in compliance with guidelines provided by the Institutional Animal Care and Use Committee (IACUC). Results: GTKO.hCD46.hTBM donors (n=4) were found to have no intracardiac thrombus with survival up to 30 days post-transplant, but one with ongoing survival at the time of this abstract submission. However, non-hTBM donors (n=2) had an average survival of 7 days and were found to have a large intracardiac thrombus burden with propagation into major vascular structures such as the aorta, pulmonary artery and coronary sinus. Gross examination of thrombi indicated acute and subacute components, suggesting early formation of the thrombus postoperatively. Additionally, early clinical signs of thrombus formation included profound hypocalcemia requiring continuous calcium infusions in the first 48-72 hours postoperatively. These phenomena were not prevented by continuous heparin infusion. Histologic myocardial examination revealed microscopic and macroscopic thrombotic phenomena, likely related to accelerated antibody mediated rejection in non-hTBM containing grafts. Conclusion: Non-hTBM containing xenografts exhibited accelerated antibody mediated rejection. While immunologic rejection has been circumvented with novel immunosuppression regimens and GTKO, it is likely that hTBM or other transgenes involved in regulation of coagulation, may be needed for prevention of thrombotic complications and accelerated antibody mediated rejection.

Human Thrombomodulin Transgene Expression Prevents Intracardiac Thrombus in Life Supporting Pig-to-Baboon Cardiac Xenotransplantation

Transplantation of organs from animals to humans (xenotransplantation) has been proposed to address the critical shortage of organs for transplantation. The use of genetically engineered organ xenografts, including knock-out (KO) of alpha 1-3 galactosyltransferase (GTKO) along with insertion of a human complement regulator genes (hCD46, hDAF) and other cell surface carbohydrate KOs, has been helpful in circumventing acute and subacute rejection. However, thrombotic complications still remain. Xenografts with additional human transgenes, including hTBM, have been generated to address this barrier. Here, we studied the importance of hTBM in preventing coagulation by comparing two transplanted groups utilizing GE donors with or without hTBM. Specific pathogen-free baboons of either sex weighing 15-30 kg (2-3 years of age) were used as recipients. 6 to 8-week-old genetically modified pigs with hTBM (GTKO.hCD46.hTBM) or without hTBM (triple knock out-GTKO.B4KO.CMAHKO, with or without hCD46 and hDAF) were used as donors, provided by Revivicor. Expression of transgenes were consistent and high level across all pigs. All animals were used in compliance with guidelines provided by the Institutional Animal Care and Use Committee (IACUC). GTKO.hCD46.hTBM donors (n=3) were found to have no intracardiac thrombus with survival up to 30 days post-transplant. However, all non-hTBM donors (n=3) were found to have a large intracardiac thrombus burden with propagation into major vascular structures such as the aorta, pulmonary artery and coronary sinus. Gross examination of thrombi indicated acute and subacute components, suggesting early formation of the thrombus postoperatively. Additionally, early clinical signs of thrombus formation included profound hypocalcemia requiring continuous calcium infusions in the first 48-72 hours postoperatively. These phenomena were not prevented by continuous heparin infusion. Histologic examination revealed no signs of rejection. hTBM prevents intracardiac thrombus in this model. While immunologic rejection has been circumvented with novel immunosuppression regimens and GTKO, it is likely that hTBM or other transgenes involved in regulation of coagulation may be needed for prevention of thrombotic complications.

Molecular Beam Epitaxy Growth and Characterization of Germanium‐Doped Cubic AlxGa1−xN

In cubic (c‐)GaN Ge has emerged as a promising alternative to Si for n‐type doping, offering the advantage of slightly improved electrical properties. Herein, a study on Ge doping of the ternary alloy c‐AlxGa1−xN is presented. Ge‐doped c‐AlxGa1−xN layers are grown by plasma‐assisted molecular beam epitaxy. In two sample series, both the Al mole fraction x and the doping level are varied. The incorporation of Ge is verified by time‐of‐flight secondary ion mass spectrometry. Ge incorporation and donor concentrations rise exponentially with increasing Ge cell temperature. A maximum donor concentration of 1.4 × 1020 cm−3 is achieved. While the incorporation of Ge is almost independent of x, incorporation of O, which acts as an unintentional donor, increases for higher x. Dislocation densities start increasing when doping levels of around 3 × 1019 cm−3 are exceeded. Also photoluminescence intensities begin to drop at these high doping levels. Optical emission of layers with x > 0.25 is found to originate from a defect level 0.9 eV below the indirect bandgap, which is not related to Ge. In the investigated range 0 ≤ x ≤ 0.6, Ge is a suitable donor in c‐AlxGa1−xN up to the low 1019 cm−3 range.

Quantitative Assessment of Tetrel Bonding Utilizing Vibrational Spectroscopy.

A set of 35 representative neutral and charged tetrel complexes was investigated with the objective of finding the factors that influence the strength of tetrel bonding involving single bonded C, Si, and Ge donors and double bonded C or Si donors. For the first time, we introduced an intrinsic bond strength measure for tetrel bonding, derived from calculated vibrational spectroscopy data obtained at the CCSD(T)/aug-cc-pVTZ level of theory and used this measure to rationalize and order the tetrel bonds. Our study revealed that the strength of tetrel bonds is affected by several factors, such as the magnitude of the σ-hole in the tetrel atom, the negative electrostatic potential at the lone pair of the tetrel-acceptor, the positive charge at the peripheral hydrogen of the tetrel-donor, the exchange-repulsion between the lone pair orbitals of the peripheral atoms of the tetrel-donor and the heteroatom of the tetrel-acceptor, and the stabilization brought about by electron delocalization. Thus, focusing on just one or two of these factors, in particular, the σ-hole description can only lead to an incomplete picture. Tetrel bonding covers a range of −1.4 to −26 kcal/mol, which can be strengthened by substituting the peripheral ligands with electron-withdrawing substituents and by positively charged tetrel-donors or negatively charged tetrel-acceptors.

Germanium Template Assisted Integration of Gallium Arsenide Nanocrystals on Silicon: A Versatile Platform for Modern Optoelectronic Materials

AbstractMetal organic vapor phase epitaxy is used to grow gallium arsenide (GaAs) nanocrystals (NCs) on germanium (Ge) templates on nanoscopic silicon (Si) threads prepared by reactive ion etching. Scanning transmission electron microscopy with energy dispersive X‐ray measurements shows an epitaxial growth of the GaAs on the Ge template that is supported by the Si thread, and that Ge doping is induced to the GaAs by the template. On Ge templates of about 60 nm diameter, as‐grown GaAs NCs show a very regular rhombic‐dodecahedral outer shape that can be explained by a preferential growth along the <110> plane. Photoluminescence measurements of the Ge/GaAs structures reveal radiative emission peaks on top of the GaAs band‐to‐band emission and at sub‐band gap energies. While high energy peaks are originating from Ge acceptor levels in GaAs, sub‐band gap peaks can be explained by radiation from Ge donor and acceptor bands that are amplified by photonic modes hosted in the rhombic‐dodecahedral GaAs NCs. This study shows that a template‐assisted crystal growth at the nanoscale opens up routes for a versatile integration of strongly emitting nanomaterials for a use in on‐chip solid state lighting and photonics.

Divacancy-tin related defects in irradiated germanium

A new absorption spectrum has been detected in the region of 770–805 cm−1 following the annealing of low temperature irradiated Sn-doped Ge. The spectrum develops simultaneously with the disappearance of the V2-related absorption band. The new spectra arise both in p- (doping with gallium) and n- (doping with antimony) type samples and are completely identical to the absorption spectrum of the corresponding dopants. The studies have shown that the defects responsible for the registered spectra have hydrogen-like excited states similar to those observed for hydrogen-like group-III acceptors and group-V donors in Ge. The defects are identified as SnV2Ga and SnV2Sb. The formation of the revealed complexes consists of two stages. During the first stage, the defects are created as a result of the direct interaction of SnV2 diffusing upon the annealing with atoms Ga or Sb. The second stage arises, apparently, due to the participation of SnV2 in the formation of intermediate defects that are optically inactive and transform into the revealed defects at annealing temperatures Tann. > 243 K.

Fabrication of Ge-on-insulator wafers by Smart-CutTM with thermal management for undamaged donor Ge wafers

Newly engineered substrates consisting of semiconductor-on-insulator are gaining much attention as starting materials for the subsequent transfer of semiconductor nanomembranes via selective etching of the insulating layer. Germanium-on-insulator (GeOI) substrates are critically important because of the versatile applications of Ge nanomembranes (Ge NMs) toward electronic and optoelectronic devices. Among various fabrication techniques, the Smart-CutTM technique is more attractive than other methods because a high temperature annealing process can be avoided. Another advantage of Smart-CutTM is the reusability of the donor Ge wafer. However, it is very difficult to realize an undamaged Ge wafer because there exists a large mismatch in the coefficient of thermal expansion among the layers. Although an undamaged donor Ge wafer is a prerequisite for its reuse, research related to this issue has not yet been reported. Here we report the fabrication of 4-inch GeOI substrates using the direct wafer bonding and Smart-CutTM process with a low thermal budget. In addition, a thermo-mechanical simulation of GeOI was performed by COMSOL to analyze induced thermal stress in each layer of GeOI. Crack-free donor Ge wafers were obtained by annealing at 250 °C for 10 h. Raman spectroscopy and x-ray diffraction (XRD) indicated similarly favorable crystalline quality of the Ge layer in GeOI compared to that of bulk Ge. In addition, Ge p-n diodes using transferred Ge NM indicate a clear rectifying behavior with an on and off current ratio of 500 at ±1 V. This demonstration offers great promise for high performance transferrable Ge NM-based device applications.

Quantum gates with donors in germanium

Recent work has shown that electron spins in germanium (Ge) nanoscale transistors can be electrically tuned and have encouraging coherence times. Based on a complete and validated theory of Ge-donor electron states, we propose that Ge spin qubits could have significant advantages over silicon (Si) in the implementation of a donor-based quantum processor architecture. Our work shows that the intrinsic features of the Ge band structure allow for a speedup of selective (local) one-qubit gates of up to two orders of magnitude as compared to Si. Further, we find that fast, robust two-qubit gates in Ge pose less stringent fabrication constraints than in Si devices: Ge donors spaced three times farther apart than in Si show comparable exchange couplings, allowing more space for readout and control gates. In addition, for realistic position uncertainty in donor placement, Ge:P spin couplings have a $33%$ chance of being within an order of magnitude of the largest coupling, compared with only $10%$ in Si:P. It is therefore possible that a Ge-based platform would enable fast, parallel, and robust architectures for quantum computing.

Donors in Ge as qubits —Establishing physical attributes

Quantum electronic devices at the single-impurity level demand the understanding of the physical attributes of dopants with an unprecedented accuracy. Germanium-based technologies have been developed recently, creating the necessity to adapt the latest theoretical tools to the unique electronic structure of this material. We investigate basic properties of donors in Ge which are not known experimentally, but are indispensable for qubit implementations. Our approach provides a description of the wave function at multiscale, associating microscopic information from density functional theory and envelope functions from state-of-the-art multivalley effective mass calculations, including a central-cell correction designed to reproduce the energetics of all group-V donor species (P, As, Sb and Bi). With this formalism, we predict the binding energies of negatively ionized donors ( state). Furthermore, we investigate the signatures of buried donors to be expected from scanning tunneling microscopy (STM). The naive assumption that attributes of donor electrons in other semiconductors may be extrapolated to Ge is shown to fail, similarly to earlier attempts to recreate in Si qubits designed for GaAs. Our results suggest that the mature techniques available for qubit realizations may be adapted to germanium to some extent, but the peculiarities of the Ge band structure will demand new ideas for fabrication and control.

Positron annihilation spectroscopy of vacancy-related defects in CdTe:Cl and CdZnTe:Ge at different stoichiometry deviations.

Positron annihilation spectroscopy (PAS) was used to examine the effect of defined Cd-rich and Te-rich annealing on point defects in Cl-doped CdTe and Ge-doped CdZnTe semi-insulating single crystals. The as-grown crystals contain open-volume defects connected with Cd vacancies . It was found that the Cd vacancies agglomerate into clusters coupled with Cl in CdTe:Cl, and in CdZnTe:Ge they are coupled with Ge donors. While annealing in Cd pressure reduces of the density, subsequent annealing in Te pressure restores . The CdTe:Cl contains negatively-charged shallow traps interpreted as Rydberg states of A-centres and representing the major positron trapping sites at low temperature. Positrons confined in the shallow traps exhibit lifetime, which is shorter than the CdTe bulk lifetime. Interpretation of the PAS data was successfully combined with electrical resistivity, Hall effect measurements and chemical analysis, and allowed us to determine the principal point defect densities.

Synthesis and unexpected reactivity of germyliumylidene hydride [:GeH]+ stabilized by a bis(N-heterocyclic carbene)borate ligand.

Employing the potassium salt of the monoanionic bis(NHC)borate 1 (NHC = N-Heterocyclic Carbene) enables the synthesis and isolation of the bis(NHC)borate-stabilized chlorogermyliumylidene precursor 2 in 61% yield. A Cl/H exchange reaction of 2 using potassium trisec.-butylborhydride as a hydride source leads to the isolation of the first germyliumylidene hydride [HGe:(+)] complex 3 in 91% yield. The Ge(II)-H bond in the latter compound has an unexpected reactivity as shown by the reaction with the potential hydride scavenger [Ph3C](+)[B(C6F5)4](-), furnishing the corresponding HGe: → CPh3 cation in the ion pair 4 as initial product. Compound 4 liberates HCPh3 in the presence of 3 to give the unusual dinuclear HGe: → Ge: cation in 5. The latter represents the first three-coordinate dicationic Ge(II) species stabilized by an anionic bis(NHC) chelate ligand and a Ge(II) donor. All novel compounds were fully characterized, including X-ray diffraction analyses.

Ultrathin-body Ge-on-insulator wafers fabricated with strongly bonded thin Al2O3/SiO2 hybrid buried oxide layers

An ultrathin-body Ge-on-insulator (GeOI) wafer having a bonded thin Al2O3/SiO2 hybrid buried oxide layer was fabricated using an epitaxially grown Ge film on Si as a Ge donor layer. The epitaxial Ge film was confirmed to have a negligibly low density of crystal-defect-induced p-type carriers and was successfully transferred to form the GeOI wafer. Strong Al2O3/SiO2 bonding effectively suppressed Ge exfoliation during the wafering process. The obtained device-grade GeOI layer and strong bonding strength between Al2O3 and SiO2 are potentially advantageous for future Si-based complementary metal–insulator–semiconductor (CMIS) fabrication processes utilizing large-diameter Si wafers.