Germanium Incorporation Research Articles

Enhanced Photodetection and Air Stability of Lead‐Free Tin Perovskite Photodiodes via Germanium Incorporation and Organic Cation‐Mediated Dimensionality Control

AbstractThis work presents the advancement of lead‐free tin perovskite photodiodes in terms of their photodetection and air stability by incorporating germanium (Ge) and ethylenediamine (EDA) to formamidinium tin iodide (FASnI3). EDA0.01FA0.98SnI3:Ge‐based photodiodes demonstrate a significantly improved specific detectivity (1.6 × 1012 Jones at −0.1 V), cut‐off frequency (6.6 × 105 Hz), response speed (0.53 µs), and signal‐to‐noise ratio (45 dB) compared with control devices. The superior performance is attributed to the stronger Ge─I bond, the passivation of Sn2+ and I– vacancies by smaller Ge2+ ions, the promotion of a fully 3D perovskite structure, the elevation of the conduction band energy level, and the formation of a protective GeO layer. Various film analyses, including X‐ray photoelectron spectroscopy, UV photoelectron spectroscopy, density functional theory, as well as device testing using time‐of‐flight secondary ion mass spectrometry and voltage‐dependent admittance, support and explain the mechanisms behind the enhancements. Ge‐ and EDA‐incorporated photodiodes exhibit excellent air stability, as evidenced by the time‐dependent ultraviolet visible spectra and the considerably high certified power conversion efficiency without encapsulation in air, demonstrating their potential for practical applications. The obtained photodetection performance is highest among the published lead‐free tin‐based perovskite photodetectors, presenting a monumental progress from the previous report of the same group.

Analog and linearity performance analysis of ferroelectric vertical tunnel field effect transistor with and without source pocket

AbstractThis study examines the electrical performance characteristics of a ferroelectric vertical tunnel field‐effect transistor (TFET) with and without a source pocket (Si0.5Ge0.5). The incorporation of Germanium in the source of the TFET aims to enhance the on‐current. The Silvaco TCAD simulation tool is utilized to simulate the proposed structure. To improve device performance, a ferroelectric layer with a vertical length is employed in the gate of the TFET. When the ferroelectric layer partially controls the channel region, device characteristics, such as on‐current and subthreshold swing (SS) can be improved (i.e., ION = 15.21 × 10−5 A/μm, ION/IOFF = 5.03 × 109, and a minimum SS of 20.87 mV/decade at 300 K). This article studied a comparison between ferroelectric vertical TFETs and nonferroelectric vertical TFETs, as well as ferroelectric vertical TFETs with and without source pockets. The comparison is done on the basis of DC and RF parameters. Analysis of this comparison represents that ferroelectric vertical TFET with source pocket has improved characteristics.

Investigating solid solutions: Geometric transformations triggered by germanium incorporation in Cu2ZnGexSn1−xS4

Through experimental exploration, diverse phases—tetragonal and orthorhombic—have been observed within the Cu2ZnGexSn1−xS4 region (0 ≤ x ≤ 1), hinting at potential miscibility gaps. To complement these findings, our computational investigation, employing density functional theory (DFT), delves into the Ge substitution-induced phase transition in Cu2ZnGexSn1−xS4. Contrary to a single-phase behavior, our FP-LAPW at zero temperature results reveal a compelling shift from stannite (Sn-rich) to Wurtzite-Stannite (Ge-rich) at xGe ≈ 80%. Negative enthalpy of formation values indicates the inherent stability of these structures. The calculations reveal an estimated 8.884 meV per atom difference in enthalpies of formation between the Stannite and Wurtzite-Stannite phases for Cu2ZnSnS4. For Cu2ZnGeS4, the Wurtzite-Stannite structure emerges as the most stable, closely trailed by the Stannite structure, with enthalpies of formation at − 4.833 eV·atom−1 and − 4.804 eV·atom−1, respectively. Furthermore, our quasi-harmonic Debye model facilitates the analysis of phase transitions triggered by the introduction of germanium. This is achieved by calculating the Gibbs energy, which remains unaffected by variations in temperature and pressure. As the tin cation is replaced by the smaller germanium cation, there is an observable decrease in the cell parameters. The corresponding reduction in cell volume adheres to the principles of Vegard's Law. Exploring the behavior of these materials in diverse conditions can significantly contribute to enhancing the performance and stability of devices built upon Cu2ZnGexSn1−xS4.

Effect of Ge doping on the material properties of sprayed Cu2SnS3 thin films

A facile spray pyrolysis processing of ternary Cu2SnS3 and Cu2Sn1−xGexS3 absorbers is presented. The Cu2SnS3 and Cu2Sn1−xGexS3 thin films were sprayed onto both glass and Mo substrates at 350 °C and then annealed at 550 °C with S and SnS/GeS crystals. The impacts of germanium incorporation on the properties and solar cell device performance of the Cu2SnS3 layers were studied. X-ray diffraction and Raman measurements confirmed the monoclinic crystal structure of both Cu2SnS3 and Cu2Sn1−xGexS3 layers, with a slight peak shift observed in the Cu2Sn1−xGexS3 samples due to the substitutional incorporation of Ge into the Sn site in the Cu2SnS3 lattice. The introduction of Ge also increased the optical bandgap from 0.93 eV for Cu2SnS3 to 0.99 eV for Cu2Sn1−xGexS3 samples. Furthermore, Cu2Sn1−xGexS3 layers exhibited enhanced grain growth, leading to an improved device performance from 1% for Cu2SnS3 to 2.1% for Cu2Sn1−xGexS3 solar cells.

Realizing Both Antibacterial Activity and Cytocompatibility in Silicocarnotite Bioceramic via Germanium Incorporation.

The treatment of infective or potentially infectious bone defects is a critical problem in the orthopedic clinic. Since bacterial activity and cytocompatibility are always contrary factors, it is hard to have them both in one material. The development of bioactive materials with a good bacterial character and without sacrificing biocompatibility and osteogenic activity, is an interesting and valuable research topic. In the present work, the antimicrobial characteristic of germanium, GeO2 was used to enhance the antibacterial properties of silicocarnotite (Ca5(PO4)2SiO4, CPS). In addition, its cytocompatibility was also investigated. The results demonstrated that Ge-CPS can effectively inhibit the proliferation of both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), and it showed no cytotoxicity to rat bone marrow-derived mesenchymal stem cells (rBMSCs). In addition, as the bioceramic degraded, a sustainable release of germanium could be achieved, ensuring long-term antibacterial activity. The results indicated that Ge-CPS has excellent antibacterial activity compared with pure CPS, while no obvious cytotoxicity was observed, which could make it a promising candidate for the bone repair of infected bone defects.

Incorporation of germanium into amines via deoxygenative germylation of aromatic amides with hydrogermanes

The development of novel strategies for the efficient incorporation of germanium into widespread molecular structures, especially for the synthesis of potentially bioactive molecules, is of interest to researchers. In this context, carbene-mediated insertion reactions of Ge−H bonds are appealing strategies for the construction of C−Ge bonds. However, the utilization of α-aminocarbene intermediates generated from readily available precursors in Ge–H bond insertion remains a longstanding challenge, although it would be a straightforward method for the synthesis of biologically important α-germylamines. Herein, we present a practical and general protocol for the synthesis of α-germylamines via Mg/SmI 2 -mediated deoxygenative cross-coupling of amides with hydrogermanes. The process is proposed to proceed via reductive deoxygenation of amides to an α-aminocarbene intermediate, which can undergo a Ge–H bond insertion process. This method allows for the incorporation of germanium structures into several drug-molecule-derived amides, offering a promising approach to altering their pharmacological profiles. • Insertion of germanium is achieved with an α-aminocarbene intermediate • Synthesis of α-germyl amines under mild conditions is shown • Deoxygenative functionalization of inert amides is facilitated via the α-aminocarbene The development of novel strategies for the incorporation of germanium into bioactive molecules is of great significance. Here, Wang et al. develop a deoxygenative cross-coupling of amides with germanes via α-aminocarbene intermediates, leading to a suite of functionally and structurally diverse α-germyl amines.

Substitutional Carbon Incorporation in SiGeC/Si Heterostructures: Influence of Silicon Precursors

The incorporation of germanium and carbon by RP-CVD epitaxy in silicon brings lots of interest in silicon devices thanks to the variety of properties that can be addressed: band gap or lattice parameter engineering, dopant diffusion reduction, chemical properties, optical properties...For all the applications requiring SiGeC materials, carbon atoms must be incorporated in fully substitutional site (Cs) despite its low bulk solubility into the Si and SiGe lattice (3x1017 at.cm-3 at the Si melting point). Beyond a total carbon concentration (depending on process parameter), carbon atoms are also incorporated into interstitial sites (Ci). These Ci atoms usually form extended defects such as clusters or SiC precipitates which are harmful for devices performances.Solubility limits of carbon can be extended into the metastable domain by optimizing the epitaxy process. Indeed, it is well established that low temperature and high growth rate are favorable to obtain high Cs atoms incorporation [1].This work compares silane (SiH4) and disilane (Si2H6) precursors coupled with germane (GeH4) and methylsilane (SiH3CH3 or MS) to process low temperature thin film of SiGeC with the highest amount of Cs without Ci.First, the SiGe growth kinetics using silane and disilane have been studied. The temperature range investigated varied from 500 °C to 600 °C at low pressure. Using similar atomic fluxes of Si, and with all the other parameters constant, a higher growth rate and lower germanium content has been observed with disilane compared to silane. For instance, there is a factor of 1.85 at 550°C. The germanium concentration was varying from 30.4 to 22.3 % and from 19.4 to 15.7 % for silane and disilane, respectively. To have a better understanding about this kinetics difference, an impoverishment rate or theoretical yield, of the gas phase, in reactive species has been calculated. The hypothesis is that the impoverishment rate is linked to the reactivity of a molecule, and thus related to the sticking probability of a molecule onto a same surface [2].The impoverishment rate is defined as the ratio between the number of moles of Si (or Ge) deposited per minute (nDeposited) and the number of moles of silicon precursor (or germanium) injected per minute(nInjected) in the epitaxy reactor: αPrecursor = nDeposited/nInjected. The impoverishment rate of the disilane molecule increases much more rapidly than the silane molecule as the temperature increases (Fig.1a). Disilane is more consumed than silane which is relevant of the higher reactivity of disilane compared to silane.Moreover, the impoverishment of germane increases more rapidly with disilane than with silane (Fig.1b). The GeH4 contribution to epitaxy is more significant using disilane than silane. The impoverishment rate of precursors according to the germane flow will be presented later.Then, silane and disilane precursors have been compared with respect to the C incorporation at 550 °C. Ge concentration was fixed to 20 % with both silicon precursors. This leads to a growth rate of SiGe equal to 2.9 and 14.1 nm.min-1 using silane and disilane, respectively. XRD has been used to gain access to the “apparent” Ge concentration in Si1-x-yGexCy layers (Fig.2(a), (b)). Carbon atoms, much smaller than silicon and germanium, compensate the compressive strain induced by germanium in the SiGe layers. It then yields smaller Ge concentration in XRD than the real Ge concentration. The carbon in substitutional position can therefore be extracted using this coefficient: 1 % of carbon compensate 12 % of Ge [3].Using disilane, the substitutional carbon concentration linearly increases with the MS flow over the whole studied range (Fig.3). However, using silane, a deviation from the linearity is observed (above 0.7 %). In the linearity part of the curves, all the carbon incorporated are in substitutional site (as the total amount of carbon atoms increasing linearly with the MS flow [4]). When a non-linearity occurs, C atoms started to be incorporated in interstitial position also. SIMS measurement will be performed to confirm that. At 550 °C, the growth rate of SiGe is more important with disilane precursor due its higher reactivity than silane. Its leads to a better substitutional carbon incorporation. Indeed, using disilane, up to 1.15 % of fully substitutional carbon can be reached while using silane, only 0.7 % is reached.[1] V. Loup et al., J. Vac. Sci. Technol. B 21(1), Jan/Feb 2003.[2] D.J. Robbins et al., Journal of Applied Physics 69, 3729 (1991).[3] D. De Salvador et al., Phys. Rev. B, vol. 61, pp. 13005, 2000.[4] V. Loup et al., J. Vac. Sci. Technol. B 20(3), May/Jun 2002. Figure 1

Ge incorporation in kesterite thin films by solution processing route: An in-depth study of structural and optoelectronic properties

Herein, we report a promising solution-processing method for the controlled incorporation of germanium (Ge) into Cu2ZnSnS4 (CZTS) films using a nontoxic molecular ink. The effect of Ge concentration on structural, optical, electrical and electronic properties of the films were systematically investigated. The successful Ge alloying in CZTS was confirmed by XRD analysis and exploring the sensitivity of Raman scattering. The as-synthesized Cu2ZnSn1-xGexS4 (CZTGS; x = 0, 0.1, 0.15, 0.2 and 0.25) films exhibit strong absorption in the visible region with the gradual increment in the band gap energy from 1.46 to 1.61 eV by increasing x from 0 to 0.25. A decrease in Urbach energy at higher [Ge]/[Sn + Ge] ratio supports the reduction of overall disorder into the system. The information about the correct oxidation states of the constituent elements and optimal chemical composition of the CZTGS films was obtained from X-ray photoelectron spectroscopy (XPS). The decrease in SnII/SnIV signal ratio with the increase in Ge further supports the suppression of deep-trap SnZn antisite defects. The XPS valence band spectra reveal that the position of valence band maximum ascended from 0.09 to 0.15 eV with increasing Ge content in the films. Several relevant optical constants were determined of the CZTGS films which are important for applications in solar cell devices as well as for simulation purpose.

Diffusion kinetics in germanium doped lithium titanate anode material through potential sweep analysis

The inevitable demand for the energy sources for the present world's living has increased the pace of exploration towards developing sustainable and superior performing energy storage devices. Lithium-ion battery technology has been in the front since its invention. The introduction of spinel structured lithium titanate (Li4Ti5O12) as an anode material for lithium-ion batteries led to revolutionary improvements in rate-capability, long cyclability, and safety. The diffusion kinetics studies have been carried out on germanium doped lithium titanate (Li4GexTi5-xO12, x = 0.05, 0.10, 0.15, and 0.20) through cyclic voltammetry analysis. The studies revealed that the lithium-ion kinetics in the lithium titanate has significantly improved the electrochemical performance through germanium incorporation. The lithium-ion diffusion coefficient of Li4Ge0.1Ti4.9O12 (1.12×10−11 cm2 s−1) was found to have one order higher than that of the pristine phase (2.71×10−12 cm2 s−1). This enhancement in the lithium-ion diffusion has pushed the discharge capacity of Li4Ge0.1Ti4.9O12 to 161 mAh g−1 from 145 mAh g−1 at 0.1C rate.

Output parametric optimization of CZTGS bilayer absorber layer: A numerical study

Numerical simulation and modeling of Germanium doped stacked CZTS has been accomplished by using wx-AMPS in this current work. This study envisages the overall copper zinc tin sulfide (CZTS) solar cell performance by Germanium incorporation. Now a days Germanium is treated as a promising candidate to be added in CZTS, which partially replaces the tin in the compound. In this work a stack structure containing copper zinc tin germanium sulfide (CZTGS) top layer and copper zinc tin sulfide (CZTS) bottom layer was used for simulation. Layer optimization was done by varying the input parameters (Material, Electrical and Optical) and optimizing the output parameters. The highest efficiency of germanium doped bilayer CZTS solar cell was recorded as 17.31%.

Formation and functionalization of Ge-nanoparticles in ZnO

Semiconductor nanocrystals are often proposed as a viable route to improve solar energy conversion in photovoltaics and photoelectrochemical systems. Embedding the nanocrystals in, e.g. a transparent and conducting electrode of a solar cell will promote the photon absorption and subsequent transfer of the generated charge carriers from the nanocrystal, and thereby enhance the function of the electrode. This can be accomplished by embedding a semiconducting nanocrystal with a small bandgap in a transparent conducting oxide (TCO), which is commonly utilized as electrode in new generation solar cells. Here, we demonstrate the incorporation, formation, and functionalization of germanium (Ge) nanocrystals in zinc oxide utilizing ion implantation, where post implantation annealing at 800 °C results in diamond cubic Ge nanocrystals with sizes between 2 and 20 nm. Photoluminecence spectra show a distinct emission around 0.7 eV arising from the Ge nanocrystals, and with additional emission features up to 1.15 eV due to quantum confinement, demonstrating a novel functionalization and tunability of the TCO electrode.

First principle study on structural and optoelectronic properties and band-gap modulation in germanium incorporated tin (IV) oxide

First principle calculations on pure and germanium (Ge) incorporated tin (IV) oxide (SnO2) are performed to understand their structural, electronic, and optical properties at the microscopic level. The optimized ground state structures exhibited a reduction in their lattice parameters as well as total energy with increasing germanium concentration. From the band structures of the pristine and doped SnO2, we have observed a reduction in the energy gap due to the incorporation of germanium into stannic oxide (SnO2). As conduction band minimum near Fermi level reaching a lower energy level with an increase in doping concentration, the electron affinity is increasing. The calculated band gaps of pure, 6.25 %, 12.5 % and 25 % ‘Ge’ incorporated tin (IV) oxides are 1.76, 1.73, 1.56 and 1.53 eV, respectively, and all are direct in nature. Further, the calculated electron effective mass at the conduction band minimum is lower than the hole effective mass at the valence band maximum. Hence, the mobility of electrons is found to be higher, suggesting the n-type semiconducting property. The contributions of different atoms on valence and conduction band are studied by calculating the density of states spectra. Optical properties, such as real and imaginary dielectric constants, absorption, reflectivity, refraction and extinction coefficient, loss function, real and imaginary optical conductivity are calculated. The calculated optical absorption shows that both un-doped and doped materials preserve the optical transparency in the infra-red region. Our analysis shows that Ge-doped SnO2 has a tunable band gap and work function, which makes it suitable for applications in photovoltaic devices.

Effect of Germanium Incorporation on the Electrochemical Performance of Electrospun Fe2O3 Nanofibers-Based Anodes in Sodium-Ion Batteries

Fe2O3 and Fe2O3:Ge nanofibers (NFs) were prepared via electrospinning and thoroughly characterized via several techniques in order to investigate the effects produced by germanium incorporation in the nanostructure and crystalline phase of the oxide. The results indicate that reference Fe2O3 NFs consist of interconnected hematite grains, whereas in Fe2O3:Ge NFs, constituted by finer and elongated nanostructures developing mainly along their axis, an amorphous component coexists with the dominant α-Fe2O3 and γ-Fe2O3 phases. Ge4+ ions, mostly dispersed as dopant impurities, are accommodated in the tetrahedral sites of the maghemite lattice and probably in the defective hematite surface sites. When tested as anode active material for sodium ion batteries, Fe2O3:Ge NFs show good specific capacity (320 mAh g−1 at 50 mA g−1) and excellent rate capability (still delivering 140 mAh g−1 at 2 A g−1). This behavior derives from the synergistic combination of the nanostructured morphology, the electronic transport properties of the complex material, and the pseudo-capacitive nature of the charge storage mechanism.

Uncooled microbolometer arrays for ground-based astronomy

ABSTRACT We describe the design and commissioning of a simple prototype, low-cost 10 μm imaging instrument. The system is built using commercially available components including an uncooled microbolometer array as a detector. The incorporation of adjustable germanium reimaging optics rescale the image to the appropriate plate scale for the 2 m diameter Liverpool Telescope. From observations of bright Solar system and stellar sources, we demonstrate a plate scale of 0.75 arcsec per pixel and confirm the optical design allows diffraction limited imaging. We record a ∼10 $\, {\rm per\, cent}$ photometric stability due to sky variability. We measure a 3σ sensitivity of 7 × 103 Jy for a single, ∼0.11 s exposure. This corresponds to a sensitivity limit of 3 × 102 Jy for a 60 s total integration. We present an example science case from observations of the 2019 January total lunar eclipse and show that the system can detect and measure the anomalous cooling rate associated with the features Bellot and Langrenus during eclipse.

Bottom up engineering of single crystal diamond membranes with germanium vacancy color centers

Color centers in diamond have garnered significant attention for applications in integrated quantum photonics. The availability of thin (∼ hundred of nanometers) diamond membranes is paramount to achieve this goal. In this paper, we describe in detail a robust, reproducible and cost effective fabrication method that enables engineering high quality thin diamond membranes with uniform distribution of germanium vacancies employing microwave plasma chemical vapor deposition. We use a combination of different germanium precursors for homogeneous doping of the membranes to increase the probability of germanium incorporation into the diamond lattice. Our fabrication methodology can be further extended to implementation of other color centers in thin diamond membranes and be used for engineering quantum photonic devices.

Organogermanium suppresses cell death due to oxidative stress in normal human dermal fibroblasts

Reactive oxygen species (ROS) are very harmful to dermal cells, and it is thus important to develop cosmetics that protect the skin from ROS and other stimuli. Repagermanium is a synthetic water-soluble organogermanium polymer, and in this study, we attempted to visualize the incorporation of germanium into normal human dermal fibroblasts (NHDFs) using isotope microscopy. In addition, the content of 3-(trihydroxygermyl)propanoic acid (THGP), a hydrolyzed monomer of repagermanium, in NHDFs was determined through liquid chromatography mass spectrometry (LC-MS/MS), and the dose-dependent incorporation of THGP was confirmed. We then evaluated the preventive effects of THGP against ROS-induced NHDF death and confirmed the observed preventive effects through gene profiling and expression analysis. The addition of 0.59–5.9 mM THGP reduced cell death resulting from ROS damage caused by the reaction between xanthine oxidase and hypoxanthine and the direct addition of H2O2. Furthermore, this study provides the first demonstration that the effect of THGP was not due to the direct scavenging of ROS, which indicates that the mechanism of THGP differs from that of general antioxidants, such as ascorbic acid. The gene profiling and expression analysis showed that THGP suppressed the expression of the nuclear receptor subfamily 4 group A member 2 (NR4A2) gene, which is related to cell death, and the interleukin 6 (IL6) and chemokine (C-X-C motif) ligand 2 (CXCL2) genes, which are related to the inflammatory response. Furthermore, the production of IL6 induced by H2O2 was suppressed by the THGP treatment. Our data suggest that the preventive effect of THGP against ROS-induced cell death is not due to antioxidant enzymes or ROS scavenging.

In Situ Doping of Black Phosphorus by High-Pressure Synthesis.

Black phosphorus is a two-dimensional semiconductor with promising properties for catalysis, energy storage, and conversion as well as electronic device applications, and control of its electronic structure is critical for such applications. Substitutional doping of phosphorus by electron donating (e.g., sulfur) or electron accepting elements (e.g., germanium) can significantly change its properties, especially charge carrier concentration. Here, we report the in situ doping of black phosphorus by its direct synthesis from a mixture of red phosphorus and a dopant by high pressure synthesis. In detail, we study the incorporation of germanium, sulfur, selenium, and tellurium within black phosphorus, showing significant differences in incorporation of individual elements and assess their suitability for potential electrochemical applications.

Atomic layer deposition of energy band tunable tin germanium oxide electron transport layer for the SnS-based solar cells with 400 mV open-circuit voltage

Tin germanium oxide, (Sn,Ge)O2, films were prepared using atomic layer deposition and tailored to a SnS absorber layer by incorporating various amounts of germanium into tin oxide to adjust band alignments at the interfaces of SnS/(Sn,Ge)O2 photovoltaic devices. Carrier concentrations of (Sn,Ge)O2 were suppressed from 1020 to 1018 cm−3 with germanium incorporation, with nitrogen doping further reducing carrier concentrations by another order of magnitude. Excellent tunability of both band energy levels and carrier concentrations of (Sn,Ge)O2 allowed optimizing SnS-based solar cells. SnS/(Sn,Ge)O2:N devices were demonstrated, with an open-circuit voltage as high as 400 mV, due to the effective mitigation of interfacial recombination of photogenerated carriers at the SnS/(Sn,Ge)O2:N absorber-buffer heterojunction interface.

Germanium doping of cubic GaN grown by molecular beam epitaxy

We present a study of germanium as an alternative to silicon for n-type doping of cubic GaN. We find that Ge is a well-suited donor impurity. Our layers were grown by plasma-assisted molecular beam epitaxy on 3C-SiC/Si (001) substrates. Germanium-doped layers were fabricated with donor concentrations ranging over several orders of magnitude up to 3.7 × 1020 cm−3. For comparison, silicon-doped layers with donor concentrations of up to 3.8 × 1019 cm−3 were also grown. Incorporation of germanium into the cubic GaN layers was verified by time-of-flight secondary ion mass spectrometry. The crystalline quality of our layers was analyzed using high-resolution x-ray diffraction. Germanium- as well as silicon-doped layers with donor concentrations above 1019 cm−3 exhibited an increase of the dislocation density with increasing dopant concentration. The surface topography of our layers was investigated by atomic force microscopy. Comparable values for the surface roughness were measured for germanium- as well as silicon-doped layers. Optical properties were investigated by photoluminescence spectroscopy at 13 K. Doping with silicon resulted in a spectrally slightly narrower luminescence than doping with germanium. Donor concentrations and carrier mobilities were determined by Hall effect measurements at room temperature and we observe 20% higher electron mobilities for Ge-doping compared to Si-doping in the case of high dopant concentrations.

Doping in bulk HVPE-GaN grown on native seeds – highly conductive and semi-insulating crystals

Results of gallium nitride crystallization on native seeds by Hydride Vapor Phase Epitaxy method are described. The seeds are high quality ammonothermal GaN crystals. Properties of unintentionally doped HVPE-GaN are briefly presented. A review on doping with donors and acceptors is prepared. Intentional incorporation of silicon or germanium is proposed in order to grow highly conductive HVPE-GaN. Carbon, iron, or manganese was introduced to increase the resistivity of crystallized material. GaN samples with different dopants are described in terms of their structural, optical, and electrical properties.