Dopant Flow Research Articles

Gas-phase dopant flow to modify nanoLC-MS and nanoESI protein charge

A miniature permeation device is used to add controlled amounts of gas-phase dopant to the air around two types of atmospheric pressure nanoflow electrospray source: a pulled glass capillary needle in a custom mount, and for the first time a commercial nano-liquid chromatography emitter in a commercial ion source housing. Intact proteins sprayed at 300 nL/min are charge-reduced by the addition of nitrogen doped with diethylamine, and the reaction is assisted by adjusting flow rate, positioning, and enclosure of the nanoflow emitter. Charge distribution is shifted to lower charge states with increasing amounts of dopant. The maximum signal of the most abundant charge state and the total signal abundance are increased to an extent dependent on the mass and isoelectric point of the protein.

X-ray-activated long afterglow in Tb-doped CaZnOS-layered semiconductors

Long afterglow materials feature long-lasting luminescence after the cessation of the excitation source. The rising demand for afterglow materials in many applications such as deep tissue imaging, ultrasensitive sensing, and radiation detection has led to extensive research on X-ray-activated afterglow systems. However, the progress in this field is constrained by the limitation and shortage of radiation-induced afterglow materials. Herein, a newly X-ray-excited long afterglow phosphor CaZnOS:Tb3+ has been developed by using lithium-assisted synthetic protocol. Afterglow properties of Tb3+-doped CaZnOS microcrystals are systematically investigated by considering the dopant concentration, reaction temperature, reaction time, reaction atmosphere, and gas flow. As the gas flow of argon atmosphere increases from 0.05 to 0.5 L/min, the CaZnOS:Tb3+ microcrystals exhibit a distinct change in trap depth from 0.59 to 0.75 eV, corresponding to a gradual increase in afterglow time. Together with thermoluminescence analysis, the long afterglow mechanism is also discussed in this work. These results highlight the importance of reaction gas flow for the efficient regulation of traps and defects in afterglow materials. Furthermore, they provide a fundamental design principle and new route for the creation of lanthanide-doped CaZnOS afterglow phosphors.

(G03 - Best Student Presentation Award) Advances in In-situ Boron and Phosphorous Doping of SiGeSn

A CMOS compatible, direct bandgap material for optical interconnects can be obtained by alloying Ge with Sn 1, applying tensile stress to Ge 2 or both 3. Lasing in GeSn was demonstrated in 2015 4 by Wirths et al., followed in 2020 by electrically pumped lasing up to 100K 5 and, in 2022, optically pumped lasing at room temperature 6,7. In-situ doped SiGeSn might offer high dopant incorporation, while delivering good electronic confinement, improving thereby the performances of devices. Such doped layers can be used in photodetectors 8–10, light-emitting diodes 11–13 and modulators 14,15 operating at wavelengths higher than 1.55 µm, enabling their use in future CMOS compatible lab-on-a-chip devices with integrated light sources 5,16,17.The in-situ doping of SiGeSn was compared to that of GeSn. All layers were grown at 349 °C, 100 Torr in a 200 mm Epi Centura 5200 RP-CVD tool from Applied Materials. Ge strain relaxed buffers were used to accommodate the lattice mismatch between (Si)GeSn and the Si substrates 18. The F(Ge2H6)/F(H2), F(Si2H6)/F(H2) and the F(SnCl4)/F(H2) Mass-Flow Ratios (MFRs) were constant at 7.92x10-4, 1.25x10-3, and 4.69x10-5, respectively.In-situ doped SiGeSn Growth Rates (GRs), shown in Figure 1 (a), were around 30 nm min.-1. They were below that of GeSn:B and GeSn:P (40 nm min.-1). The latter significantly increased for high dopant flows. Meanwhile, SiGeSn:B GR slightly increased and SiGeSn:P GR decreased as the dopant flow increased. B2H6 and PH3 might have opened surface sites for GeSn and SiGeSn:B, while the formation of gas phase intermediates might have reduced the SiGeSn:P GR.Interestingly, the surface quality improved significantly for in-situ doped SiGeSn, reaching the same quality as that of GeSn for high dopant flows, as shown in Figure 1 (b). Surfaces had RMS roughness values below 0.40 nm, close to that of GeSn, with a full surface cross-hatch recovery.There was, for in-situ doped GeSn, a Sn content reduction for high dopant flows (Figure 1 (c)+(d)) most likely because SnCl4 was mass-transport limited19 and not impacted by a larger amount of open surface sites. The influence of dopants on the layer composition was even more pronounced in SiGeSn:B. Si/Sn ratios of 3.5, with Si contents of up to 25%, were obtained, which should result in improved electrical confinement. The formation of Si and Ge gas phase intermediates might explain why Sn contents were higher, in SiGeSn:P, for high PH3 flows. Such insights should yield better control of Si and Sn contents in stacks for optical or electronic purposes.Electrically active carrier concentrations c active of the order of 2x1020 cm-3 were achieved in SiGeSn:B (Figure 1 (e)). These were seven times higher than the 3x1019 cm-3 obtained for GeSn:B. For GeSn:P, c active was likely limited by the formation of SnmPnV nanoclusters. It was at most 7x1019 cm-3 (Figure 1 (f)). Four times higher c active values were obtained for SiGeSn:P with at most 3x1020 cm-3. No decrease of c active was observed for high PH3 flows in SiGeSn:P. This might have been due to the formation of fewer SnmPnV nanoclusters.Such c active values and better electrical confinement were used to fabricate (Si)GeSn based photodiodes with improved electroluminescent integrated intensity compared to photodiodes with doped Ge contact layers. Gassenq, A. et al. Appl. Phys. Lett. 109, 242107 (2016).Elbaz, A. et al. Nat. Photonics 14, 375–382 (2020).Chrétien, J. et al. ACS Photonics 6, 2462–2469 (2019).Wirths, S. et al. Nat. Photonics 9, 88–92 (2015).Zhou, Y. et al. Optica 7, 924 (2020).Chrétien, J. et al. Appl. Phys. Lett. 120, 051107 (2022).Bjelajac, A. et al. Opt. Express 30, 3954 (2022).Li, X. et al. Photonics Res. 9, 494 (2021).Zhou, H. et al. Opt. Express 28, 10280 (2020).Wu, S. et al. IEEE J. Sel. Top. Quantum Electron. 28, 1–9 (2022).Stange, D. et al. Optica 4, 185 (2017).Oehme, M. et al. IEEE Photonics Technol. Lett. 26, 187–189 (2014).Schwartz, B. et al. Opt. Lett. 40, 3209 (2015).Bertrand, M. et al. 2020 IEEE Photonics Conference (IPC) 1–2 (IEEE, 2020).Zhou, H. et al. Opt. Express 28, 34772 (2020).Casiez, L. et al. 2020 IEEE Photonics Conference (IPC) 1–2 (IEEE, 2020).Soref, R. Nat. Photonics 4, 495–497 (2010).Hartmann, J. M. & Aubin, J. J. Cryst. Growth 488, 43–50 (2018).Margetis, J. et al. Vac. Sci. Technol. A 37, 021508 (2019). Figure 1

Magnesium doped semipolar (11–22) p-type gallium nitride: Impact of dopant concentration variants towards grain size distributions and crystalline quality

In this study, the effect of biscyclopentadienyl magnesium flow rate for the growth of p-type gallium nitride thin films was varied from 20 to 40 standard cubic centimeter per minute to acquire the optimum doping concentration level. The growth of semi-polar (11–22) p-type gallium nitride thin films on m-plane sapphire was accomplished via metal organic chemical vapor deposition. Atomic force microscopy reveals the occurrence of dissimilar grain size distributions upon the utilization of different dopant flow rates. Statistical data shows that the utilization of optimized biscyclopentadienyl magnesium flux of 30 standard cubic centimeter per minute would significantly reduce the grain size to as low as ∼ 550 nm (±1 nm), yielding a root mean square roughness of 6.00 nm. X-ray rocking curve analysis observed that a moderate biscyclopentadienyl magnesium flow rate of 30 standard cubic centimeter per minute leads to narrowing in full width at half maximum, indicating an enhanced crystallinity with a reduction of the basal stacking fault density of 8.18 × 104 cm−1 with the use of 30 standard cubic centimeter per minute of biscyclopentadienyl magnesium. Moreover, the mobilities and carrier concentrations were improved to as high as 1.8 cm2.V − 1.s − 1 and 5.5 × 1017 cm−3 with a moderate biscyclopentadienyl magnesium flow rate of 30 standard cubic centimeter per minute. The analysis suggests that with the optimum biscyclopentadienyl magnesium flow rate (30 standard cubic centimeter per minute), preferential sites for magnesium incorporation can be enhanced.

Stacked Diodes for Pulsed Power Applications: New Process Integration Scheme

Since Boff, Moll, and Shen’s discovery of the high-speed switching effect inherent in initially forward-biased silicon diodes that are suddenly reverse-biased in 1960 [1]; DSRD’s (as termed by Grekhov and Kardo-Sysoev in 1985 [2]) performance has not increased as their deep-diffusion manufacturing process remains the same as it was over 60 years ago. Albeit new pulse generator topologies which utilize diodes like DSRDs, i.e., SOS diodes (termed by Rukin in 1992 [3]) have shown improvement at circuit level given they operate under a higher direct-current density compared to that of DSRD-based pulsers – the voltage-to-risetime, dV/dt, of these silicon-based solid-state diodes remain on the order of 1012 V/s. Furthermore, all possible ways to improve pulse performance of DSRD made by deep diffusion have been extensively investigated and exhausted. To achieve the 1013 V/s (10 kV/ns) voltage-to-risetime required by an all-solid-state pulse generation utilized to support of the missions, improving DSRD manufacturing techniques must ensue.The process flow is schematically illustrated by Fig. 1. On starting degenerate doped wafer, two epitaxial layers are grown, first n- then p-type doped thus forming p-n junction of the diode.The doping profile is controlled by changing dopant flow into epi chamber. It allows getting an optimal diode doping profile predicted by simulation. Notice, the old diffusion process allows only predetermined doping profile (complementary error function) which is not optimal.After forming the blanket p-n junction structure on entire wafers, individual diode dies are separated by wafer patterning. Though the wafers remain intact. This is opposite to the old process where the wafers were cut into individual diode dies. In our technology, V-grooves are formed by anisotropic etching process resulting in structure shown on Fig. 2. Squares surrounded by the v-grooves will become diodes, Inner slopes of v-grooves become side walls of the diodes. Notice, in old technology side walls were usually vertical, which creates a weak point for electrical breakdown: it is limited by surfacee breakdown properties, not bulk silicon properties.Next is diode side surface insulation. It is achieved by thermal oxidation. Thus, the diodes get the best surface passivation (i.e., thermal SiO2). The p-n junction is located near middle of the V-groove slope. Thus, there is no local spike of electric field where avalanche breakdown starts. Eventually, the breakdown properties of this diode are much closer to bulk silicon limit – as compared to old technology where the breakdown was surface limited.At next stage the silicon dioxide layer is removed on top surface but remains on v-groove slopes. Now we have wafers with diode arrays, terminated and passivated by side surfaces.Further, selective electroplating of copper is performed to form electrical contacts. Also, it is a step in preparation to wafer stacking. In old technology, metallization was at much earlier stage of flow and thus it interfered with side insulation. In selective electroplating, copper is deposited only on silicon surfaces, and does not deposit on SiO2 surfaces of v-groove insulation.To finish preparation for wafer bonding, tin is selectively deposited over copper. Then, wafers are aligned and stacked. The wafer stack is heated above tin melting temperature. By solid-liquid interdiffusion, Cu/Sn intermetallic compound is formed. It has much higher melting point compared to tin. Bonding process continues until entire tin layer is consumed.Now the bonded wafer stack is ready for last step in the processing – cutting into stacked DSRDs. The cutting is regular mechanical sawing. The saw lines are along the lines of v-grove bottoms.The process and resulting device design are patented [4].On next step of this project, electrical performance of final stacked DSRDs will be compared to performance of stacked DSRDs manufactured by traditional deep diffusion-based technology. Boff, A., J. Moll, and R. Shen. "A new high-speed effect in solid-state diodes." in 1960 IEEE International Solid-State Circuits Conference. Digest of Technical Papers, vol. 3, pp. 50-51. IEEE, 1960. Grekhov, I. V., V. M. Efanov, A. F. Kardo-Sysoev, and S. V. Shenderey. "Power drift step recovery diodes (DSRD)." Solid-State Electronics 28, no. 6 (1985): 597-599..Rukin, S. N. "Pulsed power technology based on semiconductor opening switches: A review." Review of Scientific Instruments 91, no. 1 (2020): 011501.Bellinger, A.Caruso, A.Usenko, US Patent Application “Stacked Diode with Side Passivation and Method of Making the Same” filed 09/10/2021. Figure 1

Boron and Phosphorous Doping of GeSn for Photodetectors and Light Emitting Diodes

The holy grail of group-IV light emission would be electrically pumped lasing at Room Temperature (RT). In CEA-LETI, the performance of p-i-n light emitting diodes is limited by the use of in-situ doped Ge layers beneath and above the active layer stack [1]. To overcome Sn segregation during the growth of the top electrode and, in thick GeSn/Ge stacks, avoid plastic relaxation, it would be ideal to switch over to in-situ doped GeSn grown at temperatures similar to that of the active region. We have therefore explored the in-situ boron and phosphorous doping of GeSn on Ge strain relaxed buffers with Ge2H6+SnCl4+ B2H6 and Ge2H6+SnCl4+PH3 chemistries. Growth pressure, temperature, F(Ge2H6)/F(H2) and F(SnCl4)/F(H2) Mass Flow Ratio (MFR) were 100 Torr, 349 °C, 7.92x10-4 and 4.78x10-5.X-Ray Diffraction (XRD) measurements were conducted to gain access to the GeSn composition and layer thickness, as shown in Fig. 1 and Fig. 2. As the GeSn peak position was determined by the Sn content and also the B or P substitutional concentrations, the actual layer composition could not be unambiguously determined. Therefore, the Sn content in the following is an apparent Sn content. Thickness fringes outline the high GeSn crystalline quality.As the F(B2H6)/F(Ge2H6) or the F(PH3)/2 F(Ge2H6) MFRs increased, the apparent Sn content stayed at first roughly around 6.5 %, as shown in Fig. 3. This value was the same for i-GeSn, GeSn:B and GeSn:P, in contrast to previous literature findings [2]. As the MFRs reached the highest values, the apparent Sn content reduced significantly for GeSn:B (from 6.5 % down to 4.6 %) and less significantly GeSn:P (from 6.6 % down to 5.6 %). The significantly smaller size of B compared to P (aB = 3.852 Å <=> aP = 5.014 Å) reduced the compressive strain in GeSn:B 2.8 times more than in GeSn:P for the same dopant concentrations, explaining the more pronounced effect. We quantified the substitutional B and P incorporation by assuming that the Sn content was not impacted by B or P incorporation. The estimated B and P substitutional concentrations then increased from 2.8x1019 cm-3 up to 3.8x1020 cm-3 and from 2.5x1019 cm-3 up to 5.4x1020 cm-3 (highest four MFRs for GeSn:B and GeSn:P), shown in Fig. 4. Those values are close indeed to the highest substitutional B or P concentrations obtained in Ge:B or Ge:P layers grown at 350°C, 100 Torr with Ge2H6: 4.8x1020 cm-3 [3] and 4.1x1020 cm-3 [4], respectively.We determined elemental growth rates by multiplying the GR by the Ge or apparent Sn content to have a more detailed look at the growth mechanics (Fig. 5). The introduction of SnCl4 catalyzed the growth rate of GeSn compared to that of pure Ge, in line with the literature [4]. As the F(B2H6)/F(Ge2H6) or the F(PH3)/2F(Ge2H6) MFR increased, the Sn GR component stayed constant at around 2.5 nm min.-1. Meanwhile, the Ge GR component was constant at around 37 nm min.-1 for lower MFRs. For high dopant flows, the Ge GR component increased significantly for GeSn:B and reached 48 nm min.-1. The increase was less significant for GeSn:P, with at most 40 nm min.-1. This is to our knowledge, the first time an increase of the GeSn:P GR is reported for high dopant flows. Similar increases were found for Ge:P and Ge:B grown at 350°C, however [3-4]. The constant Sn GR component and the increase of the Ge GR component at high MFRs are likely due to an increased incorporation of Ge thanks to B and P opening surface sites (Indeed, the Ge GR component is surface rate limited, while the Sn GR component is reaction rate limited [5]).A cross-hatch along <110> was found by Atomic Force Microscopy for all layers, which were otherwise smooth and featureless, as shown in Fig. 6 top for GeSn:B and Fig. 6 bottom for GeSn:P. The only exceptions were the GeSn:B samples grown at the three highest MFRs. There were then some islands, which were likely due to B and/or Sn surface segregation. Other studies will be performed to gain access to the Sn, P and B contents.[1] M. Bertrand et al., 2018 IEEE International Conference on Group-IV Photonics, pp. 45-46.[2] J. Margetis et al., Mater. Sci. Semicond. Process. 70, 38 (2017).[3] J.M. Hartmann et al., ECS PRIME 2020 Meeting ID 138196, Symposium G03.[4] J. Aubin et al., ECS J. Solid State Sci. Technol. 6, 1 (2017).[5] J. Margetis et al., J. Vac. Sci. Technol. A 37, 021508 (2019). Figure 1

Influence of hydrogen dilution and doping gas on the material properties of plasma-deposited polycrystalline silicon thin films

We studied the effects of precursor gas composition and the addition of dopant gas, PH3, on polycrystalline silicon films deposited using plasma-enhanced chemical vapor deposition. Spectroscopic ellipsometry measurement and modeling results revealed that the poly-Si films consist of a subsurface layer and a bulk layer. The sample deposited under greater hydrogen dilution exhibited a fully crystallized subsurface layer and a denser bulk layer. We also studied the effects of various dopant gas flow rates on structural and electrical properties of the poly-Si films. Ellipsometry, X-ray diffraction, and Raman analyses revealed that the film deposited using a large dopant-gas flow rate exhibits decreased grain size and increased void fraction. Furthermore, the doped poly-Si films show a trend of Raman peak shift, which was attributed to tensile stress. The stress of the doped poly-Si films increases with higher dopant-gas flow rate. Measurement of the temperature-dependent dark conductivity shows saturation of the electrical conductivity of heavily doped films.

Coupled boron-doping and geometry control of tin-catalyzed silicon nanowires for high performance radial junction photovoltaics.

Geometry and doping control in silicon nanowires (SiNWs) are both crucial aspects in fabricating three-dimensional (3D) radial junction thin film solar cells, while the coupling between them remains a peculiar aspect to be better understood. In this work, we focus on the geometry evolution and the doping effects realized in tin-catalyzed SiNWs grown via a plasma-enhanced vapor-liquid-solid procedure by using different diborane (B2H6) dopant flows. It is shown that with the increase of B2H6 flow rate from 0.3 to 2.1 SCCM, the radial growth of SiNWs is greatly accelerated by more than 30%, while the length is shortened to 50%. This can be related to the enhanced chemisorption probability of SiHx radicals, with the addition of B2H6, on the SiNW sidewall during silane (SiH4) plasma deposition in PECVD system, which leads to easier nucleation directly on the sidewalls and faster radial expansion of the SiNWs. A trade-off has to be sought between seeking a strong light trapping and ensuring a sufficient doping for high-quality PIN junction with the increase of B2H6 doping flow. These new understandings lay a critical basis for understanding and searching for an optimal growth control for constructing high-performance 3D radial junction thin-film solar cells.

Size effect of electronic properties in highly arsenic-doped silicon nanowires

The unique electrostatic properties of semiconductor nanowires enable the realization of novel transistor types by the possibility to use surround gate architectures resembling ideal gate electrostatic control. Nevertheless one fundamental issue of semiconducting nanowire channels is the reliable control of doping to adjust the charge carrier concentration. Indeed, as dimensions scale down the surrounding media and the interfaces become more important. In this study we experimentally investigate the role of surface depletion and dielectric mismatch on the electronic charge transport of highly arsenic doped and bottom-up grown silicon nanowires. Electrical characterization of silicon nanowires (SiNWs) synthesized by Au catalyzed vapour-liquid-solid (VLS) growth and in-situ arsine (AsH3) doping is reported for the first time. We demonstrate that high n-type doping is possible by adjusting the dopant precursor flow ratio during growth. Based on electrical measurements of individual nanowires, reproducible donor concentrations of up to 5.2 × 1019 cm−3 could be revealed. By measuring the electrical characteristics for individual nanowires in dependence of their radius, we show that the electrically active carrier density drastically reduces for small nanowires at radii much larger than those at which quantization or dopant surface segregation effects are expected to occur. Furthermore, enhancement of the contact transparency for small radii nanowires is demonstrated through dopant segregation upon metal silicidation. Size dependent measurement of electrical characteristics revealed improved contact resistivities as low as 1.4 × 10−11 Ωm2.

La-doped diamond films prepared through microwave plasma chemical vapor deposition

La-doped diamond films were deposited through a microwave plasma chemical vapor deposition (MPCVD) system. The effects of La addition on the morphology, microstructure, and quality of the diamond films were systematically investigated. The analysis of secondary ion mass spectroscopy and X-ray photoelectron spectroscopy indicates that lanthanum atoms were incorporated into the diamond films through MPCVD with lanthanum (III) acetate as a precursor. The characterization results reveal that different lanthanum dopant flows can affect the morphology, the preferred orientation of the crystal, and the diamond phase fraction in the films. Upon the lanthanum addition with the dopant flow of 30 sccm, the intensity ratio of the (220) to (111) peaks [I(220)/I(111)] decreases from 20% to 17% and the sp3/sp2 ratio is reduced from 8.53 to 5.89. However, with the increase of the lanthanum dopant flow to 90 sccm, the intensity ratio of I(220)/I(111) rises up to 39% and the sp3/sp2 ratio increases to 8.99. Therefore, a certain amount of lanthanum addition can promote the growth of (110) orientation grains and enhances the sp3 phase fraction in the deposited diamond films. The results obtained from this study provide a hint for adjusting the morphology and microstructure of diamond films with rare earth element doping.

Exploring the Internal Radiative Efficiency of Selective Area Nanowires

Nanowires are ideal building blocks for next-generation solar cell applications. Nanowires grown with the selective area (SA) approach, in particular, have demonstrated very high material quality, thanks to high growth temperature, defect-free crystalline structure, and absence of external catalysts, especially in the InP material system. A comprehensive study on the influence of growth conditions and device processing on optical emission is still necessary though. This article presents an investigation of the nanowire optical properties, performed in order to optimize the internal radiative efficiency. In an initial preamble, the motivation for this study is discussed, as well as the morphology and crystallinity of the nanowires. The effect on the nanowire photoluminescence of several intrinsic and extrinsic parameters and factors are then presented in three sections: first, the influence of basic growth conditions such as the temperature and the precursor ratio is studied. Subsequently, the effects of varying dopant molar flows are explored, keeping in mind the intended solar cell application. Third, the manner in which the processing and the passivation affect the nanowire optical emission is discussed. Precise control of the growth conditions allows maximizing the nanowire internal radiative efficiency and thus their performance in solar cells and other optoelectronic devices.

Nanoscale analysis of electrical junctions in InGaP nanowires grown by template-assisted selective epitaxy

We report the analysis of the electrical properties of Inx−1GaxP nanowires (NWs) grown by template-assisted selective epitaxy. The individual NW properties are investigated by means of electron beam induced current microscopy (EBIC) and current-voltage curves acquired on single nano-objects. First, a set of samples containing n-doped InGaP NWs grown on a p-doped Si substrate are investigated. The electrical activity of the hetero-junction between the NWs and the substrate is demonstrated and the material parameters are analyzed, namely, the n-doping level is determined in relation to the dopant flow used during the growth. These results were used to design and elaborate InGaP NWs containing a p-n homo-junction. The electrical activity of the homo-junction is evidenced using EBIC mapping on single NWs, and material parameters (namely, the doping and the minority carrier diffusion lengths) for the p- and n-doped InGaP segments are estimated. Finally, the first proof of a photovoltaic effect from the NW homo-junctions is obtained by photocurrent measurements of a contacted NW array under white light irradiation.

Effect of a halogen-based precursor on dopant incorporation in 3C-SiC film epitaxy

Silicon carbide thin films were synthesised by vapour phase epitaxy technique on silicon substrates using silane and propane as precursors. Methyltrichlorosilane (MTS) was added, and nitrogen was used as dopant precursor. Samples with different doping concentrations were obtained varying the nitrogen flow during the growth. Doping level for each sample was assessed using Raman technique, and a correlation between dopant flow and doping level was confirmed. The influence of MTS on nitrogen incorporation is analysed and discussed: the introduction of MTS increases the growth rate and increases the doping level. We exclude a direct doping effect by the MTS, but we think that it promotes the incorporation of nitrogen doping species. The crystalline quality of the as-grown films was evaluated using X-ray diffraction, assessing the good crystalline quality even in samples obtained using high growth rates and high doping level.

Germanium doping of GaN by metalorganic chemical vapor deposition for polarization screening applications

We demonstrate n-type doping of GaN with Ge by MOCVD at high concentrations that are necessary to fully screen the polarization fields in c-plane InGaN/GaN quantum wells. Hall measurements show linear Ge incorporation with dopant flow rate and carrier concentrations exceeding 1×1020cm−3. GaN:Ge layers exhibit excellent electron mobility, high conductivity, and contact resistivity comparable to the best unannealed contacts to Si-doped GaN. However, the surface morphology begins to degrade with Ge concentrations above 1×1019cm−3, resulting in severe step bunching and a network of plateaus and trenches, even in layers as thin as 10nm.

A comprehensive LC/MS analysis of novel cyclopentenedione library

Cyclopentenediones (CPDs) are compounds with a variety of applications ranging from the preparation of functional polymers to the development of antimicrobial agents, suggesting the potential use of CPDs as novel bioactive compounds or drugs. For this reason, a detailed characterization of CPDs and the development of robust analytical methods for their trace analysis are being sought. Here we focused on the design and synthesis of a library of novelized benzylidene CPD derivatives that were consequently characterized by ultra-high performance liquid chromatography (UHPLC) on-line connected with tandem mass spectrometry (MS/MS). The library design was based on a 2-benzylidene-4-cyclopentene-1,3-dione skeleton substituted with a variety of hydroxy, methoxy, halogen, linear aliphatic, heterocyclic and saccharide moieties, primarily modulating the skeleton’s hydrophobicity. The prepared CPDs were effectively ionized by positive/negative atmospheric pressure photoionization (APPI) and atmospheric pressure chemical ionization (APCI). After careful optimization of the dopant composition and flow rate, positive-mode APPI proved to be more sensitive than APCI. In negative mode, both ionization techniques gave similar results. Further, a detailed MS fragmentation study was performed, confirming the structure of the compounds and enabling positional isomers of CPDs to be differentiated on the basis of their collision spectra analysis. Finally, an optimization of the composition of the mobile phase and reversed-phased separation mode were done, followed by a selection of the most suitable UHPLC stationary phases, i.e. C18, C8 and phenyl. The applicability of the method was evaluated by the inclusion of the other two substances in the study, i.e. monomeric and dimeric bioactive CPDs, compound TX-1123 and nostotrebin 6 with cytostatic and antimicrobial activities, respectively. The results presented here could be used in further investigations of the chromatographic retention and MS behavior of CPDs, which could be utilized for their isolation, detailed characterization and analysis in biological systems.

Zinc-induced lattice contraction in metalorganic vapor phase epitaxy grown AlGaInP

p-Type Zn doped (AlxGa1-x)0.5In0.5P layers have been grown on (001) GaAs substrates by metalorganic vapor phase epitaxy. The lattice constants have been carefully measured by X-ray double crystal diffraction. Mismatches between the substrates and epitaxial layers are observed in the direction corresponding to lattice contraction. The variation of fully-relaxed lattice constants calculated from symmetric (004) and asymmetric (115) diffraction shows that the contraction is related to both increasing inlet dopant flows and increasing growth temperatures. Secondary ion mass spectrometry is employed to analyze the elements in the epitaxial layers. The variations of Al, Ga, In and Zn components indicate that a decrease of In incorporation during the growth leads to the contracted lattice, although Zn atoms, which incorporate into the sites of In atoms during the doping, are smaller in covalent radius. The decrease is supposed to be caused by the competition between In and Zn atoms on the growth surface, which is well fit by the surface adsorption-trapping model. In addition, the suppression of Al and Ga incorporation by inlet dopant flows is observed. The possible cause might be the ethane generated by the pyrolysis of dopant source, which impedes the decomposition process of metalorganic sources of Al and Ga atoms.

Transmission mode desorption atmospheric pressure photoionization.

Desorption atmospheric pressure photoionization (DAPPI) is an ambient mass spectrometry (MS) technique that is suitable for the direct analysis of polar and nonpolar compounds from a variety of surfaces. Conventional DAPPI uses reflection geometry, but here transmission mode (TM)-DAPPI is introduced for fast and easy analysis of liquid samples. Stainless steel and PEEK meshes were used as sampling support in TM-DAPPI. The sample was applied either in the form of a droplet on the mesh, or by dipping the mesh in the sample solution. Physical parameters affecting the ionization efficiency were optimized for TM-DAPPI. The mesh materials were used to extract compounds from aqueous samples, which were then analyzed by TM-DAPPI. TM-DAPPI and conventional DAPPI were compared. In TM-DAPPI, intense signals for the analytes were achieved with less heating power, and lower nebulizer gas and dopant flow rates than optimally used in conventional DAPPI. Either due to this, or the different sample support material used, a much lower background and improved sensitivity compared to conventional DAPPI was achieved. The analytes could be extracted and concentrated from liquid samples on the mesh material used in TM-DAPPI, which was especially efficient for the nonpolar benzo[a]pyrene. This effect was utilized in the analysis of triacylglycerols from cow milk. While conventional DAPPI is still the method of choice for solid samples, TM-DAPPI can be utilized as a fast, easily automated method for analyzing liquid samples. The mesh materials can be utilized for extraction of low polarity compounds, such as steroid hormones or PAHs from dilute, aqueous solutions, followed by subsequent analysis by TM-DAPPI.

Study of carrier concentration in single InP nanowires by luminescence and Hall measurements

The free electron carrier concentrations in single InP core–shell nanowires are determined by micro-photoluminescence, cathodoluminescence (CL) and Hall effect measurements. The results from luminescence measurements were obtained by solving the Fermi–Dirac integral, as well as by analyzing the peak full width at half maximum (FWHM). Furthermore, the platform used for Hall effect measurements, combined with spot mode CL spectroscopy, is used to determine the carrier concentrations at specific positions along single nanowires. The results obtained via luminescence measurements provide an accurate and rapid feedback technique for the epitaxial development of doping incorporation in nanowires. The technique has been employed on several series of samples in which growth parameters, such as V/III-ratio, temperature and dopant flows, were investigated in an optimization procedure. The correlation between the Hall effect and luminescence measurements for extracting the carrier concentration of different samples were in excellent agreement.

Strain and morphology compliance during the intentional doping of high-Al-content AlGaN layers

This study presents analysis of the residual strain and related surface morphology of high-Al-content Al0.82Ga0.18N layers doped by silicon up to the level of 3 × 1019 cm−3. We focus on understanding the basic mechanisms which underlie the formation of the distinct surface morphology of the Al0.82Ga0.18N:Si layers and their conductivity. We discuss the development of certain facet structure (nanopipes) within the doped layers, which is apparent at the high Si doping levels. The formation of nanopipes influences the conductivity of the layers. It is anticipated to give rise to facets with SiN-related coverage, outcompeting the incorporation of Si at substitutional donor sites in the lattice. We do not find evidence for kinetic stabilization of preferential crystallographic facets when a dopant flow of bis(cyclopentadienyl)magnesium (Cp2Mg), instead of silane (SiH4), is implemented in the doping process.

Application of a novel metabolomic approach based on atmospheric pressure photoionization mass spectrometry using flow injection analysis for the study of Alzheimer׳s disease

The use of atmospheric pressure photoionization is not widespread in metabolomics, despite its considerable potential for the simultaneous analysis of compounds with diverse polarities. This work considers the development of a novel analytical approach based on flow injection analysis and atmospheric pressure photoionization mass spectrometry for rapid metabolic screening of serum samples. Several experimental parameters were optimized, such as type of dopant, flow injection solvent, and their flows, given that a careful selection of these variables is mandatory for a comprehensive analysis of metabolites. Toluene and methanol were the most suitable dopant and flow injection solvent, respectively. Moreover, analysis in negative mode required higher solvent and dopant flows (100µlmin−1 and 40µlmin−1, respectively) compared to positive mode (50µlmin−1 and 20µlmin−1). Then, the optimized approach was used to elucidate metabolic alterations associated with Alzheimer׳s disease. Thereby, results confirm the increase of diacylglycerols, ceramides, ceramide-1-phosphate and free fatty acids, indicating membrane destabilization processes, and reduction of fatty acid amides and several neurotransmitters related to impairments in neuronal transmission, among others. Therefore, it could be concluded that this metabolomic tool presents a great potential for analysis of biological samples, considering its high-throughput screening capability, fast analysis and comprehensive metabolite coverage.