bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Moderate Temperature Mg Diffusion Doping of GaN
Authors: Voss Lars F. , Frye Clint D. , Allen Noah A. , Harrison Sarah E. , Kweon Kyoung , Varley Joel Basile , Lordi Vincenzo , Nikolic Rebecca , Anderson Travis J. , Hite Jennifer K. 
Published: December 2020

Ex-situ p-type doping of GaN has been a long-standing challenge and prevented adoption of numerous devices. While regrowth of p-GaN on etched surfaces and ion implantation have made progress, technical challenges remain. Diffusion of Mg into GaN has received considerably less attention, primarily due to the extremely low diffusivity of Mg in GaN as well as the instability of GaN at the temperatures required (typically >1000oC), as well as its propensity to form compensating defects. Here, we report on a new technique for diffusion doping of GaN with Mg at relevant temperatures (under 1000oC). This approach uses a bi-layer structure, with a solid Mg source in contact with the GaN combined with a metal capping layer. Using this approach, we have measured significant diffusion of Mg into GaN by Secondary Ion Mass Spectrometry at temperatures as low as 800oC and time on the order of minutes (Figure 1) with concentrations exceeding 1019 cm-3 and Mg extending >100 nm into the GaN film. Room temperature Hall effect measurements confirm p-type conductivity under a limited set of diffusion conditions. In other cases, compensation of the diffused Mg by formation of defects during diffusion resulted in highly resistive layers. Photo-Hall measurements using sub-band gap light of different wavelengths was used to excite both holes and electrons, depending on the wavelength. Samples with higher measured Mg concentration show correspondingly increased hole density under illumination with 2 eV light. These results strongly imply the diffusion of Mg through Ga sites, but with corresponding formation of compensating defects as the material becomes more p-type. Density functional theory (DFT) calculations on the diffusivity of Mg through various pathways as well as the formation energies of various compensating defects suggest a path towards achieving higher Mg concentrations with high free hole concentrations.
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, LLNL-ABS-810935. This support does not constitute an express or implied endorsement on the part of the Government. The information, data, or work presented herein was funded in part by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, PNDIODES program monitored by Dr. Isik Kizilyalli.
Figure 1: Mg profiles after diffusion at 800oC for 5 minutes

Figure 1
Characterization of Dislocations in 4H-SiC Single Crystals at the Initial Growth Stage by Synchrotron X-ray Topography
Authors: Ailihumaer Tuerxun , Peng Hongyu , Liu Yafei , Raghothamachar Balaji , Dudley Michael 
Published: December 2020

In recent years, 4H-SiC has become a widely acknowledged material applied in high power electronics. 4H-SiC-based devices are able to operate at high voltage, high current and high temperature due to its superior physical properties. However, they have yet to reached to the requirements for mass production, due to the fact of SiC’s relatively inferior crystal quality. Over the past few decades, the effect of various dislocations existing in the crystals such as threading screw/mixed dislocations (TSD/TMDs), threading edge dislocations (TEDs) and basal plane dislocations (BPDs) has been studied and revealed to be main source for degrading the reliability of SiC power devices[1-2]. Recently, studies on the early stages of physical vapor transport (PVT) growth of SiC have been reported by several groups regarding to the investigation of the step morphology and lattice plane bending [3-5]. However, dislocation propagation behavior and their formation mechanism at the early growth stages are yet to be studied in detail.
This paper describes the investigation of dislocation behavior during the early stages of PVT-grown 6-inch 4H-SiC crystals by synchrotron monochromatic beam x-ray topography (SMBXT) technique. Ray tracing simulation was applied to simulate the dislocation images. Our studies show that most of the TSDs/TMDs are replicated into the newly grown crystal while most TEDs are generated by either nucleation in pairs at the seed/crystal interface or by redirection of BPDs in the seed crystal. Most BPDs in the newly grown layer are of screw type with 1/3[11-20] and this has been verified by comparison with ray tracing simulated images. TEDs with the same and opposite sign of Burgers vector are found to be deflected on to same basal plane by the overgrowth of macro-steps and start to glide in the same and opposite directions respectively. TMDs deflected on to the basal plane by macro-steps get dissociated into c and a components, with the a segment undergoing glide to form V-shaped configurations.
[1] St.G. Muller, J.J. Sumakeris, M.F. Brady, R.C. Glass, H.M. Hobgood, J.R. Jenny, R. Leonard, D.P. Malta, M.J. Paisley, A.R. Powell, V.F. Tsvetkov, S.T. Allen, M.K. Das, J.W. Palmour, and C.H. Carter. Jr., Eur. Phys. J. Appl. Phys. 27, 29 (2004).
[2] R. Singh and M. Pecht, IEEE Ind Electron M 2, 19 (2008).
[3] E.K. Sanchez, J.Q. Lin, M.De. Graef, M. Skowronski, W.M. Vetter, M. Dudley, J. Appl. Phys. 91 (3) (2002) 1143.
[4] C. Ohshige, T. Takahashi, N. Ohtani, M. Katsuno, T. Fujimoto, S. Sato, H. Tsuge, T. Yano, H. Matsuhata, M. Kitabatake, J. Cryst. Growth 1-6, 408 (2014).
[5] N. Ohtani, C. Ohshige, M. Katsuno, T. Fujimoto, S. Sato, H. Tsuge, W. Ohashi, T. Yano, H. Matsuhata, M. Kitabatake, J. Cryst. Growth 9-15, 386 (2014).

Figure 1
Real Impacts of Ligand-Capped Nanocrystals in Perovskite Solar Cells
Authors: Gong Oh Yeong , Kim Youngsik , Kim Dong Hoe , Han Gill Sang , Jeong Sohee , Jung Hyun Suk 
Published: December 2020

Perovskite solar cells (PSCs) has been reached the certified power conversion efficiency (PCE) of 25.2 % in 2019. They are having received large attention because of their superior optoelectronic properties (such as high charge carrier mobility, tunable bandgap, high absorption coefficient) and even the cost-effective process.
In the latest fabrication process for high-efficiency PSCs, surface-defect engineering of perovskite film has attracted tremendous attention. Because, the control of surface-defects can play a critical role in grain boundaries of perovskite, and interfaces between perovskite and charge transport layer, leading to PSCs with further improved photovoltaic (PV) performance and long-term stability. There are many exertion for reducing surface-defects state densities of perovskite film by applying an additional passivation layer, for instance cross-linked molecules and two-dimensional (2D) materials (2D-perovskite, graphene, and MoS2) at surface of perovskite film.
Most recently, perovskite nanocrystals (NCs) are being investigated as an additional layer for high-efficiency PSCs owing to anticipation of their multifunctional properties including high light-harvesting properties, efficient charge transport by carrier cascade effect, and surface passivation effect. However, it seems to remain under question whether these functions are related to the light-harvesting, suitable band alignment, and surface passivation for PSCs, due to ligand capped NCs.
In this study, we investigated that the functions of NCs layer in PSCs with various NCs capped same ligand. To confirm the effects of NC layer in PSCs, we fabricated n-i-p planar devices, which follow FTO/c-TiO2/Perovskite/NC layer/Spiro-OMeTAD/Au structure with three kinds of NCs (CsPbBr3, CsPbI3, and InP). All these NCs have different electrical and optical properties, but nevertheless the devices with each NC layer showed similarly improved PV performance.
In analysis results of each function of the NC layer, there were no light-harvesting effects by all NCs layer due to high absorption coefficient and sufficient thickness of perovskite film. In addition, NC layer could not work as a carrier cascade layer at the interface between the perovskite film and hole transport layer due to poor electrical properties of capping ligand. Finally, the NC layer affected only on the surface passivation of perovskite film, and furthermore we found that Oleylamine (OLA) ligand of the NCs was a major cause of the surface passivation effect. We believe that the optimization of the surface passivation effect of fatty amine ligands can further improve the PV performance of PSCs.
Fabrication of Oriented FTO Film Grown By Spray Pyrolysis
Authors: Yoshino Kenji , Kamimizutaru Koki , Narita Yuki , Minemoto Takashi , Iikubo Satoshi , Shen Qing , Hayase Shuzi 
Published: December 2020

SnO2 behaves like an n-type semiconductor with a wide energy gap (~ 3.8 eV) and has a tetragonal structure which is similar to the rutile structure. Of the various potential dopants for SnO2, fluorine is preferred because F-doped SnO2 (FTO) films show high transparency and good conductivity. The spray pyrolysis method is the most convenient method because of its simple and inexpensive experimental arrangement and the ease with which doping materials can be added. However, there are few reports on the growth and detailed analysis of FTO films deposited by spray pyrolysis.
In previous work1, transparent conducting oxide films of non-doped SnO2 and FTO were deposited on glass substrates at 500 °C by spray pyrolysis in order to determine the effect of spray solution concentration and substrate temperature. The films were all polycrystalline with tetragonal crystal structures. The best electro-optic properties were achieved with a fluorine doping concentration of 17 mol%. These conditions resulted in a film with an average optical transmittance of 82%, a resistivity of 4.0 × 10-4 Ωcm, a carrier concentration of 4.7 × 1020 cm-3 and a mobility of 34 cm2 (V s)-1.
In this work, oriented SnO2 and FTO films were deposited on glass substrates by spray pyrolysis. The (110) or (200) orientation film could be obtained by means of the Sn solution concentration. Furthermore, low surface roughness could be also obtained by means of the sample thickness. Oriented FTO film with low surface roughness could be obtained by controlling two methods such as the Sn solution concentration and thickness.

1 M. Oshima, M and K. Yoshino, J. Electron. Mater. 2010, 39, 819-822.
TCAD Simulation of a 3D NAND Memory Utilizing In-Ga-Zn-Oxide: "3D OS NAND" with 4 V Drive, High Endurance and Density
Authors: Kunitake Hitoshi , Kimura Hajime , Tsuda Kazuki , Godo Hiromichi , Murakawa Tsutomu , Sawai Hiromi , Baba Haruyuki , Sasagawa Shinya , Ikeda Takayuki , Yamazaki Shunpei 
Published: December 2020

Memory-centric computing has been actively researched for AI application. To achieve this, there are growing demands on memories for high density and high endurance. To demonstrate the application, a variety of emerging memory technologies have been proposed; however, they still have difficulties in achieving a density comparable to NAND flash and in improving endurance.
CAAC-IGZO, with a wide bandgap and a heavy hole effective mass, can be applied to a field-effect transistor that is characterized by its extremely-low off-leakage current. Use of CAAC-IGZO FET in non-display fields has been reported in recent years, and 3D NAND utilizing CAAC-IGZO FET has been researched. However, the reported memory cell architecture involves through-dielectric charge trapping in MONOS structures, and has low endurance in the same way as conventional Si-based NAND flash.
In view of the above, we propose a 3D OS NAND memory, a vertically-stackable 2Tr-1C memory having CAAC-IGZO FETs. Potentially, this memory not only enjoys main features of NAND flash such as high density and non-volatility, but also achieves a DRAM-like endurance. In this study, we evaluated our novel memory architecture with TCAD Sentaurus produced by Synopsys.
The cross section, circuit diagram, and 3D overall structure of the memory cell are shown in Fig. 1(a), Fig. 1(b), and Fig. 1(c), respectively. The 3D OS NAND has a memory cell architecture in which a pair of vertically-positioned transistors on the A-A' plane is connected in series to another pair in the Z-axis direction. Taking advantage of extremely-low off-leakage current of CAAC-IGZO FET, the memory cell is composed of only a switching CAAC-IGZO FET and a MIM capacitor. The timing chart of a string of four memory cells connected in the Z-axis direction is shown in Fig. 1(d). Write operation is performed by sequentially lowering the voltage of WG from the bottom with respect to the Z-axis direction, and read operation is performed by lowering the voltage of CG of the memory cell being read. The retention properties of memory cells to which a checker pattern is written are shown in Fig. 1(e). The device simulation indicates a possibility that a memory cell composed of only an CAAC-IGZO FET and a MIM capacitor achieves a retention time of 109 sec or longer.
In this paper, we propose a novel memory architecture with CAAC-IGZO FET by discussing the overview of 3D OS NAND and its write and read performance.
Fig. 1(a) Cross section of 3D OS NAND memory cell, (b) circuit diagram of 3D OS NAND memory cell, (c) 3D structure of 3D OS NAND, (d) timing chart of 3D OS NAND, and (d) retention properties of 3D OS NAND

Figure 1
Low Temperature Growth of Wafer-Scale 2D MoS2 Thin Films By Pulsed Plasma-Enhanced Chemical Vapor Deposition
Authors: Choi Jeong-Hun , Lee Seung Won , Kim Hyo-Bae , Ha Min-Ji , Ahn Ji-Hoon 
Published: December 2020

Layered two-dimensional molybdenum sulfide (MoS2) has attracted great interest for a promising candidate material for opto-electronic, sensing and catalysis applications due to its outstanding mechanical, electrical and optical properties. In order to apply MoS2 to the industrial field, significant efforts have been placed in obtaining a wafer-scale uniform MoS2. There have been many progressions in various methods such as thermal-CVD [1] and ALD [2], but these methods have crucial limitation that they demand either high growth temperature or post-thermal treatment. In the present study, to overcome the limitation of traditional method, pulsed plasma-enhanced chemical vapor deposition was adopted for the growth of MoS2 thin films. By using H2S plasma reactant, the growth temperature could be significantly lower than in the previous way. The pulsing of Mo precursor injection properly regulates the Mo precursor partial-pressure ratio that is crucial for the synthesis of MoS2. Through these strategies, mono to few layers of MoS2 thin films was deposited uniformly on SiO2/Si substrates. X-ray photoelectron spectroscopy and transmission electron microscopy demonstrated the composition and crystallinity of MoS2 thin films depends on the plasma conditions. Furthermore, through optimizing the plasma conditions, the potential of MoS2 for electric device component was investigated.
Fig1. (a) Raman spectra of MoS2 thin films (b) XPS spectra of Mo 3d(left), S 2p(right) obtained from MoS2 thin films deposited by pulsed PECVD.

References [1] Hyun Cheol-Min, et al. Journal of Alloys and Compounds, 2018, 765: 380-384.
[2] TAN, Lee Kheng, et al. Nanoscale, 2014, 6.18: 10584-10588.

Figure 1
Enhanced Thermoelectric Performance of Porous SrTiO3 with Exsolved Ni Nanoparticles
Authors: Ohtaki Michitaka , Hirata Shinji , Suekuni Koichiro 
Published: December 2020

Nanocomposite structuring is one of the key directions to improve the thermoelectric performance of bulk materials by enabling a significant reduction of the thermal conductivity and a possible enhancement in the power factor at the same time. In this paper, we report a strongly enhanced thermoelectric performance of porous SrTiO3 (STO) doped with Nb and Ni, which subsequently contained Ni nanoparticles formed after an exsolution reaction caused by a reducing post-treatment.
Samples with a representative composition of Sr0.95(Ti0.8Nb0.2)0.95Ni0.05O3 (STNNO) were prepared by conventional solid state reaction of SrCO3, TiO2, Nb2O5, and NiO. The mixed raw powders were calcined once at 1273 K and twice at 1623 K in air to achieve the single phase of the STO structure. The resulting powder was mixed with a graphite powder and heated in air to remove graphite, forming loosely sintered bodies with a porous structure. The samples were finally heated at 1693 K for 10 h in air for sintering, and subsequently reduced at 1623 K for 20 h in 0% - 20% H2/N2.
While the XRD patterns remained the same as the single phase of the STO structure even after the reducing treatment, SEM/EDS observation of the cross section of the samples revealed discretely dispersed Ni nanoparticles of ca. 50 nm in diameter inside of the sintered bodies. Whereas the electrical conductivity, σ, of the sample reduced in 20% H2 was significantly higher than that reduced in 5% H2, the Seebeck coefficient, S, of the former was just negligibly lower than the latter, being very insensitive to the sintering temperature and reducing atmosphere. However, the lattice thermal conductivity, κ
ph, was the lowest for the sample reduced in 20% H2, resulting in ZT = 0.6 at 1073 K as the highest value among the STNNO-based oxides so far reported. These results imply that the reducing treatment caused the electron doping in STO as well as the exsolution of Ni nanoparticles simultaneously, resulting in the increased σ and the suppressed κ
ph. The barely noticeable changes in S might be related to the large effective mass of electrons in the Ti 3d orbitals.
MFe2O4(M=Co, Mn)@MG as an Efficient Counter Electrode for Dye-sensitized Solar Cells
Authors: Zhang Meili , Chen Xiang , Zhou Cheng , Dong Hongzhou , Pang Beili , Yu Liyan , Dong Lifeng 
Published: December 2020

Dye-sensitized solar cells (DSSCs) are considered as low-cost and eco-friendly alternatives for conventional silicon solar cells. Dye-sensitized metal oxide photoelectrode, electrolyte and counter electrode (CE) are the three major components of a DSSC. An ideal CE material should have superior electrocatalytic activity and distinguished conductivity, excellent chemical stability, and low cost. Noble metal Pt CE has an efficient capacity for collecting electrons from external circuits and facilitating the catalytic reduction of I3
- to I-. However, its high cost seriously restricts mass production and commercialization of DSSCs. Therefore, carbon composite materials, inorganic compounds, conducting polymers and their derivatives have been widely explored as CEs in DSSCs.
Recently, multiple transition metals and their derivative have been investigated as the CE materials for DSSCs. Theoretically, binary or ternary transition metals display intrinsic electrocatalytic activity toward the reduction of I3
- with rapid charge-transfer ability and cost-effectiveness. Thus, transition-metal ferric acid MFe2O4 (M=Mn, Co) composited with modified graphene (MG) is a novel strategy to achieve an advanced CE material with remarkable electrochemical performance. As we all know, graphene microstructure has a lamellar structure. Through a process of catalytic reduction, a curly structure modified graphene not only displays a large specific surface area to facilitate charge transfer and promote catalytic performance during photoelectric conversion, but also the conjugated structure with continuous sp2 hybridized carbon centers can induce electronic mobility.
Ferrite is a unique hierarchical nanostructure material mainly composed of transition metal (i.e., Co, Mn, Ni), iron (Fe), and oxygen (O). Transition-metal ions M2+ (M2+ =Mn2+, Co2+) have excellent electrocatalytic capability, and active Fe atoms can synergize with carbon atoms in graphene to significantly improve catalytic activity. This work offers a strategy to apply MFe2O4(M=Mn, Co)@MG composite as the CE of DSSCs to optimize catalytic sites and improve catalytic performance. The device based on the CoFe2O4@MG CE achieves a PCE of 7.78%, and the device based on MnFe2O4@MG CE has a PCE of 5.55%. Moreover, the device was prepared by a simple process with an excellent stability in the air atmosphere without encapsulation (maintaining 93.3% of an initial PCE after 30 days), which can facilitate large-scale production in the future.
(Invited) Programmed Assembly of Designer Solids from Molecular Building Blocks: A Route Towards Digitalization of Materials Research?
Authors: Woell Christof 
Published: December 2020

Realizing multifunctional “Designer Solids” by programmed assembly of building units taken form libraries is a very appealing objective in connection with Materials Research entering the Information Era. Metal-organic frameworks (MOFs) have attracted a huge interest in this context, owing to their enormous wealth of different compounds – the number of characterized elements of this rapidly growing class of materials has just exceeded 100.000. Here, we will focus on a subset of MOF-based functional materials, including electrochemical, photoelectrochemical, photovoltaic and optical devices. In addition to 3D structures, also 2D interfaces in MOF heterostructures are of interest, e.g. with regard to photon-upconversion. Since the fabrication of reliable and reproducible contacts to MOF-materials represent a major challenge, we have developed a layer-by-layer (lbl) deposition method to produce well-defined, highly oriented and monolithic MOF thin films on a number of different substrates. The resulting films are referred to as SURMOFs [1,2]. The fabrication of hetero-multilayers (see Fig. 1) is rather straightforward with this lbl method. In this talk, we will describe the principles of SURMOF fabrication as well as the results of systematic investigations of electrical and photophysical properties exhibited by empty MOFs and after loading their pores with functional guests. As a final point, we will discuss further applications realized by loading MOFs with nanoparticles or quantum dots. We will close with a more general discussion on the potential of programming functionalities into MOFs using in-silico screening methods.[3]

References:

[1] J. Liu, Ch. Wöll, Chem. Soc. Rev. 46, 5730-5770 (2017)
[2] L. Heinke, Ch. Wöll, Advanced Materials 31 (26), 1970184 (2019)
[3] R. Haldar, A. Mazel, M. Krstic, Q. Zhang, M. Jakoby, I. A. Howard, B. S. Richards, N. Jung, D. Jacquemin, S. Diring, W. Wenzel, F. Odobel, Ch. Wöll, Nature Comm., 10, 2048 (2019)