Suchergebnisse

In the quest of developing high performance electronic and optical devices and more cost effective fabrication processes of monoclinic beta-Ga2O3, new growth techniques and fundamental electronic and optical properties of defects have to be explored. By heating of dissolved metallic Ga in HCl in a NH3 and N-2 atmosphere, nano-flake films of monoclinic beta-phase Ga2O3 were grown as confirmed by XRD. From optical measurements, we observe two strong emissions. A red band peaking at similar to 2.0 eV and a UV band at similar to 3.8 eV. The band at similar to 2.0 eV is attributed to donor-acceptor pair recombination where the donor and acceptor level is suggested to be related to VO and nitrogen, respectively. By studying the dependence of the intensity of the UV band at 3.8 eV versus excitation density, a model is suggested. In the model, it is assumed that local potential fluctuations forming minima (maxima), where the carriers would be localized with a summarized band offset for conduction and valence band of 1 eV. The origin of the fluctuations is tentatively suggested to be related to micro-inclusions of different phases in the film. ; Funding Agencies|Swedish Research Council (VR); Swedish Energy Agency; Swedish Government Strategic Research Area in Materials Science on Functional Materials (AFM); Carl Triggers foundation; Angpanneforeningen; Russian Science Foundation [16-12-10503]; FP7 IRSES HyMeCav; FP7 ITN NOTEDEV

Freestanding n-type intentionally doped GaN layers grown by halide vapor phase epitaxy (HVPE) were studied by transient photoluminescence (PL). Concentrations of silicon and oxygen were varied in the range between 10(17) and 10(18) cm(-3), as confirmed by secondary ion mass spectroscopy (SIMS). We show that a reduction of the background silicon concentration by one order of magnitude compared to the background level in undoped samples can be achieved by incorporation of oxygen during the growth. A strong band gap narrowing (BGN) of similar to 6 meV was observed with increasing doping in the studied samples. The low temperature PL recombination time for donor-bound excitons (DBEs) was found to depend significantly on donor concentration. A model assuming generation of DBEs by capturing of free excitons by neutral donors explains the experimental results at low temperature. From fitting the experimental DBE lifetime to the model, the donor concentration dependence for O and Si donors could be reproduced. An effective exciton capture cross-section was found to be similar to 9.4 x 10(-15) and 1.2 x 10(-14) cm(2) for silicon and oxygen donors, respectively. ; Funding Agencies|Swedish Research Council (VR)||Swedish Energy Agency||Swedish Governmental Agency for Innovation Systems (VINNOVA)||

The effect of Mg doping on stacking fault (SF) formation in c-plane GaN grown by metal-organic chemical-vapor deposition has been studied for Mg concentration between 2 x 10(18) cm(-3) and 5 x 10(19) cm(-3). Transmission electron microscopy studies demonstrate a direct correlation between the increasing Mg content and the number of small (3-10-nm long) SFs present. The energy dispersive x-ray analysis (EDX) line profile of a SF shows that the Mg-impurity atom resides at a distance approximately 5 nm from the SF. Cathodoluminescence (CL) mapping reveals that the Mg-doped regions radiate at energies corresponding to known SF emission peaks. SF-related peaks in CL spectra show metastability, which may be attributed to transfer processes involving Mg acceptors and nearby associated SFs. ; Funding Agencies|Swedish Energy Agency||Swedish Research Council (VR)||Swedish Governmental Agency for Innovation Systems (VINNOVA)||

Metal halide perovskites have demonstrated impressive properties for achieving efficient monochromatic light-emitting diodes. However, the development of white perovskite light-emitting diodes (PeLEDs) remains a big challenge. Here, we demonstrate a single-emissive-layer all-perovskite white PeLED using a mixed halide perovskite film as the emissive layer. The perovskite film consists of separated mixed halide perovskite phases with blue and red emissions, which are beneficial for suppressing halide anion exchange and preventing charge transfer. As a result, the white PeLED shows balanced white light emission with Commission Internationale de L'Eclairage coordinates of (0.33, 0.33). In addition, we find that the achievement of white light emission from mixed halide perovskites strongly depends on effective modulation of the halide salt precursors, especially lead bromide and benzamidine hydrochloride in our case. Our work provides very useful guidelines for realizing single-emissive-layer all-perovskite white PeLEDs based on mixed halide perovskites, which will spur the development of high-performance white PeLEDs. ; Funding agencies: ERC Starting Grant (717026), Swedish Energy Agency Energimyndigheten (no. 48758-1), Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (Faculty Grant SFO-Mat-LiU no. 2009-00971), China Scholarship Council

We report on cathodoluminescence (CL) and transmission electron microscopy (TEM) studies of m-plane Mg-doped GaN layers grown by metal-organic vapor phase epitaxy (MOVPE). The layers contain basal plane and prismatic stacking faults (SFs) with a density of ~106 cm-1. Broad emission peaks commonly ascribed to SF were found to be insignificant in these samples. However, a set of quite strong and sharp lines were detected in the same spectral region 3.36-3.42 eV. The observed peaks are tentatively explained as excitons bound to some point defects by analogy with p-type GaAs, since donor-acceptor pair (DAP) recombination was ruled out by the CL mapping experiments. ; funding agencies|Swedish Energy Agency||Swedish Research Council (VR) Linnaeus Environment LiLi-NFM at Linkoping||Carl Trygger Foundation||Swedish Governmental Agency for Innovation Systems (VINNOVA)||National Science Foundation, Division of Materials Research||

InP thin films have been grown on InP/Si substrate by epitaxial lateral overgrowth (ELOG). The nature, origin and filtering of extended defects in ELOG layers grown from single and double openings in SiO2 mask have been investigated. Whereas ELOG layers grown from double openings occasionally exhibit threading dislocations (TDs) at certain points of coalescence, TDs are completely absent in ELOG from single openings. Furthermore, stacking faults (SFs) observed in ELOG layers grown from both opening types originate not from coalescence, but possibly from formation during early stages of ELOG or simply propagate from the seed layer through the mask openings. A model describing their propagation is devised and applied to the existent conditions, showing that SFs can effectively be filtered under certain conditions. ELOG layers grown from identical patterns on InP substrate contained no defects, indicating that the defect-forming mechanism is in any case not inherent to ELOG itself. ; Funding Agencies|Swedish Research Council (VR)||Swedish Foundation for Strategic Research (SSF)||Swedish Governmental Agency for Innovation Systems (Vinnova)||Knut and Alice Wallenberg foundation through the Myfab network and Intel Corporation through the URO program||

Although perovskite light-emitting diodes (PeLEDs) have recently experienced significant progress, there are only scattered reports of PeLEDs with both high efficiency and long operational stability, calling for additional strategies to address this challenge. Here, we develop perovskite-molecule composite thin films for efficient and stable PeLEDs. The perovskite-molecule composite thin films consist of in-situ formed high-quality perovskite nanocrystals embedded in the electron-transport molecular matrix, which controls nucleation process of perovskites, leading to PeLEDs with a peak external quantum efficiency of 17.3% and half-lifetime of approximately 100 h. In addition, we find that the device degradation mechanism at high driving voltages is different from that at low driving voltages. This work provides an effective strategy and deep understanding for achieving efficient and stable PeLEDs from both material and device perspectives. ; Funding Agencies|ERC Starting GrantEuropean Research Council (ERC) [717026]; European Commission Marie Skodowska-Curie Actions [691210]; Swedish Foundation for International Cooperation in Research and Higher Education [CH2018-7736]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009-00971]; China Scholarship CouncilChina Scholarship Council; Jardine Foundation; Cambridge Trust; Linkoping University