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Su X.,CAS Suzhou Institute of Nano Technology and Nano Bionics | Zhang J.,CAS Suzhou Institute of Nano Technology and Nano Bionics | Zhang J.,Suzhou Nanowin Science and Technology Co. | Huang J.,CAS Suzhou Institute of Nano Technology and Nano Bionics | And 4 more authors.
Journal of Crystal Growth | Year: 2017

Defect structures were investigated by transmission electron microscopy for AlN/sapphire (0 0 0 1) epilayers grown by high temperature hydride vapor phase epitaxy using a growth mode modification process. The defect structures, including threading dislocations, inversion domains, and voids, were analyzed by diffraction contrast, high-resolution imaging, and convergent beam diffraction. AlN film growth was initiated at 1450 °C with high V/III ratio for 8 min. This was followed by low V/III ratio growth for 12 min. The near-interfacial region shows a high density of threading dislocations and inversion domains. Most of these dislocations have Burgers vector b = 1/3〈1 1 2 0〉 and were reduced with the formation of dislocation loops. In the middle range 400 nm < h < 2 μm, dislocations gradually aggregated and reduced to ∼109 cm−2. The inversion domains have a shuttle-like shape with staggered boundaries that deviate by ∼ ±5° from the c axis. Above 2 μm thickness, the film consists of isolated threading dislocations with a total density of 8 × 108 cm−2. Most of threading dislocations are either pure edge or mixed dislocations. The threading dislocation reduction in these films is associated with dislocation loops formation and dislocation aggregation-interaction during island growth with high V/III ratio. © 2017 Elsevier B.V.


Sun M.S.,CAS Suzhou Institute of Nano Technology and Nano Bionics | Sun M.S.,Shanghai University | Zhang J.C.,CAS Suzhou Institute of Nano Technology and Nano Bionics | Zhang J.C.,Suzhou Nanowin Science and Technology Co | And 5 more authors.
Journal of Crystal Growth | Year: 2016

AlN thin films have been grown on GaN/sapphire templates, 6 H-SiC and sapphire by hydride vapor phase epitaxy. The influence of growth conditions and substrates on the crystal qualities and growth mode has been investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM). The results showed that the low pressure was favorable for high-quality AlN thin film growth around 1000 °C. The full-width at half-maximum (FWHM) of (0002) XRD of 200-nm AlN thin film grown on GaN/sapphire, 6 H-SiC and sapphire are 220, 187 and 260 arc s, respectively. While the corresponding counterparts of (10-12) are 1300, 662 and 2650 arc s, respectively. Both suggested that low dislocation density in AlN grown on 6 H-SiC. The morphology of AlN thin film on sapphire showed islands without coalescence initially, and then changed to be coalescent with atomic steps at 1200 nm. However, those for samples on 6 H-SiC and GaN/sapphire showed smooth surface with clear atomic steps at thickness of 200 nm. The result indicated different growth modes of AlN on different substrates. It was believed that the different lattice mismatchs between AlN and substrates led to the different crystal qualities and growth modes. © 2015 Elsevier B.V. All rights reserved.


Zhang M.,CAS Suzhou Institute of Nano Technology and Nano Bionics | Zhang M.,CAS Institute of Physics | Zhang M.,University of Chinese Academy of Sciences | Zhou T.F.,CAS Suzhou Institute of Nano Technology and Nano Bionics | And 15 more authors.
Applied Physics Letters | Year: 2012

A study on the bound states of Fe impurities in GaN by ultraviolet photoluminescence (PL) emissions is presented. Two elusive PL lines were observed at 3.463 eV (L1) and 3.447 eV (L2), respectively. The intensities of the two lines are proportional to the Fe concentration. The temperature dependence of L1 and L2 revealed acceptor-like and strong localized characteristic, respectively. Furthermore, Raman analysis indicated that L2 is correlated to an exciton bound to a nitride-vacancy (V N) related complex, i.e., [Fe 2+-V N]. By co-doping with Si, the [Fe 2+-V N]-related bound state will enable the spin-coupling between isolated iron ions. © 2012 American Institute of Physics.


Fan Y.,CAS Suzhou Institute of Nano Technology and Nano Bionics | Fan Y.,University of Chinese Academy of Sciences | Liu Z.,CAS Suzhou Institute of Nano Technology and Nano Bionics | Xu G.,CAS Suzhou Institute of Nano Technology and Nano Bionics | And 9 more authors.
Applied Physics Letters | Year: 2014

The propagation properties of surface acoustic waves (SAWs) in semi-insulating Fe-doped GaN films grown on sapphire substrates by hydride vapor phase epitaxy are investigated. Compared with native n-type GaN, Fe-doped GaN exhibits a higher electromechanical coupling coefficient due to its high electrical resistivity. In addition, guided longitudinal leaky surface acoustic wave (LLSAW) was observed experimentally with a very high phase velocity (about 7890m/s), and this mode was verified by numerical simulations. The small propagation attenuation of LLSAW along liquid/solid interfaces was demonstrated in glycerol solutions, which implies the potential applications in high-frequency chemical sensing. © 2014 AIP Publishing LLC.


Huang J.,CAS Suzhou Institute of Nano Technology and Nano Bionics | Huang J.,CAS Institute of Semiconductors | Huang J.,University of Chinese Academy of Sciences | Xu K.,CAS Suzhou Institute of Nano Technology and Nano Bionics | And 12 more authors.
Applied Physics Letters | Year: 2011

The dislocation multiplication and movement mechanism in GaN single crystals has been studied using nanoindentation and cathodoluminescence. Dislocation loops can multiply and move from plane to plane by cross-slip, thus producing a wide plastic deformation in GaN during indentation. This mechanism is further supported by the remarkable movement of indentation induced dislocations during annealing. Furthermore, the so-called pop-in events, in which the indenter suddenly enters deeper into the material without the application of any additional force, can be better understood by considering the cross-slip mechanism. © 2011 American Institute of Physics.


Zhong H.,CAS Suzhou Institute of Nano Technology and Nano Bionics | Zhong H.,University of Chinese Academy of Sciences | Liu Z.,CAS Suzhou Institute of Nano Technology and Nano Bionics | Xu G.,CAS Suzhou Institute of Nano Technology and Nano Bionics | And 9 more authors.
Applied Physics Letters | Year: 2012

Understanding the contact properties of graphene on semiconductors is crucial to improving the performance of graphene optoelectronic devices. Here, we show that when graphene is in contact with a semiconductor, the charge carrier transport into graphene leads to a self-adaptive shift of the Fermi level, which tends to lower the barrier heights of the graphene contact to both n- and p-type semiconductors. A theoretical model is presented to describe the charge carrier transport mechanism and to quantitatively estimate the barrier heights. These results can benefit recent topical approaches for graphene integration in various semiconductor devices. © 2012 American Institute of Physics.


Zhong H.,CAS Suzhou Institute of Nano Technology and Nano Bionics | Xu K.,CAS Suzhou Institute of Nano Technology and Nano Bionics | Xu K.,Suzhou Nanowin Science and Technology Co. | Liu Z.,CAS Suzhou Institute of Nano Technology and Nano Bionics | And 8 more authors.
Journal of Applied Physics | Year: 2014

Graphene has been proposed as a material for semiconductor electronic and optoelectronic devices. Understanding the charge transport mechanisms of graphene/semiconductor Schottky barriers will be crucial for future applications. Here, we report a theoretical model to describe the transport mechanisms at the interface of graphene and semiconductors based on conventional semiconductor Schottky theory and a floating Fermi level of graphene. The contact barrier heights can be estimated through this model and be close to the values obtained from the experiments, which are lower than those of the metal/semiconductor contacts. A detailed analysis reveals that the barrier heights are as the function of the interface separations and dielectric constants, and are influenced by the interfacial states of semiconductors. Our calculations show how this behavior of lowering barrier heights arises from the Fermi level shift of graphene induced by the charge transfer owing to the unique linear electronic structure. © 2014 AIP Publishing LLC.


Zhong H.,CAS Suzhou Institute of Nano Technology and Nano Bionics | Liu Z.,CAS Suzhou Institute of Nano Technology and Nano Bionics | Shi L.,CAS Suzhou Institute of Nano Technology and Nano Bionics | Xu G.,CAS Suzhou Institute of Nano Technology and Nano Bionics | And 8 more authors.
Applied Physics Letters | Year: 2014

The wrinkles of single layer graphene contacted with either n-GaN or p-GaN were found both forming ohmic contacts investigated by conductive atomic force microscopy. The local I-V results show that some of the graphene wrinkles act as high-conductive channels and exhibiting ohmic behaviors compared with the flat regions with Schottky characteristics. We have studied the effects of the graphene wrinkles using density-functional-theory calculations. It is found that the standing and folded wrinkles with zigzag or armchair directions have a tendency to decrease or increase the local work function, respectively, pushing the local Fermi level towards n- or p-type GaN and thus improving the transport properties. These results can benefit recent topical researches and applications for graphene as electrode material integrated in various semiconductor devices. © 2014 AIP Publishing LLC.


Liu Z.,CAS Suzhou Institute of Nano Technology and Nano Bionics | Ren G.,CAS Suzhou Institute of Nano Technology and Nano Bionics | Ren G.,Suzhou Nanowin Science and Technology Co. | Shi L.,CAS Suzhou Institute of Nano Technology and Nano Bionics | And 5 more authors.
CrystEngComm | Year: 2015

The effect of different carbon types, including carbon nanotubes, active carbon, graphene, graphite, and ordered mesoporous carbon, on the suppression of polycrystal generation and morphology of GaN polycrystals grown by the Na flux method has been studied for the first time. The results of GaN growth by adding different purity graphite indicate that graphite with higher purity is better than lower purity ones at suppressing polycrystal generation. Furthermore, by comparing the different types of carbon, it is found that the suppression effect increases in the following order: carbon nanotubes, active carbon, graphene, graphite, and ordered mesoporous carbon, accompanied by the evolution of morphology. First-principles calculation and specific surface area measurement show that the C-N bond energy in carbon plays a key role in suppressing the polycrystals, rather than the specific surface area of carbon. A mechanism of C-N bonding in Na-Ga melts has been proposed to illustrate the difference in suppressing polycrystal generation and morphology evolution. © The Royal Society of Chemistry 2015.


Xu K.,CAS Suzhou Institute of Nano Technology and Nano Bionics | Xu K.,Suzhou Nanowin Science and Technology Co. | Wang J.-F.,CAS Suzhou Institute of Nano Technology and Nano Bionics | Wang J.-F.,Suzhou Nanowin Science and Technology Co. | And 2 more authors.
Chinese Physics B | Year: 2015

Three main technologies for bulk GaN growth, i.e., hydride vapor phase epitaxy (HVPE), Na-flux method, and ammonothermal method, are discussed. We report our recent work in HVPE growth of GaN substrate, including dislocation reduction, strain control, separation, and doping of GaN film. The growth mechanisms of GaN by Na-flux and ammonothermal methods are compared with those of HVPE. The mechanical behaviors of dislocation in bulk GaN are investigated through nano-indentation and high-space resolution surface photo-voltage spectroscopy. In the last part, the progress in growing some devices on GaN substrate by homo-epitaxy is introduced. © 2015 Chinese Physical Society and IOP Publishing Ltd.

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