Hexagonal GaN films were prepared by nitriding Ga_2O_3 films with flowingammonia. Ga_2O_3 films were deposited on Ga-diffused Si (111) substrates by radio frequency (r.f.)magnetron sputtering. This paper have investig...Hexagonal GaN films were prepared by nitriding Ga_2O_3 films with flowingammonia. Ga_2O_3 films were deposited on Ga-diffused Si (111) substrates by radio frequency (r.f.)magnetron sputtering. This paper have investigated the change of structural properties of GaN filmsnitrided in NH_3 atmosphere at the temperatures of 850, 900, and 950 deg C for 15 min and nitridedat the temperature of 900 deg C for 10, 15, and 20 min, respectively. X-ray diffraction (XRD),scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectronspectroscopy (XPS) were used to analyze the structure, surface morphology and composition ofsynthesized samples. The results reveal that the as-grown films are polycrystalline GaN withhexagonal wurtzite structure and GaN films with the highest crystal quality can be obtained whennitrided at 900 deg C for 15 min.展开更多
We present the growth of CaN epilayer on Si （111） substrate with a single A1GaN interlayer sandwiched between the GaN epilayer and A1N buffer layer by using the metalorganic chemical vapour deposition. The influence...We present the growth of CaN epilayer on Si （111） substrate with a single A1GaN interlayer sandwiched between the GaN epilayer and A1N buffer layer by using the metalorganic chemical vapour deposition. The influence of the AlN buffer layer thickness on structural properties of the GaN epilayer has been investigated by scanning electron microscopy, atomic force microscopy, optical microscopy and high-resolution x-ray diffraction. It is found that an A1N buffer layer with the appropriate thickness plays an important role in increasing compressive strain and improving crystal quality during the growth of AlGaN interlayer, which can introduce a more compressive strain into the subsequent grown GaN layer, and reduce the crack density and threading dislocation density in GaN film.展开更多
High-quality and nearly crack-free GaN epitaxial layer was obtained by inserting a single A1GaN interlayer between GaN epilayer and high-temperature AlN buffer layer on Si （111） substrate by metalorganic chemical va...High-quality and nearly crack-free GaN epitaxial layer was obtained by inserting a single A1GaN interlayer between GaN epilayer and high-temperature AlN buffer layer on Si （111） substrate by metalorganic chemical vapor deposition. This paper investigates the effect of AlCaN interlayer on the structural properties of the resulting CaN epilayer. It confirms from the optical microscopy and Raman scattering spectroscopy that the AIGaN interlayer has a remarkable effect on introducing relative compressive strain to the top GaN layer and preventing the formation of cracks. X-ray diffraction and transmission electron microscopy analysis reveal that a significant reduction in both screw and edge threading dislocations is achieved in GaN epilayer by the insertion of AlGaN interlayer. The process of threading dislocation reduction in both AlGaN interlayer and GaN epilayer is demonstrated.展开更多
We report the reduced-strain gallium-nitride （GaN） epitaxial growth on （0001） oriented sapphire by using quasiporous GaN template. A GaN film in thickness of about 1 μm was initially grown on a （0001） sapphire ...We report the reduced-strain gallium-nitride （GaN） epitaxial growth on （0001） oriented sapphire by using quasiporous GaN template. A GaN film in thickness of about 1 μm was initially grown on a （0001） sapphire substrate by molecular beam epitaxy. Then it was dealt by putting into 45% NaOH solution at 100℃ for lOmin. By this process a quasi-porous GaN film was formed. An epitaxial GaN layer was grown on the porous GaN layer at 1050℃ in the hydride vapour phase epitaxy reactor. The epitaxial layer grown on the porous GaN is found to have no cracks on the surface. That is much improved from many cracks on the surface of the GaN epitaxial layer grown on the sapphire as the same as on GaN buffer directly.展开更多
Cubic phase MgxZn1-x O/MgO multilayer heterostructures （c-Mgx Zn1-xO/MgO MHs） are grown on Si（100） and quartz substrates by reactive electron beam evaporation at low temperature （250℃）. Cross-sectional morpholo...Cubic phase MgxZn1-x O/MgO multilayer heterostructures （c-Mgx Zn1-xO/MgO MHs） are grown on Si（100） and quartz substrates by reactive electron beam evaporation at low temperature （250℃）. Cross-sectional morphology observations by field-emission scanning electron microscopy show the legible interfaces of c-MgxZn1-x O/MgO MHs. X-ray diffraction demonstrates that c-MgxZn1-xO/MgO MHs are of highly （100）-oriented. Optical trans- mission investigations of c-Mgx Zn1-x O/MgO MHs on quartz substrates reveal the coexistence of the two phases, c-MgxZn1-xO and MgO. Photoluminescence examination indicates the emergence of deep-ultraviolet emission centred at about 290nm along with the blue shift of the ultraviolet emission from 405nm to 39Gnm when the nominal thickness of c-MgxZn1-xO well layers of MHs is diminished to 3nm, which is probably originated from quantum confinement effect.展开更多
BiFeO3 (BFO) thin films were prepared on Pt(111)/TiO2/SiO2/Si(100) substrates by the pulsed-laser deposition (PLD) technique at a low temperature of 450℃. The XRD results indicate that the BFO thin films are of perov...BiFeO3 (BFO) thin films were prepared on Pt(111)/TiO2/SiO2/Si(100) substrates by the pulsed-laser deposition (PLD) technique at a low temperature of 450℃. The XRD results indicate that the BFO thin films are of perovskite structure with the presence of small amount of second phases. The oxygen pressures have great effect on the crystalline structures and dielectric properties of BFO thin films. The dielectric constant of the BFO thin films decreases with increasing oxygen pressures, achieving 186, 171 and 160 at the frequency of 104 Hz for the oxygen pressures of 0.666, 1.333 and 13.332 Pa, respectively. The BFO thin films prepared at the oxygen pressure of 0.666 Pa reveal a saturated hysteresis loop with the remanent polarization of 7.5 μC/cm2 and the coercive field of 176 kV/cm.展开更多
Canti-bridged epitaxial lateral overgrowth （CBELO） of GaN is performed by metalorganic chemical vapour deposition （MOCVD） on maskless V-grooved sapphire substrates prepared by wet chemical etching with different m...Canti-bridged epitaxial lateral overgrowth （CBELO） of GaN is performed by metalorganic chemical vapour deposition （MOCVD） on maskless V-grooved sapphire substrates prepared by wet chemical etching with different mesa widths. The wing tilt usually observed in ELO is not found in the CBELO GaN with wide mesa widths, while it can be detected obviously in the GaN with narrow mesa widths. The wing tilt of CBELO GaN grown on a grooved sapphire substrate with narrow mesa can be controlled by adjusting the thickness of the nucleation layer. The dependence of the wing tilt on the nucleation layer thickness is studied. Cross-sectional scanning electron microscopy is used to characterize the geometry of the wing regions, and double crystal x-ray diffraction is used to analyse the structural characteristics and to measure the magnitude of the crystalline wing tilt. It is found that the crystalline wing tilt can be eliminated completely by first growth of a thin nucleation GaN layer then the CBELO GaN. Possible reason and the origin of the wing tilt in CBELO GaN films are also discussed.展开更多
基金This work was financially supported by the Science Research Foundation of Shandong Jiaotong University (No. Z200503) and the National Natural Science Foundation of China (No. 90301002).
文摘Hexagonal GaN films were prepared by nitriding Ga_2O_3 films with flowingammonia. Ga_2O_3 films were deposited on Ga-diffused Si (111) substrates by radio frequency (r.f.)magnetron sputtering. This paper have investigated the change of structural properties of GaN filmsnitrided in NH_3 atmosphere at the temperatures of 850, 900, and 950 deg C for 15 min and nitridedat the temperature of 900 deg C for 10, 15, and 20 min, respectively. X-ray diffraction (XRD),scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectronspectroscopy (XPS) were used to analyze the structure, surface morphology and composition ofsynthesized samples. The results reveal that the as-grown films are polycrystalline GaN withhexagonal wurtzite structure and GaN films with the highest crystal quality can be obtained whennitrided at 900 deg C for 15 min.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60506001,60476021,60576003,60776047and 60836003)the National Basic Research Program of China (Grant No. 2007CB936700)the Project of Technological Research and Development of Hebei Province,China (Grant No. 07215134)
文摘We present the growth of CaN epilayer on Si （111） substrate with a single A1GaN interlayer sandwiched between the GaN epilayer and A1N buffer layer by using the metalorganic chemical vapour deposition. The influence of the AlN buffer layer thickness on structural properties of the GaN epilayer has been investigated by scanning electron microscopy, atomic force microscopy, optical microscopy and high-resolution x-ray diffraction. It is found that an A1N buffer layer with the appropriate thickness plays an important role in increasing compressive strain and improving crystal quality during the growth of AlGaN interlayer, which can introduce a more compressive strain into the subsequent grown GaN layer, and reduce the crack density and threading dislocation density in GaN film.
基金Project supported by the National Natural Science Foundation of China (Grant Nos 60506001, 60476021, 60576003, 60776047 and 60836003)the National Basic Research Program of China (Grant No 2007CB936700)Project of Technological Research and Development of Hebei Province (Grant No 07215134)
文摘High-quality and nearly crack-free GaN epitaxial layer was obtained by inserting a single A1GaN interlayer between GaN epilayer and high-temperature AlN buffer layer on Si （111） substrate by metalorganic chemical vapor deposition. This paper investigates the effect of AlCaN interlayer on the structural properties of the resulting CaN epilayer. It confirms from the optical microscopy and Raman scattering spectroscopy that the AIGaN interlayer has a remarkable effect on introducing relative compressive strain to the top GaN layer and preventing the formation of cracks. X-ray diffraction and transmission electron microscopy analysis reveal that a significant reduction in both screw and edge threading dislocations is achieved in GaN epilayer by the insertion of AlGaN interlayer. The process of threading dislocation reduction in both AlGaN interlayer and GaN epilayer is demonstrated.
文摘We report the reduced-strain gallium-nitride （GaN） epitaxial growth on （0001） oriented sapphire by using quasiporous GaN template. A GaN film in thickness of about 1 μm was initially grown on a （0001） sapphire substrate by molecular beam epitaxy. Then it was dealt by putting into 45% NaOH solution at 100℃ for lOmin. By this process a quasi-porous GaN film was formed. An epitaxial GaN layer was grown on the porous GaN layer at 1050℃ in the hydride vapour phase epitaxy reactor. The epitaxial layer grown on the porous GaN is found to have no cracks on the surface. That is much improved from many cracks on the surface of the GaN epitaxial layer grown on the sapphire as the same as on GaN buffer directly.
基金Supported by the National Natural Science Foundation of China under Grant No 50472058.
文摘Cubic phase MgxZn1-x O/MgO multilayer heterostructures （c-Mgx Zn1-xO/MgO MHs） are grown on Si（100） and quartz substrates by reactive electron beam evaporation at low temperature （250℃）. Cross-sectional morphology observations by field-emission scanning electron microscopy show the legible interfaces of c-MgxZn1-x O/MgO MHs. X-ray diffraction demonstrates that c-MgxZn1-xO/MgO MHs are of highly （100）-oriented. Optical trans- mission investigations of c-Mgx Zn1-x O/MgO MHs on quartz substrates reveal the coexistence of the two phases, c-MgxZn1-xO and MgO. Photoluminescence examination indicates the emergence of deep-ultraviolet emission centred at about 290nm along with the blue shift of the ultraviolet emission from 405nm to 39Gnm when the nominal thickness of c-MgxZn1-xO well layers of MHs is diminished to 3nm, which is probably originated from quantum confinement effect.
基金Project (50472098) supported by the National Natural Science Foundation of China
文摘BiFeO3 (BFO) thin films were prepared on Pt(111)/TiO2/SiO2/Si(100) substrates by the pulsed-laser deposition (PLD) technique at a low temperature of 450℃. The XRD results indicate that the BFO thin films are of perovskite structure with the presence of small amount of second phases. The oxygen pressures have great effect on the crystalline structures and dielectric properties of BFO thin films. The dielectric constant of the BFO thin films decreases with increasing oxygen pressures, achieving 186, 171 and 160 at the frequency of 104 Hz for the oxygen pressures of 0.666, 1.333 and 13.332 Pa, respectively. The BFO thin films prepared at the oxygen pressure of 0.666 Pa reveal a saturated hysteresis loop with the remanent polarization of 7.5 μC/cm2 and the coercive field of 176 kV/cm.
基金Supported by the National Key Basic Research Programme of China under Grant No 2002CB311900, and the National Natural Science Foundation of China under Grant Nos 10474126 and 10574148.
文摘Canti-bridged epitaxial lateral overgrowth （CBELO） of GaN is performed by metalorganic chemical vapour deposition （MOCVD） on maskless V-grooved sapphire substrates prepared by wet chemical etching with different mesa widths. The wing tilt usually observed in ELO is not found in the CBELO GaN with wide mesa widths, while it can be detected obviously in the GaN with narrow mesa widths. The wing tilt of CBELO GaN grown on a grooved sapphire substrate with narrow mesa can be controlled by adjusting the thickness of the nucleation layer. The dependence of the wing tilt on the nucleation layer thickness is studied. Cross-sectional scanning electron microscopy is used to characterize the geometry of the wing regions, and double crystal x-ray diffraction is used to analyse the structural characteristics and to measure the magnitude of the crystalline wing tilt. It is found that the crystalline wing tilt can be eliminated completely by first growth of a thin nucleation GaN layer then the CBELO GaN. Possible reason and the origin of the wing tilt in CBELO GaN films are also discussed.
