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Synthesis and structural analysis of nano-semiconductor material 2005 2

. 2005 2

(1) MOCVD ZnO (2) MOCVD gallium oxide < gallium oxide > < gallium oxide >

(3) Thermal evaporation gallium oxide (4) MOCVD 1 indium oxide

Abstract (1) Synthesis of ZnO nanorods by an MOCVD system The ZnO nanorods have synthesized on Si(100) substrates without a metal catalyst by a reaction of a diethylzinc (DEZn) and oxygen (O 2 ) mixture. At a substrate temperature of 450, the growth structure has changed from clusters to nanorods with increasing Ar/O 2 gas flow ratio. The ZnO nanorods had an average diameter of 30-70 nm, and transmission electron microscopy (TEM) showed a single crystalline structure. (2) Synthesis of gallium oxide nanowires by an MOCVD system < Single crystal gallium oxide nanowires> The monoclinic gallium oxide (β-ga 2 O 3 ) nanowires have synthesized on Au-coated Si substrates by a reaction of a trimethylgallium (TMGa) and oxygen (O 2 ) mixture. The β-ga 2 O 3 nanowires became progressively thinner from bottom to top, with diameters ranging from 10 to 200 nm and lengths of several micrometers. We found that Au-containing nanoparticles were attached to the tips of β-ga 2 O 3 nanowires and thus the nanowire growth could be a vapor-liquid-solid (VLS) process. < Amorphous gallium oxide nanowires> The large-scaled gallium oxide nanowire arrays have prepared on Si(100) substrates using a reaction of a trimethylgallium (TMGa) and oxygen (O 2 ) mixture. The cross-section of the gallium oxide

nanowires had a circular shape with the diameter of about 40-110 nm. Transmission electron microscopy and x-ray diffraction analysis together showed that the nanowires were amorphous phase. (3) Synthesis of gallium oxide nanobelts by thermal evaporation The production of gallium oxide (Ga 2 O 3 ) nanobelts demonstrated on various substrates by thermal evaporation of GaN powders. Scanning electron microscopy revealed that the product consisted of nanobelts with widths in the range of 100-10000 nm. X-ray diffraction and high-resolution electron microscopy indicated that the nanobelts were single-crystalline monoclinic structure of Ga 2 O 3. The photoluminescence spectrum under excitation at 325 nm showed a broad band with a prominent emission peak around 433 nm. (4) Catalyst-free MOCVD growth of In 2 O 3 one-dimensional materials One-dimensional (1-D) indium oxide (In 2 O 3 ) arrays have succeeded in synthesizing by metalorganic chemical vapor deposition (MOCVD) method. We have characterized the products by means of X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). SEM images showed that the 1-D materials with the serrated surfaces had the cross sections of acute triangle. XRD and TEM studies revealed that the 1-D materials possessed single-crystalline cubic structure and had preferentially grown along the [111] direction.

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p x = 2 h 2π h 2 2 p ( k) E = = k 2µ 2µ µ

E = E 0 2 2 π 1 1.8e + 2 2r µ ε r 2 2 r ε2

(a) 0-demension nanorod nanowire nanotube nanocable nanobelt (b) 1-demension (c) 2-demension Fig 2-1. The type of nanomaterials

Fig. 3-1. Schematic drawing of MOCVD system.

(a) (b) (c) 200nm 200nm 200nm Fig. 3-2. Plan-view SEM images of ZnO deposits grown at 450 with Ar/O 2 gas flow ratio (a) 0.3, (b) 1 and (c) 4.

(a) (b) Si substrate Fig. 3-3. Cross-sectional SEM images of ZnO nanorods at 450C with Ar/O 2 gas flow ratio (a) 1 and (b) 4.

Intensity (arb. units) 100 101 002 102 103 112 20 30 40 50 60 70 80 2θ (deg.) Fig. 3-4. XRD patterns recorded from deposits

(a) (b) 001 100 50nm [010] 100nm Intensity (arb. units) (c) C Zn O Cu Zn Zn 0 2 4 6 8 10 Energy (kev) Fig 3-5. Bright field TEM images of (a) ZnO nanorods grown on the Si substrate and (b) a ZnO nanorod (the inset shows corresponding SAED pattern recorded along the [010] zone axis). (c) Typical EDS spectrum of a ZnO nanorod ( the Cu and C peaks come from the supporting carbon-coated copper grids in TEM sample preparation).

(a) (b) Fig 3-6. SEM images of ZnO deposits grown at 400C (a) plan-view (b) cross-sectional

(a) (b) Fig 3-7. Growth mechanism of the ZnO nanorods grown by MOCVD system without catalyst (a) reality and (b) ideal.

(a) (b) (c) (d) (e) (f) Ga 2 O 3 thin film Fig. 4-1. SEM images of gallium oxide deposits grown on Si(100) substrate at 600C when Ar carrier gas flow rate is 30sccm and O 2 gas flow rate is (a,b) 0sccm, (c,d) 6sccm, (e,f) 10sccm.

(a) (c) (e) (b) (d) (f) Fig. 4-2. SEM images of gallium oxide nanowires grown on Si(100) substrate at (a) 600C, (b) 650C, (c-f) 700C when Ar carrier gas flow rate is 30sccm and O 2 gas flow rate is 6sccm.

20 30 40 50 60 70 80 90 2θ (deg.) Intensity (arb. units) Fig. 4-3. X-ray diffraction patterns recorded from Ga 2 O 3 nanowires.

(a) (b) 500nm 100nm (c) Intensity (arb. units) C Ga O Cu Ga Cu Ga 0 2 4 6 8 10 Energy (kev) Fig. 4-4. TEM characterization of the Ga 2 O 3 nanowires. (a) Low magnification TEM image. (b) High resolution TEM image (inset : corresponding electron diffraction pattern). (c) EDS spectra of the nanowire.

Fig. 4-5. Growth mechanism of the Ga 2 O 3 nannowires grown by MOCVD system without catalyst.

(a) (b) Fig. 4-6. (a) Plan-view and (b) side-view SEM images of the deposited nanowires.

β 30 40 50 60 70 80 90 2θ (deg.) Intensity (arb. units) 004 211 304 017 024 10 10 Fig. 4-7. X-ray diffraction patterns recorded from the Ga 2 O 3 nanowires

(a) 100nm (c) C O Ga Au Tip Cu Cu Ga (b) Amorphous layer 10nm d=0.46nm (102) 0 2 4 6 8 10 0 2 4 6 8 10 C O Ga Energy (kev) Stem Fig. 4-8. (a) TEM and (b) HRTEM images of a single β-ga 2 O 3 nanowire. The nanowire terminates with a nanoparticle. (c) EDS spectra of the nanowire tip and the nanowire stem. Cu Cu Ga

Fig. 4-9. Growth mechanism of the Ga 2 O 3 nannowires using Au catalyst by MOCVD system.

4 GaN ( s ) 4 Ga ( g ) + 2 N 2( g ) Ga( s) + 3O ( g) 2Ga O ( ) 4 2 2 3 s Upper holder Out Heating units Distance (5mm) Substrate GaN powder N 2 In Lower holder Themocouple Fig. 5-1. Schematic drawing of thermal furnace system.

Intensity (arb. units) 004 or 104 202 111 111 113 213 217 20 30 40 50 60 70 80 2θ (deg.) Fig. 5-2. XRD pattern of the as-deposited products on Si(100) substrate

Ǻ Ǻ Ǻ (a) (b) (c) (d) 2nm Si(100) Fig. 5-3. (a),(b),(c) SEM and (d) TEM images showing ther general morphology of as-deposited products. (a) plan-view image, (b) side-view image, (c) high-magnification image and (d) high resolution images.

(a) (b) (c) (d) Fig. 5-4. SEM images of gallium oxide deposits using Ir catalyst. Gallium oxide deposits grown at (a),(b) 900C and (c),(d) 970C.

970 C 900 C 200 300 400 500 600 700 800 900 Wavelength (nm) Fig. 5-5. Room temperature PL spectra of the products at growth temperatures of 900 º C and 970 º C with an excitation wavelength of 325 nm. Intensity (arb. units)

(a) (b) 101 113 111 202 500nm 500nm [121] (c) 101 2nm Fig. 5-6. (a) TEM image of Ga 2 O 3 nanobelts. (b) TEM image of a β- Ga 2 O 3 nanobelt. The inset shows the corresponding SAED pattern recorded. (c) HRTEM image.

. 2 1 1 Intensity (arb. units) β-(004) β-(104) β-(202) β-(111) β-(111) Ir-(111) GaIr-(110) β-(113) β-(213) Ir-(200) 25 30 35 40 45 50 55 2θ (deg.) Fig. 5-7. XRD pattern of the as-deposited products on Pt-coated SiO 2 substrate at 900 º C

(a) (b) Fig. 5-8. SEM images of gallium oxide deposits using Pt catalyst. (a) Side-view image and (b) high-magnification image of gallium oxide deposits at 900C

200 300 400 500 600 700 800 900 Wavelength (nm) Intensity (arb. units) Fig. 5-9. Room temperature PL spectrum of the products with an excitation wavelength at 325nm 1

(a) (b) 111 111 100 [011] 0.5µm 0.2µm (c) 111 111 (d) 200 [011] d=0.56nm (100) 1µm 2nm Fig. 5-10. (a) TEM image of the products. TEM image of a single Ga 2 O 3 nanobelt with (b) a width of 150nm and (c) a with of 1000nm. The insets are the corresponding SAED pattern recorded along the [011] zone axis. (d) HRTEM image of a monoclinic β-ga 2 O 3 nanobelts.

(a) (b) (c) (d) Fig. 5-11. SEM images showing ther general morphology of as-deposited products grown with Au-coated Si substrate. (a) Side-view image, (b) plan-view image, (c),(d) high-magnification image.

(a) (b) [100] 100 002 1µm 5nm [010] (c) [010] (d) d=0.28nm (202) 111 111 020 [101] [010] 202 [101] 1µm 2nm Fig. 5-12. (a) Low magnification TEM image of the nanobelts. (b) TEM image of a single β-ga 2 O 3 nanobelt (Inset: Corresponding SAED pattern recorded along the [010] zone axis). (c) Low magnification TEM image of a piece of a wide nanobelt (Inset: Corresponding SAED pattern recorded along the [101] zone axis). (d) HRTEM image corresponding to an area enclosed by the square in Fig. 5-12 (c).

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(a) (b) Si substrate (c) (d) Fig. 6-1. SEM images of indium oxide deposits grown on Si(100) substrate at 350C when Ar carrier gas flow rate is 20sccm and O2 gas flow rate is 5sccm. (a) Side-view image, (b) plan-view image, (c),(d) highmagnification image.

(a) (b) (c) (d) Fig. 6-2. SEM images of indium oxide deposits grown on Si(100) substrate at 350C when deposition time is (a), (c) 5min and (b), (d) 10min. (a), (b) Plan-view image, (c), (d) side-view image.

(222) Intensity (arb. units)(444) Si-(004) 2θ ( deg.) Fig. 6-3. XRD patterns recorded from indium oxide deposits

(a) Intensity (arb. units) c (b) Cu Cu 0 4 8 12 14 18 22 Energy (kev) [111] 62 Fig. 6-4. (a) Typical EDS spectrum and (b) side-view schematic drawing of a single 1-D materials.

(c) 100 nm 101 321 222 [121] (d) 2 nm d = 0.29 nm ( 2 2 2 ) d = 0.72 nm ( 1 0 1 ) Fig. 6-4. (c) TEM image showing the tip part of a 1-D material. The inset shows a typical SAED pattern taken perpendicular to the stem of the 1-D materials. (d) Lattice-resolved HRTEM image of the rectangular box marked in Fig. 6-4 (c).

(e) [111] 031 222 211 100 nm [213] (f) d = 0.32 nm ( 0 3 1 ) d = 0.29 nm ( 2 2 2 ) d = 0.41 nm ( 2 1 1 ) 5 nm Fig. 6-4. (e) TEM image showing nanobumps residing along the exterior of a 1-D material. The inset is a SAED pattern taken perpendicular to the stem of the nanobumps. (f) Lattice-resolved HRTEM image corresponding to the rectangular box marked in Fig. 6-4 (e).

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