• 沒有找到結果。

The effects of oxygen annealing on the electrical characteristics of hydrothermally grown zinc oxide thin-film transistors

N/A
N/A
Protected

Academic year: 2021

Share "The effects of oxygen annealing on the electrical characteristics of hydrothermally grown zinc oxide thin-film transistors"

Copied!
5
0
0

加載中.... (立即查看全文)

全文

(1)

The effects of oxygen annealing on the electrical characteristics

of hydrothermally grown zinc oxide thin-film transistors

Jyh-Liang Wang

a,⇑

, Po-Yu Yang

b

, Tsang-Yen Hsieh

a

, Chuan-Chou Hwang

a

, Der-Chi Shye

a

, I-Che Lee

b a

Department of Electronics Engineering, Ming Chi University of Technology, New Taipei 24301, Taiwan

b

Department of Electronics Engineering and Institute of Electronics, National Chiao Tung University, Hsinchu 30010, Taiwan

a r t i c l e

i n f o

Article history:

Available online 3 July 2012 Keywords:

Zinc oxide (ZnO)

Hydrothermal growth (HTG) Thin-film transistors (TFTs) Oxygen annealing Lateral-grain growth

a b s t r a c t

High-performance transparent zinc oxide (ZnO) thin-film transistors (TFTs) with location-controlled lat-eral-grain growth were fabricated by hydrothermal method. The ZnO active channel was laterally grown with aluminum-doped ZnO (AZO) seed layer underneath the Ti/Pt film. Compare to the unannealed ZnO TFTs, the annealed devices reveal the high-quality ZnO layer with the compensated structural defects in the channel region after oxygen ambient annealing at 400 °C. Therefore, the superior device perfor-mances (i.e. the excellent filed-effect mobility of 9.07 cm2/V s, positive threshold voltage of 2.25 V, high on/off current ratio of 106, and low gate leakage current of <1 nA) of hydrothermally grown ZnO TFTs can be achieved with oxygen ambient annealing.

Ó 2012 Elsevier Ltd. All rights reserved.

1. Introduction

Lately, zinc oxide (ZnO) has been attracting particular interest as a result of its remarkably optical and electronic properties. Its significantly optical transparency combined with an excellent elec-trical conductivity made ZnO as a promise material for the fabrica-tion of optoelectronic devices [1–4]. ZnO is an n-type II–VI compound semiconductor, and it possesses a direct energy wide-bandgap (i.e. 3.37 eV) at room temperature, a large exciton bind-ing energy (i.e. 60 meV), good photoelectric and piezoelectric properties, and high optical transparency for visible light[1]. ZnO has been investigated as an active channel layer for transparent thin film transistor (TFT)[2–4]and compared with organic TFTs

[5–7] and amorphous silicon TFTs [8,9]. Essentially, the organic TFTs may degrade in atmospheric conditions [10,11]and amor-phous silicon TFTs have been demonstrated for some limitations of optical applications, such as light sensitivity, light degradation and opaqueness[12]. On the contrary, ZnO TFTs disclose not only the high transparency within the visible-light spectra but also the relatively high field effect mobility, less light sensitivity, and excellent chemical and thermal stability[13], indicating the poten-tials of ZnO-based thin films applied in TFTs. The ZnO-based thin films have been prepared by various vacuum-based deposition techniques, for instance pulsed laser deposition (PLD)[2], sputter-ing[3], atomic layer deposition[4], and chemical vapor deposition (CVD)[14], which usually suffer the issues of expensive facilities, low throughput, complicated operating conditions and high energy

consumption. In contrast, a solution-based hydrothermal method has the advantages of low reaction temperature, low-cost facility, capabilities of large-area and uniform fabrication, and environ-mental friendliness[15]. Nevertheless, the low-temperature fabri-cation of hydrothermal ZnO thin films generally contain enormous structural defects (i.e. oxygen vacancies, oxygen interstitials, zinc vacancies, and zinc interstitials)[16]. The structural defects of me-tal oxide produce potential wells that can trap and affect the move-ment of carriers, and degrade device performances. Therefore, a post-annealing in oxygen ambience should be considered for de-vice fabrication to inhibit the structural defects formed in pro-cesses[17–19]. In this work, a simple hydrothermal method was adopted for the ZnO thin film growth. The annealing effects and re-lated devices performances of hydrothermally grown (HTG) ZnO TFTs are also addressed.

2. Experimental details

Fig. 1illustrates the schematic fabrication of HTG ZnO TFTs with the technique of location-controlled nucleation. A 200 nm-thick sputtered indium–tin–oxide (ITO) film was sputtered as the gate electrode on the glass substrate. After cleaning, a 200 nm-thick tet-raethylorthosilicate silicon dioxide (TEOS-SiO2) layer was depos-ited as gate dielectric by a plasma-enhanced chemical vapor deposition (PECVD) at 350 °C. Sputtered aluminum-doped ZnO (AZO) film (200 nm) and Ti (100 nm)/Pt (50 nm) films were sequentially deposited at room temperature and patterned by lift-off process. The sputtered AZO film can act as seed layer for ZnO growth during hydrothermal method. The samples were dipped in 0.001 M H3PO4to under-cut the AZO seed layer and then

0038-1101/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.

http://dx.doi.org/10.1016/j.sse.2012.05.015

⇑Corresponding author. Tel.: +886 2 29089899x4861; fax: +886 2 29085247. E-mail address:joewang@mail.mcut.edu.tw(J.-L. Wang).

Contents lists available atSciVerse ScienceDirect

Solid-State Electronics

(2)

immersed in the mixed hydrothermal solution to grow the lateral ZnO film. The growth solution was prepared by mixing with 0.25 M zinc nitrate hexahydrate (Zn(NO3)2 6H2O) with 0.25 M hexameth-ylenetetramine (HMTA) in deionized water at 85 °C for 3 h. Subse-quently, the samples were thoroughly rinsed with deionized water in order to eliminate the residual salts and dried in air at room temperature. Finally, some of the samples were annealed in oxygen ambience to evaluate the annealing effects. The oxygen ambient annealing was executed in a tube furnace with the parameters as oxygen gas flow rate of 60 sccm, process pressure of 1 atm, and annealing temperature of 400 °C for 1 h duration.

After TFTs formation, an automatic measurement system that combines IBM PC/AT, semiconductor parameter analyzer (4156C, Agilent Technologies) and a probe station were used to measure the I–V characteristics. The surface morphologies were observed by a field-emission scanning electron microscopy (FE-SEM, Hitachi S-4700I). The optical emission properties were analyzed by photo-luminescence (PL) spectra with He–Cd laser (i.e. k = 325 nm) exci-tation. An analytical field-emission transmission electron microscopy (JEM-2100FX, JEOL Ltd.) was employed to reveal the cross-sectional image and microstructure of the HTG ZnO layer in the channel region of ZnO TFTs. The samples of cross-sectional TEM were prepared by focused-ion-beam (FIB) technique (Nova 200, FEI Company), which can exactly locate and capture the chan-nel region of ZnO TFTs.

3. Results and discussion

Fig. 2a and b gives the FE-SEM images for the channel morphol-ogy of HTG ZnO TFTs without or with annealing at 400 °C for one hour in oxygen ambience. The images of unannealed and annealed HTG ZnO TFTs reveal similar channel morphology. The ZnO growth only existed between the sputtered Ti/Pt electrodes and no ZnO thin film is observed on the electrodes. The location-controlled lat-eral growth started from the edges of AZO seed layer beneath the Ti/Pt films, and extended toward the middle of the channel from opposite both sides. The achievable distance of lateral growth using this hydrothermal method is about half channel length (5

l

m) while the distance between source and drain is 10

l

m.

An analytical TEM technique was also conducted to display the cross-sectional image and microstructure in the channel region of annealed HTG ZnO layer, shown inFig. 2c. The capping oxide layer was used to protect device structure from the bombardment dam-age induced by FIB during TEM sample preparation. The growth of HTG ZnO from opposite sides impinged with each other at the mid-dle of the channel region above the gate oxide. The thickness of ZnO layer is not uniform and roughly estimated as 0.15–0.2

l

m in the central channel region after 3 h HTG. The inset presents the selected area electron diffraction (SAED) pattern and corre-sponding high-resolution TEM (HRTEM) image for the selected dis-trict in HTG ZnO channel. Spot pattern of SAED indicates that HTG

ZnO grains in the channel regions were single-crystalline wurtzite structure. Moreover, HRTEM image clearly reveals a well-resolved lattice image with an orientation along the [0 0 1] direction (c-axis of ZnO crystal) which is the fastest growth direction of ZnO crys-tals. It is evident that the location-controlled lateral grains grew from the opposite direction and collided at the middle of channel, resulting in nearly a single vertical grain boundary cross to the channel direction. In brief, the hydrothermally lateral-grain growth can be artificially controlled in the desired location and the vertical grain boundary perpendicular to the current flow in the channel region can be reduced to single one as a result of the proper design of source/drain structure with under-cut AZO seed layer. The local-ized potential barriers of grain boundaries could retard the trans-portation of carriers from grain to grain [20]. The presence of vertical grain boundary perpendicular to the current flow in the channel region of ZnO TFTs has a dramatic influence on the

electri-Gate Oxide Pt/Ti Pt/Ti HTG ZnO AZO AZO ITO Glass Substrate Gate Oxide Pt/Ti Pt/Ti HTG ZnO AZO AZO ITO Hydrothermally Grown (HTG) ZnO Film Gate Oxide Pt/Ti Pt/Ti HTG ZnO AZO AZO ITO Glass Substrate Gate Oxide Pt/Ti Pt/Ti HTG ZnO AZO AZO ITO Glass Substrate Oxygen Ambient Annealing at 400 C Gate Oxide Ti/Pt AZO AZO ITO Glass Substrate Ti/Pt Gate Oxide Ti/Pt AZO AZO ITO Glass Substrate Ti/Pt

Under-cut AZO Seed by H3PO4Dip L Lateral Growth W Gate Oxide Pt/Ti Pt/Ti HTG ZnO AZO AZO ITO Gate Oxide Pt/Ti Pt/Ti HTG ZnO AZO AZO Gate Oxide Pt/Ti Pt/Ti HTG ZnO AZO AZO ITO Glass Substrate Gate Oxide Pt/Ti Pt/Ti HTG ZnO AZO AZO ITO Glass Substrate Gate Oxide Ti/Pt AZO AZO ITO Glass Substrate Ti/Pt Gate Oxide Ti/Pt AZO AZO ITO ITO Glass Substrate Ti/Pt 3 L Lateral Growth W

Fig. 1. Schematic illustration for the fabrication of hydrothermal grown (HTG) ZnO TFTs with post-annealing at 400 °C for 1 h in oxygen ambience.

HTG ZnO Capping Oxide

Gate Oxide 100 nm

Vertical Grain Boundary

(c)

3 nm [001] Channel Length (L)

(a)

4 µm Channel Length (L)

(b)

4 µm

Fig. 2. The FE-SEM images show the channel morphology of HTG ZnO TFTs (a) without or (b) with annealing at 400 °C for 1 h in oxygen ambience (c) cross-sectional TEM image reveals the vertical gain boundary cross to the channel of HTG ZnO TFTs. The inset presents the SAED pattern and corresponding HRTEM image for the selected district in HTG ZnO channel.

(3)

cal characteristics. Thus, only single vertical grain boundary in channel region can be expected to make the advanced device per-formance of ZnO TFTs.

Fig. 3shows the PL emission spectra of the unannealed and an-nealed HTG ZnO TFTs. The PL emission spectra are distinguished into two components: one is the UV emission owing to the near band-edge emission (NBE) [21], and the other is the deep level emission (DLE) in the visible region due to the existence of struc-tural defects (i.e. oxygen vacancies, oxygen interstitials, zinc vacancies, and zinc interstitials)[22–24]. It is observed that the DLE intensity decreased and quenched after the annealing in oxy-gen ambience. The zinc interstitials can be rearranged and its num-ber will be reduced by annealing process [17]. The oxygen vacancies also can be inhibited and compensated with oxygen ambience in thermal process [18]. As well, the increased NBE intensity can associate to the reduced structural defects. Hence, the relative PL intensity ratio of NBE intensity to DLE intensity (INBE/IDLE) was extracted to evaluate the structural defects and structural quality of HTG ZnO layers[23]. The values of INBE/IDLE were calculated as 0.8 and 5.03 according to the unannealed and annealed samples. The higher INBE/IDLEof annealed ZnO TFTs re-flected the fewer structural defects [22,23], which usually links to the better crystal quality. As the reported study[24], the crystal-linity of hydrothermal ZnO nanostructures was evidently enhanced after 400 °C oxygen ambient annealing. Therefore, the weaker DLE and stronger NBE intensities recommend the fewer structural de-fects and better crystal quality in annealed ZnO TFTs, which may lead to an improved electric characteristics.

Fig. 4depicts the drain current vs. gate voltage (the plots of IDS vs. VGSand I1=2DS vs. VGS) of transfer characteristics and gate leakage current (IGS) for the unannealed and annealed HTG ZnO TFTs with channel width (W) of 250

l

m and channel length (L) of 10

l

m at the drain voltage (VDS) of 20 V. The threshold voltage (VTH) and field-effect mobility (

l

FE) were calculated with a line fitting of the square root of drain current vs. gate voltage, defined by the cur-rent formula of saturated regions[25]:

IDS;SAT¼

lWC

OX

2L ðVGS VTHÞ

2

; ð1Þ

where IDS,SATis the saturated drain current, and COXis the capaci-tance per unit area of gate insulator, respectively. The unaneled HTG ZnO TFTs indicate the VTHand on/off current ratio as 0.55 V and 1.32  103, respectively. The calculated

l

FEis about hundreds of cm2/V s and shows meaningless due to the extremely huge I

DS, while the unaneled ZnO film loses its semiconductor behaviors

and presents approximately conductive property. Contrarily, the annealed ZnO TFTs reveal the distributions of VTHand

l

FE in the ranges of 1.25–3 V and 6–12 cm2/V s with the measurement of twenty annealed devices. The extracted superior device perfor-mances of annealed ZnO TFTs from the IDSVGSand I1=2DS  VGScurves, the excellent

l

FEof 9.07 cm2/V s, positive VTHof 2.25 V, and high on/ off current ratio (i.e. above 106), which can be linked to the high-quality ZnO layer with the compensated structural defects in the

300 400 500 600 700 800

DLE

NBE

Intensity (Arb. Unit)

Wavelength (nm)

Unannealed Annealed

Fig. 3. Room-temperature PL emission spectra of the unannealed and annealed HTG ZnO TFTs. 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 -20 -15 -10 -5 0 5 10 15 20 1E-12 1E-11 1E-10 1E-9 1E-8 1E-7 1E-6 1E-5 1E-4 1E-3 0.01 0.1 IDS1/2 IGS Unannealed Annealed (Drain Current) 1/2 (A) 1/2 IDS Current (A) Gate Voltage (V)

Fig. 4. Transfer characteristics (IDSVGSand I 1=2

DS VGS) and gate leakage current (IGS)

of the unannealed and annealed HTG ZnO TFTs with channel width (W) of 250lm and channel length (L) of 10lm at the drain voltage (VDS) of 20 V.

0 5 10 15 20 0 5 10 15 20 25 30

Drain Current (mA)

Drain Voltage (V) V GS

(a)

0 5 10 15 20 0 100 200 300 400 500 600 0 5 10 15 20 0 100 200 300 400 500 600 Drain Current ( µ A) Drain Voltage (V) VGS

(b)

Fig. 5. Output characteristics (IDSVDS) of the (a) unannealed and (b) annealed HTG

(4)

channel region after oxygen ambient annealing. The positive gate voltage was applied to turon TFTs, suggesting the behavior of n-channel enhancement-mode devices. Furthermore, the gate leakage current (IGS) of annealed ZnO TFTs is less than 1 nA and far lower than that of unannealed ones. Therefore, the superior device perfor-mances (i.e. the excellent

l

FE, high on/off current ratio, and low gate leakage current) of HTG ZnO TFTs can be made with oxygen ambi-ent annealing.

Fig. 5shows the drain current–drain voltage (IDSvs. VDS) plot of output characteristics for unannealed and annealed HTG ZnO TFTs under the gate voltage (VGS) of 0–20 V with the step of 5 V. It is demonstrates that annealed ZnO TFTs exhibit the higher driving current than that of unannealed ZnO TFTs under the same bias con-dition, which is related to the high field effect mobility. The drain current of annealed ZnO TFTs increased linearly with drain voltage at lower values and saturation behavior was observed at high drain voltages due to pinch-off effect by accumulation layer. On the con-trast, it obviously indicates the non-saturated curves of IDSVDSfor unannealed devices. Additionally, the major electrical characteris-tics of the annealed HTG ZnO TFTs in this work can be comparable to those of the other solution-based ZnO TFTs in literatures[26– 29], listed inTable 1. This experimental result recommends that the proposed HTG ZnO TFTs with oxygen ambient annealing at 400 °C can achieve the superior electrical characteristics (i.e. the relatively smaller threshold voltage and higher mobility) than those of the other solution-based ZnO TFTs prepared at higher tem-peratures. The relatively lower field effect mobilities of the re-ported solution-based ZnO TFTs may be connected to the result of more grain boundaries, poorer crystallinity, and film porosity. The results suggest that the hydrothermally grown ZnO TFTs with oxygen ambient annealing can contribute excellent device perfor-mances (i.e. the excellent

l

FE, small positive VTH, high on/off cur-rent ratio, and low gate leakage curcur-rent).

Fig. 6points out the optical transmission spectra vs. wavelength for the ITO/glass substrate and entire structure of annealed HTG

ZnO TFTs. The optical transmittances in the visible portion for the ITO/glass substrate and entire structure of HTG ZnO TFTs are 85–90% and 53–71%, separately. The reduced transmission of the entire structure is considered with the reflection of Ti/Pt electrodes and absorption coming from gate oxide/HTG ZnO layers owing to the existence of structural defects. The use of smaller Ti/Pt elec-trodes and superior crystal quality of ZnO layer can further im-prove the transparency.

4. Conclusion

The hydrothermally grown (HTG) transparent ZnO TFTs has been fabricated on the glass substrates at 85 °C. The location-con-trolled lateral-grain growth started from the edges of aluminum-doped ZnO (AZO) seed layer beneath the Ti/Pt films, and extended toward the middle of channel from the opposite directions, result-ing in only sresult-ingle grain boundary perpendicular to the channel direction. The few vertical grain boundaries in channel region can be expected to make the advanced device performance of ZnO TFTs. After oxygen ambient annealing at 400 °C, the weaker deep level emission (DLE) and stronger band-edge emission (NBE) intensities of annealed ZnO TFTs reflected the better crystal quality and fewer structural defects compared to the unannealed devices. The positive gate voltage was applied to turn-on TFTs, sug-gesting the behavior of n-channel enhancement-mode devices. Consequently, the superior device performances (i.e. the excellent filed-effect mobility of 9.07 cm2/V s, positive threshold voltage of 2.25 V, high on/off current ratio of 106, and low gate leakage cur-rent of <1 nA) of HTG transpacur-rent ZnO TFTs can be made with an oxygen post-annealing.

Acknowledgments

Thanks are due to the Center for Thin Film Technologies and Applications (CTFTA) in Ming Chi University of Technology, the Nano Facility Center (NFC) in National Chiao Tung University, and the National Nano Device Laboratory (NDL) for the technical supports.

References

[1] Lim SJ, Kwon S, Kim H. ZnO thin films prepared by atomic layer deposition and rf sputtering as an active layer for thin film transistor. Thin Solid Films 2008;516:1523–8.

[2] Kao CJ, Kwon YW, Heo YW, Norton DP, Pearton SJ, Ren F, et al. Comparison of ZnO metal–oxide–semiconductor field effect transistor and metal– semiconductor field effect transistor structures grown on sapphire by pulsed laser deposition. J Vac Sci Technol B 2005;23:1024–8.

[3] Navamathavan R, Choi CK, Yang EJ, Lim JH, Hwang DK, Park SJ. Fabrication and characterizations of ZnO thin film transistors prepared by using radio frequency magnetron sputtering. Solid-State Electron 2008;52:813–6. [4] Carcia PF, McLean RS, Reilly MH. High-performance ZnO thin-film transistors

on gate dielectrics grown by atomic layer deposition. Appl Phys Lett 2006;88:123509–11.

[5] Islam MN, Mazhari B. Comparative analysis of unity gain frequency of top and bottom-contact organic thin film transistors. Solid-State Electron 2009;53:1067–75.

Table 1

Comparisons of electrical characteristics for the annealed HTG ZnO TFTs in this work and the other solution-based ZnO TFTs in literatures.

Preparation method This study [26] [27] [28] [29]

Hydrothermal method Sol–gel method Chemical bath method

Sol–gel and chemical bath deposition combined method

Facile sonochemical method

Max. process temperature (°C) 400 500 100 230 525

Threshold voltage (V) 2.25 16.1 18 6 11.7

Mobility (cm2

/V s) 9.07 1.16 0.248 0.67 0.7

On/off current ratio 1.75  106

8.1  107 105 107 3.2  105 300 400 500 600 700 800 0 20 40 60 80 100 Transmittance (% ) Wavelength (nm) HTG ZnO TFT ITO/Glass Substrate

Fig. 6. Optical transmission spectra for the ITO/glass substrate and entire structure of HTG ZnO TFTs.

(5)

[6] Tsamados D, Cvetkovic NV, Sidler K, Bhandari J, Savu V, Brugger J, et al. Double-gate pentacene thin-film transistor with improved control in sub-threshold region. Solid-State Electron 2010;54:1003–9.

[7] Chou DW, Huang CJ, Su CM, Yang CF, Chen WR, Meen TH. Effect of rapid thermal annealing on pentacene-based thin-film transistors. Solid-State Electron 2011;61:76–80.

[8] Kim SH, Kim EB, Choi HY, Kang MH, Hur JH, Jang J. A coplanar hydrogenated amorphous silicon thin-film transistor for controlling backlight brightness of liquid-crystal display. Solid-State Electron 2008;52:478–81.

[9] Tang Z, Park MS, Jin SH, Wie CR. Drain bias dependent bias temperature stress instability in a-Si:H TFT. Solid-State Electron 2009;63:225–33.

[10] Hyung GW, Park J, Kim JH, Koo JR, Kim YK. Storage stability improvement of pentacene thin-film transistors using polyimide passivation layer fabricated by vapor deposition polymerization. Solid-State Electron 2010;54:439–42. [11] Katz HE, Johnson J, Lovinger AJ, Li W. Naphthalenetetracarboxylic

diimide-based n-channel transistor semiconductors: structural variation and thiol-enhanced gold contacts. J Am Chem Soc 2000;122:7787.

[12] Staebler DL, Wronski CR. Reversible conductivity changes in discharge-produced amorphous Si. Appl Phys Lett 1977;31:291.

[13] Tsay CY, Fan KS, Chen SH, Tsai CH. Preparation and characterization of ZnO transparent semiconductor thin films by sol–gel method. J Alloy Compd 2010;495:126–30.

[14] Natsume Y, Sakata H, Hirayama T. Low-temperature electrical conductivity and optical absorption edge of ZnO films prepared by chemical vapour deposition. Phys Status Solidi A 1995;148:485–95.

[15] Li C, Li Y, Wu Y, Ong BS, Loutfy RO. ZnO field-effect transistors prepared by aqueous solution-growth ZnO crystal thin film. J Appl Phys 2007;102:076101-3.

[16] Yang PY, Wang JL, Tsai WC, Wang SJ, Lin JC, Lee IC, et al. Photoresponse of hydrothermally grown lateral ZnO nanowires. Thin Solid Films 2010;518:7328–32.

[17] Lim J, Shin K, Kim HW, Lee C. Effect of annealing on the photoluminescence characteristics of ZnO thin films grown on the sapphire substrate by atomic layer epitaxy. Mater Sci Eng B 2004;107:301–4.

[18] Meng X, Lin B, Gu B, Zhu J, Fu Z. A simple growth route towards ZnO thin films and nanorods. Solid State Commun 2005;135:411–5.

[19] Bong H, Lee WH, Lee DY, Kim BJ, Cho JH, Cho K. High-mobility low-temperature ZnO transistors with low-voltage operation. Appl Phys Lett 2010;96:192115-3.

[20] Hossain FM, Nishii J, Takagi S, Ohtomo A, Fukumura T, Fujioka H, et al. Modeling and simulation of polycrystalline ZnO thin-film transistors. J Appl Phys 2003;94:7768–77.

[21] Kong YC, Yu DP, Zhang B, Fang W, Feng SQ. Ultraviolet-emitting ZnO nanowires synthesized by a physical vapor deposition approach. Appl Phys Lett 2001;78:407–9.

[22] Wang RC, Liu CP, Huang JL, Chen SJ. Single-crystalline AlZnO nanowires/ nanotubes synthesized at low temperature. Appl Phys Lett 2006;88:023111–3. [23] Yang PY, Wang JL, Tsai WC, Wang SJ, Lin JC, Lee IC, et al. Field-emission characteristics of Al-doped ZnO nanostructures hydrothermally synthesized at low temperature. J Nanosci Nanotechnol 2011;11:6013–9.

[24] Yang PY, Wang JL, Tsai WC, Wang SJ, Lin JC, Lee IC, et al. Oxygen annealing effect on ultraviolet photoresponse of p-NiO-nanoflowers/n-ZnO-nanowires heterostructures. J Nanosci Nanotechnol 2011;11:5737–43.

[25] Hsieh HH, Wu CC. Scaling behavior of ZnO transparent thin-film transistors. Appl Phys Lett 2006;89:041109-3.

[26] Jones GAC, Xiong G, Anderson D. Fabrication of nanoscale ZnO field effect transistors using the functional precursor zinc neodecanoate directly as a negative electron beam lithography resist. J Vac Sci Technol B 2009;27:3164–8.

[27] Cheng HC, Chen CF, Lee CC. Thin-film transistors with active layers of zinc oxide (ZnO) fabricated by low-temperature chemical bath method. Thin Solid Films 2006;498:142–5.

[28] Cheng HC, Chen CF, Tsay CY. Transparent ZnO thin film transistor fabricated by sol-gel and chemical bath deposition combination method. Appl Phys Lett 2007;90:012113-3.

[29] Oh JY, Park J, Kang SY, Hwang CS, Shim HK. Room temperature fabrication of ZnO nanorod films: synthesis and application as a channel layer of transparent thin film transistors. Chem Commun 2009:4545–7.

數據

Fig. 1. Schematic illustration for the fabrication of hydrothermal grown (HTG) ZnO TFTs with post-annealing at 400 °C for 1 h in oxygen ambience.
Fig. 3. Room-temperature PL emission spectra of the unannealed and annealed HTG ZnO TFTs
Fig. 6 points out the optical transmission spectra vs. wavelength for the ITO/glass substrate and entire structure of annealed HTG

參考文獻

相關文件

好了既然 Z[x] 中的 ideal 不一定是 principle ideal 那麼我們就不能學 Proposition 7.2.11 的方法得到 Z[x] 中的 irreducible element 就是 prime element 了..

volume suppressed mass: (TeV) 2 /M P ∼ 10 −4 eV → mm range can be experimentally tested for any number of extra dimensions - Light U(1) gauge bosons: no derivative couplings. =&gt;

For pedagogical purposes, let us start consideration from a simple one-dimensional (1D) system, where electrons are confined to a chain parallel to the x axis. As it is well known

The observed small neutrino masses strongly suggest the presence of super heavy Majorana neutrinos N. Out-of-thermal equilibrium processes may be easily realized around the

• Thermal annealing in vacuum generates oxygen vacancies which generate dynamic scattering defects, causing orbital Kondo effect. • The orbital Kondo effect is suppressed in

incapable to extract any quantities from QCD, nor to tackle the most interesting physics, namely, the spontaneously chiral symmetry breaking and the color confinement.. 

• Formation of massive primordial stars as origin of objects in the early universe. • Supernova explosions might be visible to the most

Twilight of the Gods: The Beatles in Retrospect (London 1973).. The Complete Beatles Recording Sessions