Correlation between the Annealing Effect and the Electrical Characteristics of the Depletion Region in ZnO, SnO 2 and ZTO Films

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TRANSACTIONS ON ELECTRICAL AND ELECTRONIC MATERIALS Vl. 17, N. 2, pp. 104-108, April 25, 2016 Regular Paper pissn: 1229-7607 eissn: 2092-7592 DOI: http://dx.di.rg/10.4313/teem.2016.17.2.104 OAK Central: http://central.

1 TRANSACTIONS ON ELECTRICAL AND ELECTRONIC MATERIALS Vl. 17, N. 2, pp , April 25, 2016 Regular Paper pissn: eissn: DOI: OAK Central: Crrelatin between the Annealing Effect and the Electrical Characteristics f the Depletin Regin in ZnO, and ZTO Films Teresa Oh Department f Semicnductr Engineering, Chengju University, Chengju 34134, Krea Received December 16, 2015; Revised March 24, 2016; Accepted March 30, 2016 T research the crrelatin between xygen vacancy and the electrical characteristics f ZTO, which is made by using a target mixed ZnO: =1:1, the ZnO, and ZTO were analyzed by PL, XPS, XRD patterns and electrical prperties. It was cmpared with the electrn rbital spectra f O 1s in accrdance with the electrical characteristics f ZnO, and ZTO. The electrical characteristics f ZTO were imprved by increasing the temperatures, due t the high degree f crystal structures at a high temperature, and the physical prperties f ZTO was similar t that f ZnO. The amrphus structure f was increased with increasing the temperature. The Schttky cntact f xide semicnductrs was frmed using the depletin regin, which is increased by the electrn-hle cmbinatin due t the prcesses. ZnO shwed the Ohmic cntact in spite f a high temperature, but and ZTO had Schttky cntact. As such, it was cnfirmed that the electrical prperties f ZTO are affected by the mlecules f. Keywrds: ZnO,, ZTO, XPS, Oxygen vacancy, Depletin regin, XRD 1. INTRODUCTION Zink based xide semicnductr has been attracting attentin due t its ptential applicatin in transparent displays, slar cell, transparent electrnic skins and transparent electrdes [1-3]. ZnO instead f ITO (Indium Tin Oxide) has usually been used with impurity dping, such as Al, In, Ga, Cu r Sn fr high cnductivity, and it is knwn that the electrical prperties f Zink based xide semicnductrs usually imprves with the prcesses. The current f xide semicnductrs riginates frm the cnductivity, due t the dnr, such as Zn ins (Zni 2+ ) r xygen vacancy ins (V 2+ ). ZTO is made by the mixing f ZnO:, 1:1, and there are ZnO f n-type and f p- type. ZTO withut an indium has a merit lw prductin cst. Authr t whm all crrespndence shuld be addressed: teresa@cju.ac.kr Cpyright 2016 KIEEME. All rights reserved. This is an pen-access article distributed under the terms f the Creative Cmmns Attributin Nn-Cmmercial License ( which permits unrestricted nncmmercial use, distributin, and reprductin in any medium, prvided the riginal wrk is prperly cited. Zink based xide semicnductrs with high mbility must decrease the resistivity and mismatching at the interface between a channel and dielectric material [4-9]. Als, the understanding that a cntact mechanism at the interface in a device is als an imprtant factr. The Schttky and Ohmic cntacts fr semicnductrs depend n the Schttky barrier, and the Ohmic cntact has n ptential barrier, s the current-vltage curves has linear prperties. The Schttky barrier has a ptential barrier and has a nn-linear I-V curve, because f the depletin layer, which is due t the electrn-hle cmbinatin [10-12]. There are many studies cncerning the xygen vacancy and structure, but the crrelatin between xygen vacancy [13-15], structure and electrnic prperties remain un-researched. In this study, it was demnstrated the effects f xygen vacancy and electrnic prperties by using the ZnO, and ZTO. T understand the electrical prperties f ZTO, ZnO, and ZTO, they were prepared with an xygen gas flw rate f 20 sccm n p-type Si wafers. As-depsited films annealed at 100 and 200 t generate the difference in depletin layer in accrdance with the inizatin state. All samples were analyzed in terms f the PL, XRD, XPS and cntact prperties bserved frm the I-C Cpyright 11 KIEEME. All rights reserved

2 Trans. Electr. Electrn. Mater. 17(2) 104 (2016): T. Oh 105 curves. The crrelatin between the xygen vacancy and bnding structures with increasing the temperatures was induced. 2. EXPERIMENTS ZnO, and ZTO were depsited with xygen gas flw rates f 20 sccm n p-type Si substrates at rm temperature using RF magnetrn sputtering fr 10 minutes [16]. As-depsited samples were annealed at 100 and 200 in an air cnditin t bserve the temperature dependency f inic diffusin currents and cnductins by the xygen vacancy. The ZnO and ZTO targets (99.99% purity) were supplied by ANP C., LTD. Al surce/drain electrdes were evaprated by a thermal evapratr. The current-vltage were measured using MIS (metal/sioc film/si) structure and mask pattern with a diameter f 200 μm. Aluminum was used as the electrde surce. Electrical characteristics f current vs vltage were measured using the semicnductr parameter analyzer (4155A). Measurements were carried ut in dark cnditins, in air. All samples were analyzed in terms f the PL, XRD and XPS. 3. RESULTS AND DISCUSSION Figure 1 shws the PL spectra used t research the ptical prperties f the xide semicnductrs f ZnO, and ZTO. Fig. 2. Electrical prperties f xide semicnductrs in accrdance with rm temperature () and temperatures, ZnO,, and ZTO. Fig. 1. PL spectras f xide semicnductrs in accrdance with the temperature, ZnO,, and ZTO. The wave length f ZnO was bserved as the lngest, and that f was the secnd lngest, and that f ZTO was the shrtest. As such, it culd be frecast that the energy gap f ZTO is the highest, and that its electrical prperties can be imprved mre than ZnO and. The ZnO, and ZTO films were depsited and then annealed at 100 and 200, t research the crrelatin between xygen vacancy and the electrical prperties. Figure 2 shws the electrical prperties f ZnO, and ZTO with a structure f Al/semicnductr/p-Si. A ZnO film demnstrated the Ohmic cntact depending n the vltages in accrdance with the temperatures. Hwever, that f and ZTO are nnlinear Schttky cntacts. Mrever, the current decreases with increased temperatures because the xygen vacancy as an inic state decreased during the prcesses. In spite f this, the effect f the xygen vacancy did nt affect the ZnO film, which has Ohmic cntact despite. The Ohmic cntact is due t the impurity

3 106 Trans. Electr. Electrn. Mater. 17(2) 104 (2016): T. Oh ZnO/Si ZnO_Air SnO 2 /Si V O V m C V Intensity (arb.units) ZnO Fig. 3. XRD patterns f xide semicnductrs in accrdance with temperatures, ZnO,, and ZTO. /Si ZTO_air V C (d) (d) ZTO ZnO Temperature ( C) cntent (%) ZTO_air Depletin (e) ZTO dping carriers, and the xygen vacancy (V 2+ ) as an inic state is weakly related t the Ohmic cntact [17,18]. T bserve the relatinship between the xygen vacancy and crystallizatin during the prcesses, all samples were analyzed fr their XRD patterns. Figure 3 shws the crystallizatin prperties f ZnO, and ZTO. Oxygen semicnductrs cmmnly shw the peaks at 33.5 degrees. A ZnO has 33.5 and 34.7 degrees with a bradened peak. A film decreased the crystallizatin with increased temperatures, in spite f ZTO f high crystallizatin with increased temperatures. The crystallizatin f ZnO and ZTO increased at high temperatures, because f their high density structure due t arrangement between the dping carriers. Hwever, the structure f an annealed becmes amrphus because f a depletin layer due t the electrn-hle cmbinatin frm the xygen vacancy and metal xygen prepared after depsitin. The increase in the depletin layer causes the Schttky cntact and limits the current as is shwn in Fig. 2. Usually, it is knwn that the cnductivity f an xide semicnductr depends n its xygen vacancy. One atm f xygen becmes tw electrns, after the inizatin by r depsitin. The xygen vacancy (V 2+ ) as the dnr ins can cntribute a cnductance after the extractin f electrns. As such, the xide semicnductr after the increases the density f xygen vacancies and imprves the electrical prperties. Hwever, the xygen vacancy fills with xygen frm the air during the and then decreases the cnductivity, as is shwn in Fig. 2. It was cnfirmed that the ZnO with prcesses is 536 Fig. 4. Variance f xygen vacancy in accrdance with temperature, ZnO,, ZTO, (d) cmparisn f xygen vacancies, and (e) frmatin f a depletin regin instead f an xygen vacancy. nt related t the frmatin f xygen vacancy frm the results f Fig. 2 and Fig. 3. The xygen vacancy is generally defined by the analysis f O 1s spectra, using the XPS. Figure 4 utlines the decnvluted O 1s spectra f all samples. There are the first Om (metal xygen), the secnd xygen vacancy (V 2+ ) and the third peaks, each with the highest binding energy [19,20]. Figure 4 and shws hw the bnding decreased with an increase in temperatures. Figure 4 displays the main peak, with a shift t lw binding energy in accrdance with the increase in temperatures. Figure 4(d) shws the relative cntent (%) f xygen vacancy (V 2+ ) btained frm the O 1s spectra. The xygen vacancy f ZnO did nt increase with increments f temperatures. The xygen vacancy f ZnO annealed at 100 steeply decreased, and that f ZnO annealed at 200 in cmpared with as-depsited ZnO () film was als lw cntent. Hwever, the xygen vacancy f annealed at 100 decreased, and that annealed at 200 steeply increased. These results indicate that the prperties f ZTO b-

4 Trans. Electr. Electrn. Mater. 17(2) 104 (2016): T. Oh 107 Fig. 5. Temperature dependence f electrical characteristics f xide semicnductrs, rm temperature, annealed at 100, and annealed at 200. Fig. 6. Temperature dependence f the electrical characteristics f an xide semicnductr in a range f < current <,, 100, and 200. served frm xygen vacancy fllw the characteristics f. The xygen vacancy f ZTO annealed at 100 decreased, and that annealed at 200 steeply increased. As seen in Figs. 2 and 4, the xygen vacancy was related t the electrical prperties, which was affected by the amrphus structure. Hwever, the xygen vacancy was nt related t the crystal structure. Mrever, the xygen vacancy f ZnO with a high crystal structure decreases with increasing the temperature. The electrical prperties f ZnO did nt change with increasing the temperature as shwn in Fig. 2. Therefre, it is natural that the xygen vacancy is related t the depletin regin as shwn in Fig. 4(e). + H 2 O+xygen (depsitin) (1) - + O+ Depletin regin (xidatin) (2) grups frmed during a depsitin were evaprated during the prcess and the recmbinatin between metal xygen and the xygen vacancy became a depletin regin. ZnO had an Ohmic cntact and a structure f crystallizatin with increased temperature because f the absence f inic charges and a depletin regin. invlves a Schttky cntact because f the depletin regin due t the cmbinatin f inic grups, such as xygen vacancy and metal ins with increased temperature. The frmatin f a depletin regin in the semicnductrs is an imprtant cnditin t becme a Schttky cntact. Figure 5 shws the current-vltage characteristics depending n the temperature t study the cntact prperties f ZnO, and ZTO, as shwn in Fig. 2. Figure 5 shws the I-V curves f ZnO with nn-cnductivity cmpared with and ZTO with Schttky cntacts. Figure 5 is the I-V curves f annealed at 100 with gd cnductivity. Figure 5 shws the I-V curves f ZTO annealed at 200 with an ambiplar Schttky cntact. T cmpare the relative electrical prperties f ZnO, and ZTO, Fig. 6 shws the temperature dependence f the electrical characteristics f ZnO, and ZTO in a range f <current<. The I-V curves f ZnO reveal a very lw current, similar t an insulatr. The ZnO annealed at a high temperature had relatively lw current, but the I-V curves f ZTO shwed a high current. ZTO had the electrical prperties f and crystallin-

5 108 Trans. Electr. Electrn. Mater. 17(2) 104 (2016): T. Oh ity f ZnO, with increments f increased temperatures. These prperties f ZTO imprved the electrical prperties depending n the temperature, because has a Schttky cntact. 4. CONCLUSIONS The xide semicnductrs, ZnO, and ZTO were annealed at varius temperatures were analyzed by XPS, XRD and I-V curves t research the crrelatin between their electrical prperties and structures. ZnO had an Ohmic cntact and crystal structure. Hwever, and ZTO shwed Schttky cntact with increments f increased temperatures. The effect f xygen vacancy was nt prprtinate t the electrical prperties f xide semicnductrs. Oxygen vacancy was clsely related t Schttky cntact and weakly related t the Ohmic cntact. The prgress was enhanced upn the cmbinatin f xygen vacancy and metal xygen, and made the depletin regin a Schttky cntact. The electrical prperties f ZTO with a Schttky cntact, due t the, became stable and had imprved perfrmance with increased temperature. REFERENCES [1] T. Oh, Materials Research Bulletin, 77, 1 (2016). [DOI: dx.di.rg/ /j.materresbull ] [2] O. Mitrfanv and M. Mantra, J. Appl. Phys., 95, 6414 (2004). [DOI: [3] M. E. Lpes, H. L. Gmes, M.C.R. Medeirs, P. Barquinha, L. Pereira, E. Frtunat, R. Martins, and I. Ferreira, Appl. Phys. Lett., (2009). [DOI: rg/ / ] [4] T. Hira, M. Furuta, T. Hiramatsu, T. Matsuda, C. Li, H. Furuta, H. Hkari, M. Yshida, H. Ishii, and M. Kakegawa, IEEE Trans. Electrn Devices, 55, 3136 (2008). [DOI: TED ] [5] J. Maserjian and N. Zamani, Appl. Phys. Lett., 53, 559 (1982). [6] L. Plantier et al., Micrelectrn. Eng. 83, 2407 (2006). [DOI: / /14/7/12] [7] A. Grill and D. A. Neumayer, J. Appl. Phys. 94, 6697 (2003). [ [8] S. H. Lee, K. T. Park, and Y. G. Sn, Krea Jurnal f Materials Reasearch, 12, 240 (2002). [DOI: MRSK ] [9] H. Hsn, J. Nncrystralline Slids, 352, 851 (2006). [DOI: [10] O. Mitrfanv and M. Manfra, J. Appl. Phys., 95, 6414 (2004). [DOI: [11] T. Oh and C. H. Kim, IEEE Trans. Plasma Science, 38, 1598 (2010). [DOI: [12] T. Oh, Transactins f the Materials Research Sciety f Japan, 39, 475 (2014). [DOI: [13] J. Raja, K. S. Jang, C.P.T. Nguyen, and J. S. Yi, N. Balaji and S. Q. Hussain, and S. Chatterjee, TRANSACTIONS ON ELECTRICAL AND ELECTRONIC MATERIALS, 16, 234 (2015). [DOI: dx.di.rg/ /teem ] [14] K. C. Park and T. Y. Ma, J. Krean Inst. Electr. Electrn. Mater. Eng., 26, 373 (2013). [DOI: JKEM ] [15] T. Y. Ma, J. Krean Inst. Electr. Electrn. Mater. Eng., 25, 304, (2012). [DOI: [16] L. S. Vlasenk and G. D. Watkins, Phys. Lett. B, 71, (2005). [DOI: [17] T. Oh, Jurnal f nanscience and nantechnlgy, 14, 9047 (2014). [DOI: [18] H. G. Kim, Trans. Electr. Electrn. Mater., 16, 285 (2015). DOI: [19] T. Oh, EML, 11, 853 (2015). [DOI: s ] [20] T. Oh and C. K. Chi, J. Krean Phys. Sc., 56, 1150 (2010). [DOI:

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