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Influence of illumination on the output characteristics in pentacene thin film transistors
Materials Chemistry and Physics 142 (2013) 428e431
Contents lists available at ScienceDirect
Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Influence of illumination on the output characteristics in pentacene thin film transistors Yow-Jon Lin*, Bo-Chieh Huang Institute of Photonics, National Changhua University of Education, Changhua 500, Taiwan
h i g h l i g h t s Light illumination may lead to an increase in the drain current. This is because of the light-induced acceptor activation. The field-effect mobility is insensitive to light illumination. Electron trapping is responsible for the illumination-dependent output behavior.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 31 January 2012 Received in revised form 25 June 2013 Accepted 29 July 2013
The influence of illumination on the output characteristics of pentacene-based organic thin film transistors (OTFTs) was researched in this study. It is shown that light illumination may lead to an increase in the drain current, shifting the threshold voltage towards positive gateesource voltages. This is because of the light-induced acceptor activation, which is a new concept for illumination-dependent output characteristics of OTFTs. However, the field-effect mobility is insensitive to light illumination. It is found that electron trapping is responsible for the experimentally observed illumination-dependent output behavior of charge transport in OTFTs. Ó 2013 Elsevier B.V. All rights reserved.
Keywords: A. Organic compounds A. Thin films D. Defects D. Electrical properties
1. Introduction Pentacene (C22H14), a simple compound consisting of five fused benzene rings, has emerged as a viable candidate for the semiconducting transport layer in organic thin film transistors (OTFTs) [1e10]. Many researchers have devoted their efforts to improve OTFT-performance parameters [1e6,9,11e13]. The OTFTs can exhibit significant degradations in electrical performance such as a reduction in the field-effect mobility (m) and a shift of the threshold voltage (VTH). Gateesource voltage (VGS)-dependent drain current (ID) measurements at a constant drainesource voltage (VDS) provide a method to examine the performance characteristics of OTFTs and the relationship between VTH and m. In addition to display application of OTFTs, sensors and detectors made of OTFTs were fabricated and characterized because of their high sensitivity to external stimuli such as illumination, pressure, heating, etc [14e 18]. However, still little is known about the optical properties of
* Corresponding author. Tel.: þ886 4 7232105x3379; fax: þ886 4 7211153. E-mail address: [email protected] (Y.-J. Lin). 0254-0584/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matchemphys.2013.07.041
pentacene-based OTFTs. The influence of illumination on the output characteristic of pentacene-based OTFTs was researched in this study. We studied the current decay under dark and illumination in order to understand the illumination-dependent or illumination-independent charge trapping in OTFT. The regions inbetween crystalline grains, the disordered areas and the bulk of pentacene may influence the trapping [19e22]. The states at the pentacene/dielectric interface may also influence the trapping [23]. We consider that the knowledge of trap-induced effects from both charge types can be a useful tool for understanding and interpreting the OTFT measurements under dark and illumination. 2. Experimental details A SiO2 layer was grown on the heavily doped n-type Si (nþ-Si) wafer using a dry oxidation process as a gate oxide layer. The thickness of the SiO2 film is 265 nm according to ellipsometric measurements. A 70 nm thick pentacene (Luminescence Technology Corp., Hsinchu, Taiwan) layer was deposited on the SiO2/nþ-Si substrates by vacuum thermal evaporation and the evaporation rate was 4.2 nm min1. Then, the source and drain electrodes were
Y.-J. Lin, B.-C. Huang / Materials Chemistry and Physics 142 (2013) 428e431
fabricated by depositing Au metal on the pentacene layer through a shadow mask. The devices have the channel width (W) of 700 mm and the channel length (L) of 100 mm. The currentevoltage characteristics of OTFTs were measured at room temperature using a Keithley Model-4200-SCS semiconductor characterization system. The illumination effect was measured under 100 mW cm2 and illumination intensity from a 150 W solar simulator with an AM 1.5G filter. The illumination effect was measured by recording the ID versus time (t) while light illumination was turned on and off by a shutter. 3. Results and discussions Fig. 1(a) shows the output characteristics of OTFTs in the dark. Fig. 1(b) shows the output characteristics of OTFTs under illumination. The ID versus VDS curves were scanned from 0 to 40 V, with fixed VGS at 5, 10, 15, 20, 25, 30, 35 or 40 V. The significant increase of jIDj, when the device is under illumination, can be attributed to an increase in the carrier density in the channel of the device due to electron trapping. For the case of our devices, the most likely carrier photogeneration process is through the lightinduced acceptor activation rather than the exciton route [16]. This expected phenomenon is observed in Fig. 2. VDS-dependent ID measurements at a constant VGS provide a method to examine the performance characteristics of OTFTs and the relationship between VTH and m [8]. Fig. 1(c) shows ID at VDS ¼ 40 V [Fig. 1(a) and (b)] as the function of VGS. The fitting curve using the polynomial method is also shown in Fig. 1(c). By fitting a curve to the IDeVGS characteristic [Fig. 1(c)] based on the equation of jIDj ¼ (mWCi/2L)(VGS VTH)2 [where Ci is the insulator
429
capacitance per unit area (13.4 nF cm2 obtained from capacitanceevoltage measurement)], VTH and m can be calculated. Two fitting parameters (VTH and m extracted from the output characteristics) are listed in Table 1. We find the constant extracted m validates the illumination-independent hole trapping. However, positive VTH shift was observed under illumination. Its effect can arise from charge trapping in the states at the semiconductor/ dielectric interfaces or the creation of defects in the semiconductor [24e26]. Moreover, the existence of electron traps near the pentacene/dielectric interface of extrinsic origin was proposed by Völkel et al. [23]. According to the previously reported results, we suggest that electron traps in pentacene, which are filled by light illumination, can enhance ID due to a higher number of available free charge carriers. The electron (hole) traps here are assumed neutral when empty and negative (positive) when occupied and hence are acceptor-like (donor-like) [24]. We conclude that the light-induced electron trapping may cause a shift of the onset of ID towards positive gateesource voltages. However, there were no significant changes of m. This is because of the illuminationindependent hole trapping. To confirm the influence of illumination on electron and hole trapping, time dependent measurements were performed under dark and illumination. An initial gateesource voltage (VINGS ¼ 40 or 40 V) applied for 100 s at VDS ¼ 0 V in the dark before abruptly stepping the gate bias to VGS, which was then varied from 40 to 40.001 V for 300 s at VDS ¼ 40 V under dark or illumination. Fig. 2 shows ID versus t curves of OTFTs under dark and illumination. jIDj should decay in the same manner, since the decaying trapped electron population results in a decaying extra hole population to balance it. The time domain data (Fig. 2) confirm the
Fig. 1. (a) ID versus VDS curves of OTFTs in the dark, (b) ID versus VDS curves of OTFTs under illumination and (c) ID at VDS ¼ 40 V [(a) and (b)] as the function of VGS.
430
Y.-J. Lin, B.-C. Huang / Materials Chemistry and Physics 142 (2013) 428e431
Fig. 2. Time domain measurement data of OTFTs: (a) ID versus time for a device tested with VINGS ¼ 40 V at VDS ¼ 0 V in the dark and VGS varying from 40 to 40.001 V at VDS ¼ 40 V under dark or illumination and (b) ID versus time for a device tested with VINGS ¼ 40 V at VDS ¼ 0 V in the dark and VGS varying from 40 to 40.001 V at VDS ¼ 40 V under dark or illumination.
Table 1 Fitting parameters and results.
Dark Illumination
Table 2 Fitting results based on the normalized jIDj decays (Fig. 3). VTH (V)
m (cm2 V1 s1)
13.9 6.1
0.1 0.1
electron trap model. In Fig. 2(a), we find that jIDj under illumination is higher than jIDj in the dark, owing to the increased number of trapped electrons. Some of trapped electrons can be easily detrapped (that is, the formation of the neutral electron-trap density) when negative VINGS is applied because of the hole accumulation. When light is turned on, some of electrons will be naturally trapped. Since the increased number of trapped electrons under illumination results in an increase in the hole concentration (that is, the light-induced acceptor activation), jIDj should increase in the same manner. This can explain why exposing the device to
Fig. 3. The normalized jIDj decays extracted from IDetime measurements (VINGS ¼ 40 V) under (a) dark and (b) illumination [Fig. 2(b)]. The normalized jIDj decays extracted from IDetime measurements (VINGS ¼ 40 V) under (c) dark and (d) illumination [Fig. 2(a)].
Dark [Fig. 3(a)] Illumination [Fig. 3(b)] Dark [Fig. 3(c)] Illumination [Fig. 3(d)]
s1 (s)
A1 (%)
s2 (s)
A2 (%)
11 10 7 7
36.0 35.5 30.0 26.9
159 164 320 248
64.0 64.5 70.0 73.1
white light can cause changes of ID and VTH. However, in Fig. 2(b), the ID versus t curve under illumination is similar to that in the dark, implying that electron traps are almost filled at VINGS ¼ 40 V. Therefore, light illumination could not lead to the increased number of trapped electrons. A large number of electrons can be easily trapped (that is, the formation of the high negative electron-trap density) when positive VINGS is applied because of the electron accumulation. If the carrier photogeneration process is through the exciton route, the enhanced drain current is expected under illumination. Fig. 3 shows the normalized jIDj decays extracted from IDet measurements shown in Fig. 2. To demonstrate the domination of short-lifetime or long-lifetime electron trapping, we fit the data to exponential decay functions [jID0 j ¼ A1e(t/s1) þ A2e(t/s2)] [9,24]. jID0 j is the normalized jIDj. This equation reflects two different charge trapping mechanisms with time constants s1 and s2 (s1 < s2). The values of A1 and A2, where A1þA2 ¼ 1, represent weighing factors that quantify the contribution of each mechanism to the decay process. The first (second) term, which can be attributed to short-lifetime (long-lifetime) electron trapping, dominates the decay process [9,24]. Four fitting parameters are listed in Table 2. It is shown that A1 (A2) extracted from the jID0 jet characteristics [Fig. 3(a)] is similar to A1 (A2) extracted from jID0 jet characteristics [Fig. 3(b)]. However, we find that A1 (A2) extracted from jID0 jet characteristics [Fig. 3(d)] is smaller (larger) than A1 (A2) extracted from jID0 jet characteristics [Fig. 3(c)], indicating that light illumination may lead to the great contribution of longlifetime electron trapping to the decay process. It is shown that electron trapping plays an important role in enhancing the acceptor activation. 4. Conclusions The influence of illumination on the output characteristics of pentacene-based OTFTs was examined in this study. Light
Y.-J. Lin, B.-C. Huang / Materials Chemistry and Physics 142 (2013) 428e431
illumination may lead to an increase in jIDj, shifting the VTH. This is because of the light-induced acceptor activation. According to the experimental results, we found that the light-induced electron trapping within the pentacene layer controlled the carrier flow, increasing jIDj. It is important to identify the illumination effect for understanding the actual device operation mechanism and enhancing the device performance. Acknowledgment The authors acknowledge the support of the National Science Council of Taiwan (contract no. 100-2112-M-018-003-MY3) in the form of grants. References [1] M.J. Powell, C. van Berkel, J.R. Hughes, Appl. Phys. Lett. 54 (1989) 1323. [2] P.M. Zeitzoff, C.D. Young, G.A. Brown, Y. Kim, IEEE Electron Dev. Lett. 24 (2003) 275. [3] D. Gupta, M. Katiyar, D. Gupta, Org. Electron. 10 (2009) 775. [4] S.J. Kang, M. Noh, D.S. Park, H.J. Kim, C.N. Whang, C.H. Chang, J. Appl. Phys. 95 (2004) 2293.
431
[5] S. Ogawa, T. Naijo, Y. Kimura, H. Ishii, M. Niwano, Appl. Phys. Lett. 86 (2005) 252104. [6] C. Ucurum, H. Goebel, F.A. Yildirim, W. Bauhofer, W. Krautschneider, J. Appl. Phys. 104 (2008) 084501. [7] T.W. Kelley, P.F. Baude, C. Gerlach, D.E. Ender, D. Muyres, M.A. Haase, D.E. Vogel, S.D. Theiss, Chem. Mater. 16 (2004) 4413. [8] Y.J. Lin, C.L. Tsai, B.C. Huang, Appl. Phys. Lett. 97 (2010) 203509. [9] B.C. Huang, Y.J. Lin, Appl. Phys. Lett. 99 (2011) 113301. [10] Y.J. Lin, Synth. Met 160 (2010) 2628. [11] Y.J. Lin, B.C. Huang, Microelectron. Eng. 103 (2013) 76. [12] M.Y. Tsai, Y.J. Lin, Microelectron. Eng. 96 (2012) 24. [13] H.Y. Tsao, Y.J. Lin, Appl. Phys. Lett. 101 (2012) 113306. [14] S. Jung, T. Ji, V.K. Varadan, Appl. Phys. Lett. 90 (2007) 062105. [15] Y. Liang, G. Dong, Y. Hu, L. Wang, Y. Qiu, Appl. Phys. Lett. 86 (2005) 132101. [16] M.C. Hamilton, S. Martin, J. Kanicki, IEEE Trans. Electron Devices 51 (2004) 877. [17] C.H. Kim, M.H. Choi, S.H. Lee, J. Jang, S. Kirchmeyer, Appl. Phys. Lett. 96 (2010) 123301. [18] I. Manunza, A. Bonfiglio, Biosens. Bioelectron. 22 (2007) 2775. [19] M. Tello, M. Chiesa, C.M. Duffy, H. Sirringhaus, Adv. Funct. Mater. 18 (2008) 3907. [20] A. Salleo, F. Endicott, R.A. Street, Appl. Phys. Lett. 86 (2005) 263505. [21] J.B. Chang, V. Subramanian, Appl. Phys. Lett. 88 (2006) 233513. [22] R. Häusermann, B. Batlogg, Appl. Phys. Lett. 99 (2011) 083303. [23] A.R. Völkel, R.A. Street, D. Knipp, Phys. Rev. B 66 (2002) 195336. [24] G. Gu, M.G. Kane, J.E. Doty, A.H. Firester, Appl. Phys. Lett. 87 (2005) 243512. [25] D. Knipp, R.A. Street, A.R. Völkel, J. Ho, J. Appl. Phys. 93 (2003) 347. [26] J. Lee, J.H. Kim, S. Im, D.Y. Jung, J. Appl. Phys. 96 (2004) 2301.
Contents lists available at ScienceDirect
Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Influence of illumination on the output characteristics in pentacene thin film transistors Yow-Jon Lin*, Bo-Chieh Huang Institute of Photonics, National Changhua University of Education, Changhua 500, Taiwan
h i g h l i g h t s Light illumination may lead to an increase in the drain current. This is because of the light-induced acceptor activation. The field-effect mobility is insensitive to light illumination. Electron trapping is responsible for the illumination-dependent output behavior.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 31 January 2012 Received in revised form 25 June 2013 Accepted 29 July 2013
The influence of illumination on the output characteristics of pentacene-based organic thin film transistors (OTFTs) was researched in this study. It is shown that light illumination may lead to an increase in the drain current, shifting the threshold voltage towards positive gateesource voltages. This is because of the light-induced acceptor activation, which is a new concept for illumination-dependent output characteristics of OTFTs. However, the field-effect mobility is insensitive to light illumination. It is found that electron trapping is responsible for the experimentally observed illumination-dependent output behavior of charge transport in OTFTs. Ó 2013 Elsevier B.V. All rights reserved.
Keywords: A. Organic compounds A. Thin films D. Defects D. Electrical properties
1. Introduction Pentacene (C22H14), a simple compound consisting of five fused benzene rings, has emerged as a viable candidate for the semiconducting transport layer in organic thin film transistors (OTFTs) [1e10]. Many researchers have devoted their efforts to improve OTFT-performance parameters [1e6,9,11e13]. The OTFTs can exhibit significant degradations in electrical performance such as a reduction in the field-effect mobility (m) and a shift of the threshold voltage (VTH). Gateesource voltage (VGS)-dependent drain current (ID) measurements at a constant drainesource voltage (VDS) provide a method to examine the performance characteristics of OTFTs and the relationship between VTH and m. In addition to display application of OTFTs, sensors and detectors made of OTFTs were fabricated and characterized because of their high sensitivity to external stimuli such as illumination, pressure, heating, etc [14e 18]. However, still little is known about the optical properties of
* Corresponding author. Tel.: þ886 4 7232105x3379; fax: þ886 4 7211153. E-mail address: [email protected] (Y.-J. Lin). 0254-0584/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matchemphys.2013.07.041
pentacene-based OTFTs. The influence of illumination on the output characteristic of pentacene-based OTFTs was researched in this study. We studied the current decay under dark and illumination in order to understand the illumination-dependent or illumination-independent charge trapping in OTFT. The regions inbetween crystalline grains, the disordered areas and the bulk of pentacene may influence the trapping [19e22]. The states at the pentacene/dielectric interface may also influence the trapping [23]. We consider that the knowledge of trap-induced effects from both charge types can be a useful tool for understanding and interpreting the OTFT measurements under dark and illumination. 2. Experimental details A SiO2 layer was grown on the heavily doped n-type Si (nþ-Si) wafer using a dry oxidation process as a gate oxide layer. The thickness of the SiO2 film is 265 nm according to ellipsometric measurements. A 70 nm thick pentacene (Luminescence Technology Corp., Hsinchu, Taiwan) layer was deposited on the SiO2/nþ-Si substrates by vacuum thermal evaporation and the evaporation rate was 4.2 nm min1. Then, the source and drain electrodes were
Y.-J. Lin, B.-C. Huang / Materials Chemistry and Physics 142 (2013) 428e431
fabricated by depositing Au metal on the pentacene layer through a shadow mask. The devices have the channel width (W) of 700 mm and the channel length (L) of 100 mm. The currentevoltage characteristics of OTFTs were measured at room temperature using a Keithley Model-4200-SCS semiconductor characterization system. The illumination effect was measured under 100 mW cm2 and illumination intensity from a 150 W solar simulator with an AM 1.5G filter. The illumination effect was measured by recording the ID versus time (t) while light illumination was turned on and off by a shutter. 3. Results and discussions Fig. 1(a) shows the output characteristics of OTFTs in the dark. Fig. 1(b) shows the output characteristics of OTFTs under illumination. The ID versus VDS curves were scanned from 0 to 40 V, with fixed VGS at 5, 10, 15, 20, 25, 30, 35 or 40 V. The significant increase of jIDj, when the device is under illumination, can be attributed to an increase in the carrier density in the channel of the device due to electron trapping. For the case of our devices, the most likely carrier photogeneration process is through the lightinduced acceptor activation rather than the exciton route [16]. This expected phenomenon is observed in Fig. 2. VDS-dependent ID measurements at a constant VGS provide a method to examine the performance characteristics of OTFTs and the relationship between VTH and m [8]. Fig. 1(c) shows ID at VDS ¼ 40 V [Fig. 1(a) and (b)] as the function of VGS. The fitting curve using the polynomial method is also shown in Fig. 1(c). By fitting a curve to the IDeVGS characteristic [Fig. 1(c)] based on the equation of jIDj ¼ (mWCi/2L)(VGS VTH)2 [where Ci is the insulator
429
capacitance per unit area (13.4 nF cm2 obtained from capacitanceevoltage measurement)], VTH and m can be calculated. Two fitting parameters (VTH and m extracted from the output characteristics) are listed in Table 1. We find the constant extracted m validates the illumination-independent hole trapping. However, positive VTH shift was observed under illumination. Its effect can arise from charge trapping in the states at the semiconductor/ dielectric interfaces or the creation of defects in the semiconductor [24e26]. Moreover, the existence of electron traps near the pentacene/dielectric interface of extrinsic origin was proposed by Völkel et al. [23]. According to the previously reported results, we suggest that electron traps in pentacene, which are filled by light illumination, can enhance ID due to a higher number of available free charge carriers. The electron (hole) traps here are assumed neutral when empty and negative (positive) when occupied and hence are acceptor-like (donor-like) [24]. We conclude that the light-induced electron trapping may cause a shift of the onset of ID towards positive gateesource voltages. However, there were no significant changes of m. This is because of the illuminationindependent hole trapping. To confirm the influence of illumination on electron and hole trapping, time dependent measurements were performed under dark and illumination. An initial gateesource voltage (VINGS ¼ 40 or 40 V) applied for 100 s at VDS ¼ 0 V in the dark before abruptly stepping the gate bias to VGS, which was then varied from 40 to 40.001 V for 300 s at VDS ¼ 40 V under dark or illumination. Fig. 2 shows ID versus t curves of OTFTs under dark and illumination. jIDj should decay in the same manner, since the decaying trapped electron population results in a decaying extra hole population to balance it. The time domain data (Fig. 2) confirm the
Fig. 1. (a) ID versus VDS curves of OTFTs in the dark, (b) ID versus VDS curves of OTFTs under illumination and (c) ID at VDS ¼ 40 V [(a) and (b)] as the function of VGS.
430
Y.-J. Lin, B.-C. Huang / Materials Chemistry and Physics 142 (2013) 428e431
Fig. 2. Time domain measurement data of OTFTs: (a) ID versus time for a device tested with VINGS ¼ 40 V at VDS ¼ 0 V in the dark and VGS varying from 40 to 40.001 V at VDS ¼ 40 V under dark or illumination and (b) ID versus time for a device tested with VINGS ¼ 40 V at VDS ¼ 0 V in the dark and VGS varying from 40 to 40.001 V at VDS ¼ 40 V under dark or illumination.
Table 1 Fitting parameters and results.
Dark Illumination
Table 2 Fitting results based on the normalized jIDj decays (Fig. 3). VTH (V)
m (cm2 V1 s1)
13.9 6.1
0.1 0.1
electron trap model. In Fig. 2(a), we find that jIDj under illumination is higher than jIDj in the dark, owing to the increased number of trapped electrons. Some of trapped electrons can be easily detrapped (that is, the formation of the neutral electron-trap density) when negative VINGS is applied because of the hole accumulation. When light is turned on, some of electrons will be naturally trapped. Since the increased number of trapped electrons under illumination results in an increase in the hole concentration (that is, the light-induced acceptor activation), jIDj should increase in the same manner. This can explain why exposing the device to
Fig. 3. The normalized jIDj decays extracted from IDetime measurements (VINGS ¼ 40 V) under (a) dark and (b) illumination [Fig. 2(b)]. The normalized jIDj decays extracted from IDetime measurements (VINGS ¼ 40 V) under (c) dark and (d) illumination [Fig. 2(a)].
Dark [Fig. 3(a)] Illumination [Fig. 3(b)] Dark [Fig. 3(c)] Illumination [Fig. 3(d)]
s1 (s)
A1 (%)
s2 (s)
A2 (%)
11 10 7 7
36.0 35.5 30.0 26.9
159 164 320 248
64.0 64.5 70.0 73.1
white light can cause changes of ID and VTH. However, in Fig. 2(b), the ID versus t curve under illumination is similar to that in the dark, implying that electron traps are almost filled at VINGS ¼ 40 V. Therefore, light illumination could not lead to the increased number of trapped electrons. A large number of electrons can be easily trapped (that is, the formation of the high negative electron-trap density) when positive VINGS is applied because of the electron accumulation. If the carrier photogeneration process is through the exciton route, the enhanced drain current is expected under illumination. Fig. 3 shows the normalized jIDj decays extracted from IDet measurements shown in Fig. 2. To demonstrate the domination of short-lifetime or long-lifetime electron trapping, we fit the data to exponential decay functions [jID0 j ¼ A1e(t/s1) þ A2e(t/s2)] [9,24]. jID0 j is the normalized jIDj. This equation reflects two different charge trapping mechanisms with time constants s1 and s2 (s1 < s2). The values of A1 and A2, where A1þA2 ¼ 1, represent weighing factors that quantify the contribution of each mechanism to the decay process. The first (second) term, which can be attributed to short-lifetime (long-lifetime) electron trapping, dominates the decay process [9,24]. Four fitting parameters are listed in Table 2. It is shown that A1 (A2) extracted from the jID0 jet characteristics [Fig. 3(a)] is similar to A1 (A2) extracted from jID0 jet characteristics [Fig. 3(b)]. However, we find that A1 (A2) extracted from jID0 jet characteristics [Fig. 3(d)] is smaller (larger) than A1 (A2) extracted from jID0 jet characteristics [Fig. 3(c)], indicating that light illumination may lead to the great contribution of longlifetime electron trapping to the decay process. It is shown that electron trapping plays an important role in enhancing the acceptor activation. 4. Conclusions The influence of illumination on the output characteristics of pentacene-based OTFTs was examined in this study. Light
Y.-J. Lin, B.-C. Huang / Materials Chemistry and Physics 142 (2013) 428e431
illumination may lead to an increase in jIDj, shifting the VTH. This is because of the light-induced acceptor activation. According to the experimental results, we found that the light-induced electron trapping within the pentacene layer controlled the carrier flow, increasing jIDj. It is important to identify the illumination effect for understanding the actual device operation mechanism and enhancing the device performance. Acknowledgment The authors acknowledge the support of the National Science Council of Taiwan (contract no. 100-2112-M-018-003-MY3) in the form of grants. References [1] M.J. Powell, C. van Berkel, J.R. Hughes, Appl. Phys. Lett. 54 (1989) 1323. [2] P.M. Zeitzoff, C.D. Young, G.A. Brown, Y. Kim, IEEE Electron Dev. Lett. 24 (2003) 275. [3] D. Gupta, M. Katiyar, D. Gupta, Org. Electron. 10 (2009) 775. [4] S.J. Kang, M. Noh, D.S. Park, H.J. Kim, C.N. Whang, C.H. Chang, J. Appl. Phys. 95 (2004) 2293.
431
[5] S. Ogawa, T. Naijo, Y. Kimura, H. Ishii, M. Niwano, Appl. Phys. Lett. 86 (2005) 252104. [6] C. Ucurum, H. Goebel, F.A. Yildirim, W. Bauhofer, W. Krautschneider, J. Appl. Phys. 104 (2008) 084501. [7] T.W. Kelley, P.F. Baude, C. Gerlach, D.E. Ender, D. Muyres, M.A. Haase, D.E. Vogel, S.D. Theiss, Chem. Mater. 16 (2004) 4413. [8] Y.J. Lin, C.L. Tsai, B.C. Huang, Appl. Phys. Lett. 97 (2010) 203509. [9] B.C. Huang, Y.J. Lin, Appl. Phys. Lett. 99 (2011) 113301. [10] Y.J. Lin, Synth. Met 160 (2010) 2628. [11] Y.J. Lin, B.C. Huang, Microelectron. Eng. 103 (2013) 76. [12] M.Y. Tsai, Y.J. Lin, Microelectron. Eng. 96 (2012) 24. [13] H.Y. Tsao, Y.J. Lin, Appl. Phys. Lett. 101 (2012) 113306. [14] S. Jung, T. Ji, V.K. Varadan, Appl. Phys. Lett. 90 (2007) 062105. [15] Y. Liang, G. Dong, Y. Hu, L. Wang, Y. Qiu, Appl. Phys. Lett. 86 (2005) 132101. [16] M.C. Hamilton, S. Martin, J. Kanicki, IEEE Trans. Electron Devices 51 (2004) 877. [17] C.H. Kim, M.H. Choi, S.H. Lee, J. Jang, S. Kirchmeyer, Appl. Phys. Lett. 96 (2010) 123301. [18] I. Manunza, A. Bonfiglio, Biosens. Bioelectron. 22 (2007) 2775. [19] M. Tello, M. Chiesa, C.M. Duffy, H. Sirringhaus, Adv. Funct. Mater. 18 (2008) 3907. [20] A. Salleo, F. Endicott, R.A. Street, Appl. Phys. Lett. 86 (2005) 263505. [21] J.B. Chang, V. Subramanian, Appl. Phys. Lett. 88 (2006) 233513. [22] R. Häusermann, B. Batlogg, Appl. Phys. Lett. 99 (2011) 083303. [23] A.R. Völkel, R.A. Street, D. Knipp, Phys. Rev. B 66 (2002) 195336. [24] G. Gu, M.G. Kane, J.E. Doty, A.H. Firester, Appl. Phys. Lett. 87 (2005) 243512. [25] D. Knipp, R.A. Street, A.R. Völkel, J. Ho, J. Appl. Phys. 93 (2003) 347. [26] J. Lee, J.H. Kim, S. Im, D.Y. Jung, J. Appl. Phys. 96 (2004) 2301.