alinn resistive ammonia gas sensors

Accepted Manuscript Title: AlInN resistive ammonia gas sensors Authors: W.Y. Weng, S.J. Chang, T.J. Hsueh, C.L. Hsu, M.J. Li, W.C. Lai PII: S0925-4005(09)00340-2 DOI: doi:10.1016/j.snb.2009.04.017 Reference: SNB 11487 To appear in: Sensors and Actuators B Received date: 1-12-2008 Revised date: 14-4-2009 Accepted date: 16-4-2009 Please cite this article as: W.Y. Weng, S.J. Chang, T.J. Hsueh, C.L. Hsu, M.J. Li, W.C. Lai, AlInN resistive ammonia gas sensors, Sensors and Actuators B: Chemical (2008), doi:10.1016/j.snb.2009.04.017 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Page 1 of 18 Accepted Manuscript 1 AlInN resistive ammonia gas sensors W. Y. Weng 1 , S. J. Chang 1 , T. J. Hsueh 2,* C. L. Hsu 3 , M. J. Li 3 and W. C. Lai 4 1 Institute of Microelectronics and Department of Electrical Engineering Advanced Optoelectronic Technology Center Center for Micro/Nano Science and Technology National Cheng Kung University, Tainan 70101, TAIWAN 2 National Nano Device Laboratories, Tainan 741, Taiwan. 3 Department of Electronic Engineering National University of Tainan, Tainan 700, TAIWAN 4 Institute of Electro-Optical Science and Engineering, National Cheng Kung University, Tainan 70101, TAIWAN Abstract We report the growth of AlInN epitaxial layer and the fabrication of AlInN resistive NH 3 gas sensor. It was found that surface morphology of the AlInN was rough with quantum dot like nano-islands. It was also found that the conductance of these AlInN nano-islands increased as NH 3 gas was introduced into the test chamber. At 350 o C, it was found that measured incremental currents were around 105 μA, 127 μA, 147 μA and 157 μA when concentration of the injected NH 3 gas was 500, 1000, 2000 and 4000 ppm, respectively. Keywords: AlInN, nano-island, gas sensor, ammonia sensor Email:tj.Hsueh@gmail.com TEL: (+886) 6-2757575-62400-1208 ; FAX: (+886) 6-2761854 Page 2 of 18 Accepted Manuscript 2 Introduction Ammonia (NH 3 ) is a colorless gas with a special odor. It is commonly used in various industrial sectors [1]. Although NH 3 is extensively used in our daily life, people may develop a burning sensation in eyes, nose and throat when exposed to NH 3 . Inhalation of NH 3 vapor could also cause acute poisoning to people. Hence, detecting and measuring NH 3 vapor concentration in the environment is necessary. The most commonly used method to detect gaseous NH 3 was either by potentiometric electrodes [2] or by infrared devices [3]. However, these devices are expensive and bulky. It is also possible to detect NH 3 vapor concentration by semi-conducting metal oxide materials [4-9]. It has been shown that near surface conductivity of these materials changes upon exposure to certain gas molecules. Furthermore, it was found that such resistance change is related to various defects such as oxygen vacancy, metal vacancy or others [10, 11]. Recently, it was found that III-nitride epitaxial layer can also be used to detect gaseous butane, propane, ethyl alcohol and carbon monoxide [12]. Although III-nitride-based materials are extensively used as light emitting diodes [13, 14], ultraviolet photodetectors [15] and high power electronics [16], only few reports on III-nitride-based sensor for volatile organic compounds can be found in the literature [12]. Compared with metal oxide sensors, we should be able to integrate III-nitride-based gas sensors with III-nitride-based photodetectors and electronic devices on the same chip. Other than the binary GaN, ternary AlInN has attracted much Page 3 of 18 Accepted Manuscript 3 attention in recent years. Compared with AlGaN and InGaN, AlInN is much less known due to the difficulty in growing high quality crystal [17]. It has been shown that AlInN can be grown lattice matched to GaN with an indium content of ~17-18%. However, it is still difficult to grow high quality AlInN due to severe phase separation caused by the large disparity in cation sizes as well as by differences in thermal properties of the binary constituents [18]. It has also been reported that epitaxial AlInN layers are defective in general with a significant amount of aluminum vacancy, indium vacancy or nitrogen vacancy. Similar to metal oxide sensors, these defects should be able to enhance the reaction of gas molecular on sample surface and thus enhance the responsivity of AlInN-based gas sensors. In this study, we report the growth of AlInN. Sensing properties of the fabricated AlInN resistive NH 3 gas sensors will also be discussed. Experimental Samples used in this study were grown on a c-plane (0001) sapphire (Al 2 O 3 ) substrate by metalorganic chemical vapor deposition. Details of the growth can be found elsewhere [19]. Prior to the growth, we annealed the sapphire substrates at 1060°C in H 2 ambient to remove surface contamination. We then deposited a 30-nm-thick low-temperature GaN nucleation layer at 530°C, a 2- μm-thick n-type unintentionally doped GaN (n=3×10 16 cm -3 ) buffer layer at 1020°C, and a 500-nm-thick n-type unintentionally doped AlInN (n=5×10 19 cm -3 ) active layer at 650°C. A JEOL JSM-7000F field emission scanning electron microscope (FESEM) operated at 10 keV was then used to characterize structural properties of Page 4 of 18 Accepted Manuscript 4 the as-grown AlInN epitaxial layer. The cross-sectional image of the AlInN layer was prepared by an FEI Nova-200 NanoLab Dual-Beam Focused Ion Beam (DB-FIB) system. Crystal qualities of the as-grown samples were evaluated by a BEDE D1 double-crystal X-ray diffraction (DCXRD) system. The source of X-ray is 1.54056 Å wavelength (Cu K α ). For the fabrication of NH 3 gas sensors, we carefully smeared the colloidal silver onto the sample surface to serve as contact electrodes. The sample was then annealed at 350°C for 15 min in Ar ambient to form good ohmic contacts between sliver and the underlying AlInN. Figure 1 shows schematic diagram of the fabricated AlInN resistive gas sensor. To evaluate NH 3 gas sensing properties, we placed the fabricated sensor in a sealed chamber and measured current-voltage (I-V) characteristic of the sample in air from the two electrodes. It should be noted that the sealed chamber has an inlet port connected to a gas inlet valve and an outlet port connected to an air pump. We first closed the outlet port and injected NH 3 gas into the chamber through a gas-injecting syringe. At this stage, we measured I-V characteristic of the sample continuously in the presence of NH 3 gas (i.e., air+ NH 3 ). After the chamber was stabilized, we opened the outlet port so that the air pump can pump the NH 3 gas away. At the same time, we also opened the inlet valve to introduce air into the chamber. In other words, the chamber was kept in atmospheric pressure throughout the experiment. At the end of the experiment, we measured I-V characteristic of the sample in air again. Result and Discussion From Hall measurements, it was found that the sheet resistances of our GaN and AlInN layers were 1.09×10 6 Ω/sq and 394 Ω/sq, respectively. Page 5 of 18 Accepted Manuscript 5 These values suggest that parallel conduction which might occur in the GaN buffer layer should be negligible. Figure 2 shows top-view FESEM image of the AlInN epitaxial layer. The inset shows cross-sectional image of the AlInN layer that prepared by DB-FIB. It was found that thickness of the AlInN epitaxial layer was around 545 nm, which agreed well with our initial design. It was also found that surface morphology of the AlInN was rough with quantum dot like nano-islands. Similar result has also been reported previously [20]. It also was found that the diameter and height of the nano-islands were around 100 nm and 160 nm, respectively. It should be noted that these nano-islands could provide us a larger surface area, which in term will result in a large sensor response. It should also be noted that the Pt layer shown in the inset was intentionally deposited to protect the underneath AlInN and GaN from e-beam etching during DB-FIB sample preparation. No such Pt layer was used during the fabrication of NH 3 sensors. Figure 3(a) shows DCXRD spectrum of the sample with two clear peaks. It was found that full-width-half-maximum (FWHM) of the (0002) GaN peak was around 130 arcsec, suggesting good crystal quality. In contrast, FWHM of the AlInN peak was significantly larger (i.e., 758 arcsec). Based on Vegard’s rule, it was found that indium content in the AlInN layer was around 62%. The fact that no other peaks were observed suggests that no phase separation occurred in the sample [21]. Figure 3(b) shows energy dispersive spectrum (EDS) measured from the fabricated devices. It can be seen that aluminum, indium and nitrogen peaks could all be clearly observed in the spectrum. It was also found that the atomic weight percent of indium in the AlInN layer was 62.6%, which agrees well with that observed from the DCXRD measurement. Page 6 of 18 Accepted Manuscript 6 Figure 4 shows I-V characteristics of the fabricated sensor measured in air. It can be seen that the measured current increased linearly with the applied bias. Such linear behavior reveals that good ohmic contacts were formed between the Ag electrodes and the AlInN epitaxial layer. For gas sensing, it is known that oxygen is adsorbed at the N vacancies of III-nitrides semiconductors [12]. Thus, oxygen sorption plays an important role in electrical transport properties of AlInN epitaxial layer. It is also known that oxygen ionosorption removes conduction electrons and thus lowers the conductance of AlInN. Hence, the sensing mechanism of AlInN NH 3 gas sensor may be described as follows: First, reactive oxygen species such as O 2 − , O 2− and O − are adsorbed on AlInN surface at elevated temperatures. It should be noted that chemisorbed oxygen species depend strongly on temperature. At low temperatures, O 2 − is commonly chemisorbed. At high temperatures, however, O − and O 2− are commonly chemisorbed while O 2 − disappear rapidly [22]. The reaction kinematics can be described as follows [23]: O 2 (gas) ↔ O 2 (absorbed) (1) O 2 (absorbed) + e − ↔ O 2 − (2) O 2 − +e − ↔ 2O − (3) Thus, the conductance of AlInN nano-islands increased as NH 3 gas was introduced into the test chamber due to the exchange of electrons between ionosorbed species and AlInN nano-islands. The reaction between NH 3 gas and the ionic oxygen species can be described by [24]: 2NH 3 + 3O − (ads) ↔ 3H 2 O + N 2 + 3e − (4) Page 7 of 18 Accepted Manuscript 7 Figure 5 shows response of the fabricated AlInN NH 3 gas sensor measured with 2000 ppm NH 3 gas at various temperatures. Here, we define the response as the incremental current, ∆I, before and after the introduction of NH 3 gas. With this definition, it was found that measured ∆I were around 15 μA, 52.5 μA, 75.4 μA, 147 μA and 60 μA when the device was operated at 200 o C, 250 o C, 300 o C, 350 o C and 400 o C, respectively. Figure 6 shows response variation of the AlInN sensor exposed to NH 3 gas injection and pumping. These measurements were performed by injecting various amounts of NH 3 gas into the sealed chamber following by pumping at 350 o C. It was found that measured sensor responses were around 105 μA, 127 μA, 147 μA and 157 μA when concentration of the injected NH 3 gas was 500, 1000, 2000 and 4000 ppm, respectively. In other words, sensor response increased with the increase of NH 3 gas concentration. It was also found that measured sensor response rapidly as we injected NH 3 gas into the chamber and pumped them away. Such a result indicates that the response speed of the fabricated sensor is good. Conclusion In summary, we report the growth of AlInN epitaxial layer and the fabrication of AlInN resistive NH 3 gas sensor. It was found that surface morphology of the AlInN was rough with quantum dot like nano-islands. It was also found that the conductance of these AlInN nano-islands increased as NH 3 gas was introduced into the test chamber. At 350 o C, it Page 8 of 18 Accepted Manuscript 8 was found that measured incremental currents were around 105 μA, 127 μA, 147 μA and 157 μA when concentration of the injected NH 3 gas was 500, 1000, 2000 and 4000 ppm, respectively. Acknowledgements: This work was granted by the Center for Frontier Materials and Micro/Nano Science and Technology, National Cheng Kung University, Taiwan (D97-2700). This work was also in part supported by the Advanced Optoelectronic Technology Center, National Cheng Kung University, under projects from the Ministry of Education. Page 9 of 18 Accepted Manuscript 9 Figure Captions Figure 1. Schematic diagram of the fabricated AlInN resistive gas sensor Figure 2. Top-view FESEM image of the AlInN epitaxial layer. The inset shows cross-sectional image of the AlInN layer. Figure 3. (a) DCXRD and (b) EDS spectra of the AlInN layer. Figure 4. I-V characteristics of the fabricated sensor measured in air. Figure 5. Response of the fabricated AlInN NH 3 gas sensor measured with 2000 ppm NH 3 gas at various temperatures. Figure 6. Response variation of the AlInN sensor exposed to NH 3 gas injection and pumping. [...]... K Pufler and I Babusik, Personal ammonia sensor for industrial environments, J Environ Monit 1 (1999) cr 417-422 [2] M E Meyerhoff, Polymer membrane electrode-based potentiometric us ammonia gas sensor, Anal Chem 52 (1980) 1532-1534 an [3] P S Kumar, A V Scaria, C P G Vallabhan, V P N Nampoori and P Radhakrishnan, Long-period grating in multimode fiber for ammonia gas detection, Proc SPIE 5279, (2004)... of Ti-doped In2O3 ceramics as an ammonia sensor, Sens Actuators B 114 (2006) 762-767 [9] B Karunagaran, P Uthirakumar, S J Chung, S Velumani and E K Suh, TiO2 thin film gas sensor for monitoring ammonia, Mater 10 Page 10 of 18 Characterization 58 (2007) 680-684 [10] K Ihokura and J Watson, “The performance of the stannic oxide ceramic gas sensor, in: The stannic oxide gas sensor: Principles and ip t... [22] D Kohl, The role of noble-metals in the chemistry of solid-state gas sensors, Sens Actuators B 1 (1990) 158-162 [23] P P Sahay, Zinc oxide thin film gas sensor for detection of acetone, J Mater Sci 40 (2005) 4383-4385 [24] M S Wagh, G H Jain, D R Patil, S A Patil and L A Patil, Modified zinc oxide thick film resistors as NH3 gas sensor, Sens Actuators B 115 (2006) 128-133 12 Page 12 of 18 Biography... applications”, CRC press, Boca Raton, 1994 [11] K Ihokura and J Watson, “Sensitivity modification using additives, cr in: The Stannic Oxide Gas Sensor: Principles and Applications”, CRC press, Boca Raton, 1994 us [12] D S Lee, J H Lee, Y H Lee, and D D Lee, GaN thin films as gas sensors, Sens Actuators B 89 (2003) 305-310 an [13] S Nakamura, M Senoh, N Iwasa and S Nagahama, High-power InGaN single-quantum-well-structure... D Wang, X H Wu, Q Su, Y F Li and Z L Zhou, Ammonia- sensing characteristics of Pt and SiO2 doped SnO2 materials, d Solid-State Electron 45 (2001) 347-350 te [5] A K Prasad, P I Gouma, D J Kubinski, J H Visser, R E Soltis and P J Schmitz, Reactively sputtered MoO3 films for ammonia sensing, Ac ce p Thin Solid Films 436 (2003) 46-51 [6] G S T Rao and D T Rao, Gas sensitivity of ZnO based thick film sensor... Professor with the Institute of Electro-Optical Science and Engineering, NCKU, Tainan, Taiwan, R.O.C 14 Page 14 of 18 5 mm Ag Ag cr AlInN GaN ip t 15 mm 5 mm te d M an Figure 1 us Sapphire Pt AlInN Ac ce p GaN Figure 2 15 Page 15 of 18 (a) ip t DCXRD intensity (a.u.) GaN an us cr AlInN -6000 -5000 -4000 -3000 -2000 -1000 0 1000 2000 In Al Intensity (a.u.) Ac ce p N te (b) 200 d M Omega-2Theta (Arcsec) 150... Frandon, P G Lagoudakis, J J 11 Page 11 of 18 Baumberg and N Grandjean, Current status of AlInN layers lattice-matched to GaN for photonics and electronics, J Phys D 40 (2007) 6328-6344 ip t [18] C Hums, J Bläsing, A Dadgar, A Diez, T Hempel, J Christen and A Krost, Metal-organic vapor phase epitaxy and properties of AlInN cr in the whole compositional range , Appl Phys Lett 90 (2007) 022105 us [19] S... 400 M Voltage (V) te d Figure 4 NH3=2000 ppm I (A) Ac ce p 150u 100u 50u 0 200 250 300  Temperature ( C) Figure 5 17 Page 17 of 18 200.0u o Gas out Temperature=350 C 4000 ppm 2000 ppm ip t 1000 ppm 500 ppm cr 100.0u us I (A) 150.0u 50.0u 0.0 0 1000 2000 an Gas in 3000 4000 5000 M Time (Sec) Ac ce p te d Figure 6 18 Page 18 of 18 ... Tsai, GaN metal-semiconductor-metal photodetectors with low-temperature GaN cap layers and ITO metal contacts, IEEE Electron Dev Lett 24 (2003) 212-214 [16] M A Khan, X Hu, G Sumin, A Lunev, J Yang, R Gaska and M S Shur, AlGaN/GaN metal oxide semiconductor heterostructure field effect transistor, IEEE Electron Dev Lett 21 (2000) 63-65 [17] R Butte, J F Carlin, E Feltin, M Gonschorek, S Nicolay, G Christmann, . Weng, S.J. Chang, T.J. Hsueh, C.L. Hsu, M.J. Li, W.C. Lai, AlInN resistive ammonia gas sensors, Sensors and Actuators B: Chemical (2008), doi:10.1016/j.snb.2009.04.017 This. Accepted Manuscript Title: AlInN resistive ammonia gas sensors Authors: W.Y. Weng, S.J. Chang, T.J. Hsueh, C.L. Hsu,