Sains Malaysiana 40(3)(2011): 267–273

Gateless-FET pH Sensor Fabricated on Undoped AlGaN/GaNHEMT Structure

(Penderia pH FET tanpa Get difabrikasi di atas Struktur HEMT AlGaN/GaN Tidak Didop)

Maneea Eizadi Sharifabad, Mastura Shafinaz Zainal Abidin, Shaharin Fadzli AbdRahman, Abdul Manaf Hashim* & Abdul Rahim Abdul Rahman

Material Innovations and Nanoelectronics (MINE), Research Group

Faculty of Electrical Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia

Nurul Afzan Omar & Mohd Nizam Osman

Telekom Research and Development, TM Innovation Centre, 63000 Cyberjaya, Malaysia

Rabia Qindeel

Department of Physics, Faculty of Science

Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia

Diserahkan: 5 Julai 2010 / Diterima: 3 September 2010

ABSTRACT

Gallium nitride with wurtzite crystal structure is a chemically stable semiconductor with high internal spontaneous and piezoelectric polarization, which make it highly suitable materials to create very sensitive and robust sensors for the detection of ions, gases and liquids. Sensing characteristics of an open-gate liquid-phase sensor fabricated on undoped-AlGaN/GaN high-electron-mobility-transistor (HEMT) structure in aqueous solution was investigated. In ambient atmosphere, the open-gate undoped AlGaN/GaN HEMT clearly showed only the presence of linear region of currents while Si-doped AlGaN/GaN showed the linear and saturation regions of currents, very similar to those of gated devices. This seems to show that very low Fermi level pinning by surface states exists in undoped AlGaN/GaN sample. In aqueous solution, the typical current-voltage (I-V) characteristics of HEMTs with good gate controllability were observed. The potential of the AlGaN surface at the open-gate area is effectively controlled via aqueous solution by Ag/AgCl reference gate electrode. The open-gate undoped AlGaN/GaN HEMT structure is capable of stable operation in aqueous electrolytes and exhibit linear sensitivity, and high sensitivity of 1.9 mA/pH or 3.88 mA/mm/pH at drain-source voltage, VDS = 5 V was obtained. Due to large leakage current where it increases with the negative reference gate voltage, the Nernstian’s like sensitivity cannot be determined. Suppression of current leakage is likely to improve the device performance. The open-gate undoped-AlGaN/GaN structure is expected to be suitable for pH sensing application.

Keywords: AlGaN/GaN; HEMT; liquid-phase; open-gate structure; pH sensor

ABSTRAK

Galium nitrat dengan struktur hablur wurtzit adalah semikonduktor kimia yang stabil dengan polarisasi dalaman spontan dan polarisasi piezoelektrik yang tinggi, membuatkannya menjadi bahan yang sangat sesuai sebagai penderia yang sensitif dan kuat untuk mengesan ion, gas dan cecair. Pencirian penderia fasa-cecair get terbuka yang difabrikasi di atas struktur AlGaN/GaN-tidak didop transistor-pergerakan-elektron-tinggi (HEMT) dalam larutan akuas dikaji. Dalam keadaan ambien, AlGaN/GaN-tidak didop HEMT get terbuka menunjukkan dengan jelas hanya ada kawasan arus linear sementara AlGaN/GaN- Si-dop menunjukkan kawasan arus linear dan tepu, hampir serupa dengan peranti berget. Hal ini menunjukkan bahawa tahap pengepinan Fermi sangat rendah oleh permukaan dalam sampel AlGaN/GaN-tidak didop. Dalam larutan akuas, ciri arus-voltan (I-V) HEMTs dengan pengawalan get yang baik diperhatikan. Keupayaan permukaan AlGaN di kawasan get terbuka dikawal secara berkesan melalui larutan akuas dengan elektrod get rujukan Ag/AgCl digunakan. Struktur AlGaN/GaN-tidak didop HEMT get terbuka mampu beroperasi stabil di dalam elektrolit akuas dan menunjukkan sensitiviti linear, dan diperoleh sensitivitinya tinggi bernilai 1.9 mA/pH atau 3.88 mA/mm/pH pada voltan salir-punca, VDS = 5 V. Disebabkan kebocoran arus besar dan ia meningkat dengan voltan rujukan negatif, sensitiviti Nernstian tidak dapat ditentukan. Pengurangan kebocoran arus akan meningkatkan prestasi peranti. Struktur AlGaN/GaN-tidak didop HEMT get terbuka dijangkakan sesuai untuk aplikasi penderiaan pH.

Kata kunci: AlGaN/GaN; fasa cecair; HEMT; penderia pH; struktur get terbuka

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*Pengarang untuk surat-menyurat; email: manaf@fke.utm.my