Sains Malaysiana 40(1)(2011): 21–25

Testing and Calibration of an Ultraviolet-A Radiation Sensor Based on GaN Photodiode

(Pengujian dan Penentukuran Sensor Sinaran Ultra Lembayung-A Berasaskan Fotodiod GaN)

J. Theyirakumar¹*, G. Gopir^1,2, B. Yatim^1,2, H. Sanusi^2,3, P.S. Megat Mahmud¹ & T.C. Hoe¹

¹School of Applied Physics, Faculty of Science and Technology

Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia

²Institute of Space Science, Universiti Kebangsaan Malaysia

43600 Bangi, Selangor, Malaysia

³Department of Electrical Electronic and Systems Engineering, Faculty of Engineering and Built Environment

Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia

Received: 7 December 2009 / Accepted: 13 July 2010

ABSTRACT

An ultraviolet A (UVA) radiation intensity sensor with responsivity in the wavelength range of 320-360 nm was developed based on a gallium nitride (GaN) photodiode. In this sensor system, a GaN photodiode in reverse-biased mode converts the radiation intensity into current, which was then converted and amplified into an output voltage by a transimpedance amplifier (TIA), or current-voltage converter, consisting of an operational amplifier and a feedback resistor. For a narrowband UV source, the radiation intensity could be calculated from the values of the output voltage, feedback resistor, photodiode responsivity and photodiode effective area. The sensor was tested by performing measurements over different values of UV source wavelength, source distance, ambient temperature and sampling time. For calibration with a broadband UV source, the GaN-UVA sensor was used simultaneously with a standard Si-UVA sensor to measure solar radiation. The observed linear relationship between the sensors’ outputs enables us to convert the output voltage of the GaN-UVA sensor to UVA intensity. Thus, we have successfully developed, tested and calibrated an ultraviolet A radiation sensor based on the GaN photodiode.

Keywords: GaN photodiode; radiation sensor; transimpedance amplifier; ultraviolet A

ABSTRAK

Sebuah sensor keamatan sinaran ultra lembayung A (ULA) dengan responsiviti dalam julat panjang gelombang 320-360 nm telah dibangunkan berasaskan fotodiod galium nitrida (GaN). Dalam sistem sensor ini, fotodiod GaN dalam keadaan pincang-balikan menukarkan keamatan sinaran kepada arus, yang kemudiannya ditukar dan diperbesarkan kepada voltan output oleh amplifier transimpedans (ATI), atau penukar arus-voltan, yang mengandungi amplifier operasian dan perintang suapbalik. Bagi sumber UL berjalur sempit, keamatan sinaran dapat ditentukan daripada nilai-nilai voltan output, rintangan suapbalik, responsiviti fotodiod dan keluasan berkesan fotodiod. Sensor ini diuji dengan melakukan pengukuran ke atas nilai-nilai berbeza bagi panjang gelombang sumber UL, jarak sumber, suhu ambien dan masa persampelan. Bagi penentukuran dengan sumber UL berjalur lebar, sensor GaN-ULA digunakan secara serentak dengan sensor Si-ULA piawai untuk mengukur sinaran suria. Cerapan hubungan linear antara kedua-dua output sensor membolehkan kita menukar voltan output sensor GaN-ULA kepada keamatan sinaran ULA. Dengan itu, sensor sinaran ultra lembayung A berasaskan fotodiod GaN telah berjaya dibangunkan, diuji dan ditentukurkan dalam kajian ini.

Kata kunci: Amplifier transimpedans; fotodiod GaN; sensor sinaran; ultra lembayung A

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*Corresponding author; email: juliah275@yahoo.com