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GaN Metal–Semiconductor–Metal Ultraviolet
Sensors With Various Contact Electrodes
Y. K. Su, Senior Member, IEEE, S. J. Chang, C. H. Chen, J. F. Chen, Member,
IEEE, G. C. Chi, J. K. Sheu,W. C. Lai, and J. M. Tsai
IEEE SENSORS JOURNAL, VOL. 2, NO. 4, AUGUST 2002
YS. Chen
Outline
 Introduction
 Experiments
 Results and discussion
 Conclusion
 References
Introduction
 ULTRAVIOLET (UV) sensors are important devices that can
be used in various commercial and military applications.
 For example, these visible-blind UV sensors can be used in
space communications, ozone layer monitoring,and flame
detection.
Experiments
寬：2μm、長：100 μ m、間距：2 μ m
Cr/Au
device area：1000 *450 μ m2
Fig. 1. (a) Schematic structure of GaN MSM UV sensors with ITO, Ni, Pt, and Au contact
electrodes. (b) Band diagram of the MSM optical sensor under illumination.
Results and discussion
390nm
360nm
Fig. 2. Optical transmittances of as-deposited ITO, thermally annealed ITO,Ni,
Pt, and Au layers.
Fig. 3. Dark I–V characteristics of GaN MSM UV sensors with different contact electrodes.
TABLE I
Schottky barrier heights for ITO and other metals on n-GaN
Fig. 4. Illuminated I–V characteristics of GaN MSM UV sensors with different
contact electrodes.
Fig. 5. Spectral responsivity of GaN MSM UV sensors with different contact electrodes.
Fig. 6. Frequency response of 600 C-annealed ITO/n-GaN and Au/n-GaN MSM UV sensors
used in this study. The inset shows the normalized transit response of these two sensors.
Conclusion
 We could achieve a maximum 0.12 A photocurrent and a photocurrent to dark
current contrast higher than five orders of magnitude for the 600°C-annealed
ITO/n-GaN MSM UV sensor under 5-V bias voltage.
 We also found that the maximum responsivity at 345 nm was 7.2 and 0.9 A/W
when the 600 C- annealed ITO/n-GaN MSM UV sensor was biased at 5 V and
0.5 V, respectively.
 The existence of photoconductive gain in the 600 C-annealed ITO/n-GaN
MSM UV sensor also results in a slower operation speed and a smaller 3-dB
bandwidth ascompared with the metal/n-GaN MSM UV sensors.
References
 Y. K. Su, Senior Member, IEEE, S. J. Chang, C. H. Chen, J. F. Chen,
Member, IEEE, G. C. Chi, J. K. Sheu,W. C. Lai, and J. M. Tsai, “GaN
Metal–Semiconductor–Metal Ultraviolet Sensors With Various Contact
Electrodes,” IEEE SENSORS JOURNAL, VOL. 2, NO. 4 , pp. 366–371,
AUGUST 2002