GaN Metal–Semiconductor–Metal UltravioletSensors 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

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.

Cr/Au

寬： 2μm、長： 100 μ m、間距： 2 μ m

device area ： 1000 *450 μ m2

Results and discussion

Fig. 2. Optical transmittances of as-deposited ITO, thermally annealed ITO,Ni, Pt, and Au layers.

390nm

360nm

Fig. 3. Dark I–V characteristics of GaN MSM UV sensors with different contact electrodes.

TABLE ISchottky 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