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 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 m 2

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 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