Low-noise GaN ultraviolet p-i-n photodiodes on GaN substrates Yun Zhang, Shyh-Chiang Shen,Hee Jin Kim, Suk Choi, Jae-Hyun Ryou,Russell D. Dupuis, and Bravishma Narayan School of Electrical and Computer Engineering, Georgia Institute of Technology, 777 Atlantic Drive NW,Atlanta, Georgia , USA Received 3 May 2009; accepted 12 May 2009; published online 4 June 2009 陳詠升

Outline Introduction Experiments Results and discussion Conclusion References

Introduction Highly sensitive ultraviolet UV photodetectors are of great interests in numerous scientific and civilian applications. The devices are grown on a freestanding bulk GaN substrate and are fabricated using a “ledged” surface depletion technique to suppress the mesa sidewall leakage.

Experiments FIG. 1. Color online A cross-section schematic drawing of a GaN UV p-i-n PD grown on a GaN substrate with the double-mesa structure. For an 80- μm-diameter photodetector

Results and discussion FIG. 2. The room-temperature bias-dependent spectral response of a fabricated 80-μm-diameter GaN UV p-i-n PD.

FIG. 3. Reverse-biased I-V characteristics of a fabricated 80- μm-diameter GaN UV p-i-n PD with and without UV light illumination at λ =360 nm.

Noise Equivalent Power NEP=(2qI d +4kT/R V /R λ ) 1/2 R V ： 3.03 × V=−20 V 、 T ： 293 Ｋ、 R λ ： responsivity 360 ｎｍ NEP= 4.27 × 10 −17 W Hz −0.5 Detectivity D*=(A) 1/2 /NEP D*= 1.66×10 14 cm Hz 0.5 W −1 I d : dark current 、 R V ： differential resistance R λ ： responsivity 、 A ： mesa area

Conclusion For an 80- μm-diameter photodetector, the dark current density is lower than 40 pA/cm 2. A room-temperature noise equivalent power of 4.27 ×10 −17 W Hz −0.5 and a detectivity of 1.66×10 14 cm Hz 0.5 W −1 are achieved at a reverse bias of 20 V.

References Low-noise GaN ultraviolet p-i-n photodiodes on GaN substrates _8221.html