Kwangju Institute of Science

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Design and fabrication of low noise InP/InGaAs
PIN photodetector




Kwangju Institute of Science Technology(K-JIST)
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Structures of PD
P-metal
passivation
InP
U InGaAs
Buffered InP
n InP
N-metal

(b)Planar-type photodetector



Kwangju Institute of Science Technology(K-JIST)
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Overview of fabrication

• Mask for fabrication(4 masks)
• (window size-60, 80, 100 µ m, metal pad-70µm)
• Etching mask- its required to indicate align key
• Zinc diffusion-its required to open SiO2 for
  zinc diffusion
• Passivation-its required to make blocking layer
  between metal and semiconductor
• Metal contact-its required to evaporate metal by
  lift-off process

Kwangju Institute of Science Technology(K-JIST)
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Fabrication procedure (1)
Wet etchant HBrH2O2H2O 5150 etching
rate 120Å/sec etching depth for process
2500Å




Kwangju Institute of Science Technology(K-JIST)
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Align key after full process




Kwangju Institute of Science Technology(K-JIST)
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Fabrication procedure (2)
- Zinc diffusion(i)
SiO2-(2min, 300oC) deposition depth
1050Å (under condition such as 30 sccm of SiH4,
800sccm Of N2O, 1 torr of process pressure and
20W of RF Power)




Kwangju Institute of Science Technology(K-JIST)
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Fabrication procedure (2)
- Zinc diffusion(ii)
ampoule, vaccum pumping system, furnace,
powder, and welding machine are required for
zinc diffusion. The epitaxy for diffusion
experiment was grown with InP(1µm) and
InGaAs(1µm) on the InP substrate. The sample
was sealed under vacuum in a 1.5cm-diameter by
22-cm long quartz ampoule that are preloaded with
70mg of Zn3P2 The diffusion was carried out
for 9 minutes at 530oC.




Kwangju Institute of Science Technology(K-JIST)
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Fabrication procedure (2)
- Zinc diffusion(iii)




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Fabrication procedure (3)
For blocking layer between metal and
semiconductor SiO2-(4min, 300oC) deposition
depth 2200Å




Kwangju Institute of Science Technology(K-JIST)
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Fabrication procedure (4)

• p-metal contact formation
• Ti/Pt/Au(300Å/500Å/3000Å)
• contact on p-InGaAs layer
• Pattern was processed by conventional
  photolithography
• with AZ5214
• After lapping the backside up to 100µm, Ti/Au
  300Å/3000Å) was evaporated.

Kwangju Institute of Science Technology(K-JIST)
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Final figure after full process
Isolation width 40µm Window size 60, 80 ,100
µm Device size 500500 µm Device thickness
200250µm Pad size70µm




Kwangju Institute of Science Technology(K-JIST)
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Characteristics of PIN PD
- TLM pattern1




Kwangju Institute of Science Technology(K-JIST)
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Characteristics of PIN PD
- TLM pattern 2
(a)The schematic feature of TLM pattern

(c ) I-V curve for Ti/Pt/Au to p-InP



(b) TLM pattern
Kwangju Institute of Science Technology(K-JIST)
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Characteristics of PIN PD
- TLM pattern 3
The specific contact resistance of Ti/Pt/Au
to P-InP is given by




- Plot of measured resistance
Kwangju Institute of Science Technology(K-JIST)
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I-V characteristics (1)

• set-up for dark current and photocurrent

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I-V characteristics (2)




- Dark current at 80µm-diameter of window size
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3dB bandwidth

- 3dB bandwidth in the 60µm diameter of window
size



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3dB bandwidth




- 3dB bandwidth in 80µm diameter of window size
Kwangju Institute of Science Technology(K-JIST)
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Conclusion
Specific contact resistance of p was
8.7210-5?-cm2 When the size of sample measured
was 80 µm-diameter of window and 70 µm-diameter
of pad, the dark current was 352pA, 921pA and
1.145nA at 5V, -10V and 20V. In 60 µm
diameter of the window size and 70 µm diameter of
the pad size, the 3dB bandwidth of fabricated PIN
PD was 1.6GHz, 1.78GHz, 1.9GHz, and1.99GHz at
-1V, -2V, -3V, and -5V, respectively. In 80 µm
diameter of the window size and 70 µm diameter of
the pad size, the 3dB bandwidth of fabricated PIN
PD was 1.29GHz, 1.5GHz, 1.59GHz, and 1.71GHz at
-1V, -2V, -3V, and -5V,respectively.




Kwangju Institute of Science Technology(K-JIST)