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LOW DARK CURRENT TRANSPARENT SCHOTTKY BARRIER UV DETECTORS
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G. Simin , Asif Khan , J. W Yang , A. Lunev , V. Adivarahan
N. Pala
b),
M. Shur
b),
R. Gaska
b)
Department of ECE, University of South Carolina, Columbia, South
Carolina 29208, USA
Department of ECSE, Rensselaer Polytechnic Institute 110 8th Street,
Troy, NY 12180,
M. Asif Khan, 803-777-7475, Fax: 803-777-2447, [email protected]
a)
Noise Characteristics
Noise Spectral density, A /Hz.
ABSTRACT
We report on transparent schottky barrier detectors that have record
low values of leakage currents. The selection of lateral geometry
precludes the need for mesa etching which avoids surface defects and
improves leakage characteristics.
-180
Si for 5D3 at -1.35V
2
Si for3C1 at -1.35V
Samples: n-GaN epilayers grown by MOCVD over basal plane
sapphire substrate.
Experimental Details:
1. Formation of annular ohmic contacts consisting of Ti/Al/Ni/Au.
2. Formation 50-75 Angstroms Pt inner schottky contacts by standard
liftoff techniques.
-190
-200
-210
-220
-230
-240
-250
1
10
Evaluation of reverse leakage current.
100
(1/f) Frequency
Noise Measurement of photodetector.
Evaluation of response time of detector using N2 pulse laser.
RC Test Circuit
Pictorial Presentation of the characterization setup
and Fabricated UV-Photodetector device structure.
Transient Response
10 k
100
A 278, Lateral; Transparent Pt
Forward bias, 5V
Reverse bias, 5V
60
80
RC Test Circuit
Response, mV
50
Sapphire
Oscilloscope
Probe Gold Contact
Ohmic Contact
Schottky Contact
n-GaN
Buffer AlN
60
40
, ns
HP Parameter
Analyzer.
To Oscilloscope
1k
3.3 nF
+
-
DC Bias
N2 Pulse laser
40
30
20
20
0
10
0
10
20
30
40
50
0
200
400
600
800
1000
RL, Ohm
Time, ns
CONCLUSIONS
Reverse I-V Curve
-3
-2
-4.00E-09
-6.00E-09
-8.00E-09
-1.00E-08
-1.20E-08
Voltage,(V)
Current,(A)
-4
0.00E+00
-1
0
-2.00E-09
The ultra-low leakage is possible because the mesa etching is not required which
leads to less surface defects.
No Silicon Dioxide With Silicon Dioxide
2.00E-09
-5
The lateral geometry photodetector has superior leakage current as compared to the
vertical geometry device. At a reverse bias of -40V the dark current is as low as
1nA.
Forward I-V Curve
No Silicon Dioxide With Silicon Dioxide
Current,(A)
b)
9.00E-04
8.00E-04
7.00E-04
6.00E-04
5.00E-04
4.00E-04
3.00E-04
2.00E-04
1.00E-04
0.00E+00
-1.00E-04 0
The time of response for these devices are measured to be 15ns or less. This time is
RC limited. We expect the actual time of response to be in the order of 10-100 ps.
Use of Silicon Dioxide helps further to reduce the leakage and this proves that the
surface between the two films are perfect.
The use of this particular geometry involves fewer number of processing steps also.
The low frequency noise measurements indicates that the 1/f noise is dominant
factor, at 10 Hz frequency the noise spectral density is measured to be 5x10-23
A2/Hz. This is about two orders of magnitude better than previously reported for
GaN transparent Schottky devices with a MESA etch.
1
2
Voltage,(V)
3