SiC APDs and arrays for UV and solar blind detection
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Citation
Sandvik, P.M. et al. “SiC APDs and arrays for UV and solar blind
detection.” LEOS Annual Meeting Conference Proceedings,
2009. LEOS '09. IEEE. 2009. 291-292. © 2009 Institute of
Electrical and Electronics Engineers.
As Published
http://dx.doi.org/10.1109/LEOS.2009.5343240
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Institute of Electrical and Electronics Engineers
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Final published version
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Thu May 26 08:39:53 EDT 2016
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http://hdl.handle.net/1721.1/58821
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TuU1 (Invited)
13.30 - 14.00
SiC APDs and Arrays for UV and Solar Blind Detection
Peter M. Sandvik*,1, Stanislav I. Soloviev1, Alexey V. Vert1, Alexander Bolotnikov1, Jonathan Frechette2, Simon
Verghese2, Peter Grossmann2 and Gary A. Shaw2
1
2
GE Global Research Center
MIT Lincoln Laboratory
Niskayuna, NY 12309 USA
Lexington, MA 02420-9185
*sandvik@research.ge.com
Abstract- We report advancements in APDs and arrays using
4H SiC. Novel structures, array designs and specialized read out
integrated circuits have been developed towards the realization of
UV and solar-blind detector arrays exhibiting appreciable quantum
efficiency, low noise and Geiger-mode operation. Discussion will
include the design, fabrication and testing of these devices, which
may find use in a variety of applications.
was used in the area immediately under the thin-film dielectric
stack filter, that provided blocking in the UV outside the solarblind window. Here, HfO2/SiO2 films were deposited for a
total thickness of approximately 5 µm. Dry etching was used
to enable access to the device electrodes, and a cross-section is
shown in figure 1, with an example 16-element SiC APD
array shown in figure 2.
Past variations in substrate defect density, epitaxy layer
thickness and doping increased device-to-device nonuniformity lowering the likelihood that adjacent devices
performed similarly in avalanche [7], thereby limiting APD
array size without sophisticated electronics.
In this work, sections of the wafers measured were studied
for uniformity, and an example is shown in figure 3. 4x4 APD
arrays were tested at the wafer-level prior to dicing and
without incident light on an automated probe station.
Defining the breakdown voltage as the voltage at which 10 µA
was reached, the top portion of figure 3 identifies the current
bin at 95% of the breakdown voltage. The bottom identifies
the breakdown range. Leakage current and breakdown
voltage distributions show that while there are clear variations
in both parameters, groups of devices are co-located which
exhibit similar and suitable behavior for various applications.
Read-out integrated circuits (ROICs) were designed to
interface to the SiC APDs. The ROIC consists of sixteen
pixels that both detect and time-stamp avalanche events for
each SiC APD in a 4x4 array. Each APD cathode connects to
its own pixel front-end circuit that provides the necessary
overbias voltage for Geiger-mode operation. When the frontend detects an avalanche, it will actively quench the APD, and
register a capture signal which is passed to timing circuitry
within the pixel to assign a time stamp to the event. The time
stamp is passed to read-out circuitry that formats the data into
a packet and streams it off-chip via one of sixteen serial output
channels, where it may be post-processed by another device,
such as an FPGA. For applications where timing information
is not required, the timing circuitry can be bypassed and the
capture signal sent directly to the chip output. The ROICs
were fabricated in a 0.18-µm commercial CMOS process. SiC
APD arrays were mounted on top of the ROIC, and the APD
cathode-to-pixel front-end connections were made via
wirebonds, as shown in Figure 4.
Photoresponsivity, dark current and Geiger-mode
performance of these APDs will be discussed.
INTRODUCTION
APDs working in the UV are of interest for several
applications, including bio-aerosol detection, UV imaging,
harsh environment gamma sensing [1] and long-range flame
detection in the solar-blind window. Si detectors or PMTs
have partly addressed these needs, however, they generally
have limited deep-UV quantum efficiency and appreciable
visible response. To realize visible or solar blindness, optical
filtering may be required and when added, further limits their
sensitivity and applicability.
Advancements in UV APDs have been made using wide
bandgap semiconductors such as GaN [2] and SiC [3], which
offer inherent visible blindness, harsh environment capability
and low noise performance. GaN, further offers the potential
for self-filtered solar-blind detectors with sharp responsivity
cutoff [4], however, it commonly suffers from a high density
of material defects limiting APD performance [5].
SiC has seen substantial improvements in substrate quality
in part due to their usage in GaN-based light emitting diodes,
and more recently in devices such as SiC diodes. Combined
with improved fabrication methods, 3-inch wafers of 4H SiC
provide a means to realize an appreciable yield of APDs that
facilitate multi-pixel arrays.
Separate absorption and multiplication region designs were
employed to maximize quantum efficiency while suppressing
dark current originating from the bulk materials.
As
drawbacks of this design include a requirement for deeper
etching to form the mesa, higher breakdown voltages and a
reduced fill factor, p-i-n designs were also considered.
To realize SiC APD arrays, positively tapered sidewalls
were formed to reduce surface leakage current, a technique
commonly employed in power device design [6]. A 3 µm
thick SiO2 layer was deposited, then selectively etched to
realize a p and then n-type ohmic contacts using Ti/Al/Ti/Ni
(100/200/200/2000 Å) and Ni (550 Å). An annealing step at
1050 °C, then inter and pad metals using Ti/Mo (2000/8000 Å)
and Ti/Au (2000/4000 Å). An etch stop layer using 2000 Å Ni
978-1-4244-3681-1/09/$25.00 ©2009 IEEE
291
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ACKNOWLEDGMENT
This work was funded by DARPA's DUVAP program,
under W911NF-06-C-0160 and FA8721-05-C-0002. The
opinions, interpretations, conclusions and recommendations
expressed herein are those of the authors, and not necessarily
endorsed by the United States Government.
REFERENCES
[1] G. Shaw, A. Siegel, J. Model, A. Geboff, S. Soloviev, A.
Vert and P. Sandvik, "Deep UV Photon-Counting Detectors
and Applications", Proc. of SPIE DSS, Vol. 7320, 2009.
[2] R. Dupuis, J. Ryou, D. Yoo, J. Limb, Y. Zhang, S. Shen
and D. Yoder, "High-Performance GaN and AlxGa1-xN
Ultraviolet Avalanche Photodiodes Grown by MOCVD on
Bulk III-N Substrates", Proc. of SPIE, Vol. 6739, 2009.
[3] X. Bai, H. Liu, D. McIntosh, J. Campbell, " HighDetectivity and High-Single-Photon-Detection-Efficiency 4HSiC Avalanche Photodiodes", IEEE J. Quant. Elect., Vol. 45,
No. 3, p. 300-303, 2009.
[4] E. Tarsa, P. Kozodoy, J. Ibbetson, B. Keller, G. Parish
and U. Mishra, "Solar-blind AlGaN-based inverted
heterostructure photodiodes", App. Phys. Lett., Vol. 77., No.
3, p. 316-318, 2000.
[5] K. Minder, J. Pau, R. McClintock, P. Kung, C. Bayram
and M. Razeghi, "Scaling in back-illuminated GaN avalanche
photodiodes", App. Phys. Lett., Vol. 91, 073513, 2007.
[6] B. Baliga, Modern Power Devices, Wiley-Interscience,
p. 100, ISBN 0-471-81986-7.
[7] X. Guo, A. Beck, J. Campbell, D. Emerson, J.
Sumakeris, "Spatial Nonuniformity of 4H-SiC Avlanche
Photodiodes at High Gain", IEEE J. of Quant. Elect. Vol. 41,
No. 10, p. 1213-1216, 2005.
Figure 2. SiC APD array with p-type contacts at the corners
(250 µm wide), n-type contacts in the center (4 on each side).
Figure 3. Wafer-level dark current (top) and breakdown
(bottom) voltage distributions for a section of a 3 inch wafer.
Each square is an individual device and each grid element is a
4x4 array. White areas are test structures.
Figure 1. Cross-section of SiC APD array. The active area
was approximately 44 µm and the p-n junction was about 100
µm wide.
Figure 4. 4x4 SiC APD array mounted on a CMOS ROIC
with the APD cathodes wirebonded to the pixel front-ends of
the ROIC.
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