NASA Technical Reports Server (NTRS) 20130009424: Single-Photon-Sensitive HgCdTe Avalanche Photodiode Detector

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by  NASA Technical Reports Server (NTRS)

Technology Focus: Sensors
Single-Photon-Sensitive HgCdTe Avalanche Photodiode Detector
Detector provides extra dimension to lidar scene data for multi-photon returns.
Goddard Space Flight Center, Greenbelt, Maryland
The purpose of this program was to de- avalanche gain (M > 1000) without excess an anti-reflection coating is used. Excel-
velop single-photon-sensitive short-wave- multiplication noise (F = 1), and are lent yield of operable APD pixels and uni-
length infrared (SWIR) and mid-wave- therefore very good candidates for linear- formity of APD response were both ob-
length infrared (MWIR) avalanche mode photon counting. However, detec- tained, but the maximum avalanche gain
photodiode (APD) receivers based on lin- tors fashioned from these narrow- that could be achieved with SWIR-cutoff
ear-mode HgCdTe APDs, for application bandgap alloys require aggressive cooling material was deemed too low to enable
by NASA in light detection and ranging to control thermal dark current. Wider- single-photon detection. Comparison of
(lidar) sensors. Linear-mode photon- bandgap SWIR HgCdTe APDs were inves- Voxtel’s maximum gain measurements
counting APDs are desired for lidar be- tigated in this program as a strategy to re- suggests that this is an inherent material
cause they have a shorter pixel dead time duce detector cooling requirements. limitation of the SWIR alloy. Room-tem-
than Geiger APDs, and can detect se- The first objective was to build SWIR perature responsivity of about 5 kV/W
quential pulse returns from multiple ob- HgCdTe APDs, and to assess their suit- and noise-equivalent power (NEP) of
jects that are closely spaced in range. Lin- ability for photon counting in linear 33.3 nW were measured at 1550 nm when
ear-mode APDs can also measure photon mode. The second objective was to im- the APD operated at a gain of M=6.6.
number, which Geiger APDs cannot, plement manufacturing improvements Completion of development of CdTe
adding an extra dimension to lidar scene to mitigate surface dark current, im- surface passivation for MWIR HgCdTe
data for multi-photon returns. High-gain prove reliability, and eliminate peaking APDs presents the best opportunity to
APDs with low multiplication noise are re- in the spectral response. further improve receiver sensitivity, as it
quired for efficient linear-mode detec- Voxtel manufactured and character- will enable operation at much higher av-
tion of single photons because of APD ized 2.7-µm-cutoff HgCdTe APDs, pub- alanche gain with reduced dark current.
gain statistics — a low-excess-noise APD lishing excess noise data taken at the This innovation can find use with quan-
will generate detectible current pulses highest avalanche gain levels yet demon- tum information (encryption and basic
from single photon input at a much strated for SWIR HgCdTe APDs (M = 80). science), semiconductor inspection, and
higher rate of occurrence than will a Quantum efficiency was limited to ap- molecular spectroscopy.
noisy APD operated at the same average proximately 73% at 1,550 nm by partial This work was done by Andrew Hunting-
gain. MWIR and LWIR electron-ava- reflection from the non-coated optical ton of Voxtel, Inc. for Goddard Space Flight
lanche HgCdTe APDs have been shown entrance surface; quantum efficiency Center. Further information is contained in a
to operate in linear mode at high average near 94% is expected for these devices if TSP (see page 1).GSC-16140-1
Surface-Enhanced Raman Scattering Using Silica Whispering-
Gallery Mode Resonators
Silica sphere optical resonators are used to provide surface-enhanced spectroscopic signal.
NASA’s Jet Propulsion Laboratory, Pasadena, California
The motivation of this work was to have 785-nm laser excitation. The advantage of ically robust surface for sensor applica-
robust spectroscopic sensors for sensitive this non-plasmonic approach is that the tions that could be cleaned by resistively
detection and chemical analysis of or- active substrate is chemically inert silica, heating the sensor element. This is par-
ganic and molecular compounds. The so- thermally stable, and relatively simple to ticularly useful for spacecraft instruments
lution is to use silica sphere optical res- fabricate. The Raman signal enhance- used for the detection of organics in
onators to provide surface-enhanced ment is broadly applicable to a wide range planetary soils. The conventional silver-
spectroscopic signal. of molecular functional groups including based SERS substrates are limited by reac-
Whispering-gallery mode (WGM) res- aliphatic hydrocarbons, siloxanes, and es- tivity of silver. In the case of gold SERS
onators made from silica microspheres ters. Applications include trace organic substrates, high temperatures (<200 ºC)
were used for surface-enhanced Raman analysis, particularly for in situ planetary will cause diffusion in the gold that de-
scattering (SERS) without coupling to a instruments that require robust sensors grades the nanostructure. The use of
plasmonic mechanism. Large Raman sig- with consistent response. WGM SERS may also be used for surface
nal enhancement is observed by exclu- WGM SERS using microspheres or analysis in a manner similar to attenuated
sively using 5.08-micron silica spheres with quartz surface structures provide a chem- total reflectance used in infrared spec-
NASA Tech Briefs, January 2013 5