HgCdTe avalanche photodiode focal plane arrays (FPAs) and single element detectors have been developed for a large scope of photon starved applications. The present communication present the characteristics of our most recent detector developments that opens the horizon for low infrared (IR) photon number detection with high information conservation for imaging, atmospheric lidar and free space telecommunications. In particular, we report on the performance of TEC cooled large area detectors with sensitive diameters ranging from 30- 200 μm, characterised by detector gains of 2- 20 V/μW and noise equivalent input power of 0.1-1 nW for bandwidths ranging from 20 to 400 MHz.
HgCdTe avalanche photodiode focal plane arrays (FPAs) and single element detectors have been developed for a large
scope of photon starved applications. The present communication present the characteristics of our most recent detector
developments that opens the horizon for low infrared (IR) photon number detection with high information conservation
for imaging, atmospheric lidar and free space telecommunications. In particular, we report on the performance of TEC
cooled large area detectors with sensitive diameters ranging from 30- 200 μm, characterised by detector gains of 2- 20
V/μW and noise equivalent input power of 0.1-1 nW for bandwidths ranging from 20 to 400 MHz.
The remarkable properties (internal gain larger than 100 and close to unity excess noise factor) of Short Wave Infrared
(SWIR) HgCdTe electron-initiated Avalanche Photodiodes (e-APDs) are put to good use to demanding applications, i.e.
spectroscopy and LIDAR. Knowing the requirements of both situations, we have designed specific models based on
highly sensitive single elements APDs and adapted proximity electronics.
On one hand, we use the e-APDs low noise equivalent power (NEP) at 180K (few fW/Hz1/2). We simultaneously
designed a specific Transimpedance Amplifier (TIA) which allows us to take advantage of the low APD NEP. The
combination of both elements along with a dedicated cryostat enables direct LIDAR detection at moderate bandwidth
(BW = 20 MHz) without the need for long time averaging, which is crucial in far field (≥ 5 km) analysis. One the other
hand, we have optimized a low-noise and low-frequency LN2 cooled prototype operating with an external commercial amplifier. It allows us to observe the photoluminescence of Ge nanostructures in the range 1.5-2.5 μm with a
significantly increased SNR along with a reduce pump laser power. The possibility to use these detectors in the photon
counting limit will be discussed in light of our recent results. In parallel, we present preliminary time response
measurements performed on SWIR APD suggesting that a higher GHz BW could be reached with this type of detector.
This is however subjected to optical optimization at the moment.
KEYWORDS: Avalanche photodetectors, Mercury cadmium telluride, Readout integrated circuits, Mid-IR, Sensors, Short wave infrared radiation, Single photon, Electrons, Photodetectors, Signal to noise ratio
Proportional photon detection has been demonstrated using linear mode HgCdTe avalanche photodiodes (APDs)
hybridized on a specially designed read-out integrated circuit (ROIC). The ROIC was designed to detect photons at a
moderate bandwidth (10 MHz) with a low noise of 10 electrons per characteristics time of the ROIC and to be
compatible with large area-small pixel focal plane array (FPA) applications. Proportional photon counting was
demonstrated by reproducing the Poisson statics for average photon number states ranging between m=0.8 to 8 photons,
at low to moderate avalanche gains M=40-200, using both mid-wave infrared (MWIR) and (short-wave infrared) SWIR
HgCdTe APDs. The probability distribution function of the gain was estimated from the analysis of the amplitude of
detected residual thermal photons in the MWIR APDs. The corresponding probability distribution functions was
characterized by a low excess noise factor F and high asymmetry which favours a high photon detection efficiency
(PDE), even at high threshold values. An internal PDE of 90 % was estimated at a threshold level of 40 % of the average
signal for a single photon. The dark count rate (DCR) was limited by residual thermal photons in the MWIR APD to
about 1 MHz. A geometrical and spectral filtering of this contribution is important to achieve the ultimate performance
with MWIR detectors. In this case, the DCR was estimated by interpolation to about 8 kHz. The SWIR HgCdTe APD
device had a lower residual photon flux (60 kHz), but was found to be limited by tunnelling dark current noise at high
gains at a rate of 100 kHz.
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