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Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies HgCdTe Avalanche Photodiode Arrays for Wavefront Sensing and.

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Presentation on theme: "Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies HgCdTe Avalanche Photodiode Arrays for Wavefront Sensing and."— Presentation transcript:

1 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies HgCdTe Avalanche Photodiode Arrays for Wavefront Sensing and Interferometry Applications Ian Baker* and Gert Finger** *SELEX Sensors and Airborne Systems Ltd, Southampton, UK **ESO, Garching, Germany

2 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies 2 Avalanche gain in HgCdTe Avalanche photodiodes Voltage controlled gain at the point of absorption Almost no additional noise Near-zero power consumption Up to GHz bandwidth Requires no silicon real estate HgCdTe – a unique material Electron/hole mass ratio very large – electron gets all the energy – single carrier cascade process gives low added noise The conduction band of HgCdTe devoid of any low-lying secondary minima, which allows for large electron energy excursions deep into the band, and hence the high probability of impact ionization, with the generation of electron-hole pairs. Quite a useful component!

3 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies 3 Avalanche gain v. bias volts and cutoff wavelength Cut-off wavelength [μm] HgCdTe avalanche photodiodes at 77K

4 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies 4 Avalanche gain v. bias volts and cutoff wavelength Cut-off wavelength [μm] HgCdTe avalanche photodiodes at 77K Used for Burst Illumination LIDAR (BIL) imaging Potential for low background flux astronomy

5 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies 5 LPE HgCdTe layer grown on CdZnTe substrate HgCdTe monolith bonded to ROIC n p HgCdTe technology options for APDs APD array using via-hole process Multi-level APD design MOVPE HgCdTe layer grown on 75mm GaAs substrate Bump bonded to ROIC LPE material + via-hole hybrid technology - Currently gives best breakdown voltages MOVPE material + mesa hybrid technology - Under development for APDs

6 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies 6 Silicon multiplexer (ROIC) options ME770 – Dual Mode 256x320 on 24µm pitch Thermal imaging OR BIL imaging ME780 - Swallow 3D 256x320 on 24µm pitch 3D intensity and range per pixel Both ROICs can be configured to run in non-destructive readout. Parasitic capacitance is higher than a custom ROIC but results can allow for this. Both used for ESO APD study Thermal imageBIL image BIL intensity image BIL range image

7 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies 7 No avalanche gain Gate - 3900ns Avalanche gain - 4.6 Gate - 800ns Avalanche gain - 13.8 Gate - 300ns Avalanche gain - 38 Gate - 100ns Pixel to pixel uniformity of avalanche gain Short and long range uniformity of avalanche gain – no issue for data acquisition

8 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies 8 Noise proportional to: Gain. sq rt (gate time. noise figure) Detailed measurements give noise figure of 1.3 up to x97 gain Noise after avalanche gain Extra noise due to avalanche process negligible

9 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies 9 Noise spatial distribution for typical BIL detector Temp - 100K Wavelength – 4.5 μm Gate time - 160ns Ava. gain - x25 Array operability performance – BIL compared with SW The low pixel defect count of BIL detectors is due to the short gate time. Wavefront sensors need 3e5x longer integration time so dark current critical Very few defects due to short gate time

10 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies 10 Avalanche gain for wavefront sensors How does avalanche gain benefit wavefront sensors? Typical requirement: Integration time – 1.0 to 5.0 ms Waveband – 1.0 to 2.5 µm Multiple non-destructive readouts Sensitivity in noise-equivalent-photons (NEPh) – 3 photons rms [Note NEPh a better Figure of Merit for APDs]

11 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies 11 Noise-equivalent-photons (NEPh) - sensitivity figure of merit for APDs Allows for photon noise

12 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies 12 SW LPE HgCdTe layers SELEX APD Pre-development Programme for ESO 3 variable jn hybrids 5 full hybrids 2.64 μm 2.54 μm 2.50 μm ME770 – Dual Mode ME780 - Swallow 3D 2 variable jn hybrids 4 full hybrids 2 FPAs to ESO in flatpacks

13 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies 13 Experimental hybrid with variable junction diameters Variable junction diameter

14 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies 14 Result of variable junction diameter experiment Better signal with smaller junction No effect on avalanche gain Conclusion: use small junction diameters on further arrays

15 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies 15 ESO measurements on variable jn diameter array ESO measurements show strong S/N benefit from using small junctions Data: Integration time – 3ms Temperature – 60K Cut-off – 2.64 μm

16 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies 16 NEPh v. Bias Volts as function dark current - to set dark current specification Target dark current specification is <1e-11 A/cm 2 (360 e/s) Data: Integration time – 5ms Temperature – 70K Wavelength – 2.5 μm Dark current (A/cm 2 )

17 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies 17 Comparison of SELEX and ESO measurements of dark current v. temperature ESO measurements Shows dark current specification is met for temperatures below 90K Array data: Cut-off wavelength – 2.64um Target spec <1e-11 A/cm 2 Trap-assisted tunnelling behaviour

18 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies 18 ESO Electro-Optic Test Rig

19 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies 19 Signal Noise Typical output from ESO Test Rig Shows that noise is limited by photon shot noise

20 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies 20 ROIC – ME784 Bias – 7.1V Temperature – 70K TBB - 100ºC-50ºC ESO measurement of uniformity under moderate gain

21 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies 21 ESO measurement of Avalanche Gain – comparison with model ROIC – ME770 Temperature – 70K Measured data for 2.64 μm diode Fitted: APD Gain = 0.0782*2 (Vbias/1.126) +0.905 Model for 2.64 μm diode (green) Model for 2.5 μm diode (red)

22 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies 22 ESO measurement of Quantum Efficiency – 70% ROIC – ME770 Bias – 8.63V Gain - 16x Temperature – 70K

23 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies 23 ESO measurement of electrons per ADU to calibrate the detector test – 2.21 e/ADU ROIC – ME784 Gain of 6.4 Temperature – 80K Signal electrons – Q Noise electrons – Q 0.5 Signal V = Q.e.T/C (Noise V) 2 = Q.(e.T/C) 2 Signal/(Noise) 2 in ADUs = electrons/ADU T is pixel transfer function C is integration cap

24 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies 24 ESO measurement of noise at gain of 6.4 ROIC – ME784 Temperature – 60K Aval. gain – 6.4 Integration time – 5ms

25 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies 25 ESO measurement of noise at gain of 6.4 ROIC – ME784 Temperature – 60K Aval. gain – x6.4 Integration time – 5ms Theory for ME784 Theory for custom ROIC

26 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies 26 Dark current defect map under extreme conditions – effect of temperature 45K60K 70K80K Reducing temperature reduces the number of high dark current pixels

27 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies 27 Low photon flux imaging using avalanche gain FPA at 60K Average of 10 frames 6 electrons imaging Readout with avalanche gain of x1.5 Readout with avalanche gain of x7

28 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies 28 Modelled sensitivity based on measured data and with a custom ROIC Data: Integration time – 5ms Temperature – 77K Cut-off – 2.5um Avalanche gain offers an order improvement in NEPh

29 Galileo Avionica S.p.A and SELEX Sensors & Airborne Systems Limited - Finmeccanica Companies 29 Conclusions on avalanche gain for wavefront sensing applications (A-O and interferometry) Results so far Avalanche gains up to x16 at 8.6V bias achieved in 2.64 μm material 6 electrons rms achieved with existing non-optimised ROIC and electronics Optimised technology could provide 2-3 photons rms All the aspirations of wavefront and interferometric applications can be met by APD technology Future work Need to establish parameter space of APDs i.e. wavelength, temperature etc Need to design custom ROIC


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