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3. WHY APDs? THE HAWAII-2RG ARRAYS DEVELOPED FOR JAMES WEBB APPROACH THE IDEAL DETECTOR IN ALL BUT ONE RESPECT – READ NOISE! DUE TO BASIC PHYSICS OF CMOS, READ NOISE HAS IMPROVED LITTLE SINCE HUBBLE NICMOS – TECHNOLOGY LARGELY FROZEN IN TIME FOR 20 YEARS. READ NOISE LIMITS LOW BACKGROUND AND/OR HIGH SPEED APPLICATIONS Hg:Cd:Te APDs HOLD PROMISE OF THE SOLUTION.

4. EXAMPLES HIGH SPEED – MODEST FORMAT, RELAXED DARK CURRENT: - Wave-front Sensing - Fringe Tracking HIGH SENSITIVITY – LARGE FORMAT, DEMANDING DARK CURRENT: - High Resolution Spectroscopy - Low Background Space BOTH – ALSO HIGH TIME RESOLUTION: - Time Resolved Spectroscopy - Quantum Astrophysics

5. CONVENTIONAL APDs e.g. Si, Ge & GaAs IN CONVENTIONAL APD MATERIALS (e.g. Si, Ge and GaAs) BOTH ELECTRONS AND HOLES AVALANCHE (IN OPPOSITE DIRECTIONS). THIS SPREADS THE STATISTICAL AVALANCHE GAIN PRODUCING EXCESS NOISE. McINTYRE (1968) DEFINED THE EXCESS NOISE FACTOR: F = (S / B)IN / (S / B)OUT THE THEORETICAL LIMIT FOR “F” IN THE CASE WHERE BOTH ELECTRONS AND HOLES AVALANCHE IS 2 BUT IT IS OFTEN >>2. THIS DUAL AVALANCHING ALSO SIGNIFICANTLY STRETCHES OUT RESPONSE TIME. BEST CONVENTIONAL APDs REACH F VALUES ~ 2

6. McINTYRE MODEL PHOTO-IONIZATION INITIATES AVALANCHING BY BOTH ELECTRONS AND HOLES. COLLISIONS FULLY REDISTRIBUTE BOTH ELECTRONS AND HOLES BEFORE REACHING IONIZING ENERGY. EXCESS NOISE AND PULSE BLURRING INHERRENT IN PROCESS. RULES OUT “NOISELESS” (F = 1) PHOTON COUNTING IN LINEAR MODE. PHOTON COUNTING ONLY IN GEIGER MODE WITH LIMITED DUTY CYCLE, AFTER-PULSES AND REQUIREMENT FOR QUENCHING.

7. Hg:Cd:Te AVALANCHE CHARACTERISTICS IT IS WELL KNOWN THAT BY VARYING THE “x” FRACTION OF Hg(1-x):Cd(x):Te, THE CUT-OFF WAVELENGTH ?c CAN BE VARIED OVER THE RANGE ?c < 1.3 µm TO ?c > 15 µm. OVER THIS RANGE THERE ARE ALSO DRAMATIC CHANGES IN THE AVALANCHE PROPERTIES OF THE CRYSTAL LATTICE. THE NEXT CHART SHOWS LOG10 GAIN vs BAND-GAP (eV) FOR LAYERS FROM LETI, BAE, TIS & DRS, ALL @ 77K & 6V REVERSE BIAS

8. e- & h- APD REGIMES OF HgCdTe

9. e-APD GAIN - SUMMARY

10. AVALANCH PROPERTIES of HgCdTe HOLE ACCELERATION IS VERY LOW – HIGH EFFECTIVE MASS – SLOWER. e- ACCELERATION IS VERY HIGH - PHONON SCATTERING LOW – VERY FAST. HOLE IONIZATION IS VERY LOW EXCEPT FOR 0.938 eV RESONANCE e- IONIZATION IS VERY HIGH THUS FOR EB < 0.6 eV (?C > 2 µm) ONLY e- AVALANCHE (k = 0)

11. HgCdTe as an e-APD AVALANCHE GAIN INCREASES EXPONENTIALLY WITH BIAS & DECREASING EB. e- TRAJECTORIES ARE BALLISTIC BETWEEN IONIZING COLLISIONS. DETEMINISTIC SO NO EXCESS NOISE – F ~ 1. VERY FAST PULSE - GAIN BANDWIDTH > 1THZ. THERE IS NO GEIGER BREAKDOWN AND SO NO GEIGER MODE OPERATION. HOWEVER NOISELESS (F ~ 1) PHOTON COUNTING IS POSSIBLE IN THE LINEAR (PROPORTIONAL) MODE TO GAIN ~ 104. FOR ASTRONOMY, THE PRIMARY CHALLENGE IS TO REDUCE DARK CURRENT.

12. APDs in MBE HgCdTe DEPOSITION BY MBE ALLOWS A SEPARATE ABSORPTION-MULTIPLICATION (SAM) STRUCTURE. A-LAYER GRADED INTO M-LAYER TO AVOID PHOTOIONIZATION IN THE M-LAYER, ?C FOR THE A-LAYER MUST BE LONGER THAN ?C FOR THE M-LAYER. MISMATCH IN CRYSTAL LATTICE PROPERTIES MAY LIMIT THE DIFFERENCE BETWEEN THE TWO ?Cs.

13. BAND-GAP TRADE-OFF0.25 eV (?c ~ 4.5 µm) vs 0.5 eV (2.6 µm) 0.25 eV M-LAYER HAS HIGH GAIN (>5,000 @ 12.5 V) WITH MATURE PROCESSING TECHNOLOGY. BUT VERY SUSCEPTIBLE TO THERMAL BACKGROUND. 0.5 eV M-LAYER HAS MUCH LOWER GAIN BUT OFFSET BY MUCH LOWER BACKGROUND. 0.5 eV DARK CURRENT NOT DRAMATICALLY LOWER DUE TO TRAP INDUCED TUNNELING CURRENT. OPTIMUM M-LAYER BANDGAP?

14. J. ROTHMAN SUMMARY

15. EMPIRICAL MODEL for e-APD GAIN BECK (2001, 2002) DETERMINED THAT THE e-APD GAIN M VARIES WITH V AS: M = 2 (V – VTH)/(VTH/2) VTH ~ 6.8 Eg FOR ALL COMPOSITIONS: 0.2 < x < 0.5 “DEAD VOLTAGE” MODEL OF e-APD GAIN IN HgCdTe FIGURE FOR VTH = 5 Eg AND ? = 1

16. M KINCH_JEM_V37N9P1453_2008 page 1454 Fig. 2

17. M KINCH_JEM_V37N9P1453_2008 page 1454 Fig.1.(a)

18. M KINCH, EAPDs, page 122, Fig. 7.13

19. e-APD DEVELOPMENT DEFIR (Design and Future of the IR) INITIATIVE BRINGS TOGETHER SOFRADIR’S R&D WITH CEA-Leti. MCT e-APD RESEARCH TOWARD INDUSTRIALIZATION. PASSIVE AMPLIFIED IMAGING (PAI) & 3-D LADAR. DRS DALLAS (WITH SELEX) - PAI & 3-D LADAR PLUS ASTRONOMY. RAYTHEON - PAI & 3-D LADAR (PLUS ASTRONOMY?). BAE R&D. TIS – ASTRONOMY.

20. e-APDs by CEA LETI, DRS, BAE & TIS

21. e-APD ARCHITECTURE - DEFIR

22. e-APD ARCHITECTURE - DSL

24. e-APD GAIN - SUMMARY

25. DEFIR F VALUES (J. ROTHMAN)

26. e-APD GAIN s - DRS

27. e-APD GAIN s - DRS

28. e-APD GAIN s - DEFIR

29. e-APD GAIN (CUM) - DEFIR

30. e-APD GAIN vs TEMP - SUMMARY

31. e-APD GAIN vs TEMP - DEFIR

32. e-APD GNDC - DEFIR

33. e-APD GNDC vs TEMP - DEFIR

34. e-APD PULSE PROFILE - DEFIR

35. e-APD PULSE RISE TIME - DEFIR

36. e-APD PULSE DECAY TIME - DEFIR

37. h-APD APPLICATIONS TO ASTRONOMY 0.938 eV (?c ~ 1.32 µm) M-LAYER COMPATIBLE WITH A-LAYER INSENSITIVE TO ROOM TEMPERATUREBACKGROUND. ATTRACTIVE FOR HST-LIKE MISSIONS & GROUND BASED APPLICATIONS. SUBSTRATE REMOVAL FOR VISIBLE APPLICATIONS. CHALLENGES ARE DARK CURRENT & ACHIEVING F ~ 1. h-APD AVLANCHE PULSE ~ 10X SLOWER.

38. h-APD DEVELOPMENT RAYTHEON (RVS, HRL & RMS) HAS DEMONSTRATED SWIR (1.55 µm) e-APD BASED LADAR OPERATING AT 300K. THEY REPORT NO EXCESS NOISE TO GAINS >100, NEP < 1nW & GHZ BANDWIDTH. CZT => 6” Si WAFER PROCESSING.

39. PERFORMANCE OF 90 RANDOMLY SELECTED APDs - RAYTHEON

40. GOALS OF THE UH/GSFC/TELEDYNE Hg:Cd:Te APD PROGRAM THREE YEAR PROGRAM FUNDED PRIMARILY BY NASA “RESEARCH OPPORTUNITIES IN SPACE AND EARTH SCIENCES” INITIATIVE - SUPPLEMENTAL FUNDING BY GSFC. WILL UTILIZE TELEDYNE’S BROAD EXPERIENCE IN MBE Hg:Cd:Te PROCESSING TO PRODUCE APDs OPTIMIZED FOR ASTRONOMY. UH WILL MODIFY TEST FACILITIES DEVELOPED FOR THE JWST PROGRAM TO CHARACTERIZE ARRAYS IN PHOTON COUNTING MODE.

41. APPROACH SIMILAR MASKS FOR e-APD & h-APD HgCdTe INCLUDE: - PROCESS EVALUATION CHIPS (PECs). - FOUR 256 x 256 @ 18 µm PITCH SUB-ARRAYS - TWO “TADPOLES” SCREEN AND INITIAL EVALUATION OF LAYERS USING PECs. CHARACTERIZE PHOTON COUNTING WITH SUB-ARRAYS BONDED TO CORNER OF H1RG, READ OUT WITH SIDECAR ASIC. “TADPOLES” FOR HIGH SPEED (QUANTUM ASTROPHYSICS AND LADAR). GOAL IS LOW DARK WITH F ~ 1.

42. CONCEPTUAL “TADPOLE” LAYOUT

43. UH-TIS HAWAII Heritage

44. DARK CURRENT vs TEMPERATURE FOR 2.5 AND 5 UM MATERIAL

45. CURRENT STATUS FIRST RUN OF n-on-p e-APDs HAD POOR DIODE CHARACTERISTICS. ATTRIBUTED TO PROBLEMS WITH SURFACE PASSIVATION. IN 2009 CONDUCTED AN EXTENSIVE INVESTIGATION OF SURFACE PASSIVATION. READY TO PROCEED WITH 2ND RUN. FIRST RUN OF p-on-n h-APDs UNDERWAY. TESTING IN NOVEMBER. EVALUATION OF h-APD GAIN of TIS HERITAGE 0.73 eV (?co ~ 1.7 µm) p-on-n PEC

46. h-APD GAIN of TIS HERITAGE 0.73 eV (?co ~ 1.7 µm) p-on-n PEC STANDARD 0.73 eV (?co ~ 1.7 µm) p-on-n PEC. NO APD OPTIMIZATION OR SAM – ALL SAME MATERIAL. GAIN & BANDGAP CONSISTENT WITH h-APD AVALANCHING. PLAN TO EVALUATE IN H1RG. PRESENT h-APD RUN CONSISTS OF THIS MATERIAL FOR A-LAYER WITH 0.938 eV M-LAYER.

47. h-APD GAIN of TIS HERITAGE 0.73 eV (?co ~ 1.7 µm). p-on-n PEC

48. KSPEC UPGRADE - CURRENT STATUS COMPLETELY SEALED, ULTRA LOW BACKGROUND TEST FACILITY. ILLUMINATION BY IR LEDs. REFERENCE DETECTORS. HIGH GEOMETRIC ATTENUATION TO < 1 PHOTON per PIXEL per FRAME READ FIBER FEED OPTION FOR LASER PULSE MEASUREMENTS. UP TO H2-RG. < + 1 mK TEMPERATURE CONTROL OVER 30K to 200K RANGE.

51. PHOTON COUNTING WITH H1RG HYBRIDIZE 256 x 256 SUB-ARRAY TO OUTPUTS 0 – 3 IN CORNER OF H1-RG. SIDECAR ASIC READS @ 10 Mpxl/SEC. 50 – 60 RMS e- CDS READ NOISE. FRAME RATES:

52. A LOOK INTO THE CRYSTAL BALL DISCRETE APDs FOR INTENSITY INTERFEROMETRY, ADAPTIVE OPTICS & FRINGE TRACKING IN 1 -2 YEARS. MODEST ARRAYS - H-1/4RG @ 10 KHz FRAME RATE WITH ONE ASIC. H-2RG, H-4RG-15 FOR LOW BACK-GROUND SPECTROSCOPY & SPACE. SPECIALIZED READOUTS – TIME TAGGING PHOTONS.

53. CURRENT STATUS END

54. A B

55. e-APD GAIN - DEFIR

56. e-APD GAIN - DSL

57. e-APD GAIN – TIS 2004

58. e-APD GAIN - BAE

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