1. Uncooled Infrared Photon Detection Concepts and Devices Viraj Jayaweera Piyankarage Department of Physics & Astronomy Georgia State University

2. 2 Outline Introduction Infrared Detectors based on 1.Dye-Sensitization of Nanostructured Semiconductors Dye-sensitized NIR detector design, experimental results, and conclusion 1/f Noise on DS nano structures 2.Displacement Currents in Semiconductor Quantum Dots (QDs) Embedded Dielectric Media Size quantization effects QD capacitor based detector design, experimental results, and conclusion 3.Split-off Band Transitions in GaAs/AlGaAs Heterojunctions High operating temperature split-off response observed from HEIWIP design for 17μm threshold wavelength Uncooled split-off band detector design Experimental results, and conclusion 4.Free Carrier Absorption in GaSb Homojunctions GaSb HIWIP detector design, experimental results, and conclusion Future Work

3. 3 http://www.nasa.gov/centers/langley/science Visible Micro Wave Near-IRMid-IRFar-IR 0.8 – 5  m 5 - 30  m 30 - 300  m Wavelength Electromagnetic Spectrum

4. 4 –1-3 μmShort Wavelength Infrared SWIR –3-5 μmMedium Wavelength Infrared MWIR –5-14 μmLong Wavelength Infrared LWIR –14-30 μmVery Long Wavelength Infrared VLWIR –30-100 μmFar Infrared FIR –100-1000 μmSub-millimeter SubMM IR Wavelength Range Classification

5. 5 Applications Infrared Body Temperature Thermometer Remote controller and receiver http://www.netcast.com.hk/Products.htm Visible Light Infrared

6. 6 Infrared image of Orion Human suspect climbing over a fence at 2:49 AM in total darkness Night vision helmet Applications Transverse, coronal, and sagittal views across the 3D absorption image of the infant, acquired at 780 nm. www.medphys.ucl.ac.uk/research/borl/ brain imaging Blood Flow

7. 7 Thermal analysis of a fluid tank level detection Close up image of a Intel Celeron chip Faulty connection at power station Applications Bad Insulation spots www.x20.org ºFºF

8. 8 Photon Thermal IR Detectors Different Types of Infrared Detectors Bolometric Thermoelectric Pyroelectric Photovoltaic Photo- conductive Photoemissive

9. 9 Dye-Sensitized Near-Infrared Detectors (DSNID)

10. 10 Dye-sensitized electron injection to a semiconductor Light induced charge carrier generation in a semiconductor VB CB VB CB SemiconductorDye Direct and Sensitized Photo-Injection HOMO LUMO LUMO = Lowest Unoccupied Molecular Orbital HOMO = Highest Occupied Molecular Orbital

11. 11 Dye-Sensitized Near-Infrared Detectors (DSNID) n-TiO 2 nanoparticles Dye p-CuSCN V n-type Dyep-type Solid State Device (No Liquid Electrolyte) TiO 2 IR dye CuSCN

12. 12 Dye Platinum or Gold layer p-CuSCN n-TiO 2 Transparent Conducting Tin Oxide (CTO) Glass TiO 2 nanoparticles Structure of a dye-sensitized IR Detector Appl. Phys. Lett., Vol. 85, No. 23, (2004) CTO

13. 13 Appl. Phys. Lett., Vol. 85, No. 23, (2004) Energy Level Diagram: n/D/p - Heterojunction CB VB CB VB S0S0 S*S* Vacuum Energy (eV) -2 -3 -4 -5 -6 -7 -8 n-TiO 2 Dye p-CuSCN

14. 14 Anionic Dyes (readily anchor to the TiO 2 surface) Cationic Dyes (Not directly anchor to TiO 2 surface) Anionic compounds used for cationic Dyes IR 783 C 38 H 46 ClN 2 NaO 6 S 2 2-[2-[2-Chloro-3-[2-[1,3-dihydro- 3,3-dimethyl-1-(4-sulfobutyl)-2H- indol-2-ylidene]-ethylidene]-1- cyclohexen-1-yl]-ethenyl]-3,3- dimethyl-1-(4-sulfobutyl)-3H- indolium hydroxide, inner salt sodium salt IR 792 C 42 H 49 ClN 2 O 4 S 2-[2-[3-[(1,3-Dihydro-3,3-dimethyl- 1-propyl-2H-indol-2- ylidene)ethylidene]-2-(phenylthio)- 1-cyclohexen-1-yl]ethenyl]-3,3- dimethyl-1-propylindolium perchlorate Mercurochrome (MC) C 20 H 8 Br 2 HgNa 2 O 6 2′,7′-Dibromo-5′-(hydroxymercurio)fluorescein disodium salt IR 820 C 46 H 50 ClN 2 NaO 6 S 2 2-[2-[2-Chloro-3-[[1,3-dihydro-1,1- dimethyl-3-(4-sulfobutyl)-2H- benzo[e]indol-2-ylidene]- ethylidene]-1-cyclohexen-1-yl]- ethenyl]-1,1-dimethyl-3-(4- sulfobutyl)-1H-benzo[e]indolium hydroxide inner salt, sodium salt IR 1040 C 40 H 38 BCl 3 F 4 N 2 1-Butyl-2-[2-[3-[(1-butyl-6- chlorobenz[cd]indol-2(1H)- ylidene)ethylidene]-2-chloro-1- cyclohexen-1-yl]ethenyl]-6- chlorobenz[cd]indolium tetrafluoroborate Bromopyrogallol Red (BPR) C 19 H 10 Br 2 O 9 S 5′,5′′-Dibromopyrogallolsulfonephthalein The number indicates the peak absorption wavelength in nanometers IR Absorbing Dyes

15. 15 Appl. Phys. Lett., Vol. 85, No. 23, (2004) Spectral Responsivity Peak Detectivity = (9.0 ± 0.3) ×10 10 cm Hz ½ W -1 Conversion Efficiency = 0.4 %

16. 16 AdvantagesDisadvantages 1.Low Cost 2.Fully Solid State 3.Detection wavelength can be tailored using the appropriate dye 4.Panchromatic sensitization using several dyes 5.Readily applicable to large area detectors 1.Slow Response 2.Poor long term stability 3.Although wavelength can be tailored, getting a sufficiently high extinction coefficient may not be easy. 4.HOMO level should be lower than p-type VB and LUMO should be higher than n-type CB Advantages and Disadvantages of DSNID

17. 17 Colloidal Quantum Dot Detectors

18. 18 CdSe/ZnS Colloidal Quantum Dots (QDs) Emission Spectra Size Quantization Effects ~4 nm~15 nm http://www.nanopicoftheday.org/2003Pics/QDRainbow.htm Colloidal QDs are synthesized from precursor compounds dissolved in solutions.

19. 19 TEM images of different size quantum dots (CdSe/ZnS) with emission wavelength at: (A) 525; (B) 540; (C) 590; (D) 652; and (E) 691 nm. Average diameter: (A) 4.2 nm; (B) 4.6 nm; (C) 6.7 nm; (D) 10.6 nm; (E) 20.1 nm. Scale bar: 20 nm. Size Quantization Effects (H. Q. Wang et al. Journal of Colloid and Interface Science, 316 (2007) 622-627)

20. 20 Y. Wang et al. J. Chem. Phys. 87 (1987) PbS Colloidal QDs Bandgap vs. Particle size Bulk PbS direct band gap= 0.41 eV (λ t = 3 μm) 4 nm PbS QD = 1.2 eV (λ t = 1 μm) Wavelength (nm) A. Margaret et al. Adv. Mater. 15 (2003)

21. 21 QD Embedded Capacitor (QDEC) Type IR Photodetectors Micro Ammeter Appl. Phys. Lett., 91, 063114 2007 Quantum Dot Battery Dielectric Optical Chopper Incoming IR radiation

22. 22 Appl. Phys. Lett., 91, 063114 2007 Transparent Conducting layer (Fluorine-doped tin oxide) Schematics of the QDEC Type Infrared Photodetector Glass PbS QD + Dielectric medium Bottom Electrical Contact Top Electrical Contact Glass can be replaced with IR transmitting substrate such as Si, ZnSe, Sapphire, CaF 2, MgF 2, KRS Possible dielectric materials: Paraffin Wax Silicon Nitride Silicon Oxide Possible dielectric materials: Paraffin Wax Silicon Nitride Silicon Oxide

23. 23 Spectral Responsivity of the QDEC IR Detector Appl. Phys. Lett., 91, 063114 2007 PbS ~2 nm

24. 24 Summary AdvantagesDisadvantages 1.Low cost. (Fabrication does not involve sophisticated epitaxial growth techniques) 2.Can be fabricated on flexible substrates. 3.No direct wire contact to QDs. 4.Sense only the variation of light. Insensitive to the background. 5.Multi band capability using a combination of QDs. 6.Spectral range can be extended using different QD materials (PbSe, InSb, HgCdTe). 1.Optical chopper not practical for some applications. 2. Density of QDs can not increases arbitrarily. After a threshold value it start to conduct.

25. 25 HEIWIP Free Carrier Detectors (Heterounction Interfacial Workfunction Internal Photoemission)

26. 26 HEIWIP Detectors (Heterounction Interfacial Workfunction Internal Photoemission Detectors) p + -GaAsAl x Ga 1-x As VB Δ EFEF Zero Bias p + -GaAsAl x Ga 1-x As Δ Biased Absorption is due to free carriers Interface is sharp (no space charge) Barrier formed by Heterojunction (p-type) Internal workfunction Δ comes from Al fraction (x) and doping APL 78, 2241 (2001) APL 82, 139 (2003) Emitter Barrier h hνhν

27. 27 p + -GaAsAl x Ga 1-x As VB ΔxΔx EFEF Free Carrier Threshold of HEIWIP Detector Al fraction x =0.090 λ t = Threshold Wavelength ΔdΔd Wavelength (μm) EmitterBarrier N A = 3×10 18 cm -3 Doped p + GaAs Emitters Responsivity (a.u.) λtλt Δ = Δ d + Δ x

28. 28 Split-off Band Detectors

29. 29 Heavy Hole Band Split-off Band Conduction Band INTRINSIC (InSb, HgCdTe) E k Light Hole Band Infrared Detector Mechanisms Split-off Band Conduction Band Extrinsic (Si:P) E k Light Hole Band Impurity Band Heavy Hole Band SO Band QWIP (GaAs/AlGaAs) HH Band LH Band E k Intersubband levels Split-off Band Conduction Band Split-Off E k Light Hole Band Heavy Hole Band EFEF

30. 30 Split-off Detector Threshold Mechanisms SO Band EfEf E BL/H LH Band CB HH Band E BSO k Indirect absorption followed by scattering and escape Threshold Energy E ESO - E f SPLIT-OFF Intra-valence Transitions Direct absorption followed by scattering and escape Threshold Energy E ESOf - E f Indirect absorption followed by escape without scattering Threshold Energy E BSO - E f E ESO E p + -GaAsAlGaAs SO L /H IR Photon excites holes from the light/heavy hole bands to the split-off band (Solid Arrow) Excited holes can scatter into the light/heavy hole bands (Dashed Arrow) and then escape IR Photon excites holes from the light/heavy hole bands to the split-off band (Solid Arrow) Excited holes can scatter into the light/heavy hole bands (Dashed Arrow) and then escape, or escape directly from the split-off band Appl. Phys. Lett., 89 131118 (2006)

31. 31 Schematics of the Detector Substrate GaAs Bottom Contact p ++ GaAs p + GaAs (emitter) AlGaAs (barrier) Top Contact p ++ GaAs N Periods 400 μm Au contact layers <2.5μm R Bias

32. 32 Absorption and Conversion Efficiency (Initial Sample 1332, λ t = 17 μ m) Al Fraction x Δ (meV) λt(μm)λt(μm) GaAs Emitter Al x Ga 1-x As Barrier Thickness (Å) No of Periods N Doping (cm -3 )Thickness (Å) 0.1573173×10 18 188125012 Split-off Free Carrier α λ 2 Free Carrier Split-off

33. 33 Sample # Al Fraction x Δ (meV) λt(μm)λt(μm) GaAs Emitter Al x Ga 1-x As Barrier Thickness (Å) No of Periods Doping (cm -3 )Thickness (Å) SP10.2815583×10 18 18860030 Different Free Carrier Threshold (λ t ) Samples SP1 155 meV SO Band L /H Band SP20.3720763×10 18 18860030 SP30.5731043×10 18 18860030 SP2 207 meV SP3 310 meV 365 meV Appl. Phys. Lett., 93 021105 (2008)

34. 34 Sample # Δ λtλt Operating Temperature Dynamic Resistance @ 1V (Ω) Dark Current Density @ 1V (A/cm 2 ) Responsivity (mA / W) D* (Jones) (meV)(μm) SP11558140787 ± 10.663 ± 0.0032.3 ± 0.1(2.1 ± 0.1)×10 6 Results of Different λ t Samples Operating threshold dark current ~1 A/cm 2 Design flexibility for higher D* or higher operating temperature SP22076190913 ± 10.875 ± 0.0032.7 ± 0.1(1.8 ± 0.1)×10 6 SP33104 3001138 ± 10.563 ± 0.0030.29 ± 0.1(6.8 ± 0.1)×10 5 150(1.7±0.1) ×10 9 (3.4±0.1)×10 -7 (2.1±0.1)×10 -3 (2.2 ±0.1)×10 10

35. 35 Room Temperature Response ( SP3: 4 μm Free Carrier Threshold ) SP3 SO Band EfEf L/H LH Band CB HH Band SPLIT-OFF Intra-valence Transitions SO k E SO – E f = 370 meV 3.4 μm E SOf – E f = 420 meV 2.9 μm Appl. Phys. Lett., 93 021105 (2008)

36. 36 Responsivity Comparison for Different λ t Samples Sample # Free Carrier Threshold (μm) Al Fraction x Δ (meV) SP180.28155 SP260.37207 SP340.57310

37. 37 4 V Noise level 3 V 2 V 1 V Above Room Temperature Operation

38. 38 MaterialΔ SO (meV)λ SO (μm) InAs4103.2 GaAs3403.6 AlAs3004.1 InP11011 GaP8016 AlP7018 GaN2062 AlN1965 InN3410 Possibility of a room temperature dual band detector for atmospheric windows 3-5 and 8-14  m using Arsenides & Phosphides Different Material will Cover Different Split-off Ranges In 1-x Ga x As y P 1-y 110 - 379 (0.11+0.421y-0.152y²) 3.3 - 11 In 1-x Ga x P 93 - 101 0.101+0.042x-0.05x 2 12.3 - 13.3

39. 39 Summary High Operating Temperature (Uncooled or TE Cooled) Tunability (Wavelength, Detectivity, Operating Temperature) Well Developed Materials, Readout Circuits, and Integrated Circuits High Performance

40. 40 GaSb Homojunction Far-IR (THz) Detectors

41. 41 p + -GaSbUndoped GaSb VB Δ EFEF Zero Bias p + -GaSbUndoped GaSb Δ Biased Emitter Barrier Absorption is due to free carriers Barrier formed by Homo-junction (p-type) Δ comes from doping HIWIP (Homojunction Interfacial Workfunction Internal Photoemission Detectors) h hνhν A.G.U. Perera et al., JAP (77) 915 (1995)

42. 42 0.05 μm 5×10 18 cm -3 p ++ GaSb Substrate 2×10 18 cm -3 p + emitter Undoped-GaSb barrier 2×10 18 cm -3 p + emitter 5 × 10 18 cm -3 p ++ 2 μm 0.1 μm Metal contact Grown by OMCVD GaSb HIWIP Far-IR (THz) Detector Δ GaSb p + GaSb Top Contact Bottom Contact ΔEVΔEV Appl. Phys. Lett. 90, 111109 (2007)

43. 43 Appl. Phys. Lett. 90, 111109 (2007) GaSb HIWIP Far-IR (THz) Response Peak Detectivity at 36 μm = (5.7 ± 0.1)×10 11 cm Hz ½ W -1 Conversion Efficiency = 33 %

44. 44 GaSb HIWIP Far-IR (THz) Response

45. 45 GaSbGaAs Why GaSb ? GaSb THz Absorption

46. 46 InGaSb/GaSb Heterojunctions EmitterBarrierOffset GaAsAl x Ga 1-x As530x meV GaNAl x Ga 1-x N800x meV In x Ga 1-x SbGaSb40x meV InGaSb/GaSb has a small valance band offset Much better for THz heterojunctions Barrier is ~4 meV for 1 THz Corresponds to 10% variation In fraction in Sb material < 1% Al fraction for As, N materials

47. 47 Summary Higher absorption coefficient compared to GaAs High performance Responsivity 9.7 A/W, Detectivity (5.7 ± 0.1)×10 11 Jones at 36 μm and 4.9 K. Wavelength tailorability Design with 14 μm threshold expected to be work at TE cool temperatures. InGaSb/GaSb heterojunction has a small valance band offset much better for THz designs

48. 48 Future Works

49. 49 ITO Glass Substrate ~10 μm ZnO Colloidal Quantum Dot Based UV-NIR Dual-Band Detector Photo Conductive PbS QDs In preparation to Appl. Phys. Lett.

50. 50 GaAs substrate p ++ -In 0.49 Ga 0.51 P contact Al 0.8 Ga 0.2 As barrier p + -In 0.49 Ga 0.51 P emitter p ++ -InGaP emitter p ++ -GaAs contact Al 0.8 Ga 0.2 As barrier p + -GaAs emitter Al 0.57 Ga 0.43 As barrier p ++ -GaAs contact 8-14 μm Response 3-5 μm Response TC MC BC Al 0.57 Ga 0.43 As barrier Al 0.8 Ga 0.2 As p + -In 0.49 Ga 0.51 P Al 0.57 Ga 0.43 As p ++ -GaAs p + -GaAs p ++ -GaAs p ++ -In 0.49 Ga 0.51 P Proposed dual band detector for 3-5 and 8-14 μm atmospheric windows using Arsenides & Phosphides

51. 51 1.P. V. V. Jayaweera, S. G. Matsik, A. G. U. Perera, H. C. Liu, M. Buchanan and Z. R. Wasilewski "Uncooled infrared detectors for 3-5 μm and beyond", Applied Physics Letters 93, 021105, (2008) 2.P. V. V. Jayaweera, A.G.U. Perera and K. Tennakone "Why Gratzel′s cell works so well” Inorganica Chimica Acta, 361, 707-711, (2008) 3.A. G. U. Perera, P. V. V. Jayaweera, G. Ariyawansa, S. G. Matsik, M. Buchanan and H. C. Liu), "Room Temperature Nano and Micro Structure Photon Detectors", Microelectronics Journal, In Press, (2008) 4.P. V. V. Jayaweera, A. G. U. Perera, and K. Tennakone, "Displacement currents in semiconductor quantum dots embedded dielectric media: A method for room temperature photon detection" Applied Physics Letters 91, 063114- 3, (2007) 5.P. V. V. Jayaweera, S. G. Matsik, and A. G. U. Perera, Y. Paltiel, Ariel Sher and Arie Raizman, H. Luo, and H. C. Liu, “GaSb homojunctions for Far-IR (THz) Detection” Applied Physics Letters, 90, 111109, (2007) 6.P. V. V. Jayaweera, P.K.D.D.P. Pitigala, M.K.I. Seneviratne, A. G. U. Perera and K. Tennakone “1/f Noise in dye- sensitized solar cells and NIR photon detectors” Infrared Physics & Technology, 50, 270-273 (2007) 7.P. V. V. Jayaweera, S.G. Matsik, K. Tennakone, A.G.U. Perera, H.C. Liu and S. Krishna ) "Spin split-off transition based IR detectors operating at high temperatures" Infrared Physics & Technology, 50, 279-283 (2007) 8.A. G. U. Perera, S. G. Matsik, P. V. V. Jayaweera, K. Tennakone, H. C. Liu, M. Buchanan G. Von Winckel, A. Stintz, and S. Krishna) “High Operating Temperature Split-off Band Infrared Detectors” Applied Physics Letters, 89, 131118, (2006) 9.P. V. V. Jayaweera, P. K. D. D. P. Pitigala, A. G. U. Perera and K. Tennakone "1/f noise and dye-sensitized solar cells", Semicond. Sci. Technol. 20, L40–L42, (2005) 10.P. V. V. Jayaweera, A. G. U. Perera, M. K. I. Senevirathna, P. K. D. D. P. Pitigala, and K. Tennakone, “Dye- sensitized near-infrared room-temperature photovoltaic photon detectors" Applied Physics Letters 85 (23), 5754- 5756, (2004) List of Publications Relevant to Presented Results

52. 52 Acknowledgement Advisor: Dr. Unil Perera Committee Dr. Vadym M. Apalkov Dr. Douglas Gies Dr. Xiaochun He Dr. Kirthi Tennakone Dr. Brian D. Thoms Department Chair: Dr. H. R. Miller Associate Dean: Dr. William H. Nelson Group Members Dr. Steven Matsik, Dr. Gamini Ariyawansa, Ranga Jayasinghe, Dulipa Pitigala, Laura Byrum, Jiafeng Shao, Dr. Manmohan Singh, Greggory Rothmeier Group Members Dr. Steven Matsik, Dr. Gamini Ariyawansa, Ranga Jayasinghe, Dulipa Pitigala, Laura Byrum, Jiafeng Shao, Dr. Manmohan Singh, Greggory Rothmeier Department Staff: Yvette Hilaire, Felicia Watts, Carola Butler, Duke Windsor Instrument Shop: Charles Hopper, Peter Walker, Dwayne Alan Torres Department Staff: Yvette Hilaire, Felicia Watts, Carola Butler, Duke Windsor Instrument Shop: Charles Hopper, Peter Walker, Dwayne Alan Torres

53. 53 The End Oct. 28 2008

54. 54

55. 55 http://sales.hamamatsu.com/en/support/technical-notes.php

56. 56 Present Device Comparison of Gain Mechanisms Higher Trapping → Gain 1

57. 57 Proposed Device (With a Graded-Heating-Barrier) Comparison of Gain Mechanisms Higher Impact → Lower Trapping → High photogenerated space charge (SC) → High gain ~50 → High photocurrent

58. 58 Proposed Device (With a Graded-Heating-Barrier) Present Device Comparison of Gain Mechanisms Higher Impact → Lower Trapping → High photogenerated space charge (SC) → High gain ~50 → High photocurrent Higher Trapping → Gain 1

59. 59 Proposed Detector Structure with a Graded-Heating-Barrier AlGaAs p-GaAs emitter AlGaAs BC TC Unbiased Proposed Device (With a Graded-Heating-Barrier) Present Device AlGaAs p-GaAs emitter AlGaAs BC TC Biased Biased & Illuminated Lower Trapping → High Photogenerated Space Charge → High Gain ~50 Higher Trapping → Gain 1

60. 60 Optimized for single stage TE (~280 K) λ t ~ 4.5 μm Conversion Efficiency ~50% D* ~ 5 × 10 11 Jones Optimized for single stage TE (~280 K) λ t ~ 4.5 μm Conversion Efficiency ~50% D* ~ 5 × 10 11 Jones Expected Optimum Performance Optimized for room temperature (~300 K) Conversion efficiency ~50% D* ~1x10 11 Jones 60° FOV BLIP at 250K, D* 1x10 12 Jones Optimized for room temperature (~300 K) Conversion efficiency ~50% D* ~1x10 11 Jones 60° FOV BLIP at 250K, D* 1x10 12 Jones

61. 61 Spectral power density of noise (Hoog’s Formula) Where f is frequency, 0<α <2 α = 0 white noise α = 1 pink noise (strict 1 / f) α = 2 brown noise α = 1 α = 0 1/f- Noise

62. 62 Glass Substrate Conducting Tin Oxide TiO 2 R = 56 k 18 V Sample Preparation for Noise Measurements

63. 63 Vacuum N 2, H 2 O (g) Heater Sample Temp. Sensor R Low Noise Pre- Amplifier (SR560) FT Signal Analyzer (SR785) PC Noise Measurement Setup

64. 64 Semicond. Sci. Technol. 20, L40-L42 (2005) Infrared Phys. Technol. 50, 270-273 (2007) TiO 2 (N 2 ) TiO 2 (N 2 RH >40%) TiO 2 (N 2,I 2 vapor) Adsorbed molecular species such as H 2 O and I 2 can generate 1/f noise These molecular species produce electron acceptor states on the TiO 2 surface. H 2 O  H + OH (electron acceptor) It is suggested that the trapping and detrappng of electrons at the surface states is the cause of 1/f noise. α = 1.37 α = 1.25 Noise in TiO 2 Nanocrystalline Films

65. 65 TiO 2 /N3 (N 2, RH <40%) TiO 2 /N3 (N 2, RH=70%) TiO 2 /BPR (N 2, RH=70%)) TiO 2 /BPR (N 2, RH <40%) Semicond. Sci. Technol. 20, L40-L42 (2005) TiO 2 (N 2 RH=70%) TiO 2 (N 2,I 2 ) 1/f noise is suppressed when the TiO 2 surface is dye coated Higher relative humidity can partly desorbs dye from TiO 2 surface allowing water adsorption (here 1/f noise is generated again. Noise in TiO 2 Nanocrystalline Films

66. 66 Power spectral density of the dark current noise of the heterojunction n-TiO 2 /MC-IR792/p-CuSCN n-TiO2/MC-IR792/p-CuSCN Appl. Phys. Lett., 85, 5754-5756 (2004) Noise in Dye-Sensitized IR Detectors

67. 67 Sample # Δ λtλt Operating Temperature Dynamic Resistance @ 1V (Ω) Dark Current Density @ 1V (A/cm 2 ) Responsivity (mA / W) D* (Jones) (meV)(μm) SP115581407870.6632.32.1×10 6 SP220761909130.8752.71.8×10 6 SP33104 30011380.5630.296.8×10 5 1501.74×10 9 3.4×10 -7 0.00212.2×10 10 Results of Different λ t Samples Operating threshold dark current ~1 A/cm 2 Design flexibility for higher D* or higher operating temperature

68. 68 Wavelength (nm) PbS Colloidal QDs Absorption A. Margaret et al. Adv. Mater. 15 (2003) 1844 Bulk PbS direct band gap = 0.41 eV

69. 69 GaSbGaAs Why GaSb ? GaSb THz Absorption

70. 70 InGaSb/GaSb Heterojunctions EmitterBarrierOffset GaAsAl x Ga 1-x As530x meV GaNAl x Ga 1-x N800x meV In x Ga 1-x SbGaSb40x meV InGaSb/GaSb has a small valance band offset Much better for THz heterojunctions Barrier is ~4 meV for 1 THz Corresponds to 10% variation In fraction in Sb material < 1% Al fraction for As, N materials

71. 71 Colloidal Quantum Dot based UV-NIR Dual-band Detector ITO Glass Substrate ~10 μm ZnO Photo Conductive PbS QDs

72. 72 (H. Q. Wang et al. Journal of Colloid and Interface Science, 316 (2007) 622-627) UV–visible absorption and fluorescence spectra of different CdSe QDs synthesized by changing the nucleation time (nucleation time from 10 to 360 s, emission from 514 to 680 nm), measured at room temperature. Size Quantization Effects

73. 73 Al Fraction x Δ (meV) λt(μm)λt(μm) GaAs Emitter Al x Ga 1-x As Barrier Thickness (Å) No of Periods Doping (cm -3 )Thickness (Å) 0.1262201×10 18 188125016 Split-off Free Carrier α λ 2 Conversion Efficiency Absorption and Conversion Efficiency (Initial Sample HE0204, λ t = 20 μ m)

74. 74 Split-off Response for the 20 μm Free Carrier Threshold Detector SO Band EfEf Δ L/H LH Band CB HH Band SPLIT-OFF Intra-valence Transitions Δ SO k Appl. Phys. Lett., 89, 131118 (2006) E SO – E f = 370 meV 3.4 μm E SOf – E f = 420 meV 2.9 μm Δ SO – E f = 420 meV 2.9 μm HE0204 Responsivity (mA / W) E

75. 75 Outline Introduction Infrared Detectors based on 1.Dye-Sensitization of Nanostructured Semiconductors Dye-sensitized NIR detector design, experimental results and summery 1/f Noise on DS nano structures 2.Displacement Currents in Semiconductor Quantum Dots (QDs) Embedded Dielectric Media Size quantization effects QD capacitor based detector design, experimental results and summery 3.Split-off Band Transitions in GaAs/AlGaAs Heterojunction High operating temperature split-off response observed from HEIWIP design for 17 μm threshold wavelength Uncooled split-off band detector design Experimental results and Summery 4.Free Carrier Absorption in GaSb Homojunction GaSb HIWIP detector design, experimental results and summery Future Works

76. 76 Advantages over other 3-5 µm Detectors Arsenides will be used for 3 – 5 μm range material, readout circuits, and Integrated electronics already developed DetectorAdvantageProposed Split-off Detector InSb D* =1x10 11 Jones 77 KOperating Temperature 300 K HgCdTe D* =3x10 10 Jones 77-240 K ~4% Bad Pixels (256x256) Operating Temperature Uniformity 300 K ~0.1% Bad Pixels (600x512) PbSe D* =3x10 10 Jones Threshold depends on Temperature Better StabilityThreshold fixed by split-off energy

77. 77

78. 78 Sample # Δ (meV) λ t (μm) T max (K) Δ/kT max Dynamic Resistance @ 1V (Ω) Dark Current Density @ 1V (A/cm 2 ) Responsivity (mA / W) D* (Jones) SP1155814012.8787 ± 10.663 ± 0.0032.3 ± 0.1(2.1 ± 0.1)×10 6 SP2207619012.6913 ± 10.875 ± 0.0032.7 ± 0.1(1.8 ± 0.1)×10 6 SP3310430012.01138 ± 10.563 ± 0.0030.29 ± 0.01(6.8 ± 0.1)×10 5 Results of Different λ t Samples Operating threshold dark current ~1 A/cm 2 Design flexibility for higher D* or higher operating temperature Appl. Phys. Lett., 93 021105 (2008)

79. 79 Internal Photoemission Detectors Type I - N d E F ) N d : Doping of Emitter N c : Mott’s Metal Insulator Transition  E C : Band gap narrowing  = (E C n+ - E F ) +  E C E c n+  EcEc EciEci h e EFEF Unbiased Biased A.G.U. Perera et al., JAP (77) 915 (1995)

80. 80 Type II - N c < N d < N 0 ( E C n+ < E F < E C i ) N d : Doping density in the Emitter/Absorber N c : Mott’s Metal Insulator Transition N 0 : Critical concentration  = E c i - E F  Fermi level is above the conduction band edge of the emitter  Emitter becomes semi-metallic  Infrared absorption is due to free carriers A.G.U. Perera et al., JAP (77) 915 (1995)

81. 81  Fermi level is above the conduction band edge of the barrier  Conduction band edge of the Emitter and the barrier become degenerate  Space charge region at the n ++ - i interface forms the barrier  Barrier height depends on the concentration and the applied field Type III - N d > N 0 ( E F > E C i ) N d : Doping concentration of the Emitter/ Absorber N 0 : Critical concentration S. Tohyama et al., IEDM Tech. Dig. p.82 (1988)

82. 82 GaSb VB EFEF GaSb CB p + -GaSb VB EFEF CB