2900-129-R Memorandum of Project MICHIGAN ULTIMATE SENSITIVITY AND PRACTICAL PERFORMANCE OF THE TELLURIUM PHOTOCONDUCTIVE DETECTOR DAVID F. EDWARDS December 1959 SOLID-STATE PHYSICS LABORATORY THE UNIVERSITY OF MICHIGAN Ann Arbor, Michigan

DISTRIBUTION OF REPORTS Distribution control of Project MICHIGAN Reports has been delegated by the U. S. Army Signal Corps to: Commanding Officer U. S. Army Liaison Group Project MICHIGAN Willow Run Laboratories Ypsilanti, Michigan It is requested that information or inquiry concerning distribution of reports be addressed accordingly. Project MICHIGAN is carried on for the U. S. Army Signal Corps under Department of the Army Prime Contract Number DA-36-039 SC- 78801. University contract administration is provided to the Willow Run Laboratories through The University of Michigan Research Institute.

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM 2900-129-R PREFACE Documents issued in this series of Technical Memorandums are published by Willow Run Laboratories in order to disseminate scientific and engineering information as speedily and as widely as possible. The work reported may be incomplete, but it is considered to be useful, interesting, or suggestive enough to warrant this early publication. Any conclusions are tentative, of course. Also included in this series will be reports of work in progress which will later be combined with other materials to form a more comprehensive contribution in the field. A primary reason for publishing any paper in this series is to invite technical and professional comments and suggestions. All correspondence should be addressed to the Technical Director of Project MICHIGAN. Project MICHIGAN, which engages in research and development for the U. S. Army Combat Surveillance Agency of the U. S. Army Signal Corps, is carried on by the Willow Run Laboratories as part of The University of Michigan' s service to various government agencies and to industrial organizations. Robert L. Hess Technical Director Project MICHIGAN iii

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM 2900-129-R ABSTRACT Calculations of the ultimate sensitivity and measurements of the practical performance have been made for the tellurium photoconductive detector. For the condition that detector sensitivity is limited by fluctuations of background radiation, the theoretical NEP (noise equivalent power) at the peak of spectral -13 sensitivity (X = 3. 4 M) was calculated to be 5. 1 x 10 watt. For the "best" -13 tellurium detector the measured value of NEP was 3. 1 x 10 watt at the same wavelength and at the optimum chopping frequency. These values indicate that the tellurium photoconductive detector is background limited and thus is an ideal detector. INTRODUCTION The purpose of this memorandum is to report the results of calculations of the ultimate sensitivity of the tellurium detector and of measurements of sensitivity for a select few of these detectors as prepared by Suits, et al. The results indicate that the tellurium detector is an ideal detector. The fact that only one of six detectors measured approached the ultimate sensitivity indicates the need for continued development. Of the other five, two detectors had an NEP (noise equivalent power) (3. 4 M) within a factor of about 10 of the ideal. For the ideal detector, i. e., one that is background-radiation limited, the addition of a cooled radiation shield to match the aperture of the detector to that of the optics should increase the detector sensitivity by as much as a factor of 10. The use of tellurium as a photoconductor was first investigated in 1949 by Moss (References 1 and 2), who used evaporated thin films. The most sensitive cell that he reported, when cooled to liquid-nitrogen temperature, had a signal equal to the rms (root-mean-square) noise in l-cps bandwidth for incident radiation of 1. 2 x 10 watt of monochromatic radiation at 1 s. This quantity is called the NEP and is defined as the incident radiation necessary to produce a signal equal to the rms noise. This same tellurium film was only moderately sensitive (NEP = 10 to -7 10 watt, at lp and l-cps bandwidth) at room temperature. Loferski (Reference 3) in 1954 made 1

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM 2900-129-R photoconductivity measurements on single crystals of tellurium with about the same results as those obtained for evaporated films. Loferski' s data were extrapolated and the NEP was found to be about 10 to 10 watt for the most sensitive photoconductor when cooled to liquid-oxygen temperature. The single crystals used by Loferski were cut or cleaved from large tellurium crystals, ground, polished, and sometimes etched to the desired dimensions. Suits (Reference 4) in 1957 found that thin hexagonal single-crystal prisms of tellurium when cooled to liquid-nitrogen temperature had sensitivities and response times comparable to those of the lead-salt detectors. These thin single-crystal prisms were grown from the vapor phase in a low-pressure hydrogen atmosphere, starting with 99. 999+%pure material.l The electrical contacts were made by welding a hot wire, in most cases platium, to the tellurium. The crystals were then mounted in a more or less standard glass dewar with a sapphire window. 2 ULTIMATE SENSITIVITY The ultimate sensitivity was calculated for the tellurium detector for the condition that fluctuation in background radiation is the fundamental limitation of detector sensitivity. Recently, several articles have been published (References 5-8) that describe methods for calculating the ultimate sensitivity of a photoconductor for the background-limited condition. The calculations reported in the present paper follow closely those of Moss (Reference 6). The background radiation is taken as a 3000K blackbody with the spectral distribution given in Figure 1, curve (a). Only that radiation that lies within the sensitive spectral region of the detector will affect the ultimate sensitivity. The relative spectral response of the tellurium detector at 770K is given in Figure 1, curve (b). The product of these two curves is the spectral distribution of the effective radiation incident on the detector (Figure 2). It is seen that the effective wavelengths are limited to a narrow band centered at 3. 7 A. For purposes of calculation it is assumed to a good degree of approximation that the effective radiation is monochromatic with the wavelength of the peak, 3. 7 p. The area under this curve is the equivalent energy falling on the detector and equals 82. 2 microwatts/cm. This corresponds to N = 1. 5 x 10 0 quanta/cm /sec at 3. 7 p. The number of absorbed quanta producing a detector signal, N, will depend on the absorption properties of the material, the quantum efficiency, and the diffusion length of free carriers. The relation between N and N has been given by Moss (Reference 6) as s o American Smelting and Refining Co., South Plainfield, New Jersey. 2

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM 2900-129-R 2_ N - 2AN Af/(l - r- t), s 0 where A is the sensitive area of the detector, Af the bandwidth of the measuring equipment, and 2 r and t are the reflection and transmission coefficients. For a detector with A = 0. 0025 cm 6 and Af - 5 cps, N = 9. 55 x 10 quanta/sec at 3. 7 p. The reflection coefficient r (= 0. 48) was 5 calculated from the weighted average for the index of refraction (Reference 9) n = 5. 5. The transmission coefficient t (= 0. 10) was calculated from the absorption coefficient value of Loferski (Reference 3) and the sample thickness. This calculated value of N corresponds to -13 a theoretical NEP (3.4 p) 5. 1 x 10 watt at the peak of the spectral response (X = 3.4p) and represents the ultimate sensitivity of the tellurium detector for the background-radiation limited condition. 3 PRACTICAL PERFORMANCE The absolute spectral sensitivity of the "best" tellurium photoconductor measured is shown -13 in Figure 3. The measured NEP at 3. 4 p is (3. 1 ~ 0. 8) x 10 watt. This was measured for radiation chopped at 5000 cps and 5 cps bandwidth. The assumptions used in the calculation of the ultimate sensitivity result in the value of the ideal NEP being larger than the measured value. A more refined calculation does not seem warranted at this time. The monochromatic radiation calibration was made with a Reeder thermocouple that had been calibrated with a 5000 K standard blackbody and checked with a National Bureau of Standards calibrated lamp. The rms values of noise and signal voltages were calibrated with a Weston a-c thermocouple. 2Chas. M. Reeder Co., Detroit 3, Michigan. MlVodel RS-1A Blackbody, Barnes Engineering Co., Stamford, Connecticut. 3

RADIATION FLUX DENSITY (watts/cm2-) X~ o o o o 0 _ (D'q Oc O, CIO (' 0 -~~^^ ~ - 0p0 0 o o ~ ~~ o -- (C~~~~~~~~~~D 0)-s~~~~d d CD 00 C-+ ~0 (3 0CD 9 -_\ e-F I\

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM 2900-129-R 9.0 ~ 8.0 7.0 I ^ ~ ^ ~ \- ~~~~~-I 6.0~ -I ~ -~ —~~~ 5.0 4.0I 3.0 2.0-1 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 WAVELENGTH (II)

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM 2900-129-R 10-19 0 1 2 3 4 5 6 7 WAVELENGTH (II) FIG. 3. ABSOLUTE SPECTRAL SENSITIVITY OF THE TELLURIUM DETECTQR. At 770 K with a chopping frequency of 5000 cps and a 5-cps bandwidth. 6

WILLOW' RUN LABORATORIES TECHNICAL MEMORANDUM 2900-129-R REFERENCES 1. Moss, T. S., Proc. Phys. Soc. (London), 1949, Vol. A62, p. 264. 2. Moss, T. S., Photoconductivity in the Elements, London, Butterworth, 1952. 3. Loferski, J. J., Phys. Rev., 1954, Vol. 93, p. 707. 4. Suits, G. H., "Tellurium Infrared Detector, " presented at the Infrared Information Symposium, Pasadena, Calif., November 1957. 5. Burstein, E., and Picus, G. S., "Background Limited Infrared Detection, presented at the Infrared Information Symposium, Boston, Mass., 3 December 1958. 6. Moss, T. S., J. Opt. Soc. Am., 1950, Vol. 40, p. 603. 7. Petritz, R. L., Photoconductivity Conference, Atlantic City, Wiley, 1956. 8. Smith, R. A., Jones, F. E., and Chasmar, R. P., The Detection and Measurement of Infrared Radiation, London, Oxford University Press, 1957. 9. Hartig, P. A., and Loferski, J. J., J. Opt. Soc. Am., 1954, Vol. 44, p. 17. 7

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM 2900- 129-R DISTRIBUTION LIST 2, PROJECT MICHIGAN REPORTS 1 December 1959- Effective Date Copies - Addressee Copies - Addressee 1 Commanding Officer, Army Map Service 1 Commanding General Corps of Engineers, U. S. Army Ordnance Tank-Automotive Command, Detroit Arsenal Washington 25, D. C. 28251 Van Dyke Avenue, Center Line, Michigan ATTN: Document Library ATTN: Chief, ORDMC-RRS 1 Commanding General 2 Commander, Chemical Corps Research and Development Command Quartermaster Research and Engineering Command Department of the Army, Washington 25, D. C. U. S. Army, Natick, Massachusetts ATTN: Chief, Development Division 2 Chief, U. S. Army Security Agency Arlington Hall Station, Arlington 12, Virginia U. S. Army Snow, Ice and Permafrost Research Establishment, CE 2 Commander, Army Rocket and Guided Missile Agency 1215 Washington Avenue, Wilmette, Illinois Redstone Arsenal, Alabama ATTN: Coordination and Publications Branch ATTN: Technical Library, ORDXR-OTL 7 Director 20 Commanding Officer U. S. Army Engineer Research and Development Laboratories U. S. Army Signal Research and Development Laboratory Fort Belvoir, Virginia Fort Monmouth, New Jersey (1) ATTN: Chief, Topographic Engineer Department ATTN: SIGFM/EL-DR (3) ATTN: Chief, Electrical Engineering Department (3) ATTN: Technical Documents Center 1 Commanding General U. S. Army Electronic Proving Ground 1 Commanding General Fort Huachuca, Arizona U. S. Army Combat Development Experimentation Center ATTN: Technical Library Fort Ord, California 1 Office of the Director, Defense Research and Engineering 1 Commandant, U. S. Army War College Technical Library, Department of Defense Carlisle Barracks, Pennsylvania Washington 25, D. C. ATTN: Library 1 Director, Weapons Systems Evaluation Group 1 Commandant, U. S. Army Command and General Staff College Room 1E880, The Pentagon Fort Leavenworth, Kansas Washington 25, D. C. ATTN: Archives 1 Chief of Engineers Department of the Army, Washington 25, D. C. 1 Commandant, U. S. Army Infantry School Fort Benning, Georgia ATTN: Research and Development Division ATTN: Combat Developments Office 1 Office, Chief of Ordnance Research and Development Division 1 Commandant, U. S. Army Armor School Department of the Army, Washington 25, D. C. Fort Knox, Kentucky ATTN: ORDTB, Research and Special Projects ATTN: Combat Developments Group 1 Office, Chief of Research and Development 2 Assistant Commandant, U. S. Army Artillery and Missile School Department of the Army, Washington 25, D. C. Fort Sill, Oklahoma ATTN: Chief, Communications-Electronics Div. 3 Assistant Commandant, U. S. Army Air Defense School Fort Bliss, Texas 1 Office, Chief of Research and Development Department of the Army, Washington 25, D. C. 1 Commandant, U. S. Army Engineer School ATTN: Army Research Office Fort Belvoir, Virginia ATTN: Combat Developments Group I Office, Assistant Chief of Staff for Intelligence Department of the Army, Washington 25, D. C. 1 Commandant, U. S. Army Signal School ATTN: Chief, Combat Developments/G-2 Air Branch Fort Monmouth, New Jersey ATTN: SIGFM/SC-DO 2 Commanding General U. S. Continental Army Command 1 Commandant, U. S. Army Aviation School Fort Monroe, Virginia Fort Rucker, Alabama ATTN: ATSWD-G 1 President, U. S. Army Infantry Board 2 Commanding General Fort Henning, Georgia U. S. Army Combat Surveillance Agency 1124 N. Highiand Street, Arlington 1, Virginia 2 President, U. S. Army Artillery Hoard Fort Sill, Oklahoma 2 Chief, Research and Development Division Office of the Chief Signal Officer 1 President, U. S. Army Air Defense Board Department of the Army, Washington 25, D. C. Fort Bliss, Texas 8

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM 2900-129-R DISTRIBUTION LIST 2 1 December 1959- Effective Date Copies - Addressee Copies - Addressee 1 President, U. S. Army Aviation Board 2 Commander, Rome Air Development Center Fort Rucker, Alabama Griffiss Air Force Base, New York (l)ATTN: RCVSL-I I President, U. S. Army Airborne and Electronics Board (1) ATTN: RCWTR Fort Bragg, North Carolina 2 President, Army Intelligence Board 1 APGC (PGTRI) U. S. Army Intelligence Center, Fort Holabird, Maryland Eglin Air Force Base, Florida I Commanding Officer 1 Director, Air University Library U. S. Army Signal Electronic Research Unit Maxwell Air Force Base, Alabama Post Office Box 205, Mountain View, California ATTN: AUL-7971 1 Chief of Naval Operations (OP-37) Department of the Navy, Washington 25, D. C. 3 Commandant of the Marine Corps Headquarters, U. S. Marine Corps, Washington 25, D. C. 1 Office of the Chief of Naval Operations, Op-07T (2) ATTN: Code A02 Building T-3, Department of the Navy, Washington 25, D. C. (1) ATTN: Code A04E 4 Office of Naval Research (Code 463) 4 Central Intelligence Agency Department of the Navy 2430 E. Street, N. W., Washington 25, D. C. 17th and Constitution Avenue, N. W., Washington 25, D. C. ATTN: OCR Mail Room 2 Chief, Bureau of Ships Department of the Navy, Washington 25, D. C. 5 National Aeronautics and Space Administration ATTN: Code 687C 1520 H. Street, Northwest, Washington 25, D. C. 2 Director, U. S. Naval Research Laboratory 1 U. S. Army Air Defense Human Research Unit Washington 25, D. C. Fort Bliss, Texas ATTN: Code 2027 ATTN: Library 1 Commanding Officer, U. S. Navy Ordnance Laboratory 2 Combat Surveillance Project Corona, California Cornell Aeronautical Laboratory, Inc. ATTN: Library Box 168, Arlington 10, Virginia ATTN: Technical Library 1 Commanding Officer and Director U. S. Navy Electronics Laboratory, San Diego 52, California 1 The RAND Corporation ATTN: Library 1700 Main Street, Santa Monica, California 5 Department of the Air Force, Headquarters, USAF ATTN: Library Washington 25, D. C. (1) ATTN: AFOIN-1Bl 1 Chief, U. S. Army Armor Human Research Unit (1) ATTN: AFOAC-E/A Fort Knox, Kentucky (1) ATTN: AFDRD AT Administrative Assistant (1) ATTN: Directorate of Requirements (1) ATTN: AFCIN-3B3b 4 Commander in Chief 1 Chief Scientist, Research and Development Division Headquarters, Strategic Air Command Office of the Chief Signal Officer Offutt Air Force Base, Nebraska Department of the Army,- Washington 25, D. C. (2) ATTN: DINC (2) ATTN: DORQP 1 Stanford Research Institute, Document Center Menlo Park, California 4 Headquarters, Tactical Air Command ATTN: Acquisitions Langley Air Force Base, Virginia (1) ATTN: TOOA 1 Operations Research Office (3) ATTN: TORQ The Johns Hopkins University 6935 Arlington Road, Bethesda, Maryland 1 Commander, Air Technical Intelligence Center Washington 14, D. C. Wright-Patterson Air Force Base, Ohio ATTN: Chief Intelligence Division ATTN: AFCIN-4B/a 10 ASTIA (TIPCR) 1 Columbia University, Electronics Research Laboratories Arlington Hall' Station, Arlington 12, Virginia 632 W. 125th Street, New York 27, New York 8 Commander, Wright Air Development CenterATN TeciaLbry Wright-Patterson Air Force Base, Ohio TBRU: Commander, Rome Air Development Center Griffiss Air Force Base, New Turk (7) ATTN: WCLROR (1)ATTN: WCOSI -Library ATTN: RCSSTL-I1 9

WILLOW RUN LABORATORIES TECHNICAL MEMORANDUM 2900-129-R DISTRIBUTION LIST 2 1 December 1959- Effective Date Copies - Addressee Copies - Addressee 2 Cornell Aeronautical Laboratory, Inc. 2 Director, Human Resources Research Office 4455 Genesee Street The George Washington University Buffalo 21, New York P. 0. Box 3596, Washington 7, D. C. ATTN: Librarian ATTN: Library THRU: Bureau of Aeronautics Representative 1 The U. S. Army Aviation BRU 4455 Genesee Street p 0 B 4 F Alabama Buffalo 21, New York 1 Control Systems Laboratory 1 U. S. Continental Army Command Liaison Officer University of Illinois, Urbana, Illinois Project MICHIGAN, Willow Run Laboratories Ypsilanti, Michigan ATTN: Librarian THRU: ONR Resident Representative 1 Commanding Officer, U. S. Army Liaison Group 1209 W. Illinois Street Project MICHIGAN, Willow Run Laboratories Urbana, Illinois Ypsilanti, Michigan 10

+q + AD Div. 25/6 UNCLASSIFIED Willow Run Laboratories, U. of Michigan, Ann Arbor 1. Detectors- Performance Willow Run Laboratories, U. of Michigan, Ann Arbor 1. Detectors-Performance ULTIMATE SENSITIVITY AND PRACTICAL PERFORMANCE 2. Detectors - Sensitivity ULTIMATE SENSITIVITY AND PRACTICAL PERFORMANCE 2. Detectors-Sensitivity OF THE TELLURIUM PHOTOCONDUCTIVE DETECTOR by I. Title: Project MICHIGAN OF THE TELLURIUM PHOTOCONDUCTIVE DETECTOR by I. Title: Project MICHIGAN David F. Edwards. Memorandum of Project MICHIGAN. II. Edwards, David F. David F. Edwards. Memorandum of Project MICHIGAN. II. Edwards, David F. Dec 59. 7 p. incl. illus., 9 refs. III. U. S. Army Signal Corps Dec 59. 7 p. incl. ilus., 9 refs. III. U. S. Army Signal Corps (Memo no. 2900-129-R) IV. Contract DA-36-039 (Memo no. 2900-129-R) IV. Contract DA-36-039 (Contract DA-36-039 SC-78801) Unclassified memorandum SC-78801 (Contract DA-36-039 SC-78801) Unclassified memorandum SC-78801 Calculations of the ultimate sensitivity and measurement of the Calculations of the ultimate sensitivity and measurement of the practical performance have been made for the tellurium photo- practical performance have been made for the tellurium photoconductive detector. For the condition that detector sensitivity conductive detector. For the condition that detector sensitivity is limited by fluctuations of background radiation, the theo- is limited by fluctuations of background radiation, the theoretical NEP (noise equivalent power) at the peak of spectral retical NEP (noise equivalent power) at the peak of spectral sensitivity (X = 3.4 u) was calculated to be 5. 1 x 10-13 watt. sensitivity (k = 3.4 /) was calculated to be 5. 1 x 10-13 watt. For the "best" tellurium detector the measured value of NEP was For the "best" tellurium detector the measured value of NEP was 3. 1 x 10-13 watt.at the same wavelength and at the optimum 3. 1 x 10-13 watt at the same wavelength and at the optimum chopping frequency. These values indicate that the tellurium chopping frequency. These values indicate that the tellurium photoconductive detector is a background-limited detector and photoconductive detector is a background-limited detector and thus is an ideal detector. thus is an ideal detector. Armed Services Armed Services Technical Information Agency Technical Information Agency (over) UNCLASSIFIED (over) UNCLASSIFIED AD Div. 25/6 UNCLASSIFIED AD Div. 25/6 UNCLASSIFIED Willow Run Laboratories, U. of Michigan, Ann Arbor 1. Detectors- Performance Willow Run Laboratories, U. of Michigan, Ann Arbor 1. Detectors-Performance ULTIMATE SENSITIVITY AND PRACTICAL PERFORMANCE 2. Detectors - Sensitivity ULTIMATE SENSITIVITY AND PRACTICAL PERFORMANCE 2. Detectors- Sensitivity OF THE TELLURIUM PHOTOCONDUCTIVE DETECTOR by I. Title: Project MICHIGAN OF THE TELLURIUM PHOTOCONDUCTIVE DETECTOR by I. Title: Project MICHIGAN David F. Edwards. Memorandum of Project MICHIGAN. II. Edwards, David F. David F. Edwards. Memorandum of Project MICHIGAN. II. Edwards, David F. Dec 59. 7 p. incl. illus., 9 refs. III. U. S. Army Signal Corps Dec 59. 7 p. incl. illus., 9 refs. III. U. S. Army Signal Corps (Memo no. 2900-129-R) IV. Contract DA-36-039 (Memo no. 2900-129-R) IV. Contract DA-36-039 (Contract DA-36-039 SC-78801) Unclassified memorandum SC-78801 (Contract DA-36-039 SC-78801) Unclassified memorandum SC-78801 Calculations of the ultimate sensitivity and measurement of the Calculations of the ultimate sensitivity and measurement of the practical performance have been made for the tellurium photo- practical performance have been made for the tellurium photoconductive detector. For the condition that detector sensitivity conductive detector. For the condition that detector sensitivity is limited by fluctuations of background radiation, the theo- is limited by fluctuations of background radiation, the theoretical NEP (noise equivalent power) at the peak of spectral retical NEP (noise equivalent power) at the peak of spectral sensitivity (X = 3.4 /) was calculated to be 5. 1 x 10-13 watt. sensitivity (X = 3.4 u) was calculated to be 5. 1 x 10-13 watt. For the "best" tellurium detector the measured value of NEP was For the "best" tellurium detector the measured value of NEP was 3. 1 x 10-13 watt at the same wavelength and at the optimum 3. 1 x 10-13 watt at the same wavelength and at the optimum chopping frequency. These values indicate that the tellurium chopping frequency. These values indicate that the tellurium photoconductive detector is a background-limited detector and photoconductive detector is a background-limited detector and thus is an ideal detector. thus is an ideal detector. Armed Services Armed Services Technical Information Agency Technical Information Agency (over) UNCLASSIFIED (over) UNCLASSIFIED ~ -

AD UNCLASSIFIED AD UNCLASSIFIED UNITERMS UNITERMS Sensitivity Sensitivity Performance Performance Tellurium Tellurium Photoconductive Photoconductive Detector Detector Background radiation Background radiation Spectral sensitivity Spectral sensitivity Noise equivalent power Noise equivalent power UNCLASSIFIED UNCLASSIFIED AD UNCLASSIFIED AD UNCLASSIFIED UNITERMS UNITERMS Sensitivity Sensitivity Performance Performance Tellurium Tellurium Photoconductive Photoconductive Detector Detector Background radiation Background radiation Spectral sensitivity Spectral sensitivity Noise equivalent power Noise equivalent power UNCLASSIFIED UNCLASSIFIED

AD Div. 25/6 UNCLASSIFIED AD Div. 25/6 UNCLASSIFIED Willow Run Laboratories, U. of Michigan, Ann Arbor 1. Detectors - Performance Willow Run Laboratories, U. of Michigan, Ann Arbor 1. Detectors-Performance ULTIMATE SENSITIVITY AND PRACTICAL PERFORMANCE 2. Detectors - Sensitivity ULTIMATE SENSITIVITY AND PRACTICAL PERFORMANCE 2. Detectors - Sensitivity OF THE TELLURIUM PHOTOCONDUCTIVE DETECTOR by 1. Title: Project MICHIGAN OF THE TELLURIUM PHOTOCONDUCTIVE DETECTOR by I. Title: Project MICHIGAN David F. Edwards. Memorandum of Project MICHIGAN. II. Edwards, David F. David F. Edwards. Memorandum of Project MICHIGAN. II. Edwards, David F. Dec 59. 7 p. inc. illus., 9 refs. III. U. S. Army Signal Corps Dec 59. 7 p. incl. illus., 9 refs. III. U. S. Army Signal Corps (Memo no. 2900-129-R) IV. Contract DA-36-039 (Memo no. 2900-129-R) IV. Contract DA-36-039 (Contract DA-36-039 SC-78801) Unclassified memorandum SC-78801 (Contract DA-36-039 SC-78801) Unclassified memorandum SC-78801 Calculations of the ultimate sensitivity and measurement of the Calculations of the ultimate sensitivity and measurement of the practical performance have been made for the tellurium photo- practical performance have been made for the tellurium photoconductive detector. For the condition that detector sensitivity conductive detector. For the condition that detector sensitivity is limited by fluctuations of background radiation, the theo- is limited by fluctuations of background radiation, the theoretical NEP (noise equivalent power) at the peak of spectral retical NEP (noise equivalent power) at the peak of spectral sensitivity (. = 3.4 u) was calculated to be 5. I x l'13 watt. sensitivity (X- 3.41) was calculated to be 5. I x lo0- watt. For the "best" tellurium detector the measured value of NEP was - For the "best" tellurium detector the measured value of NEP was 3. 1 x1 o-13 watt at the same wavelength and at the optimum 3. 1 x 10-13 watt at the same wavelength and at the optimum chopping frequency. These values indicate that the tellurium chopping frequency. These values indicate that the tellurium photoconductive detector is a background-limited detector and photoconductive detector is a background-limited detector and thus is an ideal detector, thus is an ideal detector. Armed Services Armed Services Technical Information Agency Technical Information Agency (over) UNCLASSIFIED (over) UNCLASSIFIED AD Div. 25/6 UNCLASSIFIED AD Div. 25/6 UNCLASSIFIED Willow Run Laboratories, U. of Michigan, Ann Arbor 1. Detectors - Performance Willow Run Laboratories, U. of Michigan, Ann Arbor 1. Detectors-Performance ULTIMATE SENSITIVITY AND PRACTICAL PERFORMANCE 2. Detectors - Sensitivity ULTIMATE SENSITIVITY AND PRACTICAL PERFORMANCE 2. Detectors - Sensitivity OF THE TELLURIUM PHOTOCONDUCTIVE DETECTOR by 1. Title: Project MICHIGAN OF THE TELLURIUM PHOTOCONDUCTIVE DETECTOR by 1. Title: Project MICHIGAN David F. Edwards. Memorandum of Project MICHIGAN. II. Edwards, David F. David F. Edwards. Memorandum of Project MICHIGAN. II. Edwards, David F. Dec 59. 7 p. incl. illus., 9 refs. III. U. S. Army Signal Corps Dec 59. 7 p. incl. illus., 9 refs. III. U. S. Army Signal Corps (Memo no. 2900-129-R) IV. Contract DA-36-039 (Memo no. 2900-129-R) IV. Contract DA-36-039 (Contract DA-36-039 SC-78801) Unclassified memorandum SC-78801 (Contract DA-36-039 SC-78801) Unclassified memorandum SC-78801 Calculations of the ultimate sensitivity and measurement of the Calculations of the ultimate sensitivity and measurement of the practical performance have been made for the tellurium photo- practical performance have been made for the tellurium photoconductive detector. For the condition that detector sensitivity conductive detector. For the condition that detector sensitivity is limited by fluctuations of background radiation, the theo- is limited by fluctuations of background radiation, the theoretical NEP (noise equivalent power) at the peak of spectral retical NEP (noise equivalent power) at the peak of spectral sensitivity (X = 3.41) was calculated to be 5.l 10.13 watt. sensitivity (X = 3..4) was calculated to be 5. I 10-13 watt. For the'best" tellurium detector the measured value of NEP was For the "best" tellurium detector the measured value of NEP was 3. 1 x 1013 watt at the same wavelength and at the optimum 3. 1 x 10-13 watt at the same wavelength and at the optimum chopping frequency. These values indicate that the tellurium chopping frequency. These values indicate that the tellurium photoconductive detector is a background-limited detector and photoconductive detector is a background-limited detector and thus is an ideal detector, thus is an ideal detector. Armed Services Armed Services Technical Information Agency Technical Information Agency (over) UNCLASSIFIED (over) UNCLASSIFIED

AD UNCLASSIFIED AD UNCLASSIFIED UNITERMS UNITERMS Sensitivity Sensitivity Performance Performance Tellurium Tellurium Photoconductive Photoconductive Detector Detector Background radiation Background radiation Spectral sensitivity Spectral sensitivity Noise equivalent power Noise equivalent power o~c am OR LSD UNCLASSIFIED UNCLASSIFIED AD 00 UNCLASSIFIED AD UNCLASSIFIED UNITERMS UNITERMS Sensitivity Sensitivity Performance Performance Tellurium Tellurium Photoconductive Photoconductive Detector Detector Background radiation Background radiation Spectral sensitivity Spectral sensitivity Noise equivalent power Noise equivalent power UNCLASSIFIED UNCLASSIFIED