Presentation on theme: "High Operation Temperature (HOT) Split-off Band IR Detectors"— Presentation transcript:
1 High Operation Temperature (HOT) Split-off Band IR Detectors Viraj Jayaweera
2 Outline Introduction IR Range, Applications, Types of IR detectors Interfacial Workfunction Internal Photoemission (IWIP) DetectorsDetector Structure, HIWIP, HEWIP MechanismDetector Measurements and CharacterizationSplit-off Band DetectorsPossible Material Systems to Extend Spectral Range.Conclusion and Future Studies
3 Discovery of Infrared Sir Frederick William Herschel (1738-1822) musician and an astronomerfamous for his discovery of the planet Uranus in 1781Discover “calorific rays” in 1800 later renamed as “Infrared rays”
4 (the prefix infra means `below‘) What is Infrared (IR) ?(the prefix infra means `below‘)The electromagnetic spectrum includes gamma rays, X-rays, ultraviolet, visible, infrared, microwaves, and radio waves. The only difference between these different types of radiation is their wavelength or frequency.
5 Infrared is usually divided into 3 spectral regions Micro waveVisiblenear-IRmid-IRFar-IR0.8 – 5 m m mCan’t see (human eye)= 0.75 mSome animals can "see" in the infrared. For example, snakes in the pit viper family (e.g. rattlesnakes) have sensory "pits," which are used to detect infrared light. This allows the snake to find warm-blooded animals.
6 This is the radiation produced by the motion of atoms and molecules in an object. Any object which has a temperature above absolute zero (0 K) radiates infrared.personholding burning matchCatInfrared image of OrionLanding space shuttleApplication: biophysics, communication, remote sensing, medical imaging, security and astrophysics.
8 Human & vehicle at total darkness thermal image in white=hot mode same image in Black=hot modeHuman Suspect climbing over fence at 2:49 AM in total darknessSuspect attempting to burglarize vehicle at 1:47 AM in total darkness.
11 Structure of the Interfacial Workfunction Internal Photoemission Detector. Au contact layersTop Contact p++ GaAs<2.5μm~1.5mmN PeriodsGaAs (barrier)p+ GaAs (emitter)HomojunctionHeterojunctionAlGaAs (barrier)p+ GaAs (emitter)Bottom Contact p++ GaAsSubstrate(photo conductive type)
12 Barrier formed by Homojunction (n-type) HIWIP(Homojunction Interfacial Workfunction Internal Photoemission Detector)n+in+ doped GaAsGaAse-hνΔΔEFECnzero biasbiasedBarrier formed by Homojunction (n-type)(Δ comes from doping)JAP 77, 915 (1995)
13 HEIWIP Barrier formed by Heterojunction (p-type) (HEterojunction Interfacial Workfunction Internal Photoemission Detector)p+ GaAsAlGaAsh+ip+hνΔbiased(not quantized)Δzero biasBarrier formed by Heterojunction (p-type)(Δ comes from Al fraction and doping)Absorption is due to free carriersInterface is sharp (no space charge)APL 78, 2241 (2001)APL 82, 139 (2003)
14 Measurements and Characterization (IVT) Current Voltage Temperature measurementsUsing IVT measurementsUniformity of sample (dark current density vs. voltage plot).Dark Current Variation with bias Voltage and Temperature.Background Limited Performance (BLIP) Temperature.Experimental Δ (slope of ln(I/T1.5) vs. 1/T plot)Switching SystemSource MeterHe close cycle refrigerator headVacuumSampleTemperature ControllerPCVLog (I)Cool fingerRadiation shield
15 time (mirror position) Measurements and Characterizationtime (mirror position)output energySpectral ResponseSourceMoving mirrorSampleRLOutputWave numberoutput energyFurrier transformationBeam splitteroThreshold wavelengthFixed mirrorFTIR Spectrometer
17 Split-off Response of the Detector HE0204 Under Different Temperatures
18 Detector mechanism consisting of three processes kHeavy Hole BandLight Hole BandSplit-off BandEfESODetector mechanism consisting of three processesPhotoabsorption. (produces excited carriers)Carrier escape.Sweep out and collection of the escaped carriers.
19 Free Carrier Absorption Response Mechanism ILight/Heavy Hole BandEkEfΔL/HFree Carrier AbsorptionescapeHeavy Hole BandLight Hole BandΔSOSplit-off BandSplit-off BandThe photoexcitation process consists of the standard free carrier absorption.
20 Response Mechanism II Light/Heavy Hole Band E k Ef ΔL/H Split-off AbsorptionHeavy Hole BandescapeLight Hole BandscatteringΔSOSplit-off BandSplit-off Banddirect photoabsorption to the split-off band, followed by a scattering to the light/heavy hole band.
21 Response Mechanism III Light/Heavy Hole BandEkEfΔL/HSplit-off AbsorptionHeavy Hole BandLight Hole BandΔSOSplit-off BandSplit-off BandescapeSingle indirect photoabsorption into the split-off band.
22 Response Mechanism IV Light/Heavy Hole Band E k Ef ΔL/H Split-off AbsorptionHeavy Hole BandescapeLight Hole BandscatteringΔSOSplit-off BandSplit-off Bandindirect photoabsorption, followed by a scattering event to the light or heavy hole band.
23 The Split-off Band Offset Energy for Different Materials ΔSO (meV)λSO(μm)Elh(meV)EsoInN3410-790-793GaN2062-1840-1860AlN1965-2640-2660InP10811-140-248GaP8016-470-550AlP7018-940-1010InAs3903.2+210-180GaAs3403.6+0-340AlAs2804.4-530-810The energies of the light/heavy hole band (Elh) and the split-off hole band (ESO) relative to the valance band maximum of GaAs.
24 Conclusion and Future Studies High Operating TemperatureThe devices tested with a threshold of ~20 µm showed a maximum operating temperature of 130 K. By reducing the threshold to ~5 µm, the operating temperature should be increased to 300 K with D* of ~5×109 Jones.Increase Quantum efficiencyAbsorption efficiency can be increase byIncreasing the no of emitter layersIncreasing the doping to the maximum possible valueDevice Design for a 15 μm Detector Operating at 200KDevice will based on p-doped GaP emitters and undoped AlGaP barriers.