Presentation on theme: "High Operation Temperature (HOT) Split-off Band IR Detectors Viraj Jayaweera."— Presentation transcript:
High Operation Temperature (HOT) Split-off Band IR Detectors Viraj Jayaweera
1.Introduction IR Range, Applications, Types of IR detectors 2.Interfacial Workfunction Internal Photoemission (IWIP) Detectors Detector Structure, HIWIP, HEWIP Mechanism 3.Detector Measurements and Characterization 4.Split-off Band Detectors 5.Possible Material Systems to Extend Spectral Range. 6.Conclusion and Future Studies Outline
Sir Frederick William Herschel ( ) musician and an astronomer famous for his discovery of the planet Uranus in 1781 Discover “calorific rays” in 1800 later renamed as “Infrared rays” Discovery of Infrared
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.
Visible Micro wave near-IRmid-IRFar-IR = 0.75 m Can’t see (human eye) Infrared is usually divided into 3 spectral regions 0.8 – 5 m m m Some 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.
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. Landing space shuttle person holding burning match Cat Infrared image of Orion Application: biophysics, communication, remote sensing, medical imaging, security and astrophysics.
Human & vehicle at total darkness thermal image in white=hot mode same image in Black=hot mode Human Suspect climbing over fence at 2:49 AM in total darkness Suspect attempting to burglarize vehicle at 1:47 AM in total darkness.
Substrate Bottom Contact p ++ GaAs p + GaAs (emitter) AlGaAs (barrier) Top Contact p ++ GaAs N Periods 400 μm Structure of the Interfacial Workfunction Internal Photoemission Detector. Heterojunction GaAs (barrier) p + GaAs (emitter) Homojunction (photo conductive type) Au contact layers <2.5μm ~1.5mm
Barrier formed by Homojunction (n-type) (Δ comes from doping) n + doped GaAs GaAs Δ zero bias e-e- in+n+ ECnECn EFEF hνhν Δ biased JAP 77, 915 (1995) HIWIP (Homojunction Interfacial Workfunction Internal Photoemission Detector)
Absorption is due to free carriers Interface is sharp (no space charge) HEIWIP (HEterojunction Interfacial Workfunction Internal Photoemission Detector) Barrier formed by Heterojunction (p-type) (Δ comes from Al fraction and doping) APL 78, 2241 (2001) APL 82, 139 (2003) AlGaAsp + GaAs Δ h+h+ ip+p+ hνhν Δ biased zero bias (not quantized)
Measurements and Characterization (IVT) Current Voltage Temperature measurements Radiation shield Cool finger Vacuum Sample Switching System Source Meter Temperature Controller He close cycle refrigerator head PC V Log (I) Using IVT measurements Uniformity 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/T 1.5 ) vs. 1/T plot)
Measurements and Characterization Spectral Response Moving mirror Fixed mirror Source Beam splitter Sample RLRL Output time (mirror position) output energy Wave number output energy Furrier transformation FTIR Spectrometer o Threshold wavelength
Split-off Response of the Detector HE0204 Under Different Temperatures
E k Heavy Hole Band Light Hole Band Split-off Band EfEf E SO Detector mechanism consisting of three processes 1. Photoabsorption. (produces excited carriers) 2. Carrier escape. 3. Sweep out and collection of the escaped carriers.
E k Heavy Hole Band Light Hole Band Split-off Band EfEf Δ L/H escape Free Carrier Absorption Light/Heavy Hole Band Split-off Band Δ SO Response Mechanism I The photoexcitation process consists of the standard free carrier absorption.
E k Heavy Hole Band Split-off Band EfEf Δ L/H escape Split-off Absorption Light/Heavy Hole Band Split-off Band scattering Δ SO Light Hole Band direct photoabsorption to the split-off band, followed by a scattering to the light/heavy hole band. Response Mechanism II
E k Heavy Hole Band Split-off Band EfEf Δ L/H escape Split-off Absorption Light/Heavy Hole Band Split-off Band Δ SO Light Hole Band Response Mechanism III Single indirect photoabsorption into the split-off band.
E k Heavy Hole Band Split-off Band EfEf Δ L/H escape Split-off Absorption Light/Heavy Hole Band Split-off Band scattering Δ SO Light Hole Band Response Mechanism IV indirect photoabsorption, followed by a scattering event to the light or heavy hole band.
Material Δ SO (meV) λ SO (μm) E lh (meV) E so (meV) InN GaN AlN InP GaP AlP InAs GaAs AlAs The Split-off Band Offset Energy for Different Materials The energies of the light/heavy hole band (E lh ) and the split-off hole band (E SO ) relative to the valance band maximum of GaAs.
Conclusion and Future Studies 1.High Operating Temperature The 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 ~5×10 9 Jones. 2.Increase Quantum efficiency Absorption efficiency can be increase by Increasing the no of emitter layers Increasing the doping to the maximum possible value 3.Device Design for a 15 μm Detector Operating at 200K Device will based on p-doped GaP emitters and undoped AlGaP barriers.