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STANFORD High-Power High-Speed Photodiode for LIGO II David Jackrel Ph.D. Candidate- Dept. of Materials Science & Eng. Advisor- Dr. James S. Harris March 15 th, 2001 LIGO-G010122-00-Z
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STANFORD Outline l Introduction l Photodiode Specifications & Development l Device Structure & Materials l Diode Electrical Characterization l Contact Resistance l I-V Characteristics l C-V Characteristics l Future Plans
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STANFORD Photodiode Specifications ParameterLIGO ILIGO II (old)LIGO II (new) Steady-State Power 0.6 W~10 W~1 W Operating Frequency 29 MHz ~100 MHz~100 kHz Quantum Efficiency 80% 90% Transient Damage 3 Joules / 10 ms 100 Joules / 10 ms (?) 100 Joules / 10 ms (?) Signal/Noise 1.4e10 Hz3.1e10 Hz Spatial Uniformity 1% RMS0.1% RMS Surface Backscatter 1e-4 / sr1e-6 / sr Detector Design Bank of 6(+) PDs1 PD (~3 mm dia.) 1 PD (1-3 mm dia.)
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STANFORD Photodiode Development l June 1999- Came on the project l Passed Quals l Began Training on MBE Machine and Processing Procedure l March 2000: 1 st Round Wafers l Materials Analysis l Electronic Properties Not Good l June 2000: 2 nd Round Wafers l Materials Analysis (Transmission, XRD, TEM, SEM) l Electronic Properties Characterized (TLM, I-V, C-V) l March 2001- Future: 3 rd Round Wafers l Electronic Properties l Optoelectronic Properties (Bandwidth, QE, Power Response)
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STANFORD P-I-N Device Characteristics l Large E-field in I- region Depletion Width Width of I- region Frequency response max ( sat /W I ) l RC time constant Tuned to a specific
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STANFORD Band Gap Diagram w/ Heterojunctions InAlAs Optically transparent to 1.06 m radiation l Absorption occurs in i-region N-layer: In.22 Al.78 As E g2 =2.0eV P-layer: In.22 Al.78 As E g2 =2.0eV I-layer: In.22 Ga.78 As E g1 =1.1eV n- i- p-
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STANFORD InGaAs/GaAs PD Structure P-I-N structure InGaAs for i-layer InAlAs for the n- and p- layers MBE Grading layer AR coating & Au/Pt contacts
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STANFORD Rear-Illuminated PD Advantages l High Power l Linear Response l High Speed Proposed PD (Rear-Illuminated)Conventional PD
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STANFORD MBE Surface Kinetics l Adsorption l Physisorption l Chemisorption l Surface migration l Incorporation l Thermal desorption
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STANFORD III-V Lattice Constants and Band Gaps l InAlAs and InGaAs well lattice matched l InAlAs much wider band gap
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STANFORD Lattice Mismatched Growth l Lattice Constant for In x Ga (1-x) As: a=5.6536+0.4054x In.4 Ga.6 As: h c 100 Å
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STANFORD TEM Images of Confined Dislocations Device Layers: -few dislocations Graded Buffer: -many dislocations
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STANFORD Graded Buffer Dislocations Biaxial stress in film causes dislocations to glide Misfit growth often results in surface striations Hsu, et al. (1992)
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STANFORD P- and N- Contacts
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STANFORD TLM (Transmission Line Model)
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STANFORD TLM Measurements: P-Contact l Short d, R, Slope l Long d, R, Slope R c = 8.2 /2 = 4.1 R s = 6.8 / 10 m = 0.68 / m
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STANFORD P-Contact Resistance (#673) 2
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STANFORD P-Contact Resistance (#649) 2
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STANFORD N-Contact Character Before Annealing: Not Ohmic (Schottky) After Annealing: Ohmic
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STANFORD N-Contact Resistance (After Anneal) Not very linear!
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STANFORD N- and P- Contact Resistance Resistance: Test Pad (1200 m 2 ) Resistance: Actual Contacts Resistivity N - Contact 2.1 0.36 m 0.00175 / m 2 P – Contact 4.5 2.8 m 0.00375 / m 2
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STANFORD I-V Characteristics (#673 Rectified, #649 Did not…)
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STANFORD I-V Characteristics: Reverse Bias l Wrong shape (defects?) l Large Current Values
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STANFORD I-V Characteristics: Semi-Log Plot IdealR-G Ideal: Slope = 11.4 q/kT = 38.6 n1 = 3.39 I 01 = 0.83 A R-G: Slope = 10.13 q/2kT = 19.3 n2 = 3.82 I 02 = 2.26 A I 0 = 3.09 A
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STANFORD Possible Explanation : Carrier Hopping l Defects in the I-layer l Alternative Transport Mechanism EvEv EcEc +-
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STANFORD I-V Characteristics: Light vs. Dark I-layer not fully depleted at zero bias…
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STANFORD C-V Characteristics (#673) Theoretical C 0.40nF depletion width 0.39 m
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STANFORD Capacitance, W D, and N D W D 0.5 m N D 10 16 cm -3 (@ 10V bias) W D 2.0 m N D 10 15 cm -3 (@ 5V bias) (Sze, S. M., Physics of Semiconductor Devices, 1969)
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STANFORD Future Plans: InGaAs/InAlAs l Less defects l Test QE l Buffer Layers l Defects l Materials Analysis l Front Illum. l Thin Substrate l Bandwidth l TLM l Test QE
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STANFORD Future Plans: Nd:YAG & Nitrides l Nd:YAG LASER Testing l Set-up at Stanford (w/ help from Mike Z.) l Compliment Faster Device Turn-Around l Nitride System: InGaNAs l Quaternary l No Graded Buffer l But, Still Rear-Illuminated
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