1. 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

2. 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

3. 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.)

4. 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)

5. 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

6. 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-

7. 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

8. STANFORD Rear-Illuminated PD Advantages l High Power l Linear Response l High Speed Proposed PD (Rear-Illuminated)Conventional PD

9. STANFORD MBE Surface Kinetics l Adsorption l Physisorption l Chemisorption l Surface migration l Incorporation l Thermal desorption

10. STANFORD III-V Lattice Constants and Band Gaps l InAlAs and InGaAs well lattice matched l InAlAs much wider band gap

11. 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

12. STANFORD TEM Images of Confined Dislocations Device Layers: -few dislocations Graded Buffer: -many dislocations

13. STANFORD Graded Buffer Dislocations Biaxial stress in film causes dislocations to glide Misfit growth often results in surface striations Hsu, et al. (1992)

14. STANFORD P- and N- Contacts

15. STANFORD TLM (Transmission Line Model)

16. 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

17. STANFORD P-Contact Resistance (#673) 2

18. STANFORD P-Contact Resistance (#649) 2

19. STANFORD N-Contact Character Before Annealing:  Not Ohmic (Schottky) After Annealing:  Ohmic

20. STANFORD N-Contact Resistance (After Anneal)  Not very linear!

21. 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

22. STANFORD I-V Characteristics (#673 Rectified, #649 Did not…)

23. STANFORD I-V Characteristics: Reverse Bias l Wrong shape (defects?) l Large Current Values

24. 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

25. STANFORD Possible Explanation : Carrier Hopping l Defects in the I-layer l Alternative Transport Mechanism EvEv EcEc +-

26. STANFORD I-V Characteristics: Light vs. Dark  I-layer not fully depleted at zero bias…

27. STANFORD C-V Characteristics (#673) Theoretical C  0.40nF  depletion width  0.39  m

28. 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)

29. 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

30. 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