1. STANFORD High-Power High-Speed Photodiode for LIGO II David Jackrel Ph.D. Candidate- Dept. of Materials Science & Engineering Advisor- Dr. James S. Harris n LIGO-G000241-00-D

2. STANFORD Outline l Motivation l Diode structure & Materials choices l Graded buffer layer l Processing procedure l Simulations l Absorption QE l Frequency response l Electronic noise l Experimental results & Future work

3. 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

4. STANFORD Photodiode Advantages l High Power l Linear Response l Optimum E g l High Speed Proposed PD (Rear-Illuminated)Conventional PD

5. STANFORD InGaAs/GaAs PD Structure InGaAs for i-layer InAlAs for the n- and p- layers P-I-N structure MBE Grading layer AR coating & Au/Pt contacts

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

8. 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

9. STANFORD Solution: Graded Buffer Layer l Dislocations propagate downwards l Active region free from dislocations Susan Marie Lord, Ph.D Thesis, Stanford Univ., 1993

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

11. STANFORD Rear Contact (#637)

12. STANFORD Processing: Slide #1

13. STANFORD Processing: Slide #2

14. STANFORD Processing: Slide #3

15. STANFORD Processing: Slide #4

16. STANFORD Absorption Simulation (1)

17. STANFORD Absorption Simulation (2)

18. STANFORD Frequency Response Simulation (1)

19. STANFORD Frequency Response Simulation (2)

20. STANFORD Electronic Noise

21. STANFORD Electronic Noise Simulation (1)

22. STANFORD Electronic Noise Simulation (2)

23. STANFORD Electronic Noise Simulation (3)

24. STANFORD I-V Curves: Mounted Diodes

25. STANFORD Possible Solution- Insulating Layer

26. STANFORD Diagnostics by Processing Step I.) MBE Growth  Transmission  XRD  TEM II.) AR Coating  Transmission III.) N- and P- Contacts  TLM  I-V Measurements  C-V Measurements IV.) Etch Mesa  I-V Measurements  C-V Measurements  Low Power LASER testing V.) Insulating Layer  I-V Measurements VI.) Mounting to Heat sink & Wire Bonding  I-V Measurements  High Power LASER Testing (10W) i. QE ii. Response Linearity iii. Bandwidth iv. Power Dissipation

27. STANFORD Transmission Spectra

28. STANFORD XRD Measurements

29. STANFORD Compositions- XRD & Transmission

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

31. STANFORD Absorption Data: #649 (w/ ARC)

32. STANFORD GaAs Substrate Absorption