1. STANFORD Advanced LIGO High-Power Photodiodes David Jackrel, PhD Candidate Dept. of Materials Science and Engineering Advisor: James S. Harris LSC Conference, LLO March 17 th -21 st, 2003 LIGO-G030069-00-Z

2. STANFORD Outline l Introduction l High-Power Results l High Efficiency Process l Predictions

3. STANFORD Photodiode Specifications ParameterLIGO IAdvanced LIGO Steady-State Power 0.6 W~1 W Operating Frequency  29 MHz 100 kHz ~ 180 MHz Quantum Efficiency  80%  90% Detector Design Bank of 6(+) PDs 1 PD

4. STANFORD GaInNAs vs. InGaAs GaInNAs 25% InGaAs 53% InGaAs 1064nm light  1.13eV

5. STANFORD InGaAs vs. GaInNAs PD Designs 2  m GaInNAs lattice-matched to GaAs!

6. STANFORD Heterojunction Band Gap Diagram N-layer: In.22 Al.78 As or GaAs E g2 =2.0- 1.4eV P-layer: In.22 Al.78 As or GaAs E g2 =2.0- 1.4eV I-layer: In.22 Ga.78 As, or Ga.88 In.12 N.01 As.99 E g1 =1.1eV n- i- p- InAlAs and GaAs transparent at 1.064  m  Absorption occurs in I-region (in  E-field  )

7. STANFORD Rear-Illuminated PD Advantages Conventional PDAdv. LIGO Rear-Illuminated PD l High Power l Linear Response l High Speed

8. STANFORD DC Device Response

9. STANFORD DC Device Efficiency Ext. Efficiency Optical Power (mW) Bias (Volts)

10. STANFORD High Efficiency Detector Process (1) 1. Deposit and Pattern P-Contact 2. Etch Mesa – H 2 SO 4 :H 2 O 2 :H 2 0 and Passivate in (NH 4 ) 2 S+ 3. Encapsulate Exposed Junction 4. Flip-Chip Bond - N+ GaAs Substrate - Epitaxial Layers - Au Contacts - Polyimide Insulator - SiN x AR Coating - AlN Ceramic

11. STANFORD High Efficiency Detector Process (2) 6. Deposit AR Coating & N-Contact 7. Saw, Package and Wire-Bond - N+ GaAs Substrate - Epitaxial Layers - Au Contacts - Polyimide Insulator - SiN x AR Coating - AlN Ceramic 5. Thin N+ GaAs Substrate

12. STANFORD Surface Passivation Results

13. STANFORD Predictions Diameters3mm4.5mm150um Saturation Power Devices OldNew 300mW~1W~2mW Bandwidth Devices OldNew 3MHz~1MHz~1GHz

14. STANFORD Conclusion l High-Power Results l 300mW (@ 3MHz B.W.) l 60% External Efficiency l High-Efficiency Process l < -30 Volts realized (on un-mounted devices) l Working out processing l Predictions (by Next LSC…) l 1 Watt (@ 1MHz B.W.) l 90% External Efficiency

15. STANFORD MBE Crystal Growth l Effusion cells for In, Ga, Al l Cracking cell for As l Abrupt interfaces l Chamber is under UHV conditions to avoid incorporating contaminants l RHEED can be used to analyze crystal growth in situ due to UHV environment l T=450-600  C N Plasma Source Atomic source of nitrogen needed  Plasma Source!

16. STANFORD P-I-N Device Characteristics l Large E-field in I- region Depletion Width  Width of I- region l RC time constant Absorbs a specific

17. STANFORD Full Structure Simulated by ATLAS

18. STANFORD DC Device Efficiency

19. STANFORD Free-Carrier Absorption N+ S-I

20. STANFORD Surface Passivation Results (2)

21. STANFORD (NH 4 ) 2 S+ Surface States (Green and Spicer, 1993) GaAs(111)AGaAs(111)B