1. High-Power High-Efficiency Photodiode for Advanced LIGO
LIGO-G Z
David Jackrel
Ph.D. Candidate- Dept. of Materials Science & Eng.
Advisor- Dr. James S. Harris
August 14th, 2001

2. Outline Introduction Experimental Results Development Plan
Photodiode Specifications
Device Structure & Materials
Experimental Results
DC Response
RF Response
Development Plan
InGaAs
GaInNAs

3. Photodiode Specifications?
Parameter
LIGO I
Advanced LIGO
Steady-State Power
0.6 W
1~10 W
Operating Frequency
 29 MHz
100 kHz ~ 180 MHz
Quantum Efficiency
 80%
 90%
Detector Design
Bank of 6(+) PDs
1 PD

4. P-I-N Device Characteristics
Large E-field in I- region
Depletion Width  Width of I- region
RC time constant
Tuned to a specific 

5. Heterojunction Band Gap Diagram
 = 1.064m  h = 1.17eV
Absorption occurs in i-region
InAlAs Optically transparent to 1.06m radiation n- p- i-
N-layer:
In.22Al.78As
Eg2=1.8eV
I-layer:
In.22Ga.78As
Eg1=1.1eV
P-layer:
In.22Al.78As
Eg2=1.8eV

6. Rear-Illuminated PD Advantages
High Power
High Speed
Linear Response
Conventional PD
Adv. LIGO Rear-Illuminated PD

7. InGaAs/GaAs PD Structure
MBE
GaAs Substrate
InGaAs for i-layer
InAlAs for the n- and p- layers
Graded Buffer layer
AR coating & Au/Pt contacts
2 m

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

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

10. Nd:YAG (NPRO) PD Test Setup
RF Amplitude
Modulator
Power
Meter PD
Power
Control
NPRO
(800mW)

11. Quantum Efficiency: #673
30%
Loss

12. QE: Power & Bias Effects

13. DC Response Linearity: #673

14. RF Response: 3dB Bandwidth
~4MHz, 3dB-Bandwidth
 ~5nF Capacitance

15. C-V Characteristics (#673)
 depletion width 1.44 m ~2.16m

16. InGaAs Development Plan
Goals: by Sept. 2002…
90% QE
Thin substrates to 50m-100m
Maximize Bandwidth
Optimize illuminated area

17. GaInNAs Lattice-Matched to GaAs
GaInNAs- Adv LIGO
InGaAs- LIGO I PD

18. Conclusion Introduction Experimental Results Development Plan
Photodiode Specifications
Device Structure & Materials
 InGaAs RI PIN PD
Experimental Results
DC Response
 70% QE
RF Response
 4MHz 3-dB Bandwidth
Development Plan
InGaAs
GaInNAs