InP/InGaAsP/InGaAs SWIR APDs Separate absorption, grading, charge, and multiplication (SAGCM) structure Carrier collection in absorber: low but finite field in absorber (avoid tunneling) Multiplication gain: high field for impact ionization i - n + InP buffer InGaAsP grading InP charge InP cap SiNx passivation p-contact metallization InP substrate n-contact metallization optical input E InGaAs absorption multiplication region p+-InP diffused region anti-reflection coating Al0.6InAsSb multiplication Long-wavelength absorber

External Quantum Efficiency 60% 30% 50% 40% 70%

External Quantum Efficiency 60% 30% 50% 40% 70%

AlInAsSb SACM APD p-type contact blocking layer graded bandgap p+:GaSb 11019, 30 nm p+: AlxIn1-xAlyAs1-y x = 0.7 to 0.4, 100 nm p+: Al0.7In0.3As0.3Sb0.7 21018, 100 nm n+: GaSb, 11018, buffer n+:GaSb Substrate n-: Al0.4In0.6As0.3Sb0.7, 1,000 nm p+: AlxIn1-xAlyAs1-y x = 0.4 to 0.7, 100 nm p: Al0.7In0.3As0.3Sb0.7 1.251017, 150 nm n-: Al0.7In0.3As0.3Sb0.7, 1,000 nm absorption layer multiplication layer n-type contact charge layer p-type contact graded bandgap blocking layer Electric field

AlInAsSb SACM Current-Voltage Characteristics 10-9 10-8 10-7 10-6 10-5 10-4 10-3 Gain Photocurrent Dark current

Noise Measurement of AlInAsSb k= 0.07 ↑ Measured with a 100 µm device. k= 0.05 from fitting, <M>=1.33 @ punch-through.

APD Comparison 100 Gb/s Ethernet 400 Gb/s Ethernet 2q(iph+idark)M2F(M)