Large spontaneous emission rate enhancement in a III-V antenna-led Seth A. Fortuna 1, Christopher Heidelberger 2, Nicolas M. Andrade 1, Eugene A. Fitzgerald 2, Eli Yablonovitch 1, and Ming C. Wu 1 1 University of California, Berkeley; Dept. of Electrical Engineering and Computer Sciences 2 Massachusetts Institute of Technology; Dept. of Materials Science and Engineering
Energy efficient on-chip optical interconnect link Electrical interconnect Optical interconnect Light source Photodetector waveguide Wires Transistors Driver Receiver Minimum energy per bit: ~ CV 2 pj/bit/cm Minimum energy per bit: ~aj/bit Drawing inspired by E. Macii, Ultra Low-Power Electronics and Design. Page 2
Light intensity Modulation bandwidth Light sources for on-chip optical interconnect LASER Light Emitting Diode (LED) Nanoscale Efficient Slow 50GHz I th Current LED Current 200MHz Page 3
Spontaneous emission λ 0 ~1000nm Page 4
Light intensity Modulation bandwidth Antenna-LED for optical communication LASER Antenna-LED Antenna-LED +100GHz 50GHz I th Current Current 200MHz Page 5
Examples of antenna-enhanced emitters Kinkhabwala et al. Stanford. Nat. Phot. 2009. Hoang et al. Duke. Nat. Comm. 2015. Arbel et al. Technion. Opt. Exp. 2011. Page 6
Electrically-injected III-V antenna-led 50nm interconnect nanoled ridge Ag Ag n-inp InGaAs(P) - Cavity-backed slot antenna 250nm p-inp + Electrical injection is straight forward Directional light emission for coupling into waveguide > 100 GHz direct modulation rate Page 7
Antenna-enhanced electroluminescence ~100-fold increase in spontaneous emission rate III-V No antenna III-V No antenna Antenna-LED Quantum efficiency τ nr τ rad Page 8
Increase QE 200-fold enhancement of spontaneous emission rate III-V 6nm InGaAs multiple quantum wells Page 9
Time-resolved light emission III-V No antenna III-V Antenna-LED Page 10
High efficiency despite high surface recomb. velocity III-V n p InGaAs active region SRV = 10 4 cm/s Vf = 0.75 V Surface Injected current Surface recombination (2kT current) Radiative recombination (kt current) Efficient Page 11
Process induced surface damage Time-resolved photoluminescence Surface needs to be protected during fabrication! Page 12
Improved process with ultra-clean surface 1 Dry etch ridge Time-resolved photoluminescence 2 Deposit sacrificial Al 2 O 3 (expose to plasma, anneal, etc.) 3 Strip sacrificial Al 2 O 3 (TMAH) 11/8/2017 Page 13
Efficient waveguide Coupling Waveguide coupling efficiency Perspective view of the parabolic reflector Cross-section of simulated power flow Acknowledgement: Nicolas Andrade (UC Berkeley) Page 14
Summary Demonstrated 200-fold enhancement of spontaneous emission rate of electrically injected nanoscale III-V LED High efficiency possible despite large surface recombination velocity of III-V surface Ultra-clean InGaAs surface using sacrificial Al 2 O 3 Efficient and broadband coupling to single-mode on-chip waveguide is possible. 11/8/2017 Page 15
Financial support Acknowledgments NSF Science and Technology Center for Energy Efficient Electronics Science (E 3 S) Air Force Office of Scientific Research (AFOSR) Berkeley Sensor & Actuator Center (BSAC) Technical support UC Berkeley Marvell Nanolab staff
Backup 11/8/2017 2017 Fall Retreat Page 17
Electrically-injected III-V antenna-led Dielectric filled cavity Cavity-backed slot antenna III-V pn junction - + n p Far-field radiation Far-field radiation Page 18
Antenna mode Top view Advantages: Electrical injection is straight forward Self-aligned Directional light emission Thermal heat-sink 11/8/2017 Page 19
Spontaneous emission enhancement measurement Antenna enhancement directly increases quantum efficiency Injected carriers Radiative Nonradiative 11/8/2017 Page 20
Can radiative recombination ever exceed non-radiative recombination? 20nm I nr Injected current III-V Radiative Nonradiative
Electroluminescence measurement Optical image (frontside) Antenna-LED Measurement setup Semiconductor parameter analyzer i f ~1μA Antenna-LED chip n-contact Electroluminescence p-contact Microscope objective n-contact Spectrograph/ IR camera 35 μm Polarizer Lens
Toward >100 GHz direct modulation rate at high efficiency Theoretical 3dB frequency and efficiency Efficiency MOCVD growth by Fitzgerald group (MIT) Multiple quantum well (MQW) active region Doped active region and cladding layers Highly doped n-contact layer
Electrically-injected III-V antenna-led Top view Advantages: Electrical injection is straight forward Self-aligned fabrication Directional light emission for coupling into waveguide > 100 GHz direct modulation rate Cut-away drawing 11/8/2017 Page 24