U.S. Army Research, Development and Engineering Command
BLACK SILICON FOR NEXT-GENERATION INFRARED SENSORS Dr. Jeffrey Warrender August 2012 Collaborators
ARDEC Jay Mathews, V. Swaminathan
RPI Peter Persans, Dave Hutchinson, Alex Katauskas
Mike Aziz, Austin Akey, Dan Recht, Aurore Said, Eric Mazur, Harvard Meng-Ju Sher, Yuting Lin
Tonio Buonassisi, Mark Winkler, Joe Sullivan, Christie Simmons, MIT Jeff Grossman, Elif Ertekin, Silvija Gradecak, Matt Smith Australian National James Williams, Supakit Charnvanichborikarn University American Malek Tabbal University Beirut Konan University Ikurou Umezu (Japan)
Fukuoka University Atsushi Kohno
Army Research Lab P. Wijewarnasuriya, Parvez Uppal, Fred Semendy
Sionyx, Inc. Martin Pralle, Jim Carey DoD applications require Infrared light
Situational Precision-guided munitions Awareness
Hyperspectral weapon sights Photovoltaics
Standoff Explosive Detection Available Materials RT operation Si Requires cooling HgCdTe InGaAs InSb Ge PbSe
eV nm 1550 nm Seekers Seekers PGMs
Range finders, Designators Hyperspectral weapon sight
NVGs FLIR FLIR
Raman, LIBS SWIR Imaging THz Silicon-based IR optoelectronics
Silicon is… Ubiquitous Inexpensive + Well-characterized Easy to integrate with readout circuitry
- Non-absorbing for wavelengths > 1100 nm
Can we dope Si to see IR response? Hyperdoping: Create mid gap states
Conduction band Conduction band Conduction band
e- e- e- hν< EG hν< EG hν< EG
h h EG
hν> EG Impurity conc. ↑, int. band broadens
h 318 Valence band Valence band Valence band Ordinary Si “Lightly” HD-Si “Heavily” HD-Si Chalcogen dopants in silicon Chalcogen dopants in silicon
Binding energies of chalcogen centers in Si Conduction band
92 82 110 116 188 206 214 248 318 307 371 390
1132 meV 1132 593 614
All energies in meV Valence band
Sulfur Selenium
Janzen et al., Phys Rev B (1984) Spiked Black Silicon Pulsed laser Harvard (Mazur)/ Sionyx
Vacuum system
Si
SF6 Crouch et al, Appl Phys Lett (2004) Spiked Black Silicon Pulsed laser Harvard (Mazur)/ Sionyx
Vacuum system
Si
SF6 Crouch et al, Appl Phys Lett (2004) Flat Black Silicon Harvard (Aziz)/ ARDEC Ion-implant chalcogen
(1) (S, Se, Te) into p-Si
Si+Ch 300 nm 300 p-Si
Kim et al, Appl Phys Lett (2006) Tabbal et al, JVST B (2007) Bob et al, submitted to J Appl Phys Flat Black Silicon Harvard (Aziz)/ ARDEC (1) Ion-implant chalcogen Pulsed-laser melting (PLM) (S, Se, Te) into p-Si (2) “heals” implant damage
ns laser, 2
~1.7 J/cm
Si+Ch 300 nm 300 p-Si
Crystalline Si, supersaturated in Ch, n- type Kim et al, Appl Phys Lett (2006) Tabbal et al, JVST B (2007) Bob et al, JAP (2010) Benet Labs’ Black Silicon setup
Nd:YAG laser λ/2 plate 1064/532/355/266 nm Ar ion laser (CW) 4 ns pulse duration 488 nm 1.2 W
Motorized Fast stage photodiode Lenses
Vacuum chamber Oscilloscope Relay-image w/pinhole Characterization Logical Flow
Absorption
• Absorption vs. wavelength • Depth profile Device Structure Optoelectronic • Modeling Properties Properties
• Dopant profile • Photoconductivity • Detectivity • Surface roughness • Spectral responsivity • Noise Equivalent • Crystallinity Electronic • Quantum Efficiency Power • Local dopant properties • IV curves • Dark current environment • Gain • Carrier sign, concentration, mobility, lifetime • Hall effect
6.1 6.2 Dopant depth profile evolution Structure
1.00E+021 as-implanted (SIMS) 1 shot (SIMS)
8.00E+020 1 shot (calculation,
) v =0 nm/s) -3 evap
6.00E+020 1 shot (calculation, v =0.27 nm/s)
evap
4.00E+020 concentration(cm 2.00E+020
0.00E+000
0 100 200 300 depth (nm) Bob et al, JAP (2010)
BUT, as laser shots ↑, vevap↓ Our approach to studying hyperdoped silicon
A mobile The carrier Path to A photon is The carrier is carrier is reaches a detection absorbed collected generated contact
No free No carriers Obstacles to No carriers carriers are reach the detection are collected generated contacts
How does Is the How far can Major absorption excitation the excitation questions occur? mobile? travel?
Experimental Direct optical Photoexcitation Transport approaches probes measurements measurements Absorption
Absorption
Winkler, Ph.D. thesis, Harvard (2010) Responsivity comparison
Optoelectronic Sionyx Properties ARDEC/Harvard 1000 Si diode 100 Si:S, 12V, no anneal
10
1
0.1 Responsivity(A/W) 0.01 800 1000 1200 1400 wavelength (nm) Said et al, APL (2011) An apparent conundrum
Strong, broadband absorption… …but no device response Possible reconciliation
Conduction band Conduction band Conduction band
e- e- e- hν< EG hν< EG hν< EG
h h EG
hν> EG Impurity conc. ↑, int. band broadens
h 318 Valence band Valence band Valence band Ordinary Si “Lightly” HD-Si “Heavily” HD-Si Other Strategies to Try Less dopant Change dopant Add dopant Conduction band Conduction band Conduction band Conduction band
Valence band Valence band Valence band Valence band Move states out of Move states Compensate conduction band deeper into band impurity band gap The Larger Black Silicon Universe Stakeholders Research Groups
Harvard Aziz System ARDEC-Benet Extended IR response, Warrender optoelectronic CERDEC- Digital RPI NVESD Nightvision X charazterization Persans USMC CLRF MIT X X Buonassisi ONR DETECT, CLRF X X Harvard Mazur White Sands Airborne Characterization of fs- Missile Range Laser X MIT structured Black Silicon Gradecak ARDEC Precision- X X guided MIT Grossman First principles modeling Illinois Ertekin
Sionyx Pralle, Carey Commercialization SiOnyx IR CMOS: Black Silicon enhanced imaging
Imaging from UV to NIR/SWIR Vis NIR SWIR
SiOnyx Black Si Starlight illumination
2 Si CCD Gen 3 I
• Low cost 8” CMOS manufacturing • Low Noise (Read noise ~2 e/pix) (Dark Current <8e/pix/frame) • Low Power (300 mW @ 800x600) • Compact Size • TRL 6 imaging device • TRL 6 wafer process
[email protected], 978-922-0684x127
¼ Moon, March 30, 2012, 8:40PM 23 Outreach Black Silicon Quarterly Black Silicon Symposium • News and recent black silicon goings-on • Held in Albany, NY • Send an email to • August 9-10 [email protected] to be added to distribution
Summary and Outlook
• Laser hyperdoped “black” silicon can be made by two different approaches • Similar properties • “Flat” black silicon easier to study
• Strong sub band gap absorption • High EQE out to 1200 nm
• ARDEC seeks to extend strong device response to 1700 nm
• Fundamental and practical questions abound
BACKUP SLIDES
Research interests at Benet
. Extending black silicon’s IR response
. Characterizing the properties of ns-spiked black Si
. Exploring broader slice of parameter space . Non-chalcogen dopants, thick layers, 5 ns pulses, non- UV wavelengths
. Increasing process cleanliness
. Black Si photovoltaics Assets
Laser/tool Purpose Capabilities Ekspla NL313 Laser melting 532 nm/ 355 nm 800/500 mJ output 5 ns pulse duration
Coherent I-306 Surface 514/488/458 nm reflectivity 2.4/1.8/0.42 W output CW Resonetics Excimer Laser melting 248 nm system 400 mJ output 20 ns pulse duration
Vacuum chamber with Wafer-scale clean 150 mm Si wafer motorized stage processing processing
Dual-beam FE- TEM sample System spec pending SEM/FIB prep, High-res imaging Optoelectronic Gain is spatially inhomogeneous Properties Optoelectronic Properties Gain is spatially inhomogeneous
1V 4V 12V Optoelectronic …but the story gets even weirder Properties
Microwave reflectivity
No detectable photoconductivity in the Si:S layer! Gain without Optoelectronic photoconductivity? Properties
1. IR photon absorbed below junction
3. More e- Gain layer V e- created by collisions IR absorbing layer h 2. e- accelerated across junction XTEM lattice image of PLM’d material