U.S. Army Research, Development and Engineering Command

BLACK FOR NEXT-GENERATION 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, , 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

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 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 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

[email protected]

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