DE-SC0002477 Phase II: 8/15/2010-8/14/2013 (Including 1-yr NCE) - - PowerPoint PPT Presentation

Segmented Rectifying and Blocking Contacts on Germanium Planar Detectors

Principal Investigator: Ethan Hull, Ph.D. DE-SC0002477 Phase II: 8/15/2010-8/14/2013 (Including 1-yr NCE)

New surface contact technologies are being developed for the fabrication of segmented planar germanium detectors. Yttrium and other metal contacts have been determined to have the correct combination of physical properties to provide segmented low-noise germanium-detector contacts. Photolithographic fabrication techniques result in functional germanium detectors having small well-defined segmented contact features.

Collaboration with Kim Lister at UMass Lowell

• Introduction to PHDs Co.
• Segmented rectifying and blocking germanium-detector contacts
• 1. New contact technology
• 2. Physically narrower inter-strip gaps
• Products – Nuclear Physics is the basis

PHDs Co. 3011 Amherst Rd, Knoxville, TN www.phdsco.com

• Germanium Detector Systems
• Concept
• Germanium refinement and crystal growth
• Mechanical-Vacuum-Cryogenic Engineering
• Detector Fabrication
• System Integration
• Information output
• Est. Fall 2004, Ethan Hull CEO, Richard Pehl CFO
• 9 FTEs + 2-3 Consultants – Technical Emphasis
• PHDs Co. sells germanium detector system products
• Nuclear Physics - NPX-M
• Security Applications - GeGI and SPG
• Nuclear Medicine - MIX

SPG

Technical area (~ 8000 ft2) Office area (~ 2000 ft2)

PHDs Co.

10,000 ft2 Facility Knoxville, TN

Germanium detector fabrication facility

Amorphous-germanium contact 500 µm gaps

• Segmented rectifying and blocking germanium-detector contacts
• New contact technology – Yttrium metal
• Physically narrower inter-strip gaps

Yttrium contact 250 µm gaps

Historic dilemma: The surface (interface states) of crystalline HPGe is p type. Most materials form an electron barrier. Damage is p-type. Lithium thermal diffusion (~ 500+ μm) forms a rugged hole-barrier contact for 99% of Ge detectors. Thick, cannot be segmented easily . Amorphous-germanium and Yttrium metal form this type of contact.

• New n+ (hole barrier) contact technology – Yttrium metal

• New n+ (hole barrier) contact technology – Yttrium metal

1.E-15 1.E-14 1.E-13 1.E-12 1.E-11 1.E-10 1.E-09 1.E-08 1.E-07 1.E-06 0.006 0.007 0.008 0.009 0.01 0.011 0.012 0.013

i (A) 1/T (K-1)

120 K

𝑗 ~ 𝑓− 𝜒

𝑙𝑈

• Yttrium metal
• Heterojunction, not Schottky barrier
• Hole barrier height ϕ ~0.4 – 0.6 eV – higher than

amorphous germanium but variable -- HJ

• Thin and segmented with photolithography
• Published and Patent Pending

1 10 100 1000 100 200 300 400 500 600 700

57Co

122 keV FWHM = 0.95 keV FWTM = 1.80 keV

500 µm gap 250 µm gap 100 µm gap

137Cs

662 keV FWHM = 1.32 keV FWTM = 2.61 keV

• Photolithograph  Narrower gaps
• Less gap charge-collection problems
• Must be amenable to fabricating a

working germanium detector

LN2 Cooled NPX Systems Mechanically Cooled NPX-M Systems Significant enabling leap forward

• Implications of narrower gaps for strip detectors

Complete NPX-M Germanium Strip Detector Systems for Nuclear Physics require only 120 VAC

60 lbs Bench top system Implications of narrower gaps for strip detectors

Amorphous-germanium contact 500 µm gaps

1 Charge loss due to gap collection

10 20 30 40 Induced Charge t (ns)

1 2 2

662 keV FWHM = 2.0 keV 122 keV FWHM = 1.2 keV Typical Individual pixel energy spectroscopy

662 keV FWHM ~ 2.2 keV 122 keV FWHM ~ 1.4 keV Typical PIXEL-TOTAL Energy Spectroscopy (The sum of all detector pixels)

500 µm gaps (Previous NPX) 250 µm gaps (NP7) 250 µm gaps (NP7 – UMass Lowell, Kim Lister, May 2012)

100 1000 10000 100000 1000000 20 40 60 80 100 120 140 160 E (keV)

500 µm gaps

100 1000 10000 100000 1000000 20 40 60 80 100 120 140 160 E (keV)

250 μm gaps

All events Pixel total (All events) (Pixel total) _ All events Pixel total (All events) (Pixel total) _

More efficient Polarimeter for Nuclear Physics Compton = Photoelectric at Eγ = 140 keV in Ge  Substantial neighboring strip scattering Less gap charge loss 10 % higher efficiency at 140 keV More efficient detector for Nuclear Medicine