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Status of III-V and Nano-Scale Photo-Cathodes at ANL. The “PC-group” @ ANL:. Bernhard Adams Klaus Attenkofer Matthieu Chollet Zeke Insepov Anil Mane Quing Peng. Thomas Prolier Matthew Wetstein Igor Veryovkin Zikri Yusof Alexander Zinovev. Overview. Physics & Technological Challenges

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status of iii v and nano scale photo cathodes at anl

Status of III-V and Nano-Scale Photo-Cathodes at ANL

The “PC-group” @ ANL:

Bernhard Adams

Klaus Attenkofer

Matthieu Chollet

Zeke Insepov

Anil Mane

Quing Peng

Thomas Prolier

Matthew Wetstein

Igor Veryovkin

Zikri Yusof

Alexander Zinovev

overview
Overview
  • Physics & Technological Challenges
    • Different Applications have Different Needs
    • The Specific Challenge of a Large Photocathode
    • Technological Challenges: Price, Simplicity, Materials- Process-Compatibility
  • The Description of the Scientific and Engineering Program
    • GaN-Family
    • GaAsP-Family
    • Nano-Structures
  • The Path:
    • Sample Preparation
    • Characterization
  • The Goals and “Measure of Success”

Large Area Detector Project: 1. Collaboration Meeting

physics technological challenges different applications have different needs
Physics & Technological ChallengesDifferent Applications have Different Needs

Hamamatsu: http://jp.hamamatsu.com/products/sensor-etd/pd014/index_en.html

  • Required spectral response still not clear (main application)
  • Future applications (combination with scintillators) will require response optimization
  • III-V are complex to grow, but:
    • Full developed industry available for production and production tools
    • Large efforts worldwide in refining growth-technology
    • This effort can be a milestone for future device development

Large Area Detector Project: 1. Collaboration Meeting

physics technological challenges the specific challenge of a large photocathode
Physics & Technological ChallengesThe Specific Challenge of a Large Photocathode
  • Good conductivity layer to avoid charging effects
  • Good homogeneity of the cathode over the full size
  • No “insitu” activation possible -> in vacuum fabrication and sealing necessary
  • Cathode has to be process compatible to sealing process and final assembly
  • Cathode has to work under “relaxed” vacuum conditions
  • The price of the detector will be largely by cathode processing determined
  • Well established doping methods available
  • Foundries with large throughput and wafer-sizes available (process parameters can be developed on lab-sizes systems)
  • High temperature resistivity (about 550C)
  • Emerging nano-technologies are available
  • Industrial standards available (yield, homogeneity)

III-V are an appropriate approach:

http://cqd.eecs.northwestern.edu/research/ebeam.php

Large Area Detector Project: 1. Collaboration Meeting

slide5
Physics & Technological ChallengesTechnological Challenges: Price, Simplicity, Materials- Process-Compatibility

Scalable production tools available

http://www.aixtron.com/index.php?id=156&L=1

  • Process parameters can be developed on lab-system and transferred to production systems
  • Complex fabrication (layer-system) will be performed in foundry with quality control
  • Ready-to-mount cathode (on window) will be transported in air, chemically cleaned and finally brought in the vacuum assembly chamber.
  • Activation requires high temperature (~600-800C) and small amounts of Cs (sub-monolayer)

Large Area Detector Project: 1. Collaboration Meeting

description of the scientific engineering program physics of semiconductor cathodes
Description of the Scientific & Engineering ProgramPhysics of Semiconductor Cathodes

The Three Functions of a Cathode:

  • Interface layer between window/substrate and active area:
    • Defines how much light gets into the active light (reflection)
    • Important for compatibility (growth on glass, bonding, transfer printing….)
    • Conductivity-layer
  • Active area:
    • Light absorption (multilayer options)
    • Electron transport (scattering/trapping)
    • Noise-suppression layers
  • Surface:
    • Electron escape
    • Responsible for dark-current
    • Surface states extreme sensitive to chemical changes

Large Area Detector Project: 1. Collaboration Meeting

description of the scientific engineering program the negative electron affinity
Description of the Scientific & Engineering ProgramThe Negative Electron Affinity

What are surface states:

Large Area Detector Project: 1. Collaboration Meeting

description of the scientific engineering program tunability of iii v
Description of the Scientific & Engineering ProgramTunability of III-V
  • Two “families”: N-based and As-based
  • Wide tunability of band-gap
  • Only for specific materials -combinations NEA available
  • No cross combination of families possible
  • “Good materials” are direct band gap

Large Area Detector Project: 1. Collaboration Meeting

description of the scientific engineering program gan family
Description of the Scientific & Engineering ProgramGaN-Family

Jim Buckley & Daniel Leopold (Wash University)

The Challenge

  • Largest variation in band-gap
  • Growth on a-Al2O3 (sapphire)
  • GaN NEA-layer exist
  • GaN is UV active
  • Perfect combination would be GaxIn(x-1)N, but:large strain -> high defect density -> large losses
  • Direct growth on ALD coated a-Al2O3 (sapphire) glass
  • InN/GaN multilayer system to adjust band-gap and minimize strain
  • Cascade structures?
  • Optimizing surface reconstruction (growth direction, temperature, coating)

The Research Program

Large Area Detector Project: 1. Collaboration Meeting

description of the scientific engineering program gaasp family
Description of the Scientific & Engineering ProgramGaAsP-Family

The Challenge

Xiuling Li and colleagues (UIUC)

  • Largest family
  • Growth on GaAs substrate
  • GaAs too much red!
  • GaAsP large strain (Similar to GaInN)
  • Alternative: AlGaAs/GaAs multilayer
  • No NEA system known for AlGaAs
  • Finding best bonding or transfer printing technique
  • Optimizing AlGaAs/GaAs film structure and doping profile
  • Surface doping & NEA layer
  • Delta-doping?

The Research Program

Large Area Detector Project: 1. Collaboration Meeting

description of the scientific engineering program nano structures
Description of the Scientific & Engineering ProgramNano-Structures

The Challenge

Jonas Johansson (university of Lund)

  • Largest variety of growth combinations
  • Radial and longitudinal growth possible
  • Ion-edging is no issue
  • Not demonstrated (but various groups have projects)
  • Growth on glass is possible
  • Dark current and field enhancement
  • Developing of a delta-doped radial structure
  • Most likely GaInN, first test structures GaAs

The Research Program

Large Area Detector Project: 1. Collaboration Meeting

the path who is involved
The Path: Who is involved?
  • “Bernhard Characterization”:
  • Bernhard Adams
  • Matthieu Chollet
  • Matth Wetstein

Common

Meetings

  • People involved (so far):
  • Klaus Attenkofer
  • Zeke Insepov
  • Matth Wetstein
  • Zikri Yusof
  • (Thomas Prolier)

By Matth Wetstein

Berkeley Activity (Ossi)

Regular Meeting

Characterization Group

By Dean Walters

  • Igor Veryovkin
  • Alex Zinovev
  • Potential sample fabrication:
  • Xiuling Li (UIUC)
  • Jim Buckley & Daniel Leopold (Wash University)
  • Jonas Johansson (first samples are waiting for characterization)
  • “Novosibirsk connection” (Zeke Insepov)
  • Thomas Prolier (ALD and?)

Technical coordination

Large Area Detector Project: 1. Collaboration Meeting

the path sample preparation
The Path: Sample Preparation
  • Production of “raw-cathode” at collaboration partner (later perhaps also own fabrication capabilities)
  • Cathode Activation in Argonne (currently work on chamber design)
  • Compatible to characterization group

Standard according Dean Walter

  • Characterization of:
  • Quantitative QE(E)
  • Noise/QE
  • Field enhancement
  • Time response

Simple thermal coating facility

Cs-source

Insitu in-plane resistivity

Insitu QE-measurement

Surface cleaning Chamber:

HCL at 1mbar

Heating

Ni-chamber or glass?

Large Area Detector Project: 1. Collaboration Meeting

the path characterization
The Path: Characterization
  • Characterization:
  • QE(E) quantitative
  • Noise/QE
  • I(EPh,Uexternal,T) (Photo current)
  • I/µd (Photo current versus absorption)
  • Calibration of simple light sources
  • Timing characterization (up to 8/25/50/70GHz?)
  • Properties:
  • Transportable
  • Fully computer controlled
  • “Bernhard compatible”
  • “small” optical table
  • Progress & Status:
  • Optics components ordered
  • Electronics components ordered
  • Calibration diodes available
  • Data-acquisition system in progress
  • Current design of vacuum system, chamber, evaporators

Large Area Detector Project: 1. Collaboration Meeting

the goals and measure of success
The Goals and “Measure of Success”

First Year:

  • Establishing of collaboration and growth of “small samples (1x1cm2)”
  • Assembly of high throughput activation/characterization chamber
  • Automatic data-acquisition and analysis system
  • Modeling of timing behavior
  • Demonstration of successful activation of the three cathode systems
  • Demonstration of QE = 15% for the three cathode systems
  • GaN
    • Evaluation of growth on ALD grown Al2O3-films
    • Demonstration and characterization (dark current/QE) of multilayer approach
    • Standard NEA-approach
  • GaAsP
    • Demonstration and characterization of transfer-printing
    • AlGaAs/GaAs verus GaAsP evaluation
    • Investigating NEA-effect and surface reconstruction/coating effects
  • Nano-structure
    • Feasibility test (dark current)

Large Area Detector Project: 1. Collaboration Meeting