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

The “PC-group” @ ANL:

Thomas ProlierMatthew WetsteinIgor VeryovkinZikri YusofAlexander Zinovev

Bernhard AdamsKlaus AttenkoferMatthieu CholletZeke InsepovAnil ManeQuing Peng

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

210/15/09

Physics & Technological Challenges

Different Applications have Different Needs

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

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Suffix

Photocathode

Input Window

-71 GaAsBorosilicate

Glass

-73Enhanced Red GaAsP

Borosilicate Glass

-74 GaAsPBorosilicate

Glass

-76 InGaAsBorosilicate

GlassNon Multialkali Synthetic Silica

-01Enhanced

Red Multialkali

Synthetic Silica

-02 Bialkali Synthetic Silica-03 Cs-Te Synthetic Silica

10/15/09

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

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)

Large Area Detector Project: 1. Collaboration Meeting

410/15/09

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

III-V are an appropriate approach:

Physics & Technological Challenges

Technological Challenges: Price, Simplicity, Materials- Process-Compatibility

Scalable production tools available

Large Area Detector Project: 1. Collaboration Meeting

510/15/09

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)

Description of the Scientific & Engineering ProgramPhysics of Semiconductor Cathodes

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

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Large Area Detector Project: 1. Collaboration Meeting

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The Three Functions of a Cathode:

Description of the Scientific & Engineering ProgramThe Negative Electron Affinity

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Large Area Detector Project: 1. Collaboration Meeting

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What are surface states:

Description of the Scientific & Engineering ProgramTunability of III-V

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•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

Description of the Scientific & Engineering Program

GaN-Family

Largest variation in band-gap Growth on -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 -Al2O3 (sapphire) glass

InN/GaN multilayer system to adjust band-gap and minimize strain

Cascade structures? Optimizing surface reconstruction (growth

direction, temperature, coating)Large Area Detector Project: 1. Collaboration Meeting

910/15/09

The Challenge

The Research Program

Jim Buckley & Daniel Leopold (Wash University)

Description of the Scientific & Engineering ProgramGaAsP-Family 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? Large Area Detector Project: 1. Collaboration Meeting

1010/15/09

The Challenge

The Research Program

Xiuling Li and colleagues (UIUC)

Description of the Scientific & Engineering ProgramNano-Structures

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

Large Area Detector Project: 1. Collaboration Meeting

1110/15/09

The Challenge

The Research Program

Jonas Johansson (university of Lund)

The Path: Who is involved?

10/15/09

Large Area Detector Project: 1. Collaboration Meeting

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

“Bernhard Characterization”:•Bernhard Adams•Matthieu Chollet•Matth Wetstein

Berkeley Activity (Ossi)

Common

Meetings

By Matth Wetstein

Characterization Group

Regular Meeting

Technical coordination

By Dean Walters

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?)

• Igor Veryovkin• Alex Zinovev

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

Large Area Detector Project: 1. Collaboration Meeting

1310/15/09

Standard according Dean Walter

Surface cleaning Chamber: HCL at 1mbarHeatingNi-chamber or glass?

Simple thermal coating facilityCs-sourceInsitu in-plane resistivityInsitu QE-measurement

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

The Path:

Characterization

Large Area Detector Project: 1. Collaboration Meeting

1410/15/09

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

The Goals and “Measure of Success”

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

1510/15/09

First Year: