PhD Wim Deferme

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PhDWim Deferme

• 19-12-2007

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Contents

• Time Of Flight
• Temperature dependence (300K to 600K)
• Different treated surfaces
• Modelling H2/O2 treatment
• Overview
• Cavity ring-down spectroscopy
• Surface Treatment
• N2 doping
• NH3 treatment
• Discussion and Future Work

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Laser Time Of Flight Set- up
Tcontroller
Sample
Heater
Z1/wC
50W strip
VS input
OSC output
FIG. 1. Time-of-Flight set-up. NdYAG pumped
optical paramagnetic oscillator (OPO), tuneable
from 420 till 700 nm is doubled by BBO crystals.
l 215 220 nm ( 218 nm) The Si-detector
trigger for the oscilloscope (OSC). FG1, FG2 are
function generators Main voltage pulse (4ms
length) that is 100x amplified and applied to the
sample. FG2 is a delaying trigger for the
Q-laser-switch. A 15m long coaxial cable is used
to dump and shift the reflections on the voltage
input side of the sample. The current is measured
using a 50 Ohm impedance
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Time Of Flight

• A comparison is made between oxidised and
  hydrogenated diamond layers. (CU 0,5pF x
  2,5V/um 1,2510-12)
• Qoxi 0,510-12 ltlt CU ? small signal TOF
• Qhydr 1.210-11 gtgt CU ? SCLC mode (space
  charge limited current)

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30C holes
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30C electrons
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180C holes
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180C electrons
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(No Transcript)
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Charge Scattering Mechanism
Holes
Electrons
RT drift limited by the phonon scattering
intrinsic diamond property !

• Optical phonon scatterring fit
• Hole a -2.5
• Electrons a -3.2

• Acoustic phonon scattering fit
• Hole a -1.5
• Electrons a -1.4

µ a Ta
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• surface treatment
• B-doping (Vincent)

Fujita et al - development of a TOF measurement
system of charge carrier dynamics in diamond thin
films using a UV pulsed laser
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H2/O2 termination of diamond

• Hydrogenation conditions
• 0 3000W, 50 Torr, 1000 sccm H2 , 700C
• 1 3000W, 50 Torr, 1000 sccm H2 , 700C 10
  sccm O2
• 4 3000W, 50 Torr, 1000 sccm H2 , 700C 40
  sccm O2
• samples in air conductive due to adsorbates
  (PRL85,3472 (2000))
• samples in UHV and annealed to 100C, the
  conductivity caused by these adsorbates vanishes.

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H2/O2 termination of diamond

• 1 H2/O2 sample STS _at_ RT show a surface bandgap
  of 3.5eV.
• According to these measurements, a model is
  proposed where the O-states at the surface pin
  the Fermi Level. Together with UPS measurements
  we can model our 1 sample as follows

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H2/O2 termination of diamond

• Zheng (DRM 10 (2001))

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H2/O2 termination of diamond

• UPS should be performed to know the exact place
  of the oxygen states.
• Thin Film Cavity Ring-down absorption technique
  in combination with transmission reflection
  spectroscopy to check the bonding formation of
  the surface oxygen. (Aarts, Journal of
  Non-Crystalline Solids (2004))

• Problems
• Diamond on SiC (1000) ? poly vs. single crystal
• Wedge like structure

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Surface Treatment

• N2-doping

• NH3-treatment

• 500sccm H2
• 2 sccm CH4
• 780 Watt
• 100 Torr
• 810C
• 50 minutes
• Sample1 100sccm N2
• Sample2 50sccm N2
• Sample3 10sccm N2
• Sample4 25sccm N2
• Singapore (Milos)

• 1) 400sccm Ar
• 20 sccm H2
• 60 Watt
• 120 mbar
• He HCl toevoegen (120 sccm) 5 min
• NH3 toevoegen (5min)
• Sample1 120 sccm (22)
• Sample2 135 sccm (25)
• Sample3 60 sccm (12)
• XPS Parijs (Milos)

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Future Work

• TOF on different surface-treated samples at
  different temperatures (300K 600K)
• TOF on B-doped samples (Vincent)
• Cavity Ring-down spectroscopy (Kees)
• XPS Parijs