Characterization of Thin Films Grown by Pulsed Laser Deposition and EBeam Vaporization

1
Characterization of Thin Films Grown by Pulsed
Laser Deposition and E-Beam Vaporization

• Theodore Robert Harris
• UNCC Electrical Engineering

National Institute of Science
Technology Materials Science and Engineering
Laboratory Electronic and Optoelectronic
Materials Group
2
Overview, Goals

• To improve p-contacts for LEDs that are
  transparent and conductive
• Variables are annealing temperature and time,
  film thickness ratios, and deposition technique

LED Structure
From Mike Ahrens, UNCC, Ni-Au Contact
Optimization, 2004
3
Cleaning Method

• Double-polished sapphire wafer
• Boil in chloroform 3 mins
• Sonicate in chloroform 3 mins
• Boil in acetone 3 mins
• Sonicate in acetone 3 mins
• Boil in methanol 3 mins
• Dry with argon

4
E-Beam System
5
E-Beam Charges
6
Element Collection
7
E-Beam Melting Au
8
PLD System
9
Deposition
10
XRD Analysis
11
AFM Analysis
AFM Image
Roughness Graph

• RMS Roughness 86-106

12
Optical Characterization

• Spectroscopic Reflectometry Bifurcated
  Fiber Optic Automated Recorded Spectra

Data
Fit
13
Collection of Data Points

• Reflectometer Apparatus

14
Reflection Spectra
5ÅNi/2ÅAu E-Beam Run
15
Annealing

• Feedback lamp control system
• Temperature time recipes
• Dry runs
• 500-700 Ar
• Very loud

16
Spectral Results
17
Spectral Results
18
Annealing Temp Vs Transmission
Working Region
19
Grain Sizes Correlation to Heat

• As depositedSmall grain size (10-20nm).Textured
  preferred orientation (111)//GaN surface
• 500-600Densification (Regrowth)Melting.Large
  grains (500-600nm).
• 700-750Island formation,discontinuous due to
  surface tension.Phases formed
• gt800Total reaction.Conductive and transparent
  but low work function

light
GaAu, GaNi, Phases
20
Electrical Properties

• TLM

From Kim, Je, Electrochemical Society, 147
From G.K. Reeves, Solid-State Electronics, 23,
487, (1980).
21
Conclusions

• Best annealing temperatures are between 625 -
  690C
• 5ÅNi/2ÅAu is more transparent than 5ÅNi/5ÅAu
• PLD films as deposited are rougher and less
  uniform than e-beam
• However, PLD shows promise for this application,
  especially in prototyping, and needs further
  research

22
Problems

• Cleaning
• PLD uniformity
• Oxidation between runs
• Dirty laser window
• Laser gas
• Heater, rotators breaking
• Crashing cryo pumps

23
Acknowledgements

• Ed Stokes, Ph. D.
• Albert Davydov, Ph. D.
• Mr. Michael T. Ahrens
• Mrs. Jianhua Li
• Mrs. Sandra Claggett
• Daniel Josell, Ph. D.
• And a special thanks to
• Peter Schenck, Ph. D.

24
Questions

• Ask a lot
• Really

25
Title

• text