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Photoelectrochemical Wet Etching of Gallium Nitride. Jack Huynh Jerry Hitchcock & Newton Cheng present. University of Illinois, Champaign-Urbana Department of Electrical and Computer Engineering ECE 345, Senior Design April 26, 2000. GaN Background and Application.

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photoelectrochemical wet etching of gallium nitride

Photoelectrochemical Wet Etching of Gallium Nitride

Jack Huynh

Jerry Hitchcock

& Newton Cheng

present

University of Illinois, Champaign-Urbana

Department of Electrical and Computer Engineering

ECE 345, Senior Design

April 26, 2000

gan background and application
GaN Background and Application
  • Wide energy band gap (3.4 eV)
  • Useful optical properties
  • Optical applications: Blue LED’s, lasers, photodetectors
  • Chemically inert material
  • High power, high frequency device applications
problems with gan
Problems with GaN
  • Grown epitaxially on a sapphire or silicon-carbide substrate
  • High density of lattice defects due to lattice mismatches in GaN-substrate interface
  • Resistive to chemical wet etching due to chemical inertness
problems with dry etching
Problems with Dry Etching
  • Ion Bombardment commonly used
  • Lattice Damage
  • Nonselective Etching
  • Cost
  • Throughput
advantages of wet etching
Advantages of Wet Etching
  • Selectivity
  • Cost
  • Throughput
  • No Lattice Damage
  • Anisotropic
enhanced wet etching
Enhanced Wet Etching
  • Photoelectrochemical (PEC)
    • Appropriate UV Source
    • Applied Bias
    • Chemical Medium Selection
  • Specialized Holder
  • LabView Data Acquisition System
  • Mask
pec reaction
PEC Reaction
  • Dissolution Process
    • 2 GaN + 6 h+ 2 Ga3+ + N2
    • 2 Ga3+ + KOH  Reaction Products
  • Reaction Products
    • Soluble
    • Insoluble
pec wet etch
PEC Wet Etch
  • Etch Time 20 Minutes
  • pH of KOH Solution (11, 12, 13)
  • UV Intensity (10mW / cm2, 20mW / cm2, 30mW / cm2)
  • Bias (0V, 1V)
etch rate results for 0v bias
Etch Rate Results for 0V Bias

Etch Rates in angstroms/min.

etch rate results for 1v bias
Etch Rate Results for 1V Bias

Etch Rates in angstroms/min.

surface morphology
Surface Morphology
  • Several different profiles
    • Smooth
    • Dislocation etching
    • Columnar nanostructure
    • Nanometer etch pit
    • Intermediate morphologies
    • Irregular etch pits
  • Follow regular evolutionary pattern
smooth morphology
Smooth Morphology

Occurs at low pH, low to mid-range intensity

dislocation etch morphology
Dislocation Etch Morphology

Occurs at low pH, low to mid-range intensity

columnar nanostructure morphology
Columnar Nanostructure Morphology

Occurs at mid to high pH, low to mid-range intensity

nanometer etch pits morphology
Nanometer Etch Pits Morphology

Occurs at high pH, high intensity

nanometer etch pit formation
Nanometer Etch Pit Formation
  • Positive uncompensated donor atoms
  • Columnar orientation
  • Macroscopic electric field
  • Increased etching between columns
irregularly shaped etch pits
Irregularly Shaped Etch Pits

Occurs at high pH, low intensity

morphology trends at 0v
Morphology Trends at 0V

S – smooth D – dislocation C – columnar nanostructures N – nanometer etch pits I – irregularly shaped etch pits

morphology trends at 1v
Morphology Trends at 1V

S – smooth D – dislocation C – columnar nanostructures N – nanometer etch pits I – irregularly shaped etch pits

conclusions
Conclusions
  • PEC Etching with applied Bias
    • Improves etch rates
    • Improves smoothness
  • Smooth Etch Conditions
    • pH below 12
    • Light intensity up to 20mW / cm2
  • High Etch Rate Conditions
    • pH between 12 and 12.5
    • Light intensity of 30mW / cm2