Epitaxial Design MOCVD

1
Epitaxial Design -- MOCVD

• Thinner graded AlGaN layer (100nm) relieve high
  stress
• 150nm UID Al0.05Ga0.95N on top
• 2DEG density 8.51012/cm2

2
Power Performance

• On SiC substrate. No passivation and no
  insulator.
• 6.3W/mm with a peak PAE of 77 at 4GHz VD30V,
  ID80mA/mm.
• 12.8W/mm with a peak PAE of 65 at 4GHz VD50V,
  ID80mA/mm.

3
Stability
-- by Y.F. Wu _at_CREE SBTC

• Grown by MOCVD
• 150C, 24-hour RF stress at 2dB gain compression
  point
• Output power, gain and drain current constant
• Gate leakage reduced slightly, due to the
  annealing affect

4
Stability
-- by Y.F. Wu _at_CREE SBTC
24-hour RF stress (2dB compression) at 150C
before
after

• No degradation of power performance
• Slight improvement due to annealing affect caused
  by heating

5
MBE vs. MOCVD
Growth temperature
MBE
MOCVD
Low growth temperature
High growth temperature
High thermal mismatch
Low thermal mismatch
Thick graded AlGaN
6
Epitaxial Design -- MBE

• Thick cap layers downgrade to 0.05, 0.1 and 0.15
• Simulated 2DEG density 1.21013/cm2 better for
  dispersion suppression

7
Growth Issues
Al composition of the AlGaN at the surface
0.05
0.10
0.15

• Grown by MBE Growth temperature 720C
  Carbon-free buffer
• Good surface morphology
• Al0.15Ga0.85N surface termination is close to the
  limitation of cracking

8
DC and pulsed I-V

• Small amount of dispersion under large load line
• Similar Gate leakages for different Al
  composition surface termination

9
Power Performance 4GHz

• Al0.15Ga0.85N surface termination. On SiC
  substrate. No passivation and no insulator.
• 6.3W/mm with a peak PAE of 75 at 4GHz VD30V,
  ID80mA/mm.
• 13.7W/mm with a peak PAE of 68 at 4GHz VD50V,
  ID80mA/mm.

10
Power Performance 4GHz
Breakdown

• Similar power performance for three different Al
  composition surface termination samples
• The degradation of power performance of
  Al0.05Ga0.95N surface termination sample is due
  to the large gate leakage and breakdown

11
Power Performance 10GHz

• Al0.15Ga0.85N surface termination. On SiC
  substrate. No passivation and no insulator.
• 5.6W/mm with a peak PAE of 54 at 10GHz VD30V,
  ID80mA/mm.
• 9.6W/mm with a peak PAE of 42 at 4GHz VD50V,
  ID80mA/mm.

12
Power Performance 10GHz

• Similar power performance for different Al
  composition surface termination samples

13
Epitaxial Field-plate -- MBE

• Gate leakage keep same or increase with longer
  LFP
• Power performance remain same
• Field-plate itself is leaky

14
Epitaxial Field-plate -- MOCVD

• Gate leakage decrease with longer LFP
• Power performance more dispersion with longer
  LFP ???