Integrated Optics - Applied Optics Fundamentals and Device Applications - page 261

Continuous-wave
laser/electron beam

Pulsed laser/electron
beam Furnace

Anneal mechanism Solid phase Solid phase Liquid phase

Optimum anneal
conditions

>850°C for best
electrical properties

one to 5S dwell with
substrate heating
(laser) and raster
scan (electron beam)

Narrow energy
window at energies
just sufficient to melt
below damage layer

Decomposition Severe at >600°C: use

cap or other
preventative
measures

Surface oxidation in
air: use inert ambient
or vacuum

Significant
decomposition only
at high powers and
pulse lengths: surface
damage at lower
powers

Microstructure Always some extended

defects

Not yet examined Extended defect-free

but often some
surface damage: likely
quenched in point
defects

Surface topography Featureless Featureless (optimum

conditions): slip and
cracking with
excessive thermal
gradients

Featureless (optimum
conditions): rough
surface at high power

Electrical
properties

Good activity: always
below 10 19 cm − 3 for n
type

Limited data but good
activity for low to
medium dose n -type:
poor results for non
optimized anneals:
mobilities close to
theory, where
available

High activity (>10 19
cm − 3 ) for both n - and
p -type: activity
decreases on
subsequent furnace
annealing: cannot
activate low-dose
n -type: mobilities
anomalously low

Implant
redistribution

Diffusion broadening
a problem with some
dopants (e.g., Zn. S)
at high temperatures

Few data exist:
probably no
redistribution

Little redistribution for
low power just above
threshold: dopant
redistribution and
“zone refining” can
occur in melt

Substitutional
solubility (to
GaAs)

Never exceeds 5 × 10 19
cm —3

Not measured Exceeds equilibrium

value (>10 20 cm − 3 )
not good correlation
with electrical activity

FIGURE 5.25
Comparison of the various annealing methods for ion-implanted GaAs.