SiN/ SiO and Si/ SiO Bragg Reflectors by low temperature PECVD

AFM images of the SiOx sufrace
at 90° C PECVD
(roughness < 8 nm)
and 250° C PECVD
(roughness < 3nm)

The electrical quality and densit
are also influenced by the difference
in temperature.

breakdown voltages (SiO)
8 E6 V/ cm down to 200° C
4 E5 V/ cm at 90 °C

BHF etch rate of SiN
10 nm/ min at 400° C
400 nm/ min at 200° C

top: SiOx/ Si for different stop band wavelengths
straight line: SiOx/ Si measured
dotted line: SiOx/ Si simulated
dashed line: measured spectrum from an AlAs/AlGaAs Bragg reflector for line shape comparison

bottom: SiOx/SiNx Bragg reflector
(measured at 15° angle of incidence)

deposition rates
10 - 20 nm / min for SiN
30 - 40 nm/ min for SiO
5 - 12 nm/ min for Si
very good uniformity
good stress control

Due to the high difference in refractive index it is possible to achieve 99.6 % reflectivity by just 5 or 6 pairs of Si/ SiO at 1300-1550 nm wavelength !

with kind permission
Dr Gottschalch
Uni Leipzig