Hi Mike, would you consider "Black Silicon"?

Anyone with a deep RIE system can treat your wafers to form a black silicon
'grass' on horizontal exposed silicon surfaces. The black silicon process is
frequently used  in tuning the process for best vertical sidewalls.

* High broadband optical absorption.
I don't know the spectral range of absorption, but it is really black, black,
black.

* Spin coatable.
No, but is that a performance requirement or an artifact of the existing process
sequence?

*
 Electrical resistivity as high as possible.
As etched the 'grass' is conductive, but a thin oxide or nitride layer can
passivate it.

*
 Patternable.
Simple. Only open the areas you want to blacken to the RIE.

* Long life.
As long lived as the silicon in the rest of the device.

I think I might be able to intercede with a fab to get samples run, if you are
interested.

Best,

Dean Hopkins
(408) 429-0501