With the evolution of infrared arrays to over four million pixels, larger f
ormats have demanded higher quality mercury cadmium telluride (MCT) wafers.
Since single defects can easily degrade multiple diodes, high operability
requires very homogeneous and nearly flawless epitaxial surfaces. Subsequen
t photolithography and hybridization also demand unprecedented levels of su
bstrate flatness and low imperfections. To consistently and reliably produc
e large area arrays, Insaco Inc., The Boeing Company, and Rockwell Internat
ional Corporation have developed major quality improvement procedures which
address all three components of the infrared material wafer architecture.
Centered on the producible alternative to cadmium telluride for epitaxy (PA
CE) process, technological advancements encompassed sapphire substrates, or
ganometallic vapor phase epitaxy (OMVPE), cadmium telluride (CdTe) buffer l
ayer growth, and liquid phase epitaxial (LPE) mercury cadmium telluride gro
wth. Processed material from these runs mated to Conexant(TM) fabricated mu
ltiplexers have successfully produced 1024 x 1024 and the first 2048 x 2048
IR short-wave (2.5 mum at 80 K) hybrid focal plane arrays. Operabilities i
n these implanted n-on-p junction devices reach 99.98% with near 70% quantu
m efficiency in the astronomy 'K' band (2.2-2.4 microns).