We investigated the thermal stability of strained layers of InGaAs and
InAlAs on InP. Epilayer and interface quality was assessed by high-re
solution x-ray diffraction and electron mobility measurements as a fun
ction of annealing cycle. Both techniques show that pseudomorphic hete
rostructures retain their high crystalline quality at annealing temper
atures of up to 700-800-degrees-C, despite exceeding the Matthews-Blak
eslee [J. Cryst. Growth 27, 118 (1974)] critical layer thickness by as
much as a factor of 4-8. On the other hand, layers which are partiall
y relaxed (incoherent) as-grown relax further during annealing. These
findings demonstrate that layers which are beyond the predicted critic
al thickness, but coherently strained after growth, are stable to norm
al device processing and operating temperatures and hence may be suita
ble for use in device heterostructures.