We report on a study of the effects of intentional thickness and doping variations on QCL performance. The measured QCL data had very similar trends to those predicted by an in-house QCL model. It was found that absolute changes to the QCL period had a very small effect on emission wavelength (wave-length/period change < 10 nm/angstrom), whereas the complementary thickness changes between the wells and barriers had a large effect (wavelength/thickness change=550 nm/angstrom). The threshold voltage also changed with these variations and generally agreed well with the model. We show through modeling and experiments that intentional structure variations can have largely different magnitudes of effect on QCL performance. (C) 2015 Elsevier B.V. All rights reserved.