The quality of epitaxial layers in quantum cascade lasers (QCLs) has a primary impact on QCL performance, and establishing correlations between epitaxial growth and materials properties is of critical importance for continuing improvements. We present an overview of the growth challenges of these complex QCL structures; describe the metalorganic vapor phase epitaxy growth of AlInAs/GaInAs/InP QCL materials; discuss materials properties that impact QCL performance; and investigate various QCL structure modifications and their effects on QCL performance. We demonstrate uncoated buried-heterostructure 9.3-um QCLs with 1.32-W continuous-wave output power and maximum wall plug efficiency (WPE) of 6.8%. This WPE is more than 50% greater than previously reported WPEs for unstrained QCLs emitting at 8.9 um and only 30% below strained QCLs emitting around 9.2 um.