Monetary Policy, Financial Frictions, and Heterogeneous R&D Firms in an Endogenous Growth Model *

Motivated by empirical facts, I construct an endogenous growth model in which heterogeneous research and development (R&D) firms are financially constrained and use cash to finance R&D investments. I also examine the optimal monetary policy. The effects of financial constraint crucially depend on whether R&D firms are homogeneous or heterogeneous regarding R&D productivity. If R&D firms are homogeneous, then the zero nominal interest rate (i.e., the Friedman rule) is always optimal under severe financial constraint. Heterogeneity in R&D productivity leads to the opposite result. With heterogeneity, severe financial constraint makes the strictly positive nominal interest rate welfare‐improving under a plausible condition.