  Most explanations of economic growth are based on knowledge spillovers, where
the development of some technologies facilitates the enhancement of others.
Empirical studies show that these spillovers can have a heterogeneous and
rather complex structure. But, so far, little attention has been paid to the
consequences of different structures of such cross-technology interactions: Is
economic development more easily fostered by homogenous or heterogeneous
interactions, by uni- or bidirectional spillovers? Using a detailed description
of an r&d sector with cross-technology interactions embedded in a simple growth
model, we analyse how the structure of spillovers influences growth prospects
and growth patterns. We show that some type of interactions (e.g., one-way
interactions) cannot induce exponential growth, whereas other structures can.
Furthermore, depending on the structure of interactions, all or only some
technologies will contribute to growth in the long run. Finally, some spillover
structures can lead to complex growth patterns, such as technology transitions,
where, over time, different technology clusters are the main engine of growth.
