Manipulation of charge carriers at the semiconductor interfaces is the basis of modern electronics. In contrast to conventional materials, van der Waals (vdW) materials release constraints on designing atomically sharp interfaces, creating additional degrees of freedom in interface engineering. Here, I will focus on interlayer interactions between vdW materials and discuss how we can engineer vdW interfaces to (i) enable advanced optical characterization beyond diffraction limit and (ii) improve monolayer semiconductor device performance. (i) vdW heterostructures with quantum well band alignment enable to measure cathodoluminescence in monolayers, which has been challenging due to their atomic thinness. This will reveal precise structure-property relationships at the nanoscale. (ii) 3D/2D and 2D/2D interface interactions modify work function and doping, reducing contact resistance by orders of magnitude, which is a prerequisite for the practical applications.