It is well-known that δ-doped layer has been used in pHEMT transistors rather than growing a uniformly doped supply layer. This can help to increase the current density of the transistors without sacrificing in Schottky performance formed on the gate. However, it comes to my attention that why do not grow a device with double or triple δ-doped layers to further improve the transistor current?

Are there any undesirable impacts that can be caused due to utilising more than one δ-doped layer?

Thanks for any answer or suggestion in advance.