Techniques are disclosed for forming group III-V material transistors employing nitride-based dopant diffusion barrier layers. The techniques can include growing the dilute nitride-based barrier layer as a relatively thin layer of III-V material in the sub-channel (or sub-fin) region of a transistor, near the substrate/III-V material interface, for example. Such a nitride-based barrier layer can be used to trap atoms from the substrate at vacancy sites within the III-V material. Therefore, the barrier layer can arrest substrate atoms from diffusing in an undesired manner by protecting the sub-channel layer from being unintentionally doped due to subsequent processing in the transistor fabrication. In addition, by forming the barrier layer pseudomorphically, the lattice mismatch of the barrier layer with the sub-channel layer in the heterojunction stack becomes insignificant. In some embodiments, the group III-V alloyed with nitrogen (N) material may include an N concentration of less than 5, 2, or 1.5 percent.