Use the Effective Mass node to set the effective mass of the particle. The default is 0.067*me_const for electron-like particles and 0.45*me_const for hole-like particles.

The default effective mass tensor type is Isotropic. Use the drop down menu to select other options: Diagonal, Symmetric, or Full. Enter the tensor elements accordingly.

It is common for electrons or holes to have different effective masses in different regions of a heterostructure. This can be easily specified by using multiple Effective Mass nodes. Later nodes overrides earlier nodes in the Model Builder tree.