Editing High-electron-mobility transistor (section)

=== Modulation doping in HEMTs ===
An important aspect of HEMTs is that the band discontinuities across the conduction and valence bands can be modified separately. This allows the type of carriers in and out of the device to be controlled. As HEMTs require electrons to be the main carriers, a graded doping can be applied in one of the materials, thus making the conduction band discontinuity smaller and keeping the valence band discontinuity the same. This diffusion of carriers leads to the accumulation of electrons along the boundary of the two regions inside the narrow band gap material. The accumulation of electrons leads to a very high current in these devices. The term "[[modulation doping]]" refers to the fact that the dopants are spatially in a different region from the current carrying electrons. This technique was invented by [[Horst Störmer]] at [[Bell Labs]].