D.A. Usanov - Dr.Sc. (Phys.-Math.), Professor, Head of the Department "Solid State Physics", Saratov State University named after N.G. Chernyshevskii. E mail: UsanovDA@info.sgu.ru
S.S. Gorbatov - Dr.Sc. (Phys.-Math.), Professor, Department "Solid State Physics", Saratov State University named after N.G. Chernyshevskii. E-mail: Gorba@yandex.ru
A.V. Fadeev - Post-graduate Student, Saratov State University named after N.G. Chernyshevskii. E-mail: Fadey24@mail.ru

Earlier investigations and numerical calculations of the field distribution and concentration of charge carriers at Gunn diode voltages from 0 to 6 Volt have been carried out. It has been shown that with increasing of current density through the diode these distributions take the form of spatial oscillations. Above 6 volt the field distribution becomes unstable and experimental measurements were impossible. In order to investigate the distribution and concentration fields at voltages higher than 6 Volt we have taken steps to eliminate low-frequency generation arising in Gunn diode on the falling part of the voltage-current characteristic. Up-to-date probe contactless techniques offer the possibility to research the distribution of charge carriers concentration in the bulk of the crystal of the semiconductor device directly in the process of its work that allows you to get accurate information about the physical processes inside the device during its functioning, in particular, about the distribution of the electric field and the charge carrier concentration for various voltages applied to it. The graphs in the article show that when the current density increases above a certain critical value before the generation threshold in the crystal the consistent increase of the number of spatial oscillations of the electric field distribution along the diode from one to four is observed. The detected regularity allows to clarify understanding of the physics of Gunn diodes work and demonstrates the possibilities of near-field microwave microscope using.