In the present work the discovery and inventive achievement of Georgi Nadjakov are examined in the field of solid state physics and measurement technique. In 1937 Georgi Nadjakov discovered the photoelectret state of substances. Later on in the forties and the fifties of the past century, his investigations on the photovoltaic effect in wide gap semiconductors lead to the discovery of the contact-potential photovoltaic effect. In the middle of the sixties when the expression of the young generation scientists – physicists in inventive activity began, Georgi Nadjakov realized his inventions in the field of electrostatic electrometry.

       The discovered photoelectret state of substances is the first recognized Bulgarian discovery in XX century. Its importance assigned Georgi Nadjakov to be on the first page of “Golden book of Bulgarian discoverers and inventors” created in 1981.

Inventive Achievement 2006, 0:48 K. Kolentsov

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