Two significant advances in materials during the past year have been (1) the growth of much better gallium arsenide and gallium phosphide single crystals through the use of liquid epitaxy techniques, and (2) the synthesis of new single-crystalline materials such as lithium tantalate and barium sodium niobate. The gallium arsenide and gallium phosphide crystals have been used in constructing improved solid-state lasers, electroluminescent lamps, and Gunn oscillators, while the latter materials have been used in nonlinear optical systems.
The greater quantum efficiencies of both red and green gallium phosphide electroluminescent diodes attained during the past year were mainly due to improved methods of crystal growth and better p-n junction preparation. The technique of liquid epitaxy was of prime importance in this development. Although red diodes are presently 50 to 100 times more efficient than green ones, they have approximately the same brightness, because the human eye and certain photographic film are approximately 20 times more sensitive to green light than to red.
This invention is epochal. It was the first of those photomechanical techniques that were soon to revolutionize the graphic arts by eliminating the hand of man in the reproduction of pictures of all kinds. It is the most important of Niepce's contributions, for it involved a principle that became basic to future techniques: the differential hardening by light of a ground that would control the etching in exact counterpart of the image.
Two significant advances in materials during the past year have been (1) the growth of much better gallium arsenide and gallium phosphide single crystals through the use of liquid epitaxy techniques, and (2) the synthesis of new single-crystalline materials such as lithium tantalate and barium sodium niobate. The gallium arsenide and gallium phosphide crystals have been used in constructing improved solid-state lasers, electroluminescent lamps, and Gunn oscillators, while the latter materials have been used in nonlinear optical systems.