Abstract: An apparatus of measuring an electric signal comprises a laser device, optical elements, an electrooptic crystal, a photoelectric converter, and an electric circuit. The electrooptic crystal is selected from the materials in the type of having properties of changing its refractive index in the direction of its optic major axes and the direction of these axes by a function of an applied electric field. In the apparatus, the electrooptic crystal is placed in the electric field applied by an electric circuit under measurement. A laser beam emitted from the laser device is incident on the electrooptic crystal. A reflected light passed through the crystal is resolved into rays in two polarized direction. Each ray is subjected to a photoelectric conversion by passing through the photoelectric converter and exerted as an electric output. A differential signal of the electric output is defined as a measurement signal.

Abstract: A method for controlling the thickness of a thin crystal film which is grown in a vacuum atmosphere, comprising the steps of: generating an electron beam in the vacuum atmosphere; directing the electron beam thus generated to a crystal being grown to obtain a diffraction pattern of the crystal; detecting the variations in time of the intensity of the diffraction pattern thus obtained; obtaining the number of oscillations from the variations thus detected; and interrupting the growth of the crystal in synchronism with the oscillations of the intensity when the number reaches a predetermined number. The composition ratio of a mixed crystal can be also determined by the ratio among the frequency of oscillations of each crystal which constitutes the mixed crystal. The oscillations of the intensity of the RHEED pattern can be observed more than 400 times so that the thickness of the grown thin crystal film can be measured with the accuracy higher than 1000 .ANG. in terms of the mono-layer.

Abstract: A semiconductor device comprises a superlattice semiconductor portion having a plurality of pairs of superlattice semiconductor thin films for forming step differences of band edge energy. The pairs of the thin films are laminated such that parameters which determine the structure of the thin films are monotonically changed in the direction of the lamination of the thin films. Electrodes are disposed to apply an electric field across both ends of the superlattice semiconductor portion. The semiconductor device has a good negative resistance characteristic and a large design freedom of semiconductor device.

Abstract: Planar semiconductor device including a crystalline layer of Ga.sub.x Al.sub.1-x Sb compound semiconductor (0.1<x<0.3) grown on a GaSB substrate and a narrow energy band gap semiconductor grown as an active layer on the crystalline layer and having electrodes formed on the active layer in the planar form.