Semiconductor optical device with light controlling layer of super-lattice structure

DETAILED DESCRIPTION It is therefore an important object of the present invention to provide a semiconductor optical device which is free from the problem inherent in the prior art semiconductor optical devices.
To accomplish the object, the present invention proposes to form a light controlling layer implemented by a type-II super-lattice structure where a first electron affinity and the top edge of the valence band of a first compound semiconductor are smaller than the electron affinity and the top edge of the valence band of a second compound semiconductor, respectively.
In accordance with the present invention, there is provided a semiconductor optical device outputting a variable light beam, comprising: a) a substrate; b) a light controlling layer formed over the substrate, and responsive to an electric field for varying the light beam, the controlling layer having a super-lattice structure formed by using a first compound semiconductor material and a second compound semiconductor material, the first compound semiconductor material having a first electron affinity and a first energy band gap, the second compound semiconductor material having a second electron affinity larger than the first electron affinity and a second energy band gap, the total of the second electron affinity and the second energy band gap being larger than the total of the first electron affinity and the first energy band gap; and c) an electrode structure for varying the electric field.
The semiconductor optical device may be one of a light modulator of the electro-absorbing type, a light modulator of the electro-refraction type and a tunable laser emitting diode.