Heterostructure devices, a light guiding layer having contiguous zones of different thickness and bandgap and method of making same

Described is a double heterostructure (DH) junction laser in which the intermediate layer in which light is guided is composed of an active and a passive zone which are disposed in tandem along the direction of light propagation. The active zone is thin and has a relatively narrow bandgap, and the passive zone is thicker and has a wider bandgap. The transition in thickness and bandgap between zones is relatively gradual. Also described is a monolithic integrated circuit including a DH laser and a DH modulator which have such an intermediate layer in common. In addition, described is an LPE growth technique for fabricating the intermediate layer in which two solutions, used to grow simultaneously zones of different composition, are placed on opposite sides of a partition which bifurcates one of the wells of the growth apparatus. The passive zone grows under the partition. In order to reduce mixing between the solutions, a pair of saturating seeds, separated by a divider which is aligned with the partition, are used to bring the bottoms of the two solutions to saturation.