Unified planar process for fabricating heterojunction bipolar transistors and buried heterostructure lasers utilizing impurity-induced disordering

One goal of optoelectronic integration is to realize a low-threshold laser structure and a transistor structure of the same substrate. In pursuit of this goal, the authors have developed a novel transistor structure which they call a lateral heterojunction bipolar transistor (L-HBT). Impurity-induced disordering (IID) accomplished by silicon diffusion is used to convert a buried p-type GaAs layer into n-type AlGaAs regions that serve as the emitter and collector of the heterojunction bipolar transistor. The resulting transistor structure is completely planar, and current flow from the emitter through the base to the collector occurs in the plane of the base layer as opposed to perpendicular to the plane of the base layer, as is the case in conventional heterojunction bipolar transistors. The authors have fabricated this transistor structure and observed transistor action with a maximum current gain of β=5-10 for base widths of 1.4 μm. They have also observed room-temperature laser operation from the transistor structure with a threshold current of 6 mA for the same 1.4-μm-wide stripe that exhibits transistor action. This threshold current value compares favorably with those routinely obtained in a more conventional buried heterostructure laser. They refer to this laser structure as a heterotransverse junction (HTJ) laser, due to the fact that current is injected along the plane of the epitaxial layers. The geometry of the laser is suitable for applications involving high-speed modulation and/or integration with other optoelectronic components