Epitaxial emitter structure

To design a transistor with a 1.6-GHz intrinsic we should examine the factors that affect the of the transistor. A simplified cross section of the epitaxial emitter structure is shown in Figure 6.23. The stripe geometry has been assumed. All microwave transistors are fabricated more or less with this geometry. The intrinsic part, directly under the emitter, is the active part of the transistor. The extrinsic part, which connects the intrinsic base (under the emitter) to the base contacts, is the parasitic part of the transistor. The effects of these two parts on the transistor can be evaluated by the following formula [22] ... 

The epitaxial emitter structure was fabricated, as shown in Figure 6.26 [23]. In this case, only 1,000-A-thick, p-type base layer doped at 2 x 10 cm is grown. This is followed by an epitaxial growth of 3,000-A-thick n emitter layer. The emitter layer is etched using RIE to stop at the base layer. The rest of the process details are similar to those described in Section 6.4. The most difficult step in this process is the etching of the emitter layer and stopping at the base layer. The uniformity of the RIE is critical at this step. 

Figure 6.26 An idealized cross-section of the epitaxial emitter structure with a pitch of 6 m.

Heterojunction Photodiode. In the early 1960s there was considerable interest in semiconductor heterojunctions for use as wide gap emitters in transistors. The heterojunctions were formed by epitaxial growth of one semiconductor, e.g. GaAs, on another, e.g. Ge, having a similar lattice structure and periodicity. Rectification properties could be observed not only in the p—n junction configuration but also in n—n and p — p configurations. The reasons for this were detailed by Anderson [2.44]. 

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