T-Shaped Emitter Metal Structures for HBTs

Metal emitter structures in a class of developmental InP-based high-speed heterojunction bipolar transistors (HBTs) have been redesigned to have Tshaped cross sections. More precisely, the modified cross sections can be characterized as having highly stylized T-shapes that are modified versions of prior trapezoidal shapes (see figure). T- cross- section metal features have been widely used in Schottky diodes and high electron- mobility transistors, but not in HBTs. As explained below, the purpose served by the present T- cross-sectional shapes is to increase fabrication yields beyond those achievable with the prior cross-sectional shapes.