Analysis of quasi-saturation phenomena for SiGe double heterojunction bipolar transistors

Abstract

In this paper, a high-voltage current-switching NPN SiGe double-heterojunction bipolar transistor (DHBT) has been analyzed and simulated using two-dimensional device simulator MEDICI. The analysis includes conducti-vity modulation, quasi-saturation phenomenon and effect of valence band offset for holes in a high-voltage SiGe DHBT and is compared with a conventional Si bipolar junction transistor (Si BJT). The valence band offset for holes is responsible for the presence of a retarding potential barrier at collector-base junction for electrons in SiGe DHBT. The retarding potential barrier formation along with reduced conductivity modulation in SiGe DHBT leads to a fall in its short-circuit current gain hFE in comparison with Si BJT. As a consequence, the quasi-saturation current density limit JCQS of SiGe DHBT degrades and leads to high-power dissipation, setting a severe limitation on its performance at high collector current density. Keywords: SiGe DHBT, Si BJT, quasi-saturation, power dissipation, valenceformer averaging 18.02% and the latter 22.26%. Adults of P. hector utilized nearly 24 floral species as nectar sources, whose sugar concentrations (1258%) corresponded with 1550% in psychophilic flowers. They displayed a hovering habit while harvesting nectar, and frequently contacted the essential organs with probosics and head, thus promoting cross-pollination.