Active solid-state devices (e.g. – transistors – solid-state diode – Heterojunction device – Bipolar transistor
Patent
1994-12-01
1997-02-25
Fahmy, Wael
Active solid-state devices (e.g., transistors, solid-state diode
Heterojunction device
Bipolar transistor
257198, 257191, H01L 310328, H01L 310336, H01L 31072
Patent
active
056061854
ABSTRACT:
A double heterojunction bipolar transistor (DHBT) is provided with a parabolic grade in bandgap at the base-collector junction. The parabolic grade in bandgap is close to parabolic in composition. The parabolic grade in bandgap is achieved by employing a chirped superlattice to mimic the parabolically varying alloy composition. Each period of the superlattice consists of one low-bandgap layer and one high-bandgap layer. The average composition in each period is determined by the relative thicknesses of these two layers. By varying the thickness ratio of these two layers approximately parabolically with (i) the distance from the base for a concave parabola and (ii) the distance from the collector for a convex parabola, the intended parabolic grade is achieved. The exact values may be computed numerically.
REFERENCES:
patent: 5170407 (1992-12-01), Schubert et al.
C. G. Van de Walle, "Band lineups and deformation potentials in the model-solid theory", Physical Review, vol. B39, pp. 1871-1881 (15 Jan. 1989).
Liu Takyiu
Nguyen Chanh
Denson-Low W. K.
Duraiswamy V. D.
Fahmy Wael
Hughes Aircraft Company
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