Modeling of junction capacitances of graded base heterojunction bipolar transistors

Abstract Capacitance models for emitter-base and collector-base junctions of graded base heterojunction bipolar transistors (HBTs) are developed. Effects of base grading on potential barriers, space-charge region (SCR) boundaries, and emitter-base and collector-base junction capacitances are investigated. The emitter-base capacitance is divided into depletion capacitance and capacitance resulting from the mobile carriers in the SCR. To obtain a closed-form solution for the capacitance, intrinsic potential is assumed to be piecewise linear. For the collector-base capacitance, depletion approximation is employed, since the junction is usually reverse-biased in normal operation. It is demonstrated that the present model is quite consistent with the measured data.

[1]  Herbert Kroemer,et al.  Heterostructure bipolar transistors: What should we build? , 1983 .

[2]  K. Morizuka,et al.  Emitter—Base bandgap grading effects on GaAlAs/GaAs heterojunction bipolar transistor characteristics , 1985, IEEE Transactions on Electron Devices.

[3]  Juin J. Liou,et al.  Forward-voltage capacitance of heterojunction space-charge regions , 1988 .

[4]  A. H. Marshak,et al.  The effect of position‐dependent dielectric constant on the electric field and charge density in a p‐n junction , 1981 .

[5]  A. H. Marshak,et al.  Electrical current in solids with position-dependent band structure , 1978 .

[6]  J. Liou.  Analytical base‐collector heterojunction capacitance model including collector current effects , 1989 .

[7]  C. T. Kirk,et al.  A theory of transistor cutoff frequency (fT) falloff at high current densities , 1962, IRE Transactions on Electron Devices.

[8]  Herbert Kroemer,et al.  Two integral relations pertaining to the electron transport through a bipolar transistor with a nonuniform energy gap in the base region , 1985 .

[9]  M. Lundstrom.  Boundary conditions for pn heterojunctions , 1984 .

[10]  B. R. Ryum,et al.  A Gummel-Poon model for abrupt and graded heterojunction bipolar transistors (HBTs) , 1990 .

[11]  R.L. Anderson.  Experiments on Ge-GaAs heterojunctions , 1962, IRE Transactions on Electron Devices.

[12]  M. Lundstrom,et al.  Modeling semiconductor heterojunctions in equilibrium , 1982 .

[13]  A. H. Marshak,et al.  Theory for nonequilibrium behavior of anisotype graded heterojunctions , 1983 .

[14]  W. Oldham,et al.  n-n Semiconductor heterojunctions , 1963 .

[15]  T. Ishibashi,et al.  High-performance AlGaAs/GaAs HBT's utilizing proton-implanted buried layers and highly doped base layers , 1987, IEEE Transactions on Electron Devices.