Current Gain Cutoff Research Articles

Analysis of the emitter-down configuration of double-heterojunction bipolar transistor

A two-dimensional numerical study of the parasitic effects on current gain beta and cutoff frequency f/sub T/ of the emitter-down configuration of AlGaAs-GaAs double-heterojunction bipolar transistors (DHBTs) is reported. The studied structures include: those with and without the extrinsic emitter regions; a structure with oxygen implantation in the extrinsic emitter region; and two structures with P/sup +/ dopant implantation of 1000 and 300 AA into the extrinsic emitter region. Analysis of the structures with and without the extrinsic emitter region shows that parasitic effects associated with the extrinsic emitter seriously degrade beta and f/sub T/, and lead to extremely asymmetric DHBT operation. The three structures with the extrinsic emitter region modified by the implantations exhibit improved beta and f/sub T/ at low bias. However, the effectivenesses of the implant approaches in minimizing the parasitics are quite different. >

First microwave characterisation of LP-MOCVD grown GaInP/GaAs self-aligned HBT

The microwave characterisation of GaInP/GaAs HBTs is reported. The structures are grown by LP-MOCVD, and carbon base doping is used. The transistor design is basically multimesas and the devices are obtained using a combination of dry and wet etching. The current and power gain cutoff frequencies of these devices are, respectively, 30 GHz and 45 GHz.

Improved current gain and f/sub T/ through doping profile selection in linearly graded heterojunction bipolar transistors

Analytical and experimental results are used to show that extension of a thin p-doped layer of base doping into the graded-gap region, close to the base, of an n-p-n AlGaAs/GaAs heterojunction bipolar transistor and removing n-type dopant from the rest of the linearly graded AlGaAs region improves current gain beta and unity gain cutoff frequency f/sub T/. Current gain is significantly improved by reducing recombination near the metallurgical interface and using the effective electric field from the grading to accelerate electrons as they are injected into the p-base. The doping profile also inhibits the formation of a potential minimum in which electrons can be stored in close proximity to the base. This greatly improves f/sub T/, and does not hamper the current injection or increase the turn-on voltage. Space-charge recombination current is also reduced, due to the carrier density reduction associated with the effective electric field due to the graded gap. >

Microwave characterization of (Al,Ga)As/GaAs modulation-doped FET's: Bias dependence of small-signal parameters

Microwave characterization on 1-µm gate (Al, Ga)As/GaAs modulation-doped field-effect transistors (MODFET's) was done using a network analyzer. Equivalent circuit parameters were computed and compared to those of GaAs MESFET's with an identical geometry. The MODFET's had higher current-gain and power-gain cutoff frequencies (18 and 38 GHz versus 14 and 30GHz) and the circuit parameters g mo , C gs , and R ds displayed sharper pinchoff effects than those of the MESFET's. C gs in the MODFET displayed a gate bias dependence due to widening of the potential well in the channel. This information should prove valuable in the development of MODFET computer models for circuit simulation.