Madjid Hafizi

The DC characteristics of GaAs/AlGaAs heterojunction bipolar transistors with application to device modeling

A complete DC model for the heterojunction bipolar transistor (HBT) is presented. The DC characteristics of the HBT are compared with the Ebers-Moll (EM) model used by conventional bipolar junction transistors (BJTs) and implemented in simulation and modeling programs. It is shown that although the details of HBT operation can differ markedly from those of a BJT, a model and a parameter extraction technique can be developed which have physical meaning and are exactly compatible with the EM models widely used for BJTs. Device I-V measurements at 77 and 300 K are used to analyze the HBT physical device performance in the context of an EM model. A technique is developed to extract the device base, emitter, and collector series resistances directly from the measured I-V data without requiring an ideal exp(qV/sub be//kT) base current as reference. Accuracies of the extracted series resistances are assessed. AC parameters of HBT are calculated numerically from the physical device structure. For modeling purposes, these parameters are shown to be comparable with those of conventional BJTs. >

Experimental study of AlGaAs/GaAs HBT device design for power applications

An experimental study of AlGaAs/GaAs heterojunction bipolar transistor (HBT) device design for optimizing key DC and RF performance parameters relevant to power device applications is reported. The design of the collector, base, and base-emitter junction is investigated for improved power device performance, and novel device structures are presented. Device scaling effects and the extent to which air-bridged interconnect can reduce parasitics in large power devices are also explored. Power HBTs employing some of the optimized design features have achieved a power output of 1.2 W (4 W/mm) with 43% power-added efficiency at 10 GHz.<<ETX>>

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. >

High-efficiency InP-based DHBT active frequency multipliers for wireless communications

We present, for the first time, the performance of AlInAs/GaInAs/InP double heterostructure bipolar transistors (DHBTs) as active frequency multipliers at frequencies of relevance to Wireless Communications applications. In particular, we present results comparing the performance of X6 (127/spl rarr/762 MHz) and X4 (762.5/spl rarr/3050.0 MHz) InP- and Si-based (NEC2107) multiplier circuits. A well-known multiplier circuit topology has been chosen as a vehicle, so that we can focus on active device comparison. The X6 InP-based multiplier exhibits output power and efficiency of +6 dBm and 11%, respectively, compared to +7.2 dBm and 4.8% of the Si-based circuit. The X4 InP-based multiplier exhibits output power and efficiency of +3.74 dBm and 8%, respectively, compared to -6.1 dBm and 0.4% of the Si-based circuit. The superior electronic properties of InP-DHBTs enable high-conversion gain/highly DC-efficient multipliers, however, their nonexponential I/sub C/-V/sub BE/ characteristic limits the maximum obtainable conversion gain at high-order frequency multiplication.