This paper describes a novel heterojunction bipolar transistor (HBT) structure, the collector-up tunneling-collector HBT (C-up TC-HBT), that minimizes the offset voltage V/sub CE,sat/ and the knee voltage V/sub k/. In this device, a thin GaInP layer is used as a tunnel barrier at the base-collector (BC) junction to suppress hole injection into the collector, which results in small V/sub CE,sat/. Collector-up configuration is used because of the observed asymmetry of the band discontinuity between GaInP and GaAs depending on growth direction. To minimize V/sub k/, we optimized the epitaxial layer structure as well as the conditions of ion implantation into the extrinsic emitter and post-implantation annealing. The best results were obtained when a 5-nm-thick 5/spl times/10/sup 17/-cm/sup -3/-doped GaInP tunnel barrier with a 20-nm-thick undoped GaAs spacer was used at the BC junction, and when 2/spl times/10/sup 12/-cm/sup -2/ 50-keV B implantation was employed followed by 10-min annealing at 390/spl deg/C. Fabricated 40/spl times/40-/spl mu/m/sup 2/ C-up TC-HBTs showed almost zero V/sub CE,sat/ (<10 mV) and a very small V/sub k/ of 0.29 V at a collector current density of 4 kA/cm/sub 2/, which are much lower than those of a typical GaInP/GaAs HBT. The results indicate that the C-up TC-HBT's are attractive candidates for high-efficiency high power amplifiers.

GaInP/GaAs collector-up tunneling-collector heterojunction bipolar transistors (C-up TC-HBTs): optimization of fabrication process and epitaxial layer structure for high-efficiency high-power amplifiers

In this paper, thermal stability in the multifinger GaInP/GaAs collector-up tunneling-collector heterojunction bipolar transistors (C-up TC-HBTs) has been investigated. Two unique structures in these C-up TC-HBTs are provided for thermal management for a stable operation. One is the base layer that is incorporated with highly resistive regions, which serves as a ballast resistor, due to the boron-ion implantation. The other is the backside via-hole structure constructed underneath the transistors called "the subtransistor via-hole structure", leading to a superior thermal conduction. In this paper, as a result, it was revealed that the effect of the via hole on the thermal stability depends on the effect of the base resistance on the thermal stability. The thermal stability in the C-up TC-HBTs, with a relatively lower base resistance due to the boron-ion implantation of 1times10 12 cm-2, is attributed to the decrease in the thermal resistance due to the via hole, while that in the C-up TC-HBTs, with a boron-ion implantation of 2times1012 cm-2, is dominated by a relatively large base resistance. Moreover, with a reduction in the finger space in the four-finger C-up TC-HBTs with a low base resistance, the range of a thermally stable operation is found to become narrower. This can be explained by the dependence of the thermal resistance on the finger space in the four-finger C-up TC-HBTs. These results are useful for the device design, so as to obtain the thermal stability in the C-up TC-HBTs with a subtransistor via-hole structure, for application in the small and high-power amplifiers

Investigation of Thermal Stability in Multifinger GaInP/GaAs Collector-Up Tunneling&#8211;Collector HBTs With Subtransistor Via-Hole Structure

AlGaAs/GaAs/GaAs and GaInP/GaAs/GaAs n-p-n heterojunction bipolar transistors (HBTs) are now in widespread use in microwave power amplifiers. In this paper, improved HBT structures are presented to address issues currently problematic for these devices: high offset and knee voltages and saturation charge storage. Reduced HBT offset and knee voltages (V/sub CE,os/ and V/sub k/) are important to improve the power amplifier efficiency. Reduced saturation charge storage is desirable to increase gain under conditions when the transistor saturates (such as in over-driven Class AB amplifiers and switching mode amplifiers). It is shown in this paper that HBT structures using a 100-/spl Aring/-thick layer of GaInP between the GaAs base, and collector layers are effective in reducing V/sub CE,os/ to 30 mV and V/sub k/ measured at a collector current density of 2/spl times/10/sup 4/ A/cm/sup 2/ to 0.3 V (while for conventional HBTs V/sub CE,os/=0.2 V and V/sub k/=0.5 V are typical). A five-fold reduction in saturation charge storage is simultaneously obtained.

Design and performance of tunnel collector HBTs for microwave power amplifiers

Temperature dependence of electron impact ionization in InGaP-GaAs-InGaP double heterojunction bipolar transistors (DHBTs) were comprehensively studied in the temperature range of 300 to 450 K. It has been found that, as the temperature increases, the electron multiplication in the InGaP collector is found to be weakly reduced, which results in a relatively small negative temperature dependence of junction breakdown. The temperature dependence of electron impact ionization at elevated temperatures for InGaP material is investigated based on the electron multiplications measured from the InGaP collector region. An empirical expression is obtained to predict the electron ionization coefficients at elevated temperature up to 450 K in the electric field range of 380 to 650 kV/cm. As compared to InP and GaP binaries, the ternary InGaP shows a lower electron ionization coefficient and much weaker temperature dependence. We found that, introducing additional scattering mechanism such as alloy scattering would provide a better interpretation on the low electron impact ionization and its weak temperature dependence observed in InGaP.

Temperature dependence of the electron impact ionization in InGaP-GaAs-InGaP DHBTs

The kink phenomenon in heterojunction bipolar transistors (HBTs) is introduced and mathematically analyzed. A novel composite transistor based on feedback theory is proposed to suppress the kink phenomenon with negligible increase in chip area and power consumption. According to the small-signal analysis, the output impedance of the composite transistor can be represented by an RC series circuit. Thus, the output resistance is a constant value over a wide frequency range. A test die using 2-μm InGaP/GaAs HBT technology from AWSC is fabricated, and a constant real part of S22 is measured from 0.1 to 20 GHz (approaching the HBT's unity-gain frequency). The proposed composite transistor can significantly ease the design for output matching and broadband amplifiers.

A Composite Transistor to Suppress Kink Phenomenon in HBTs for Broadband Design

Next-generation power amplifiers must operate at lower supply voltages without sacrificing linearity or efficiency. GaInP/GaAs double-heterojunction bipolar transistors with GaInP collectors can improve over GaAs single-heterojunction bipolar transistors (HBTs) in power-amplifier applications, based on lower offset voltage, increased breakdown electric field, and absence of saturation charge storage. To best exploit these characteristics, amplifier architectures that employ HBTs in switching mode can be used.

M.C. Vincent Ho

Papers

Application of GaInP/GaAs DHBTs to power amplifiers for wireless communications