M.W. Dvorak

300 GHz InP/GaAsSb/InP double HBTs with high current capability and BV/sub CEO/>6 V

We report MOCVD-grown NpN InP/GaAsSb/InP abrupt double heterojunction bipolar transistors (DHBTs) with simultaneous values of f/sub T/ and f/sub MAX/ as high as 300 GHz for J/sub C/=410 kA/cm/sup 2/ at V/sub CE/=1.8 V. The devices maintain outstanding dynamic performances over a wide range of biases including the saturation mode. In this material system the p+ GaAsSb base conduction band edge lies 0.10-0.15 eV above the InP collector conduction band, thus favoring the use of nongraded base-collector designs without the current blocking effect found in conventional InP/GaInAs-based DHBTs. The 2000 /spl Aring/ InP collector provides good breakdown voltages of BV/sub CEO/=6 V and a small collector signal delay of /spl sim/0.23 ps. Thinner 1500 /spl Aring/ collectors allow operation at still higher currents with f/sub T/>200 GHz at J/sub C/=650 kA/cm/sup 2/.

Heavily carbon-doped GaAsSb grown on InP for HBT applications

We present the results of Hall measurements on heavily carbon-doped GaAsSb epilayers grown by metalorganic chemical vapour deposition (MOVPE) on InP substrates. An extremely strong alloy scattering e!ect is observed in this material, dominating the Hall mobility even at doping levels in the 1019 range. This e!ect is due to the very large (1 eV) valence band o!set between GaAs and GaSb. Despite the strong alloy scattering, conductivities as high as 890 S/cm were observed at doping levels above 1020 cm~3. CCl 4 and CBr 4 were investigated as p-type dopants. Hole concentrations of up to 1.4]1020 and 3.0]1020 cm~3 were obtained at growth temperatures of 5603C and 5003C, respectively. For both carbon sources, a strong reduction in growth rate and Sb incorporation rate was observed with increasing dopant concentration at 5603C. Carbon incorporation was observed to increase linearly with Sb solid phase mole fraction. ( 2000 Elsevier Science B.V. All rights reserved.

InP/GaAsSb/InP double HBTs: a new alternative for InP-based DHBTs

We report on the physical operation and performance of MOCVD-grown abrupt heterojunction InP/GaAs/sub 0.51/Sb/sub 0.49//InP double heterojunction bipolar transistors (DHBTs). In particular, the effect of the InP collector thickness on the breakdown voltage and on the current gain cutoff frequency is assessed and a f/sub T/ of 106 GHz is reported for a DHBT with a 400 /spl Aring/ base and a 2000 /spl Aring/ InP collector with a BV/sub CEO/ of 8 V. We show that InP/GaAsSb/InP DHBTs are characterized by a weak variation of f/sub T/ as a function of temperature. Finally, we also demonstrate that high maximum oscillation frequencies f/sub MAX/>f/sub T/ can be achieved in scaled high-speed InP/GaAsSb/InP DHBTs, and provide estimates of the maximum cutoff frequencies achievable for this emergent but promising material system. Recent results on improved structures validate our performance predictions with cutoff frequencies well beyond 200 GHz.

Ultrahigh performance staggered lineup ( Type-II ) InP/GaAsSb/InP NpN double heterojunction bipolar transistors

We study the performance of staggered lineup NpN InP/GaAsSb/InP abrupt double heterojunction bipolar transistors (DHBTs) intended for ultrahigh speed applications. With a peak fT of 305 GHz (and fMAX=300 GHz), InP/GaAsSb/InP DHBTs are currently the fastest bipolar transistors ever implemented, and as such may challenge sub-100 nm gate InP HEMTs for > 40 Gb/s applications: previously published criteria suggest current device performance should be suitable for 80–100 Gb/s OEICs. InP/GaAsSb/InP DHBTs feature high breakdown voltages and low offset and knee voltages, and extremely high current drive levels enabled by the lack of collector current blocking at the staggered base/collector junction. InP/GaAsSb/InP DHBTs also feature important manufacturability advantages because the structure is entirely made up of uniform composition binary and ternary alloy layers.

Impact ionization suppression by quantum confinement: Effects on the DC and microwave performance of narrow-gap channel InAs/AlSb HFET's

InAs/AlSb heterostructure field-effect transistors (HFETs) are subject to impact ionization induced short-channel effects because of the narrow InAs channel energy gap. In principle, the effective energy gap to overcome for impact ionization can be increased by quantum confinement (channel quantization) to alleviate impact ionization related nonidealities such as the kink effect and a high gate leakage current. We have studied the effects of quantum well thickness on the dc and microwave performance of narrow-gap InAs/AlSb HFETs fabricated on nominally identical epitaxial layers which differ only by their quantum well thickness. We show that a thinner quantum well postpones the onset of impact ionization and suppresses short-channel effects. As expected, the output conductance g/sub DS/ and the gate leakage current are reduced. The f/sub MAX//f/sub T/ ratio is also significantly improved when the InAs well thickness is reduced from 100 to 50 /spl Aring/. The use of the thinner well reduces the cutoff frequency f/sub T/, the transconductance g/sub m/, and the current drive because of the reduced low-field mobility due to interface roughness scattering in thin InAs/AlSb channel layers: the low-field mobility was /spl mu/=21 000 and 9000 cm/sup 2//Vs for the 100- and 50-/spl Aring/ quantum wells, respectively. To our knowledge, the present work is the first study of the link between channel quantization, in-plane impact ionization, and device performance in narrow-gap channel HFETs.

Metalorganic vapor phase epitaxy of high-quality GaAs0.5Sb0.5 and its application to heterostructure bipolar transistors

We report the growth and characterization of high-quality InP/GaAs0.5Sb0.5/InP heterostructures and their application to double-heterojunction bipolar transistors (DHBT). The GaAs0.5Sb0.5 layer quality was evaluated by high-resolution x-ray diffraction (XRD), low-temperature photoluminescence (PL), and atomic force microscopy (AFM). The observed 4.2 K PL linewidth was 7.7 meV and XRD rocking curves matched those of dynamical scattering simulations. In contrast to previously reported InP/GaAs0.5Sb0.5/InP DHBTs, the present devices show nearly ideal base and collector currents, low turn-on and collector offset voltages, and a high current gain. Self-aligned DHBTs exhibit a cutoff frequency over 75 GHz and common-emitter current gain greater than 100 at 300 K.

Anisotropic resistivity correlated with atomic ordering in p-type GaAsSb

We have detected three- and six-fold lateral ordering in undoped and carbon-doped GaAs1−xSbx films (0.4<x<0.6), using plan-view and cross-sectional transmission electron microscopy. The samples were grown by organometallic vapor phase epitaxy onto oriented InP (001) substrates, at temperatures ranging from 500 to 600 °C. Spontaneous lateral superlattices with modulation parallel to the [110] in-plane direction occur with two periodicities, 6 or 3 times the random alloy 〈110〉 lattice parameter. The degree of ordering or domain size increases with growth temperature, as seen by increasing definition of the superlattice fringes in the images, and by a change from streaks to superlattice spots in the selected area diffraction patterns. While the formation mechanism is likely a surface mediated process, no differences were detected for samples in compression or tension, or between those undoped or carbon doped. The ordering correlates with large anisotropies of up to 150% in [110]/[11_0] sheet resistance ratios.

Abrupt junction InP/GaAsSb/InP double heterojunction bipolar transistors with F/sub T/ as high as 250 GHz and BV/sub CEO/>6 V

We report manufacturable ultrahigh-speed MOCVD-grown InP/GaAsSb/InP DHBTs with f/sub T/=270 GHz and f/sub MAX/>300 GHz and featuring BV/sub CEO/>6 V with a 250 /spl Aring/ C-doped base layer. Additionally, DHBTs fabricated with a 200 /spl Aring/ base feature f/sub T/=305 GHz and f/sub MAX/=230 GHz without reducing BV/sub CEO/. The present devices are the fastest DHBTs ever reported.

On the accuracy of direct extraction of the heterojunction-bipolar-transistor equivalent-circuit model parameters C/sub /spl pi//, C/sub BC/, and R/sub E/

Several basic small-signal equivalent-circuit models for bipolar transistors lead to simple analytical expressions for the model parameters in terms of measured values. This paper investigates the accuracy of these expressions for real transistors by applying the direct extraction equations to more complicated small-signal models. The extraction of the base/collector capacitance, base/emitter capacitance, and emitter resistance are considered. Analytically derived trends are illustrated using measurements on small-area high-speed InP/GaAsSb/InP double heterojunction bipolar transistors.

High-transconductance delta-doped InAs/AlSb HFETs with ultrathin silicon-doped InAs quantum well donor layer

Modulation-doping of InAs/AlSb quantum wells generally requires the use of chalcogenide donor impurities because silicon, the usual donor of choice in MBE, displays an amphoteric behavior in antimonide compounds. In this letter, we demonstrate the use of an ultrathin 9 /spl Aring/ silicon doped InAs well to delta-dope the current-carrying InAs channel of an InAs/AlSb heterostructure field-effect transistor (HFET). Using this new approach, we have fabricated delta-doped 0.6-/spl mu/m gate InAs/AlSb HFETs with a measured extrinsic transconductance of 800 mS/mm at V/sub DS/=0.8 V, a cutoff frequency f/sub T/=60 GHz (F/sub MAX/=87 GHz), and well-behaved I-V curves. HFETs with a 2-/spl mu/m gatelength also feature very high transconductances in the 700-800 mS/mm range at V/sub DS/=1.5 V. The present work eliminates the requirement for chalcogenide compound donor sources to delta-dope InAs/AlSb quantum wells by allowing the use of silicon in the fabrication of high-performance InAs/AlSb HFETs.