C.R. Bolognesi

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/.

TYPE II PHOTOLUMINESCENCE AND CONDUCTION BAND, OFFSETS OF GAASSB/INGAAS AND GAASSB/INP HETEROSTRUCTURES GROWN BY METALORGANIC VAPOR PHASE EPITAXY

The optical properties of lattice-matched GaAsSb/InGaAs/InP heterostructures with a varying InGaAs layer thickness (0–900 A) were investigated. These structures display strong low temperature type II luminescence, the energy of which varies with the InGaAs layer thickness and ranges from 0.453 to 0.63 eV. The type II luminescence was used to determine directly and accurately the conduction band offset of these structures. The values obtained herein are 0.36 and 0.18 eV at 4.2 K for the GaAsSb/InGaAs and GaAsSb/InP heterojunctions, respectively, with the GaAsSb conduction band higher in energy.

205-GHz (Al,In)N/GaN HEMTs

We report 55-nm gate AlInN/GaN high-electron-mobility transistors (HEMTs) featuring a short-circuit current gain cutoff frequency of fT = 205 GHz at room temperature, a new record for GaN-based HEMTs. The devices source a maximum current density of 2.3 A/mm at VGS = 0 V and show a measured transconductance of 575 mS/mm, which is the highest value reported to date for nonrecessed gate nitride HEMTs. Comparison to state-of-the-art thin-barrier AlGaN/GaN HEMTs suggests that AlInN/GaN devices benefit from an advantageous channel velocity under high-field transport conditions.

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.

Fully Passivated AlInN/GaN HEMTs With

We report the fabrication and characterization of 30-nm-gate fully passivated AlInN/GaN high-electron mobility transistors (HEMTs) with cutoff frequencies <i>f</i>_T and <i>f</i>_MAX simultaneously exceeding 200 GHz at a given bias point. The current gain cutoff frequency does not vary significantly for 2.5 <; <i>V</i>_DS <; 10 V, while <i>f</i>_MAX reaches a maximum value of <i>f</i>_MAX = 230 GHz at <i>V</i>_DS = 6 V. This is the first realization of fully passivated AlInN/GaN HEMTs with <i>f</i>_T/<i>f</i>_MAX ≥ 205 GHz, a performance enabled by the careful shaping of the gate electrode profile and the use of a thin 60-nm SiN encapsulation film.

f_{\rm T}/f_{\rm MAX}

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.

of 205/220 GHz

The realization of high-performance 0.1-mum gate AlGaN/GaN high-electron mobility transistors (HEMTs) grown on high-resistivity silicon substrates is reported. Our devices feature cutoff frequencies as high as fT = 75 GHz and fMAX = 125 GHz, the highest values reported so far for AlGaN/GaN HEMTs on silicon. The microwave noise performance is competitive with results achieved on other substrate types, such as sapphire and silicon carbide, with a noise figure F = 1.2-1.3 dB and an associated gain Gass = 8.0-9.5 dB at 20 GHz. This performance demonstrates that GaN-on-silicon technology is a viable alternative for low-cost millimeter-wave applications.

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

Grown on a (111) high-resistivity silicon substrate, 0.1-mum gate AlInN/GaN high-electron mobility transistors (HEMTs) achieve a maximum current density of 1.3 A/mm, an extrinsic transconductance of 330 mS/mm, and a peak current gain cutoff frequency as high as fT = 102 GHz, which is the highest value reported so far for nitride-based devices on silicon substrates, as well as for any AlInN/GaN-based HEMT regardless of substrate type. Continuous-wave power measurements in class-A operation at 10 GHz with VDS = 15 V revealed a 19-dB linear gain, a maximum output power density of 2.5 W/mm with an ~23% power-added efficiency (PAE), and a 9-dB large-signal gain. At VDS = 8 V, the output power is 1 W/mm, and the peak PAE reaches 50%. Results demonstrate the interest of AlInN/GaN on silicon HEMT technology for low-cost millimeter-wave and high-power applications.