S. P. Watkins

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.

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.

Low‐temperature photoluminescence of epitaxial InAs

Photoluminescence studies as well as reflectance and transmittance measurements were performed on high‐purity epitaxial InAs grown by metal‐organic chemical‐vapor deposition. We report the optical identification of excitonic, donor, and acceptor impurity related transitions at a temperature of 1.4 K. Measurements at higher temperature and in the presence of magnetic fields up to 7 T support these identifications. We find the excitonic band gap at 415.65±0.01 meV according to the minimum in the polariton reflectance feature. The donor–acceptor‐pair and acceptor‐bound exciton transitions for three different acceptors are observed by photoluminescence, and we tentatively associate one of them to a double acceptor formed by a Ga impurity on an As lattice site. A donor‐bound exciton transition is observed with a binding energy of 0.42 meV. The magnetic field dependence yields values of the electron effective mass and g factor of (0.026±0.002)m0 and −15.3±0.2, respectively, in good agreement with values obtaine...

Strain balanced InAs/InAsSb superlattice structures with optical emission to 10 μm

We report the growth and optical characterization of InAsSb/InAs strain balanced superlattice structures on GaSb substrates for potential application in midinfrared photodetectors. Photoluminescence (PL) emission was observed in the range 5 μm≤λ≤10 μm at 4 K for Sb compositions 0.14≤xSb≤0.27. The PL energy was found to depend approximately linearly on antimony, consistent with a type II band lineup. The dependence of the emission energies on the Sb mole fraction is in agreement with trends predicted by various theoretical works. The data suggest that this transition reaches zero energy for a composition of xSb=0.37.

Probing the electrical transport properties of intrinsic InN nanowires

We have studied the electrical transport properties of intrinsic InN nanowires using an electrical nanoprobing technique in a scanning electron microscope environment. It is found that such intrinsic InN nanowires exhibit an ohmic conduction at low bias and a space charge limited conduction at high bias. It is further derived that such InN nanowires can exhibit a free carrier concentration as low as ∼1013 cm−3 and possess a very large electron mobility in the range of 8000–12 000 cm2/V s, approaching the theoretically predicted maximum electron mobility at room temperature. In addition, charge traps are found to distribute exponentially just below the conduction band edge, with a characteristic energy ∼65 meV.

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.

High mobility InAs grown on GaAs substrates using tertiarybutylarsine and trimethylindium

We report transport measurements on a series of high purity InAs epilayers grown on GaAs substrates by metalorganic chemical vapor deposition using tertiarybutylarsine and trimethylindium. Perfectly specular surfaces were obtained by a two step growth method consisting of a 400 °C prelayer followed by deposition of the thick bulk layer at higher growth temperatures. Temperature dependent Hall measurements between 1.8 and 293 K showed a competition between bulk and surface conduction, with average Hall mobilities of up to 1.2×105 cm2/V s at 50 K. Large changes in the temperature dependent transport data are observed several hours after Hall contact formation and appear to be due to passivation of the surface accumulation layer by native oxide formation.