O.J. Pitts

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.

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.

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.

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.

Antimony segregation in GaAs-based multiple quantum well structures

Sb segregation effects have been studied in structures grown by organometallic vapor phase epitaxy. The structures are formedby periodic exposure of the GaAs (0 0 1) surface to trimethylantimony (TMSb), followedby GaAs growth. Reflectance-difference spectra obtained during growth show a strong influence of Sb on the surface reconstruction, reducing the concentration of As dimers. Transmission electron microscope images and X-ray diffraction (XRD) measurements show that a periodic multiple quantum well (MQW) structure is formed by the TMSb/GaAs growth sequence. A fraction of the deposited Sb is incorporated as a one monolayer thick Sb-rich quantum well in each period. The incorporation of impurity Sb, as the GaAs layers are grown, results in the formation of a graded GaAs1� xSbx barrier layer above each QW layer. The impurity profile inferredfrom XRD measurements is in goodagreement with a one-dimensional segregation model based on the partitioning of Sb between the growing barrier layer and a surface floating layer. The Sb floating layer is shown to desorb under exposure to tertiarybutylarsine. r 2003 Elsevier Science B.V. All rights reserved.

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.

Local vibrational modes of carbon in GaSb and GaAsSb

We have measured the Raman spectra of heavily carbon doped (p>1019 cm−3) GaSb and GaAsSb. A local vibrational mode (LVM) due to carbon residing on group-V lattice sites was observed at 540 cm−1 for GaSb and 568 cm−1 for GaAs0.44Sb0.56. A gap mode at 164 cm−1 was observed for GaSb. The frequency of the LVM as well as the gap mode is in quantitative agreement with recent theoretical predictions.

InAsSb and InPSb materials for mid infrared photodetectors

III-V semiconductor materials are under active investigation for use as optical detectors in the mid infrared wavelength region from 3 to 12 µm. In this paper we summarize recent progress on the development of III-V materials for this application based on the material InAsSb. We first present the results of investigations in the use of strained balanced type II superlattices of InAsSb/InAs to extend the absorption wavelength of this material system beyond the limits of the maximum InAsSb bulk value. We present results on the growth of InPSb heterojunction structures with the aim of reducing thermal diffusion current and surface leakage. Finally we present some preliminary device results indicating the promise of this material system.

Ultrahigh performance staggered lineup ("Type II") InP/GaAsSb/InP NpN DHBTs

Using a conventional emitter-up triple-mesa process, we have fabricated C-doped InP/GaAsSb/InP double heterojunction bipolar transistors (DHBTs) exhibiting both f/sub T/ and f/sub MAX/=300 GHz while maintaining a breakdown voltage BV/sub CEO/=6 V. Our devices feature stable and well-behaved common-emitter DC and RF characteristics up to J/sub C/=500 kA/cm/sup 2/ without any passivation nor heatsinking. InP/GaAsSb/InP abrupt junction DHBTs couple unprecedented performance to apparent manufacturability advantages which should enable applications well beyond 40 Gb/s and challenge InP HEMTs in the 80-100 Gb/s arena.

Structural effects of carbon in GaSb grown by metalorganic vapor phase epitaxy

High-resolution X-ray diffraction, Hall effect and secondary ion mass spectrometry measurements (SIMS) were used to study the effect of carbon doping on the lattice constant of GaSb. A linear increase in tensile strain as a function of carbon concentration was observed in the range from 1 x 10 19 to 1 x 10 20 cm -3 . The observed strains are consistent with carbon incorporating as a simple substitutional acceptor up to at least 1 x 10 20 cm -3 . SIMS measurements show that the total carbon concentration is linearly proportional to the CCl 4 source flows, whereas the hydrogen concentration increases super-linearly. Nevertheless, the ratio of hydrogen to carbon is no greater than 9% of the maximum incorporated carbon concentration.