InSb-like Interface Research Articles

Characterization of AlSb/InAs surfaces and resonant tunneling devices

We have studied the evolution of AlSb-on-InAs(001) surfaces and interfaces grown by molecular-beam epitaxy using in situ scanning tunneling microscopy. We find that forming InSb-like interfacial bonds on an InAs(001)-(2×4) surface creates surface roughness because the surface In coverage inherent to the (2×4) reconstruction is insufficient to form a complete InSb(001)-(1×3)-like surface layer. This morphological roughness can be eliminated by depositing additional In to compensate for the different compositions of the reconstructions. We have also grown three different 5-monolayer-thick films of AlSb on the InSb-like interface to study the effect of growth conditions on the film surface morphology. The AlSb surface can be improved by either raising the growth temperature or by growing the film using migration-enhanced epitaxy. Finally, we present electrical characterization of InAs/AlSb/GaSb resonant interband tunneling devices fabricated with different growth procedures. The possible effects of various growth procedures on interfacial quality and device properties are discussed.

Raman Spectroscopy of Doping Sheets and Heterointerfaces inIII-V Semiconductor Structures

Raman spectroscopy was used to study vibrational modes of Si δ-doping sheets and Si monolayers inserted in GaAs and to investigate mechanical interface modes in InAs/GaSb and InAs/AlSb heterostructures. Increasing the concentration of Si embedded in GaAs in a single layer from 1012–1013 cm−2, corresponding to typical concentrations for Si δ-doping in GaAs, to a monolayer (ML) coverage (1 ML=6.2×1014 cm−2) leads to a discontinuous change in the Raman spectrum from local vibrational modes of substitutional Si to a vibrational band at significantly higher wavenumbers. This band has been identified with vibrational modes of two-dimensional clusters of covalently bonded Si embedded in GaAs. In InAs/GaSb superlattices both GaAs-like and InSb-like interface modes were resolved, depending on the intended formation of either Ga—As or In—Sb interface bonds. For InAs/AlSb heterostructures, however, only the InSb-like interface mode was observed, indicating the formation of InSb-like interface bonds, irrespective of the intended growth of either In—Sb or Al—As interface bonds.

Raman Spectroscopy of Doping Sheets and Heterointerfaces inIIIV Semiconductor Structures

Raman spectroscopy was used to study vibrational modes of Si δ-doping sheets and Si monolayers inserted in GaAs and to investigate mechanical interface modes in InAs/GaSb and InAs/AlSb heterostructures. Increasing the concentration of Si embedded in GaAs in a single layer from 1012–1013 cm−2, corresponding to typical concentrations for Si δ-doping in GaAs, to a monolayer (ML) coverage (1 ML=6.2×1014 cm−2) leads to a discontinuous change in the Raman spectrum from local vibrational modes of substitutional Si to a vibrational band at significantly higher wavenumbers. This band has been identified with vibrational modes of two-dimensional clusters of covalently bonded Si embedded in GaAs. In InAs/GaSb superlattices both GaAs-like and InSb-like interface modes were resolved, depending on the intended formation of either Ga—As or In—Sb interface bonds. For InAs/AlSb heterostructures, however, only the InSb-like interface mode was observed, indicating the formation of InSb-like interface bonds, irrespective of the intended growth of either In—Sb or Al—As interface bonds.

Raman scattering by folded longitudinal acoustic phonons in InAs/GaSb superlattices: Resonant enhancement and effect of interfacial bonding

We have studied backfolded longitudinal acoustic (LA) phonons in InAs/GaSb superlattices (SLs) intentionally grown with either InSb-like or GaAs-like interfaces (IFs). Raman scattering by folded LA phonons was found to be resonantly enhanced for incident photon energies slightly below the 2.0 eV electronic SL interband transition, observed previously by spectroscopic ellipsometry and by resonant Raman scattering from longitudinal optical SL phonons. Under resonant excitation, InAs/GaSb SLs with InSb-like IFs showed scattering by folded LA phonons up to the 7th order. For SLs with GaAs-like IFs, the folded LA phonon modes occurred at systematically higher frequencies than for SLs with the same nominal period and InSb-like IFs. The difference in frequency increased with decreasing SL period.

Structural Properties of InAs/AlSb Superlattices

ABSTRACTShort-period (InAs)6/(AlSb)6 superlattices (SL) with AlAs-like and InSb-like interfaces (IF) grown on a relaxed AlSb buffer layer are studied by X-ray reflectivity and diffractometry measurements. Reflectivity measurements reveal average IF roughnesses between 0.6 and 1.0 nm. Measurements of the diffuse scattering show that the roughness is highly correlated from layer to layer. Triple crystal area scans illustrate that the inhomogeneous deformation of the buffer layer leads to a certain symmetric peak broadening. In the case of AlAs-like IFs an additional broadening of the SL peaks reveals lattice parameter gradients over the superlattice. This asymmetric peak broadening may be attributed to a further relaxation of the superlattice, which is inhomogeneous with depth. The diffusion of As into the AlSb layers leads to a peak shift and modifies the intensity ratios of the different satellite reflections. The best structural quality is achieved for superlattices with InSb-like IFs.

Growth of InAs/GaSb strained layer superlattices. I

InAs/GaSb strained layer superlattices (SLSs) have been grown by metalorganic vapour phase epitaxy (MOVPE) at atmospheric pressure. Whilst long period SLSs have been successfully grown by this technique, the growth of short period structures is adversely affected by step-bunching. By growing the SLSs faster and cooler, good periodicity was achieved as measured by Raman spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction (XRD) in SLSs with bilayer (GaSb + InAs) thicknesses as thin as 50 Å. We have also detected the InSb-like and GaAs-like interface modes from room temperature Raman measurements for the first time in MOVPE grown samples. The most promising samples have been assessed by FIR photoconductivity at 4.2 K and show bandgaps (dependent on the bilayer thickness) between 5 and 20 μm.

Interface formation in InAs/AlSb and InAs/AlAs/AlSb quantum wells grown by molecular-beam epitaxy

We have used resonant Raman scattering from both longitudinal-optical phonons and interface modes to study the chemical bonding across the InAs/AlSb interface in InAs/AlSb quantum wells grown by molecular-beam epitaxy. The effusion cell shutter sequence at the interfaces was selected for the deposition of either one monolayer of InSb or two to three monolayers of AlAs. In all cases an InSb-like interface mode is observed, indicating the preferential formation of In—Sb interface bonds irrespective of the shutter sequence. The deposition of two or three monolayers of AlAs at the InAs/AlSb interface results in the formation of pseudoternary AlSb1−xAsx barriers rather than binary AlAs interfaces and AlSb barriers, indicating a strong exchange among the group-V atoms. Normal (AlSb on InAs) and inverted (InAs on AlSb) InAs/AlSb interfaces have also been compared, revealing a much stronger InSb-like interface mode for the growth of AlSb on InAs than for the case of InAs grown on AlSb.

Raman spectroscopic study of heterointerfaces in GaSb and InSb on GaAs and in InAs/(AlGa)Sb quantum structures

Abstract Resonant Raman scattering by longitudinal optical (LO) phonons as well as by interface modes has been used to investigate the heteroepitaxial growth of GaSb and InSb on GaAs, which are combinations of materials exhibiting a large lattice mismatch, and to study the heterointerfaces in nearly lattice matched InAs/ (AlGa)Sb quantum wells and superlattices. Resonant LO phonon scattering is found to provide detailed insight in the initial stage of heteroepitaxial growth revealing a significant intermixing of the group V atoms at the GaAs/GaSb interface. For GaSb-capped InAs/AlSb quantum well structures tuning the incident photon energy into resonance with an appropriate band gap energy of one of the constituents allows the vibrational modes of that individual layer to be probed selectively, in spite of the almost coincident InAs and GaSb LO phonon frequencies. Similarly, in InAs/GaSb superlattices scattering by the InSb-like or GaAs-like interface modes, depending on whether the structure was grown wi...

Studies of GaSb-capped InAs/AlSb quantum wells by resonant raman scattering

We have used resonant Raman scattering to study GaSb-capped AlSb/InAs/AlSb quantum wells grown by molecular-beam epitaxy. The shutter sequence for the growth of the InAs/AlSb heterointerfaces was such as to promote the formation of an InSb-like interface. Scattering by an InSb-like mode at ⋍ 190 cm −1 is found to resonate at approximately the InAs E 1/ E 1 + Δ 1 gap energy, supporting its assignment to an interface mode. Resonance effects in scattering by longitudinal optical (LO) phonons enabled us also to distinguish between scattering by the almost degenerate LO phonon modes in the InAs quantum well and in the GaSb cap layer. The GaSb and the AlSb one-LO phonon spectra indicate the unintentional incorporation of As at concentrations up to 18–19% in the GaSb and AlSb layers for As background pressures in the growth chamber exceeding 10 −9 torr. The incorporation of As was confirmed independently by secondary ion mass spectroscopy.

Raman spectroscopic study of interfaces in InAs/AlSb AND InAs/AlAs/AlSb quantum wells grown by molecular beam epitaxy

Raman scattering from both longitudinal optical phonons and interface modes has been used to study the chemical bonding across the InAs/AlSb interface in GaSb capped InAs/AlSb quantum wells grown by solid-source molecular-beam epitaxy. The effusion cell shutter sequence for the growth of the interfaces was selected for the deposition of either 1 monolayer (ML) of InSb or g to 3 MLs of AlAs. The latter growth sequence should in principle strongly favour the formation of AlAs-like interfaces. In all cases an InSb-like interface mode is observed, indicating the preferential formation of In-Sb bonds irrespective of the shutter sequence. This behaviour is in contrast to that found for InAs/GaSb heterostructures where both types of interface bonds, InSb-like and GaAs-like, were observed according to the shutter sequence. The deposition of 2 or 3 MLs of AlAs at the InAs/AlSb interface results in the formation of pseudo-ternary AlSb 1-xAs x barriers rather than binary AlAs interfaces and AlSb barriers, indicating a strong exchange among the group V atoms. PACS: 6g.35.Ja, 68.55.Bd, 78.30.Fs

Characterization of heterointerfaces and surfaces in InSb on GaAs and in InAs/AlSb quantum wells

Resonant Raman scattering by longitudinal optical (LO) phonons and by interface modes was used to study InSb/GaAs and InAs/AlSb heterointerfaces for InSb on GaAs and for InAs/AlSb quantum wells respectively, grown by molecular beam epitaxy. Raman spectra recorded from samples with InSb layers ranging in thickness from 10 to 300 monolayers indicate that, to achieve two-dimensional growth of InSb on GaAs with good crystalline quality, the layer thickness must exceed around 100 monolayers. From the dependence on excitation power of electric-field-induced LO phonon scattering measured for a series of n- and p-type doped thick InSb layers, it is concluded that the surface Fermi level is pinned at the valence band edge. In InAs/AlSb quantum wells, scattering by an InSb-like interface mode is observed which resonates at approximately the InAs E 1 energy gap.

Effect of interface composition on the band offsets at InAs/AlSb (001) heterojunctions

X-ray photoemission spectroscopy has been used to directly measure the dependence of the valence band offset ΔEv on interface composition (AlAs-like versus InSb-like) for InAs/AlSb (001) heterojunctions grown by molecular-beam epitaxy. A staggered band alignment with a consistent average value of ΔEv = 0.16 eV is measured for three samples with the InSb-like interface. A difference of 0.07 eV is observed between the average ΔEv values for two AlAs-like interface samples (0.15 and 0.22 eV, respectively). The growth-to-growth variation in ΔEv value for the AlAs-like interface, and the 0.06 eV difference between the InSb-like ΔEv value and the larger AlAs-like ΔEv value are both attributed to interface composition differences. We interpret the ΔEv = 0.22 eV value as being most characteristic of the AlAs-like interface. A tight binding model calculation of the effect of local strain on InAs/AlSb band offsets is compared to experiment.