In InAs-AlSb quantum wells grown by molecular beam epitaxy, the two possible bonding configurations at each heterointerface (InSb-like versus AlAs-like, arising because InAs and AlSb share no common anion) were shown by Brar, Ibbetson, Kroemer and English in 1994 to shift the low-temperature photoluminescence peak by 96 meV, with linewidths of about 55 meV in both cases, pseudomorphic growth for InSb-like interfaces and heavy dislocation for AlAs-like ones. A minimal 1+1 monolayer inserted-well envelope-function estimate attributed the shift to an interface band-structure effect — a hole-attracting InSb-like interface that binds a heavy-hole state — but overestimated the absolute transition energies by about 200 meV. The study left open a linked set of questions: a quantitatively accurate, interface-resolved band-structure calculation predicting absolute transition energies and the robustness of the interface-bound heavy-hole state; the microscopic identification and influence of the thin interfacial layer formed at the growth-temperature reduction step; the origin of the large photoluminescence linewidths; a conclusive separation of intrinsic interface band-structure effects from residual defect contributions; and growth parameters that reproducibly yield high-quality AlAs-like interfaces. Later atomistic theory has established that a heavy-hole-like state bound to the In-Sb bond plane exists over a wide range of band offsets, and modern epitaxy deliberately engineers both interface types, but direct experimental confirmation of the intrinsic interface state and a validated quantitative prediction of absolute transition energies remain open.

Background

InAs, GaSb and AlSb form the so-called 6.1 Angstrom family of compound semiconductors: their natural lattice constants are nearly matched (all close to 6.1 Angstrom), so heterostructures can be grown coherently strained, while their band gaps and band-edge positions differ strongly. InAs has a narrow gap (about 0.35 eV) and AlSb a wide one (about 1.6 eV), so an InAs quantum well — a thin InAs layer sandwiched between AlSb barriers, grown by molecular beam epitaxy (MBE, a method in which beams of the elements are deposited atomic layer by atomic layer under ultra-high vacuum) — confines electrons very deeply. Unlike the common-anion (Al,Ga)As system, InAs and AlSb share no common atom: at their heterointerface both the cation and the anion change, so two distinct bond configurations are possible, commonly called InSb-like (In-Sb bonds across the interface plane) and AlAs-like (Al-As bonds). Because In-Sb bonds are about 6.3% longer, and Al-As bonds about 7.3% shorter, than the host bonds they replace, each interface is a sharply strained atomic plane; the interface bonding type can be biased by the shutter sequence used to switch between group-V elements during growth. Photoluminescence (PL, optical emission from radiative recombination of photoexcited carriers) is the standard optical probe of such wells, and x-ray diffraction (XRD) of symmetric and asymmetric reflections determines whether the structure is pseudomorphic (coherently strained to the buffer, with matching in-plane lattice constants) or relaxed by misfit and threading dislocations; transmission electron microscopy (TEM) images those dislocations directly. Before 1994, photoluminescence from narrow InAs-AlSb wells had been reported by the same group (Brar, Kroemer, Ibbetson and English, 1993), interface sequencing was known to affect electron transport, and Kroemer, Nguyen and Brar (1992) had postulated Tamm-state-like interface states — states bound to the interface plane by the discontinuity of the crystal potential rather than by defects — as possible interface donors; Dandrea and Duke (1993) had calculated from local density theory that the valence-band offset is nearly independent of the interfacial bonding, although superlattice quantum-confined states can still differ by a few hundred meV because of wave-function effects at the two interface types. Spitzer et al. (1993) had found optically that AlAs-like interfaces show relaxation and As interdiffusion while InSb-like interfaces grow pseudomorphically. In the 1994 study at the center of this problem, Brar, Ibbetson, Kroemer and English grew InAs-AlSb short-period superlattice structures with enforced InSb-like or AlAs-like interfaces (reduced As soak times, growth temperature lowered from about 600 C for the buffer to about 420 C for the superlattice) and compared them by low-temperature PL, XRD and TEM. The InSb-like sample was pseudomorphic with a PL peak 96 meV lower in energy, the AlAs-like sample was heavily dislocated, and both showed PL linewidths (full width at half maximum, FWHM) of about 55 meV. A simple envelope-function estimate — the standard effective-mass approximation in which each interface is modeled as a minimum-width 1+1 monolayer inserted well of InSb or AlAs placed between the InAs well and the AlSb barrier, using literature bulk band offsets — reproduced the sign and approximate magnitude of the shift (predicted 110 meV versus measured 96 meV) but overestimated the absolute energies by about 200 meV. Its physical mechanism is that the InSb-like interface is a thin, low-gap InSb quantum well acting as a hole-attracting potential that supports a bound heavy-hole state, whereas the AlAs-like interface repels holes. The envelope-function approximation, however, cannot represent a single strained atomic plane of foreign bonds, so a quantitatively accurate description is expected to go beyond it; atomistic electronic-structure methods (empirical tight-binding or ab initio) with spin-orbit coupling and realistic strain are natural candidates, and which description actually reproduces the measured absolute transition energies remains an open question. What remained unresolved after the 1994 experiment, and what this problem targets, is a validated quantitative account of how interface bonding modifies the band structure and optical spectra — absolute transition energies, the existence and energy of the interface-bound state, the origin of the broad linewidths, and the separation of intrinsic band-structure effects from growth-dependent disorder — together with the ability to grow AlAs-like interfaces of controlled quality.

Problem Statement

The problem, as left open by the 1994 interface-bonding study of InAs-AlSb quantum wells, is to establish a validated, quantitative, mechanism-level understanding of how interface bonding type modifies the electronic band structure and the optical and structural properties of InAs-AlSb quantum wells, and to render that understanding controllable in growth. Its linked components are: (1) provide a quantitatively accurate theoretical description of the interface-induced perturbation of the band structure — going beyond the simple 1+1 monolayer inserted-well envelope-function estimate with bulk offsets, which reproduces the 96 meV interface-type photoluminescence shift only in magnitude and sign and overestimates absolute transition energies by roughly 200 meV — an interface-resolved quantitative description that predicts the absolute low-temperature transition energies of wells with InSb-like and AlAs-like interfaces and establishes the existence, energy, and robustness of the bound heavy-hole state predicted at InSb-like interfaces; (2) determine the microscopic origin and composition of the thin interfacial layer that forms at the growth-temperature reduction step (about 600 C buffer to 420 C superlattice growth) and assess any subtle influence it has on strain or defect nucleation; (3) establish the precise origin of the relatively large photoluminescence linewidths (about 55 meV) of these narrow wells — whether the broadening arises from alloy or disorder fluctuations, interface roughness, inhomogeneous strain, carrier localization at point defects, or other mechanisms; (4) conclusively separate intrinsic interface band-structure effects from residual extrinsic disorder, that is, either confirm by experiments that more tightly control or independently vary defect density that the photoluminescence energy shift between interface types is dominated by interface band-structure physics, or determine the non-negligible contribution of structural defects; and (5) identify growth parameters that reproducibly produce high-quality AlAs-like interfaces, minimizing defect density while preserving the intended bonding sequence. These components are scope facets of a single objective — a quantitative and experimentally validated account of interface-bonding effects and their control — rather than five independent deliverables that must each be completed before the task is resolved: a solution is expected to advance that single objective as far as the available theory and experimental evidence allow, resolving each component to the extent the evidence supports and stating explicitly any component that remains open.

References

  1. B. Brar, J. Ibbetson, H. Kroemer, J. H. English, 'Effects of the interface bonding type on the optical and structural properties of InAs-AlSb quantum wells', Applied Physics Letters 64, 3392-3394 (1994). DOI: 10.1063/1.111285, https://doi.org/10.1063/1.111285
  2. B. Brar, H. Kroemer, J. Ibbetson, J. H. English, 'Photoluminescence from narrow InAs-AlSb quantum wells', Applied Physics Letters 62, 3303-3305 (1993). DOI: 10.1063/1.109053, https://doi.org/10.1063/1.109053
  3. H. Kroemer, Ch. Nguyen, B. Brar, 'Are there Tamm-state donors at the InAs-AlSb quantum well interface?', Journal of Vacuum Science & Technology B 10, 1769-1772 (1992). DOI: 10.1116/1.586238, https://doi.org/10.1116/1.586238
  4. R. G. Dandrea, C. B. Duke, 'Calculation of InAs/AlSb(001) band offsets: Effect of strain and interfacial atomic structure', Applied Physics Letters 63, 1795-1797 (1993). DOI: 10.1063/1.110665, https://doi.org/10.1063/1.110665
  5. J. Spitzer, H. D. Fuchs, P. Etchegoin, M. Ilg, M. Cardona, B. Brar, H. Kroemer, 'Quality of AlAs-like and InSb-like interfaces in InAs/AlSb superlattices: An optical study', Applied Physics Letters 62, 2274-2276 (1993). DOI: 10.1063/1.109393, https://doi.org/10.1063/1.109393
  6. F. Fuchs, J. Schmitz, H. Obloh, J. D. Ralston, P. Koidl, 'Photoluminescence of InAs/AlSb single quantum wells', Applied Physics Letters 64, 1665-1667 (1994). DOI: 10.1063/1.111824, https://doi.org/10.1063/1.111824
  7. J. Spitzer, A. Hopner, M. Kuball, M. Cardona, B. Jenichen, H. Neuroth, B. Brar, H. Kroemer, 'Influence of the interface composition of InAs/AlSb superlattices on their optical and structural properties', Journal of Applied Physics 77, 811-820 (1995). DOI: 10.1063/1.359004, https://doi.org/10.1063/1.359004
  8. M. J. Shaw, P. R. Briddon, M. Jaros, 'Interface-induced localization in AlSb/InAs heterostructures', Physical Review B 52, 16341-16344 (1995). DOI: 10.1103/PhysRevB.52.16341, https://doi.org/10.1103/PhysRevB.52.16341
  9. B. Jenichen, S. A. Stepanov, B. Brar, H. Kroemer, 'Interface roughness of InAs/AlSb superlattices investigated by x-ray scattering', Journal of Applied Physics 79, 120-124 (1996). DOI: 10.1063/1.360918, https://doi.org/10.1063/1.360918
  10. K. C. Wong, Celeste Yang, Mason Thomas, Hans-Richard Blank, 'Study of the morphology of the InAs-on-AlSb interface', Journal of Applied Physics 82, 4904-4907 (1997). DOI: 10.1063/1.366354, https://doi.org/10.1063/1.366354
  11. M. J. Shaw, 'Localization at interfaces of imperfect AlSb/InAs heterostructures', Physical Review B 58, 7834 (1998). DOI: 10.1103/PhysRevB.58.7834, https://doi.org/10.1103/PhysRevB.58.7834
  12. A. Sato, K. Ohtani, R. Terauchi, Y. Ohno, F. Matsukura, H. Ohno, 'X-ray diffraction study of InAs/AlSb interface bonds grown by molecular beam epitaxy', Journal of Crystal Growth 201-202, 861-863 (1999). DOI: 10.1016/S0022-0248(98)01475-4, https://doi.org/10.1016/S0022-0248(98)01475-4
  13. G. Theodorou, G. Tsegas, 'Theory of electronic and optical properties of bulk AlSb and InAs and InAs/AlSb superlattices', Physical Review B 61, 10782-10791 (2000). DOI: 10.1103/PhysRevB.61.10782, https://doi.org/10.1103/PhysRevB.61.10782
  14. B. Z. Nosho, B. R. Bennett, L. J. Whitman, M. Goldenberg, 'Effects of As2 versus As4 on InAs/GaSb heterostructures: As-for-Sb exchange and film stability', Journal of Vacuum Science & Technology B 19, 1626-1630 (2001). DOI: 10.1116/1.1386377, https://doi.org/10.1116/1.1386377
  15. J. Sigmund, M. Saglam, H. L. Hartnagel, V. N. Zverev, O. E. Raichev, P. Debray, G. Miehe, H. Fuess, 'Structural and transport characterization of AlSb/InAs quantum-well structures grown by molecular-beam epitaxy with two growth interruptions', Journal of Vacuum Science & Technology B 20, 1174-1177 (2002). DOI: 10.1116/1.1468658, https://doi.org/10.1116/1.1468658
  16. J. Sigmund, K. Karova, G. Miehe, M. Saglam, H. L. Hartnagel, H. Fuess, 'Investigation of a growth interruption under an As flux at AlSb/InAs interfaces with InSb bonds', Journal of Crystal Growth 251, 526-531 (2003). DOI: 10.1016/S0022-0248(02)02184-X, https://doi.org/10.1016/S0022-0248(02)02184-X
  17. H. Kroemer, 'The 6.1 Angstrom family (InAs, GaSb, AlSb) and its heterostructures: a selective review', Physica E: Low-dimensional Systems and Nanostructures 20, 196-203 (2004). DOI: 10.1016/j.physe.2003.08.003, https://doi.org/10.1016/j.physe.2003.08.003 (open-access copy: https://web.ece.ucsb.edu/Faculty/Kroemer/pubs/14_04_6_1Family.pdf)
  18. S. S. Krishtopenko, A. V. Ikonnikov, A. V. Maremyanin, K. E. Spirin, V. I. Gavrilenko, Yu. G. Sadofyev, M. Goiran, M. Sadowsky, Yu. B. Vasilyev, 'Cyclotron resonance study in InAs/AlSb quantum well heterostructures with two occupied electronic subbands', Journal of Applied Physics 111, 093711 (2012). DOI: 10.1063/1.4712042, https://doi.org/10.1063/1.4712042
  19. F. Raouafi, R. Benchamekh, M. O. Nestoklon, J.-M. Jancu, P. Voisin, 'Intrinsic interface states in InAs-AlSb heterostructures', Journal of Physics: Condensed Matter 28, 045001 (2016). DOI: 10.1088/0953-8984/28/4/045001, https://doi.org/10.1088/0953-8984/28/4/045001 (preprint arXiv:1411.6565, https://arxiv.org/abs/1411.6565)
  20. R. Benchamekh, J.-M. Jancu, P. Voisin, 'Potential-inserted quantum well design for quantum cascade terahertz lasers', physica status solidi (RRL) - Rapid Research Letters 11, 1600334 (2017; published online 29 November 2016). DOI: 10.1002/pssr.201600334, https://doi.org/10.1002/pssr.201600334
  21. Xiren Chen, Junliang Xing, Liangqing Zhu, F.-X. Zha, Zhichuan Niu, Shaoling Guo, Jun Shao, 'GaInSb/InAs/AlSb quantum wells with InSb- and GaAs-like interfaces investigated by temperature- and magnetic field-dependent photoluminescence', Journal of Applied Physics 119, 175301 (2016). DOI: 10.1063/1.4948330, https://doi.org/10.1063/1.4948330
  22. M. Vallet, Y. Claveau, B. Warot-Fonrose, C. Gatel, J. Nicolai, N. Combe, C. Magen, R. Teissier, A. N. Baranov, A. Ponchet, 'Highly strained AlAs-type interfaces in InAs/AlSb heterostructures', Applied Physics Letters 108, 211908 (2016). DOI: 10.1063/1.4952951, https://doi.org/10.1063/1.4952951
  23. Y. Claveau, M. Vallet, H. Tang, N. Combe, A. Ponchet, 'Elastic properties of AlAs-like and InSb-like strained interfaces in [InAs/AlSb] heterostructures', Applied Physics Letters 109, 041903 (2016). DOI: 10.1063/1.4959843, https://doi.org/10.1063/1.4959843
  24. S. Lee, H. J. Jo, S. Mathews, J. A. Simon, T. J. Ronningen, S. H. Kodati, D. R. Fink, J. S. Kim, M. Winslow, C. H. Grein, A. H. Jones, J. C. Campbell, S. Krishna, 'Investigation of carrier localization in InAs/AlSb type-II superlattice material system', Applied Physics Letters 115, 211601 (2019). DOI: 10.1063/1.5127198, https://doi.org/10.1063/1.5127198
  25. M. Marchewka, D. Jarosz, M. Ruszala, A. Jus, P. Krzeminski, D. Ploch, K. Mas, R. Wojnarowska-Nowak, 'Strain-Balanced InAs/AlSb Type-II Superlattice Structures Growth on GaSb Substrate by Molecular Beam Epitaxy', Materials 16, 1968 (2023). DOI: 10.3390/ma16051968, https://doi.org/10.3390/ma16051968