InSb Interface Research Articles

Interface Engineering and Electron-Hole Wave Function Overlap of InAs/AlSb Superlattice Infrared Detectors

InAs/AlSb is a material system that can be used as a low-noise avalanche detector and operates in the short-wave infrared band. The interface parameters determine the wave function overlap (WFO). Maximizing the WFO of InAs/AlSb superlattices improves the quantum efficiency (QE) of infrared avalanche photodetectors (APDs). However, this remains a huge challenge. Here, the 8-band k·p perturbation method based on Bloch wave envelope function approximation was used to calculate the energy level structure of InAs/AlSb superlattices. The results indicate that the WFO is enhanced with increasing InSb interface thickness or when the InSb (or AlAs) interface is far from the intersection of InAs and AlSb. As the AlAs interface thickness increases, the WFO enhances and then reduces. The maximum increase in WFO is 15.7%, 93%, and 156.8%, respectively, with three different models. Based on the stress equilibrium condition, we consider the interface engineering scheme proposed for enhancing WFO with an increase of 16%, 114%, and 159.5%, respectively. Moreover, the absorption wavelength shift is less than ±0.1 μm. Therefore, the interface layer thickness and position can be designed to enhance the WFO without sacrificing other properties, thereby improving the QE of the device. It provides a new idea for the material epitaxy of APDs.

Thermally tunable electromagnetic surface waves supported by graphene loaded indium antimonide (InSb) interface

The thermal agitation plays a vital role in tunability of optoelectronic, structural and chemical characteristics of the temperature sensitive materials. Graphene enables the THz optics, due to its unprecedent controlling characteristics over the traditional materials. The influence of temperature on the monolayer graphene is very negligible due to its low free charge carrier density, to enhance the thermal sensitivity of graphene, the graphene loaded temperature sensitive material interface has been proposed. A theoretical analysis has been carried out on temperature dependent propagation characteristics of electromagnetic surface waves supported by the graphene loaded semi-infinite indium antimonide (InSb). The InSb has been taken as temperature sensitive material. The Drude model has been used for the modeling of InSb in the THz region while the modeling of the graphene has been done by random phase approximation-based Kubo’s formulism. To realize the graphene loaded indium antimonide interface, the impedance boundary conditions (IBCs) have been employed. The numerical analysis has been conducted to analyze the influence of temperature on the characteristics of electromagnetic surface waves i.e., dispersion curve, effective mode index (Neff), penetration depth (δ), propagation length (Lp), phase speed (Vp) and field profile, propagating along the graphene loaded InSb. In all the numerical results, the temperature variation has been considered from 200 to 350 K. It has been concluded that the graphene–InSb interface provides more temperature assisted tunability to the interfacial surface modes, commonly known as surface waves, as compared to monolayer graphene. Further, the graphene parameters can play a vital role in the dynamical tuning of electromagnetic surface waves in THz to IR frequency range. The numerically computed results have potential applications in designing of thermo-optical waveguides, temperature assisted communication devices, thermo-optical sensors and near field thermal imaging platforms.

On the origin of carrier localization in AlInAsSb digital alloy

We compared the photoluminescence (PL) properties of AlInAsSb digital alloy samples with different periods grown on GaSb (001) substrates by molecular beam epitaxy. Temperature-dependent S-shape behavior is observed and explained using a thermally activated redistribution model within a Gaussian distribution of localized states. There are two different mechanisms for the origin of the PL intensity quenching for the AlInAsSb digital alloy. The high-temperature activation energy E 1 is positively correlated with the interface thickness, whereas the low-temperature activation energy E 2 is negatively correlated with the interface thickness. A quantitative high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) study shows that the interface quality improves as the interface thickness increases. Our results confirm that E 1 comes from carrier trapping at a state in the InSb interface layer, while E 2 originates from the exciton binding energy due to the roughness of the AlAs interface layer.

Effect of Interfacial Schemes on the Optical and Structural Properties of InAs/GaSb Type-II Superlattices.

Incorporating an intentional strain compensating InSb interface (IF) layer in InAs/GaSb type-II superlattices (T2SLs) enhances device performance. But there is a lack of studies that correlate this approach's optical and structural quality, so the mechanisms by which this improvement is achieved remain unclear. One critical issue in increasing the performance of InAs/GaSb T2SLs arises from the lattice mismatch between InAs and GaSb, leading to interfacial strain in the structure. Not only that but also, since each side of the InAs/GaSb heterosystem does not have common atoms, there is a possibility of atomic intermixing at the IFs. To address such issues, an intentional InSb interfacial layer is commonly introduced at the InAs-on-GaSb and GaSb-on-InAs IFs to compensate for the strain and the chemical mismatches. In this report, we investigate InAs/GaSb T2SLs with (Sample A) and without (Sample B) InSb IF layers emitting in the mid-wavelength infrared (MWIR) through photoluminescence (PL) and band structure simulations. The PL studies indicate that the maximum PL intensity of Sample A is 1.6 times stronger than that of Sample B. This could be attributed to the effect of migration-enhanced epitaxy (MEE) growth mode. Band structure simulations understand the impact of atomic intermixing and segregation at T2SL IFs on the bandgap energy and PL intensity. It is observed that atomic intermixing at the IFs changes the bandgap energy and significantly affects the wave function overlap and the optical property of the samples. Transmission electron microscopy (TEM) measurements reveal that the T2SL IFs in Sample A are very rough compared to sharp IFs in Sample B, indicating a high possibility of atomic intermixing and segregation. Based on these results, it is believed that high-quality heterostructure could be achieved by controlling the IFs to enhance its structural and compositional homogeneities and the optical properties of the T2SLs.

Interface effect on superlattice quality and optical properties of InAs/GaSb type-II superlattices grown by molecular beam epitaxy

We systematically investigate the influence of InSb interface (IF) engineering on the crystal quality and optical properties of strain-balanced InAs/GaSb type-II superlattices (T2SLs). The type-II superlattice structure is 120 periods InAs (8 ML)/GaSb (6 ML) with different thicknesses of InSb interface grown by molecular beam epitaxy (MBE). The high-resolution x-ray diffraction (XRD) curves display sharp satellite peaks, and the narrow full width at half maximum (FWHM) of the 0th is only 30–39 arcsec. From high-resolution cross-sectional transmission electron microscopy (HRTEM) characterization, the InSb heterointerfaces and the clear spatial separation between the InAs and GaSb layers can be more intuitively distinguished. As the InSb interface thickness increases, the compressive strain increases, and the surface “bright spots” appear to be more apparent from the atomic force microscopy (AFM) results. Also, photoluminescence (PL) measurements verify that, with the increase in the strain, the bandgap of the superlattice narrows. By optimizing the InSb interface, a high-quality crystal with a well-defined surface and interface is obtained with a PL wavelength of 4.78 μm, which can be used for mid-wave infrared (MWIR) detection.

Surface plasma wave induced second-harmonic generation on a metal-semiconductor interface: effect of self-focusing of a laser.

The effect of the self-focusing of a laser on second-harmonic generation (SHG) induced by the surface plasma waves (SPW) over the metal-semiconductor interface has been investigated. The nonlinear interactions of a laser with metal generate SPW. These high-amplitude waves could penetrate through plasmonic entities of metal and can interact with electrons of a semiconductor leading to SHG. The behavior of the beam width parameter for different metals has been analyzed. One may notice that the beam width parameter shows periodic variation with the distance, but the amplitude shows maxima in the regions of the low beam width parameter. The focusing accompanied by the increase in SHG amplitude is found to be better for the Cu-InSb interface as compared to the Ag-InSb and Al-InSb ones. The present work puts forward the metal-semiconductor interface as a good choice for SHG.

The electronic structure and half-metallic properties of zincblende TiBi (001) surfaces and TiBi(001)/InSb(001) interface

Abstract First principles calculations were performed using full potential linearized augmented plane wave (FPLAPW) method based on density functional theory (DFT) to study bulk TiBi in rock salt (RS), hexagonal NiAs, and zincblende (ZB) structures, free (001) surfaces of ZB TiBi, and interface of ZB TiBi with InSb(001). The nonmagnetic NiAs structure was ground state structure of bulk TiBi and nonmagnetic RS and ferromagnetic ZB structures were introduced as metastable structures. It was found that ZB TiBi is a half-metallic (HM) ferromagnet with a minority band gap of about 1.43 eV. The origin of half-metallicity was also discussed. The obtained phase diagram showed more stability of the Bi (001) terminated surface compared with the Ti (001) termination. The Ti (001) termination keeps HM property, while half-metallicity was destroyed at Bi (001) termination. The ZB TiBi/InSb (001) interface revealed HM property showing that InSb semiconductor is a suitable substrate for growing ZB TiBi in spintronics.

Thin InSb layers with metallic gratings: a novel platform for spectrally-selective THz plasmonic sensing.

We present a computational study of terahertz optical properties of a grating-coupled plasmonic structure based on micrometer-thin InSb layers. We find two strong absorption resonances that we interpret as standing surface plasmon modes and investigate their dispersion relations, dependence on InSb thickness, and the spatial distribution of the electric field. The observed surface plasmon modes are well described by a simple theory of the air/InSb/air tri-layer. The plasmonic response of the grating/InSb structure is highly sensitive to the dielectric environment and the presence of an analyte (e.g., lactose) at the InSb interface, which is promising for terahertz plasmonic sensor applications. We determine the sensor sensitivity to be 7200 nm per refractive index unit (or 0.06 THz per refractive index unit). The lower surface plasmon mode also exhibits a splitting when tuned in resonance with the vibrational mode of lactose at 1.37 THz. We propose that such interaction between surface plasmon and vibrational modes can be used as the basis for a new sensing modality that allows the detection of terahertz vibrational fingerprints of an analyte.

Interface optimization and fabrication of InAs/GaSb type II superlattice for very long wavelength infrared photodetectors

We developed a new strategy for the optimization of InSb interface properties of very long wavelength infrared InAs/GaSb superlattice. The superlattice structures with different InSb interface thickness were fabricated to optimize the strain balanced between the superlattice and GaSb substrate. The SL structure containing 16 ML InAs/7 ML GaSb with the InSb interface layer thickness of 0.9 ML in each period shows the smallest stain of +0.065% and full width half maximum (FWHM) of the 1st order peaks of 24 arcsec. We also demonstrated the InAs/GaSb photodiodes with PIN structure operating at 77 K. The photodiodes have a 50% cutoff wavelength of 14.4 μm. The peak responsivity of the devices at zero bias is about 0.54 A/W at12.1 μm leading to the external quantum efficiency of 5.5%. With the R0A of 0.126 Ωcm2, the device has a Johnson noise limited D* of 2.94 × 109 cmHz1/2W−1 at 77 K under zero bias.

Real-time observation of coherent acoustic phonons generated by an acoustically mismatched optoacoustic transducer using x-ray diffraction

The spectrum of laser-generated acoustic phonons in indium antimonide coated with a thin nickel film has been studied using time-resolved x-ray diffraction. Strain pulses that can be considered to be built up from coherent phonons were generated in the nickel film by absorption of short laser pulses. Acoustic reflections at the Ni–InSb interface leads to interference that strongly modifies the resulting phonon spectrum. The study was performed with high momentum transfer resolution together with high time resolution. This was achieved by using a third-generation synchrotron radiation source that provided a high-brightness beam and an ultrafast x-ray streak camera to obtain a temporal resolution of 10 ps. We also carried out simulations, using commercial finite element software packages and on-line dynamic diffraction tools. Using these tools, it is possible to calculate the time-resolved x-ray reflectivity from these complicated strain shapes. The acoustic pulses have a peak strain amplitude close to 1%, and we investigated the possibility to use this device as an x-ray switch. At a bright source optimized for hard x-ray generation, the low reflectivity may be an acceptable trade-off to obtain a pulse duration that is more than an order of magnitude shorter.

Effect of interfacial layer on the crystal structure of InAs/AlAs0.16Sb0.84/AlSb quantum wells

Ion channeling technique using MeV C2+ ions and high resolution X-ray diffraction were used to study the crystal quality of an InAs/AlSb-based quantum wells. We found that the InAs quality has a strong dependence on the type of the interface used. With the addition of the InSb-like interface, the crystal quality of the InAs channel was greatly improved. The InAs lattice was fully strained and aligned with the lattice of the buffer layer without any lattice relaxation. On the other hand, if the interface was of the AlAs type, the lattice of the InAs quantum well was relaxed and the crystal quality was poor. This explains why a superior InAs quantum well with high electron mobility and good surface morphology can be achieved with the use of the InSb interface.

Interface layer control and optimization of InAs/GaSb type-II superlattices grown by molecular beam epitaxy

We reported in the paper the optimization and control of InSb interface properties during molecular beam epitaxy growth of InAs/GaSb superlattice structures. Samples with identical structure but different growth approaches, conventional molecular beam epitaxy (MBE) and migration-enhanced epitaxy (MEE), for interface layers were first prepared and their structural, morphological and optical properties were compared. The MEE samples had significant higher As composition in InSb interface layers and higher luminescence efficiency. Samples with different InSb interface layer thickness were then prepared. By changing the interface layer thickness, one can effectively tune the lattice mismatch and photoluminescence peak wavelength. Though X-ray diffraction satellite peak linewidth and surface roughness of the grown samples changed little, the one with smallest negative lattice mismatch showed the highest luminescence efficiency. Finally a P-I-N superlattice detector structure was grown with controlled interfaces. The full width at half maximum (FWHM) of the 1st-order X-ray diffraction satellite peak of the absorption layers was only 19″. The detector structure showed a cutoff wavelength of 6.3µm at 77K. The dark current density at −50mV bias was 4.3×10−5A/cm2 and the peak detectivity was 4.2×1011cmHz1/2/W.

Band structure calculation of InAs/GaSb superlattice under 4 layers model

The band structure of InAs/GaSb superlattice was calculated using K.P theory under the envelope-function approach.The electro effective mass and absorption coefficient with different material structure were also calculated.Four-layer structure model considering two interfaces was investigated and used to modify the calculation.Comparing with the experiment results,this four layer model has closer cutoff wavelength than standard model.The results showed that different interface structure can also influence the band structure,leading to the changes of cutoff wavelength.For the same InAs/GaSb superlattice material fully compensated with InSb interface,one with symmetric InSb interfaces has shorter cutoff wavelength than superlattice with asymmetric interfaces.

Faceting of InAs−InSb Heterostructured Nanowires

We report on the morphology of InAs−InSb heterostructured nanowires grown by Au-assisted chemical beam epitaxy. Using scanning and transmission electron microscopy, along with high angle annular dark field image analysis, we show that the hexagons defining the cross section of the two segments of the nanowires are rotated one with respect to the other by 30° around the growth direction and that the corners of these hexagons are rounded off by six small facets. Six additional facets that are not parallel to the growth direction are found in the InSb segment at the InAs−InSb interface and are indexed. Finally, the relation between the dimensions of the two segments composing the nanowires is discussed quantitatively.

Interfaces as design tools for short-period InAs/GaSb type-II superlattices for mid-infrared detectors

AbstractThe effect of interface anisotropy on the electronic structure of InAs/GaSb type-II superlattices is exploited in the design of thin-layer superlattices for mid-IR detection threshold. The design is based on a theoretical envelope function model that incorporates the change of anion and cation species across InAs/GaSb interfaces, in particular, across the preferred InSb interface. The model predicts that a given threshold can be reached for a range of superlattice periods with InAs and GaSb layers as thin as a few monolayers. Although the oscillator strengths are predicted to be larger for thinner period superlattices, the absorption coefficients are comparable because of the compensating effect of larger band widths. However, larger intervalence band separations for thinner-period samples should lead to longer minority electron Auger lifetimes and higher operating temperatures in p-type SLs. In addition, the hole masses for thinner-period samples are on the order the free-electron mass rather than being effectively infinite for the wider period samples. Therefore, holes should also contribute to photoresponse. A number of superlattices with periods ranging from 50.6 to 21.2 Å for the 4 μm detection threshold were grown by molecular beam epitaxy based on the model design. Low temperature photoluminescence and photoresponse spectra confirmed that the superlattice band gaps remained constant at 330 meV although the period changed by the factor of 2.5. Overall, the present study points to the importance of interfaces as a tool in the design and growth of thin superlattices for mid-IR detectors for room temperature operation.

Investigation of a growth interruption under an As flux at AlSb/InAs interfaces with InSb bonds

We report on an optimized growth interruption time under an As flux during the AlSb/InAs interface growth of unintentionally doped InAs quantum well structures. The migration-enhanced epitaxy method is used to create InSb interface bonds. After the deposition of the first In monolayer the surface is exposed to an As flux for different time periods, before the In shutter is opened again. Time-resolved reflection high-electron-energy diffraction (RHEED) and high-resolution transmission electron microscopy are used to characterize the interface. In combination with Hall measurements of single quantum well structures the interruption time is optimized. The interface quality depends on the RHEED intensity recovering during the interruption time under an As flux. If the interruption time is sufficient to reach the same RHEED intensity level as it is for the InAs growth, the electron mobility rises from 180,000 to 255,000 cm 2/V s at 77 K. Furthermore, we observed that a disordered surface during the interface growth can be incorporated into the layer, leading to amorphous regions directly above the interface. Moreover, the disordering depends on the crystal orientation and is larger in the [1 1 ̄ : 0] azimuth.

Effects of interfacial atomic segregation and intermixing on the electronic properties of InAs/GaSb superlattices

Abrupt InAs/GaSb superlattices have In-Sb and Ga-As interfacial chemical bonds that are not present in the constituent materials InAs and GaSb. We study the effect of interfacial atomic mixing on the electronic structure of such superlattices, including electron and hole energies and wave function localization, interband transition energies, and dipole matrix elements. We combine an empirical pseudopotential method for describing the electronic structure with two different structural models of interfacial disorder. First, we use the ``single-layer disorder'' model and change in a continous way the composition of the interfacial bonds. Second, we study interfacial atomic segregation using a layer-by-layer kinetic model of molecular beam epitaxy growth, fit to the observed scanning tunneling microscopy segregation profiles. The growth model provides a detailed structural model of segregated InAs/GaSb superlattices with atomic resolution. The application of the empirical pseudopotential method to such structures reveals remarkable electronic consequences of segregation, among them a large blueshift of the band gap. This result explains the surprising gap increase with growth temperature observed for similar structures. In particular we find that (i) superlattices with only In-Sb interfacial bonds have lower band gaps (by 50 meV) than superlattices with only Ga-As interfacial bonds. (ii) Heavy-hole--to--electron transition energies increase with the number of Ga-As interfacial bonds more than light-hole--to--electron transition energies. (iii) The heavy-hole $\mathrm{hh}1$ wave functions show a strong localization on the In-Sb interfacial bonds. The heavy-hole wave functions have very different amplitudes on the Ga-As interface and on the In-Sb interface. (iv) Sb segregates at InAs-on-GaSb growth, whereas As and In segregate at GaSb-on-InAs growth, but Ga does not segregate. (v) The segregation of Sb and In induces a blueshift in the band gap. (vi) There is an in-plane polarization anisotropy due to the low symmetry of the no-common-atom InAs/GaSb superlattice. This anisotropy is reduced by interfacial segregation.

In-situ monitoring of the growth of copper phthalocyanine films on InSb by organic molecular beam deposition

Thin films of the organic semiconductor copper phthalocyanine (CuPc) have been grown on the InSb(111)A 2×2 surface by organic molecular beam deposition (OMBD). Soft X-ray photoelectron spectroscopy (SXPS) using synchrotron radiation, low energy electron diffraction (LEED) and Raman spectroscopy have been applied to monitor the bonding and energy band line-up at the CuPc–InSb interface. LEED shows that the first layer of CuPc is ordered. SXPS data reveal that the chemical interaction between the overlayer and the substrate is limited. The lineshapes of the shallow In and Sb core levels change very little during the growth of the CuPc film. Emission from the valence states of both InSb and CuPc was also monitored and the valence band offset for this hybrid system was determined to be (0.75±0.14)eV. Raman spectroscopy confirms the limited interaction at the junction and further reveals that the structure of the CuPc film changes with increasing thickness.

Comparative investigation of interface effect on transmission function of electrons and holes in InAs/AlSb-based heterostructures

The influence of interface types in InAs/AlSb based heterostructures are considered for both electrons and holes. First calculations based on the transfer matrix method and including AlAs, InSb interface types or some of their combinations show the existence of more quantized energy hole levels than can be expected in the case when no interface effects are considered. The consideration is simplified by assuming the interfaces as individual intermediate layers formed between the InAs–quantum well and AlSb barriers. While for electrons such an intermediate layer of AlAs modifies the designed barriers or quantum wells of the heterostructure, it creates narrow barriers for holes leading to the appearance of a miniband type of energy levels.

α-Sn pseudomorphic growth on InSb (111) and ( [formula omitted]) surfaces: a high-resolution photoemission study

The Sn–InSb interface and α-Sn ultrathin film formation on the sputter-annealed clean A- and B-type InSb(111) surfaces are studied by high-resolution UV photoelectron spectroscopy. The valence band and In-4d core levels, along with the relieving of the clean surface reconstruction, suggest a model for the interface formation at low coverage. At higher Sn thickness a good-quality α-Sn(111)-(1×1) layer is formed, and the In-4d and Sn-4d core-level analysis shows a slight In interdiffusion present on both substrates.