Sb Superlattices Research Articles

Growth of InAs0.32Sb0.68 on GaAs using a thin GaInSb buffer and strain superlattice layers

We report on the growth of an InAs0.32Sb0.68 layer on (001) GaAs substrates. The lattice mismatch strain between the InAs0.32Sb0.68 layer and the GaAs substrate was accommodated using a thin 50–100 nm Ga0.35In0.65Sb buffer with interfacial misfit (IMF) dislocations. The epitaxial structures were characterized using transmission electron microscopy and x-ray diffraction analysis. The threading dislocation density in the InAs0.32Sb0.68 layer was reduced successfully to ∼1 × 108 cm−2 using the combination of a Ga0.35In0.65Sb IMF buffer and InSb/Ga0.35In0.65Sb superlattice layers. Compared to GaSb/GaAs and InSb/GaAs interfaces, a significantly higher threading dislocation density (>1011 cm−2) was observed at the Ga0.35In0.65Sb/GaAs interface. Detailed analysis suggests that high threading dislocation density in the Ga0.35In0.65Sb IMF buffer could be due to the non-uniform microscopic distribution of indium and gallium atoms. This work is beneficial to the scientific community in the growth of the InAs0.32Sb0.68 material as it provides a novel approach to prepare a platform for the growth of the InAs0.32Sb0.68 material, which does not have a suitable lattice-matched substrate, on the widely available GaAs substrate.

Raman peak shifts by applied magnetic field in InSb/Al x In1−x Sb superlattices

InSb/Al x ln1−x Sb superlattices (SLs) are grown by molecular beam epitaxy on (001) InSb substrate and Raman scattering spectroscopy of the samples under magnetic field is investigated. Al contents in AlInSb of the samples are varied. All samples are characterized by atomic force microscopy (AFM), X-ray diffraction and Raman scattering spectroscopy. The Raman spectroscopy is done by using excitation laser with 633 nm wavelength and 2 μm beam spot under applied magnetic field from 0 to 170 mT. Both TO and LO Raman peaks from InSb are detected from all samples. There are Raman peak shift of both TO and LO by applied magnetic field. Stronger magnetic effect is found in LO than TO phonon modes. We attribute this effect to the symmetry breaking of the InSb/AlInSb interfaces since the observed roughness of the top InSb layer can qualitatively correlate with the shift.

Electrical properties of Si and Be doped InSb and InAlSb/InSb superlattice applied to improve the doping efficiency

Abstract 0.8 to 1 μm Si and Be doped InSb were grown by molecular beam epitaxy. X-ray diffraction and atomic force microscope indicate that growth temperature below 340 °C severely results in dislocations and undulating surface. Silicon shows amphoteric doping nature in InSb at higher growth or Si cell temperatures, for the calculation result reveals it needed more energy to take the place of Sb. ECV measurement demonstrates that InSb/In0.9Al0.1Sb superlattice buffer layer can effectively inhibit Be dopant from diffusing to the substrate in the 420 °C InSb, with which both the doping level and crystalline quality are significantly improved. 790–870 °C Be doped InSb transfer from p- to n-type during the Hall measurement temperature increasing from 77 K to 330 K. The transition temperature of each sample is linearly correlated to the Be doping temperature, which is theoretically interpreted by the excitation mechanism and carrier transportation principles inside InSb.

Minority carrier lifetime in mid-wavelength interband cascade infrared photodetectors

A simple and effective electrical method is developed to extract the thermal generation rate and minority carrier lifetime in type-II (T2) InAs/GaSb/Al(In)Sb superlattices (SLs) by taking advantage of the features of interband cascade infrared photodetectors (ICIPs). This method is more generally applicable, considers the parasitic shunt and series resistances found in practical devices, and can account for various transport mechanisms including Auger and Shockley-Read-Hall processes. The investigated ICIPs have cutoff wavelengths in the close vicinity of 4.3 μm at 300 K. The carrier lifetimes in these ICIPs at high temperatures (200–340 K) were extracted and found in the range of 8.5–167 ns, with values correlated with the material quality. The temperature dependence of the extracted carrier lifetime exhibited different characteristics from previously reported behavior obtained using other methods for T2SL detectors, especially at high temperatures.

Effect of InSb/In0.9Al0.1Sb superlattice buffer layer on the structural and electronic properties of InSb films

The effect of InSb/In0.9Al0.1Sb buffer layers on InSb thin films grown on GaAs (001) substrate by molecular beam epitaxy (MBE) is investigated. The crystal quality and the surface morphology of InSb are characterized by XRD and AFM. The carrier transport property is researched through variable temperature hall test. The sharp interface between InSb/In0.9Al0.1Sb is demonstrated important for the high quality InSb thin film. We try different superlattice buffer layers by changing ratios, 2–0.5, thickness, 300–450nm, and periods, 20–50. According to the function of the dislocation density to the absolute temperature below 150K with different periods of SL buffers, we can find that the number of periods of superlattice is a major factor to decrease the density of threading dislocations. With the 50 periods SL buffer layer, the electron mobility of InSb at the room temperature and liquid nitrogen cooling temperature is ∼63,000 and ∼4600 cm2/V s, respectively. We deduce that the interface in the SL structure works as a filter layer to prevent the dislocation propagating to the upper InSb thin films.

Significantly enhanced carrier lifetimes of very long-wave infrared absorbers based on strained-layer InAs/GaInSb superlattices

Significantly improved carrier lifetimes in very long-wave infrared (VLWIR) InAs/GaInSb superlattice (SL) absorbers are demonstrated using time-resolved microwave reflectance (TMR) measurements. A nominal 47.0 Å InAs/21.5 ÅGa0.75In0.25Sb SL structure that produces an ∼25 μm response at 10 K has a minority carrier lifetime of 140±20 ns at 18 K, which is an order-of-magnitude improvement compared with previously reported lifetime values for other VLWIR detector absorbers. This improvement is attributed to the strain-engineered ternary SL design, which offers a variety of epitaxial advantages and ultimately leads to the improvements in the minority carrier lifetime by mitigating defect-mediated Shockley–Read–Hall (SRH) recombination centers. By analyzing the temperature dependence of TMR decay data, the recombination mechanisms and trap states that currently limit the performance of this SL absorber were identified. The results show a general decrease in the long-decay lifetime component, which is dominated by SRH recombination at temperatures below ∼30 K and by Auger recombination at temperatures above ∼45 K. Since the strain-balanced ternary SL design offers a reasonably good absorption coefficient and many epitaxial advantages during growth, this VLWIR SL material system should be considered as a competitive candidate for VLWIR photodetector technology.

Minority carrier lifetimes in very long-wave infrared InAs/GaInSb superlattices

Significantly improved carrier lifetimes in very-long wave infrared InAs/GaInSb superlattice (SL) absorbers are demonstrated by using time-resolved microwave reflectance (TMR) measurements. A nominal 47.0 Å InAs/21.5 Å Ga0.75In0.25Sb SL structure that produces an approximately 25 μm response at 10 K has a minority carrier lifetime of 140 ± 20 ns at 18 K, which is markedly long for SL absorber with such a narrow bandgap. This improvement is attributed to the strain-engineered ternary design. Such SL employs a shorter period with reduced gallium in order to achieve good optical absorption and epitaxial advantages, which ultimately leads to the improvements in the minority carrier lifetime by reducing Shockley–Read–Hall (SRH) defects. By analyzing the temperature-dependence of TMR decay data, the recombination mechanisms and trap states that currently limit the performance of this SL absorber have been identified. The results show a general decrease in the long-decay lifetime component, which is dominated by the SRH recombination at temperature below ∼30 K, and by Auger recombination at temperatures above ∼45 K.

Impact of growth temperature on InAs/GaInSb strained layer superlattices for very long wavelength infrared detection

We explore the optimum growth space for a 47.0 Å InAs/21.5 Å Ga0.75In0.25Sb superlattices (SLs) designed for the maximum Auger suppression for a very long wavelength infrared gap. Our growth process produces a consistent gap of 50 ± 5 meV. However, SL quality is sensitive to the growth temperature (Tg). For the SLs grown at 390−470 °C, a photoresponse signal gradually increases as Tg increases from 400 to 440 °C. Outside this temperature window, the SL quality deteriorates very rapidly. All SLs were n-type with mobility of ∼10 000 V/cm2 and 300 K recombination lifetime of ∼70 ns for an optimized SL.

First-principles study of InAs, In xGa 1− xSb nanotubes and InAs/In xGa 1− xSb nanotube superlattices

Semiconductor InAs, GaSb and InAs/In x Ga 1− x Sb superlattices have been used for optoelectronic devices in a wide infrared region from near to long wavelength infrared. The efficiency of these devices could be increased shrinking the size and modifying the constituent structure. Nanostructured materials are natural candidates for these applications. We have implemented first-principles theory to investigate the structural and electronic properties of (10,0) InAs, GaSb, In x Ga 1− x Sb nanotubes and InAs/In x Ga 1− x Sb nanotube superlattices. The InAs and GaSb nanotubes exhibit direct band-gaps of 0.24 and 0.41 eV. The In x Ga 1− x Sb nanotubes also exhibit direct band-gaps for the whole range of In compositions, with “scissor” modified band-gap varying from 0.56 to 0.15 eV, and a negative band-gap bowing coefficient of −0.15 eV. The InAs/In x Ga 1− x Sb nanotube superlattice shows a type-II broken-gap band alignment, and the band-gap explicitly varies with the superlattice period and alloy concentration x. The results indicate the possibility of engineering the band-gaps of InAs/In x Ga 1− x Sb nanotube superlattices by adjusting nanotube segment length and alloy concentration of constituent materials.

Design for new structure InAs/In xGa 1− xSb superlattice two-color—short and long wavelength infrared photodetector

InAs/In x Ga 1− x Sb superlattices have been used in short and long wavelength infrared photodetectors, respectively, as detective material with advanced molecular beam epitaxy (MBE) technology, but this two wave bands simultaneous detection at the same photodetector using the same detection material has rarely been realized. GaAs-based two-color infrared detection arrays using double detector structure that needs more complex photolithography and epitaxial processing than one color device have been presented. Nevertheless, in that case, the fulfillment of two wave band detection is actually by two type of geometrically designed materials of the same detector, which is essentially equivalent to two type of detectors on the array wafer. In this paper, we design a new structure InAs/In x Ga 1− x Sb superlattice two-color (short and long wavelength infrared) photodetector, in which special doping and layer structure and double external electrocircuits have been utilized to separate and detect photocurrents of the two infrared spectra. Furthermore, the two-color infrared simultaneous detection is fulfilled on the same detective material.

Structures and Electronic Properties of the Bi−Sb Superlattice Nanowires and Core−Shell Structural Bi/Sb Nanowires

We systematically study the structural and electronic properties of the Bi−Sb superlattice nanowires and core−shell structural Bi/Sb nanowires by first-principles calculations. The relaxed structures of these heterostructural nanowires are first obtained and found to be similar to those of homogeneous Bi nanowires. For the Bi−Sb superlattice nanowires, band lineups of Bi and Sb zones result in multiple quantum wells, where specific states at the band edges and in band continua are confined. The confined electrons (holes) become more localized if the width of the barrier is larger. For the core−shell structural Bi/Sb nanowires, the electronic properties show dependence on the size, the atom type of core, and the chemical composition. Meanwhile, the valence bands are less affected by the chemical composition, while the conduction bands depend on it. These findings might have important implications for understanding the structural and electronic properties of the heterostructural nanowires and further utiliz...

Large Optical Transitions in Rewritable Digital Versatile Discs: An Interlayer Atomic Zipper in a SbTe Alloy

ABSTRACTChalcogenides, in particular germanium-antimony-tellurium (GeSbTe) and antimony-rich tellurium (R-SbTe) based alloys, are the most technologically significant alloys currently being applied to recordable optical storage as typified by rewritable digital versatile discs (DVD-RW), DVD random access memory, (DVD-RAM). The same alloys are also being applied to nonvolatile random access memory electrical memory in the form of phase change random access memory (PCRAM). In 2004, the phase transition mechanism of GeSbTe was first revealed, demonstrating that the amorphous state is not a random configurational network but is locally well-ordered with the crystalline to amorphous switching process being based upon Ge atoms moving between octahedral and tetrahedral symmetry positions. The kinetic barrier between these two states gives rise to the non-volatile nature of GeSbTe as a storage medium. In contrast, no theoretical analysis has been proposed for SbTe alloys because a Ge-free system. In this paper, the Sb2Te structure has been investigated using the local density approximation (LDA) using a plane-wave basis and compared with experimental results. The effect of external stress on the structure was also investigated. It was found that Sb2Te undergoes two phase-transitions at around 18 GPa (compressive) and −3 GPa (tensile). In the case of negative stress, the c-axis was found to expanded more than the other axes, giving rise a large refractive index change. We report on coherent (uniaxial) melting induced by the breaking a sigma bond between Sb2Te3 and Sb superlattices. We believe this to be the origin of the phase transition that induces a large change in physical properties.

Passivation of InAs∕(GaIn)Sb short-period superlattice photodiodes with 10μm cutoff wavelength by epitaxial overgrowth with AlxGa1−xAsySb1−y

An approach for the passivation of photodiodes based on compounds of the InAs∕GaSb∕AlSb materials family is presented. The passivation is realized by the overgrowth of patterned mesa devices with a quaternary AlxGa1−xAsySb1−y layer, lattice matched to the GaSb substrate. Proof of concept is demonstrated on infrared photodiodes based on InAs∕(GaIn)Sb superlattices with 10μm cutoff wavelength operating at 77 K where suppression of surface leakage currents is observed.

Design of InAs/Ga(In)Sb superlattices for infrared sensing

New infrared detector materials with high sensitivity, multi-spectral capability, improved uniformity and lower manufacturing costs are required for numerous infrared sensing applications. One material system has shown great theoretical and experimental promise for these applications: InAs/InxGa1−xSb type-II superlattices. These superlattices offer a large design space for adjusting not only the energy band gap of the material but also the band structure. The infrared properties of several sets of designs of InAs/GaSb superlattices were studied. These designs covered the mid-infrared spectral band from 3 to 6μm. Optimization design rules were explored. The infrared photoresponse spectra, combined with 8×8 k·p envelope function approximation modeling of superlattice band gaps and absorption spectra, provide insight into the underlying physics behind the optimized design of these materials.

Strain and interfacial bond type effects on structural quality of InAs/Ga(As,Sb) superlattices grown on InAs substrates

A series of InAs/Ga(As,Sb) superlattices were grown on InAs substrates by molecular beam epitaxy. The samples were grown in a manner that allowed the nature of the interfacial bonds (either GaAs or In(As,Sb)-like) to be controlled). In some of the samples the bond type-related strain was accommodated by adjusting the Sb mole fraction to nearly lattice match the superlattice to the substrate regardless of bond configuration. High-resolution X-ray diffraction measurements and transmission electron microscopy images reveal that samples grown with In(As,Sb)-like bonds on top of the InAs layers exhibit superior structural quality. Samples with GaAs-like bonds at both interfaces are far inferior to the others.

Investigation of trap-assisted tunneling current in InAs/(GaIn)Sb superlattice long-wavelength photodiodes

Trap centers with an energy level positioned 1/3 of the band gap below the effective conduction band edge are observed in the electroluminescence spectra of InAs/(GaIn)Sb superlattice photodiodes with a cutoff wavelength of 11 μm. The trap centers are recognized by simulating the low-temperature current–voltage characteristics of the diodes. Excellent quantitative agreement on both, the I–V characteristic and the differential resistance between the experimental data and the theoretical prediction is achieved. The quantitative simulation of the I–V characteristics shows, that the 77 K performance of InAs/(GaIn)Sb photodiodes is dominated by generation-recombination processes even at long wavelengths. Above 50 K, tunneling currents are not of importance.

Wannier-Stark localization in InAs/(GaIn)Sb superlattice diodes

We present experimental evidence for the formation of localized Wannier-Stark states in the depletion region of low band-gap InAs/(GaIn)Sb superlattice (SL) infrared photodiodes. In the photocurrent spectra of reverse-biased photodiodes, maxima are observed, that spectrally shift when the strength of the electric field in the depletion region of the diode is changed. Taking into account the spatially indirect type-II nature of interband transitions in InAs/(GaIn)Sb SL's, the spectral positions of the observed maxima can be explained in the framework of localized Wannier-Stark states. Besides photocurrent spectra, the current-voltage $(I\ensuremath{-}V)$ characteristics of the diodes were investigated. In the reverse-bias regime dominated by Zener tunneling the differential resistance of the diodes reveals an oscillatory behavior. These oscillations are due to a resonant enhancement of the Zener tunneling current by Wannier-Stark states in the depletion region of the SL diode. A model is presented that quantitatively describes the occurrence of the oscillations in the $I\ensuremath{-}V$ curves. In addition, the influence of a magnetic field on the Wannier-Stark oscillations in the Zener current was investigated. While the period of the oscillations in the $I\ensuremath{-}V$ curves is conserved, the resonances are shifted, reflecting the energy shift introduced in the Wannier-Stark states by the magnetic field. This voltage shift exhibits a strong dependence on the magnetic-field orientation.

Control of the residual doping of InAs/(GaIn)Sb infrared superlattices

Magnetotransport and photoluminescence (PL) measurements on InAs/(GaIn)Sb superlattices (SLs) grown by molecular-beam epitaxy on GaSb substrates at different substrate temperatures are reported. With increasing growth temperature, a transition of the SLs from residual n type to residual p-type doping was observed. For n-type samples, a decrease in the electron concentration leads to a strong increase in the PL intensity. In contrast, the PL intensity of p-type samples is only weakly dependent on the hole concentration. This correlation can be used to control the residual doping of the SLs.

Thermal Conductivity Of Bi/Sb Superlattice

ABSTRACTThe temperature-dependent cross-plane thermal conductivity of a 1-μm thick 50Å Bi / 50Å Sb superlattice on a (111) CdTe substrate was measured, using a differential 3-ω method. This method uses the temperature difference between the superlattice sample and a reference sample to calculate its cross-plane thermal conductivity. However, the substrate thermal conductivity is comparable to or smaller than the superlattice thermal conductivity near room temperature. This results in a very small or negative temperature difference, making the existing data reduction method inapplicable. Based on an improved model, the temperature-dependent thermal conductivity of the Bi/Sb superlattice is obtained and is about half of the literature value of Bi0.5Sb0.5 bulk alloy.

Electrical Characterization of InAs/(GaIn)Sb Infrared Superlattice Photodiodes for the 8 to 12νm Range

AbstractInAs/(GaIn)Sb superlattice photodiodes with a cutoff wavelength of 8.711μm show adynamic impedance of R0A= 1.5 kωcm2at 77 K and a responsivity of 2 A/W, corresponding to a detectivity of D*= 1 x 1012 cmv√Hz/W. Diffusion limited performance is observed above 100 K. At lower temperatures the diodesare limited by generation-recombination currents. An analysis of the influence of different diode sidewall passivations on the surface contribution to the diode leakage current is presented. The out-of-plane electron mobility as well as the relative contributions of the electron and hole diffusion currents to the diode current were determined by a measurement of the magnetic field dependence of the reverse saturation current density of the diodes