InGaSb Layers Research Articles

InGaSb Defect Filter Layer to Improve Performance of GaSb Solar Cells Grown on GaAs Substrates

The reduction of the threading dislocation density in metamorphic GaSb grown on GaAs substrates through the use of InGaSb defect filter layers has been investigated. More specifically, we study the effects of strain and thickness on the ability of a InGaSb defect filter layer to reduce threading dislocations in GaSb solar cells grown on GaAs substrates. The strain between the GaSb metamorphic layer on GaAs substrate (99.5% relaxed) and the InGaSb defect filter layer is varied by changing the indium composition in the InGaSb layer. It is demonstrated that an InGaSb defect filter layer with 0.6% strain is more effective for blocking threading dislocations compared with higher-strain layers, resulting in improved short-circuit current (Jsc) and open-circuit voltage (Voc) for the metamorphic GaSb solar cell. The optimization of the defect filter layer involves varying the thickness of the layer to achieve the lowest possible threading dislocation density. This also takes into account the critical thickness of the InGaSb layer on GaSb to avoid generation of threading dislocations from the InGaSb layer itself. It is shown that adding an In0.11Ga0.89Sb defect filter layer with thickness of 250 nm and 0.6% strain beneath a GaSb solar cell grown on a GaAs substrate improves Voc from 0.1 V to 0.16 V and Jsc from 19.7 mA/cm2 to 24.7 mA/cm2.

Resistive signature of excitonic coupling in an electron-hole double layer with a middle barrier

We study the interlayer scattering mediated by long-range Coulomb interaction between electrons (density n) and holes (p) in a double-layer system. The gated device is made of InAs (e) and InGaSb (h) quantum wells separated by a AlSb middle barrier such that the interlayer tunneling is negligibly small. By using independent-layer contacts we measure the transport tensor \r{ho}_xx and \r{ho}_xy that are solely from the InAs layer, while sweeping p in the InGaSb layer. We found a strongly enhanced resistive scattering signal as the carrier densities approach a total charge neutrality, n = p, which cannot be described by the Fermi-liquid theory. Results of data analysis for density, temperature, and magnetic field dependences are consistent with the emergence of excitonic coupling between the two layers, stressing the dominance of Coulomb interaction even in the presence of disorder.

Heteroepitaxial growth of InGaSb on GaSb/Si(111)–√3 × √3‐Ga surface phase with a two‐step growth method to investigate the impact of high‐quality GaSb buffer layer

An investigation was performed on the heteroepitaxial growth of InxGa1–xSb on GaSb/Si(111)–√3 × √3‐Ga substrate following a two‐step growth method. The buffer layer flux ratio of Ga and Sb has been controlled precisely to grow a high‐quality GaSb layer without twins, whereas the ratio of In and Ga varied for epitaxial InxGa1–xSb layers. The growth conditions during film deposition were kept the same for growth with and without a high‐quality buffer layer of GaSb. The ratio x ranges from 0.75 to 0.9 in steps of 0.05. To analyze and compare the growth, reflection high energy electron diffraction (RHEED), scanning electron microscopy (SEM) images, and X‐ray diffraction (XRD) have been performed and studied. It was found that the high‐quality (HQ) GaSb buffer layer is necessary to decrease twins in the growing InGaSb layer.

(Invited) P-Type III-Sb MOSFET on a Metamorphic Substrate: Towards All III-V CMOS

A study of lattice-mismatched epitaxial growth and related defects and their effects on electrical characteristics of hetero-epitaxial III-Sb films grown on Si is presented in this paper. Growth of 800 nm thick GaSb on Si results in a threading dislocation density of ~6x108 cm-2; density of planar defects such as microtwins of ~2x104 cm-1 and anti-phase domain boundaries on the order of ~104 cm-1, respectively. High defect-related acceptor-type doping is also observed, the effect of which is to change polarity from n-type to p-type, whilst p-type MOS shows similar characteristics as grown on GaAs substrate. The main surface features of strained InGaSb layers grown on metamorphic AlSb or AlGaSb buffers on Si are elongated bumps due to microtwins: however, hole mobility of ~650 cm2/V-s has been obtained in a buried strained quantum well channel. In this work, we study the use of the migration enhanced epitaxy technique for the growth of AlSb seed layers on Si to improve InGaSb quality.

Epitaxial growth and characterization of InAs/GaSb and InAs/InAsSb type-II superlattices on GaSb substrates by metalorganic chemical vapor deposition for long wavelength infrared photodetectors

We report on the epitaxial growth and characterization of InAs/GaSb and InAs/InAsSb type-ІІ superlattices (T2SLs) on GaSb substrates by metalorganic chemical vapor deposition. For InAs/GaSb strained T2SLs, interfacial layers were introduced at the superlattice interfaces to compensate the tensile strain and hence to improve the overall material quality of the superlattice structures. The optimal morphology and low strain was achieved via a combined interfacial layer scheme with 1 monolayer (ML) InAsSb+1 ML InGaSb layers. In contrast, the InAs/InAsSb strain-balanced T2SLs allow for a relatively easy strain management and simple precursor flow switching scheme while maintaining device-quality materials. Surface root mean square roughness of 0.108 nm and a nearly zero net strain were obtained, with effective bandgaps of 147 and 94 meV determined for two sets of InAs/InAsSb strain-balanced T2SLs.

InAs/GaSb type-II superlattice structures and photodiodes grown by metalorganic chemical vapor deposition

We report on the characterization and performance of epitaxial structures and photodiodes based on InAs/GaSb type-II superlattices grown by metalorganic chemical vapor deposition. Interfacial layers were introduced at the superlattice interfaces to compensate the tensile strain and hence to improve the overall material quality of the superlattice structures. The optimal morphology and low strain was achieved via a combined interfacial layer scheme with InAsSb+InGaSb layers. Using this scheme, a p-i-n photodiode structure with a 360-period InAs/GaSb superlattice was grown on a GaSb substrate, which operates at 78 K with a cut-off wavelength of ∼8 μm and a peak responsivity of 0.6 A/W at ∼6 μm.

Type-II InAs/GaSb superlattices for very long wavelength infrared detectors

Type-II superlattices (SLs) can be designed for semiconductor band gaps as large as 400 meV down to semimetallic. This flexibility in design makes them an excellent candidate for infrared photodiodes with cut-off wavelengths beyond 15 μm . There are relatively few options for high-performance infrared detectors to cover wavelengths longer than 15 μm , especially for operating temperatures above 15 K . In the past few years, excellent results have been obtained on photoconductive and photodiode samples designed for infrared detection in the very long wavelength infrared (VLWIR) range (λ>15 μm) . There is a variety of possible designs for these SLs which will produce the same narrow band gap by adjusting individual layer thicknesses, or indium content, in the InGaSb layer. Several of these different design options have been grown and characterized. These designs often require monolayer control per layer over hundreds of repeats in the SL. Photoresponse spectra for type-II SLs are compared to show how the design choices not only change the band gap but also the band structure, as reflected in features observed in the spectra. Theoretical modeling results are used to interpret the photoresponse spectra. SLs with cut-off wavelengths ranging from 15 to 25 μm are covered.

High purity InxGa1−xSb single crystals with cutoff wavelength of 7–8 µm grown by melt epitaxy

For the first time, InGaSb single crystals with a cutoff wavelength of 7–8 µm were successfully grown on GaAs substrates by a new growth technique named melt epitaxy. The band gap of InGaSb layers obviously narrowed compared with those with the same compositions grown by ordinary methods and the longest cutoff wavelength reached 8.3 µm. High electron mobility of 8.05×104 cm2/Vs and low carrier density of 1×1015 cm−3 at 77 K were obtained indicating high purity of InGaSb epilayers.

Superlattice parameters for optimum absorption in InAs/InxGa1−xSb superlattice infrared detectors

The linear absorption coefficient of InAs/InxGa1−xSb superlattices is optimized with respect to layer widths, indium content, substrate type and substrate orientation, interface type, and choice of buffer layers based on a model envelope-function approach (EFA) involving the solution of a 6×6 EFA Hamiltonian (heavy, light, and conduction bands) for wave functions and subband energies. Free-standing superlattices as well as superlattices matched to a number of substrates are considered. In general, increasing the indium mole content from 0 to 0.4 doubles the magnitude of absorption. Changing the substrate orientation from [001] to [111] significantly increases absorption in all cases studied due to the increased heavy-hole mass and the larger InAs-conduction-band–InGaSb-valence-band offset in the [111] direction. The use of an In0.4Ga0.6Sb substrate leads to higher absorption because all the beneficial effects of strain are placed in the InAs layer, which is more sensitive to strain than is the InGaSb layer. The larger valence–conduction-band offset for InSb than for GaAs interfaces also leads to higher absorption. The model results agree best with available data when a 100 meV InAs-conduction-band–GaSb-valence-band offset is used. Specific superlattice parameters that optimize absorption for free-standing superlattices on GaSb at three cutoff wavelengths are proposed.

Influence of the solute convection on InGaSb LPE layers on vertically mounted GaSb substrates

The influence of thermal convection on the morphology of In xGa 1− xSb(x = 0.05) layers was investigated by using modified liquid phase epitaxy. A (111) GaSb substrate was inserted vertically into the In-Ga-Sb source solution, and then InGaSb layers were grown in both sides of the substrate. During growth, electric current pulses were passed across the solution-substrate-solution interfaces to introduce impurity markers. The growth morphology obtained by calculating the convective flow agreed well with that obtained experimentally. Therefore, the convection in the source solution was found to affect the growth morphology.