GaSb Films Research Articles

Epitaxial GaSb films directly grown on on-axis Si(001) with low defect density by MBE

In recent years, GaSb-on-Si direct heteroepitaxy has been highly desirable to extend the operating wavelength range into mid-infrared and high-mobility applications, such as free-space communications, gas sensing, and hyperspectral imaging. High-quality GaSb films on Si remain challenging due to the high density of defects generated during the growth. For this purpose, epitaxial GaSb films were grown by molecular beam epitaxy on on-axis Si(001). Due to the large lattice mismatch (12.2%) between GaSb and Si, here, we proposed a radical design and growth strategy with the primary objective of achieving the annihilation of antiphase boundaries (APBs) and the reduction of threading dislocation density (TDD). Benefitting from a V-grooved Si hollow structure, we demonstrated the growth of emerging-APB-free GaSb film on Si(001) with low mosaicity. Moreover, by introducing InGaSb/GaSb dislocation filtering layers, the atomically flat surface root mean square roughness is improved to 0.34 (on Si) and 0.14 nm (on GaAs/Si). Moreover, the corresponding TDD can be reduced to 3.5 × 107 and 2 × 107 cm−2, respectively, one order of magnitude lower than the minimum value found in the literature. These reported results are a powerful lever to improve the overall quality of epitaxial Si-based antimonide, which is of high interest for various devices and critical applications, such as laser diodes, photo-detectors, and solar cells.

Generation of Q-switched pulses based on GaSb saturable absorber in an Er-doped fiber laser

In this study, we report the use of GaSb as a saturable absorber (SA) material in an Er-doped fiber (EDF) laser. The GaSb-based SA is prepared through the magnetron sputtering deposition technology, wherein a thin GaSb film is deposited on a microfiber. The modulation depth, saturable intensity, and non-saturable loss of the SA are determined to be 5.45 %, 37.3 MW/cm2, and 29.12 %, respectively. Under the Q-switching working state, the repetition frequeny is tuned from 73.15 to 93.7 kHz, and the pulse duration is changed from 5.17 to 2.33 μs at a pumping power of 310 to 500 mW. The highest average output power is 21.8 mW, which corresponds to a single pulse energy of 233.67 nJ. The generated laser pulses are in a stable state with a signal to noise ratio (SNR) of 65 dB. These results confirm the potential of GaSb as a successful saturable absorber candiatiate for building pulsed fiber lasers and in ultrafast optics applications.

Influence of the temperature and substrate modification on the formation of continuous GaSb film on Si(111) by solid phase epitaxy

The solid-state formation of gallium antimonide on Si(111) from a stoichiometric mixture of GaSb in the temperature range of 300 °C–500 °C and thicknesses of 12–40 nm was studied under ultrahigh vacuum conditions. The influence of the preformed GaSb seed islands on the morphology, composition, and structure was studied. It has been found that at 300 °C a strained continuous polycrystalline film is formed, which rupture at 350 °C. It has been shown that a continuous single-crystal GaSb film grows at 400 °C–500 °C if the sample is annealed at a weak antimony flow. This is also facilitated by the preliminary formation of a high density of nanosize GaSb seed islands. As a result, a continuous relaxed film with epitaxial relations GaSb(111)∣∣Si(111) and GaSb[1–10]∣∣Si[1–10] was obtained from a GaSb mixture 40 nm thick at 500 °C. We demonstrate a possibility of direct formation of GaSb on Si(111) without buffer layers of other chemical elements.

GaSb Film is a Saturable Absorber for Dissipative Soliton Generation in a Fiber Laser

Nanotechnology is at the forefront of scientific research and offers great prospects for the development of technology. As a type of III-V semiconductor, GaSb materials exhibit numerous outstanding optical and electrical characteristics that are very promising for nonlinear optical device applications. In this study, the electronic band structures of GaSb are theoretically calculated, and its application in dissipative soliton fiber lasers is validated. A GaSb thin film is deposited on a microfiber using magnetron sputtering deposition, and the morphology, chemical composition, structure, and nonlinear optical characteristics of the proposed microfiber-GaSb device are investigated. After incorporating it into an Er-doped fiber laser, dissipative soliton laser pulses are readily obtained with a fundamental frequency of 43.5 MHz. With increasing pump power, the fiber laser could work in the fundamental frequency mode-locking state. At a pump power of 570 mW, the pulse width and the output power are measured to be 917 fs and 49.75 mW, separately. These results reveal that GaSb can be used as an efficient saturable absorber, which will have potential applications in ultrafast optics.

Pinhole-seeded lateral epitaxy and exfoliation of GaSb films on graphene-terminated surfaces

Remote epitaxy is a promising approach for synthesizing exfoliatable crystalline membranes and enabling epitaxy of materials with large lattice mismatch. However, the atomic scale mechanisms for remote epitaxy remain unclear. Here we experimentally demonstrate that GaSb films grow on graphene-terminated GaSb (001) via a seeded lateral epitaxy mechanism, in which pinhole defects in the graphene serve as selective nucleation sites, followed by lateral epitaxy and coalescence into a continuous film. Remote interactions are not necessary in order to explain the growth. Importantly, the small size of the pinholes permits exfoliation of continuous, free-standing GaSb membranes. Due to the chemical similarity between GaSb and other III-V materials, we anticipate this mechanism to apply more generally to other materials. By combining molecular beam epitaxy with in-situ electron diffraction and photoemission, plus ex-situ atomic force microscopy and Raman spectroscopy, we track the graphene defect generation and GaSb growth evolution a few monolayers at a time. Our results show that the controlled introduction of nanoscale openings in graphene provides an alternative route towards tuning the growth and properties of 3D epitaxial films and membranes on 2D material masks.

Molecular beam epitaxy of GaSb on vicinal Si(001) substrates: influence of the conditions of layer nucleation on their structural and optical properties

GaSb films were grown by molecular beam epitaxy on vicinal Si(001) substrates with miscut angles of 6o to the (111) plane. Films were formed on AlSb(001)/Al/As/Si, AlSb(001)/Al/As/Si, GaSb(001)/Ga/P/Si and GaSb(001)/P/Ga/Si transition layers. The influence of orientation, composition, and formation conditions of transition layers on the crystal perfection and optical properties of GaSb films was studied. The GaSb film grown on the GaSb(001)/Ga/P/Si(001) transition layer has the best structural and optical properties. Keywords: molecular beam epitaxy, GaSb on Si(001), crystallographic orientation of the film, transition layers, antiphase domains, crystal perfection.

Молекулярно-лучевая эпитаксия GaSb на вицинальных подложках Si(001): влияние условий зарождения слоев на их структурные и оптические свойства

GaSb films were grown by molecular beam epitaxy on vicinal Si(001) substrates with miscut angles of 6° to the (111) plane. Films were formed on AlSb(001)/Al/As/Si, AlSb(00-1)/Al/As/Si, GaSb(00-1)/Ga/P/Si and GaSb(001)/P/Ga/Si transition layers. The influence of orientation, composition, and formation conditions of transition layers on the crystal perfection and optical properties of GaSb films was studied. The GaSb film grown on the GaSb(00-1)/Ga/P/Si(001) transition layer has the best structural and optical properties.

High Hole Mobility Polycrystalline GaSb Thin Films

In this paper, we report on the structural and electronic properties of polycrystalline gallium antimonide (poly-GaSb) films (50–250 nm) deposited on p+ Si/SiO2 by metalorganic vapour phase epitaxy at 475 °C. GaSb films grown on semi-insulating GaAs substrates are included as comparative samples. In all cases, the unintentionally doped GaSb is p-type, with a hole concentration in the range of 2 × 1016 to 2 × 1017 cm−3. Exceptional hole mobilities are measured for polycrystalline GaSb on SiO2 in the range of 9–66 cm2/Vs, exceeding the reported values for many other semiconductors grown at low temperatures. A mobility of 9.1 cm2/Vs is recorded for an amorphous GaSb layer in a poly-GaAs/amorphous GaSb heterostructure. Mechanisms limiting the mobility in the GaSb thin films are investigated. It is found that for the GaSb grown directly on GaAs, the mobility is phonon-limited, while the GaSb deposited directly on SiO2 has a Coulomb scattering limited mobility, and the poly-GaAs/amorphous GaSb heterostructure on SiO2 displays a mobility which is consistent with variable-range-hopping. GaSb films grown at low temperatures demonstrate a far greater potential for implementation in p-channel devices than for implementation in ICs.

Pulsed laser deposited stoichiometric GaSb films for optoelectronic and phase change memory applications

Phase-change memory (PCM) holds great potential in realizing the combination of DRAM-like speeds with non-volatility and large storage capacity for future electronic devices including in-memory computing. However, various (reliability) issues related to e.g. too high programming current (power consumption), resistance drift, data retention (low crystallization temperature), phase separation and density change upon switching stand in the way to make PCM really attractive. GaSb thin films have interesting optical and electrical properties which are attractive for optoelectronic and PCM applications but so far reported stoichiometric GaSb compositions are Sb-rich which produced reliability issues in PCM devices. In this study, we managed to deposit stoichiometric GaSb thin films using pulsed laser deposition (PLD) by varying deposition parameters and conditions. Using electron microscopy, the morphology of deposited films and target surface and the compositional deviation from exact stoichiometry have been investigated. We show that the directional nature of laser-target interaction is directly responsible for film quality in PLD in which particulates with high number density are generated due to directional pillar formation. Suppressing this pillar formation, by a simple 180° target rotation, showed an increase in deposition yield by 60%, exact stoichiometric transfer from target to substrate, and large reduction in particulate density. Moreover, from XRD analysis, we show that exact stoichiometric transfer from target to substrate is crucial for structural integrity of the produced films. Temperature induced structural transformation from resistivity vs. temperature measurements show a high crystallization temperature of 250 °C for stoichiometric GaSb thin film. We believe the exact stoichiometric GaSb thin films with reduced particulate densities and favorable structural and (opto)electronic properties are attractive for future PCM devices.

Spectral absorptance of a metal-semiconductor-metal thin-multilayer structured thermophotovoltaic cell.

Spectral absorptance of a metal-semiconductor-metal (MSM) thin-multilayer structured thermo-photovoltaic cell was experimentally investigated. A MSM consists of a thin GaSb-semiconductor sandwiched between a top fishnet-type electrode and a flat backside electrode made of gold. A thin GaSb layer was grown on a substrate made of InAs using molecular beam epitaxy, and then all of the InAs substrate was removed using wet etching. The GaSb film was bonded on a surface of gold, which was sputtered on a Si substrate, using a van der Waals bonding method. The top fishnet-type electrode was made using electron beam lithography and a lift-off process. In the case of a 115 nm thick GaSb layer and a square fishnet aperture of a 300 nm × 310 nm size, the spectral absorptance of MSM reached a local peak (95%) at a wavelength of 1.66 µm, which is similar to spectra predicted by numerical simulation. Moreover, the equivalent resonance cavity model and LC circuit model functioned well to indicate the wavelength of several distinct peaks of absorptance.

A transmission electron microscopy study of dislocation propagation and filtering in highly mismatched GaSb/GaAs heteroepitaxy

Monolithic integration of lattice-mismatched semiconductor materials opens up access to a wide range of bandgaps and new device functionalities. However, it is inevitably accompanied by defect formation. A thorough analysis of how these defects propagate and interact with interfaces is critical to understanding their effects on device parameters. Here, we present a comprehensive study of dislocation networks in the GaSb/GaAs heteroepitaxial system using transmission electron microscopy (TEM). Specifically, the sample analyzed is a GaSb film grown on GaAs using dislocation–reduction strategies such as interfacial misfit array formation and introduction of a dislocation filtering layer. Using various TEM techniques, it is shown that such an analysis can reveal important information on the dislocation behavior including filtering mechanism, types of dislocation reactions, and other interactions with interfaces. A novel method that enables plan-view imaging of deeply embedded interfaces using TEM and a demonstration of independent imaging of different dislocation types are also presented. While clearly effective in characterizing dislocation behavior in GaSb/GaAs, we believe that the methods outlined in this article can be extended to study other heteroepitaxial material systems.

Effect of the Crystallographic Orientation of GaSb Films on Their Structural Properties during MBE Heteroepitaxy on Vicinal Si(001) Substrates

GaSb films are grown by molecular-beam epitaxy using AlSb/As/Si transition layers on vicinal Si(001) substrates miscuted by 6° in (111) plane direction. The effect of GaSb films crystallographic orientation on their structural properties and surface morphology is investigated. It is found that the GaSb(00 $$\bar {1}$$ )/Si films are characterized by better structural perfection, a lower concentration of point defects, as well as a more planar and isotropic surface morphology as compared with the GaSb(001) films. The possible cause for the observed othernesses between the GaSb films with different orientations is an increased density of antiphase domains in GaSb(001) films. The morphological features of the grown films are caused mainly by the edges of terraces and, to a lesser extent, by anisotropy of the incorporation of Ga adatoms into the edges of the terraces.

Higher electrical activation of ion-implanted Si over S in GaSb epitaxial layers

Ion implantation of the amphoteric dopant Si compared to the natural n-type dopant S in GaSb epitaxial films results in a higher dopant activation with better surface morphology and crystallinity. GaSb films were grown by molecular beam epitaxy (MBE) on semi-insulating GaAs (001) substrates. Ion implantation for both ions was carried out at an energy of 50 keV and a fluence of 1 × 1015 ions/cm2. Raman spectroscopy revealed a better crystallinity as well as a lower Sb out-diffusion for Si implantation as compared to S after annealing. Van der Pauw Hall measurements confirm the donor nature of the amphoteric dopant Si and with a dopant activation that is 3 times higher than the natural donor S. The electrical activation for both implants increases significantly after thermal annealing. Using temperature (20 K–300 K) vs conductivity measurement and displacement per atom (dpa) estimation, implantation-induced defect-related conduction mechanism is discussed. The results suggest the scope of Si as a viable n-type dopant in GaSb.

Swift heavy ion irradiation of GaSb: From ion tracks to nanoporous networks

Ion track formation, amorphisation, and the formation of porosity in crystalline GaSb induced by 185 MeV $^{197}$Au swift heavy ion irradiation is investigated as a function of fluence and irradiation angle relative to the surface normal. RBS/C and SAXS reveal an ion track radius between 3 nm and 5 nm. The observed pore morphology and saturation swelling of GaSb films shows a strong irradiation angle dependence. Raman spectroscopy and scanning electron microscopy show that the ion tracks act as a source of strain in the material leading to macroscopic plastic flow at high fluences and off normal irradiation. The results are consistent with the ion hammering model for glasses. Furthermore, wide angle X-ray scattering reveals the formation of nano crystallites inside otherwise amorphous GaSb after the onset of porosity.

Crystallization behavior and electrical characteristics of Ga–Sb thin films for phase change memory

In this work, we investigated the structural and conductivity stability of Ga–Sb thin films for phase change memory (PCM). The mass density and thickness change are significant for stability and reliability of PCM. The Ga–Sb thin films were deposited on SiO2/Si (100) wafer using magnetron co-sputtering method. Phase identification revealed that nanoscale face center cubic structure GaSb and rhombohedral structure Sb formed in Ga–Sb thin films, the formation of phase Sb was more obvious in Ga20Sb80. Ga–Sb film exhibits an unusual behavior upon crystallization with less mass density and thickness change. The microstructure of Ga45Sb55 thin films improved their structural (density and film thickness) characteristics: the crystal growth of {111} and {110} oriented grains in Ga–Sb thin films is obvious, the grains growth in Ga45Sb55 thin films was more even and the bonding states in Ga–Sb thin films were more stable. In addition, the conductivity activation energy of Ga–Sb decreased with increasing Sb contents, thus the temperature stability of conductivity was improved. The structure transformation and conductivity activation energy of Ga–Sb phase change materials are in favor of mechanical stresses reduction and reliability enhancement of PCM. This study introduces the influence mechanism of structural and conductivity stability in Ga–Sb thin films and may provide reference for further testing in higher endurance performance phase change materials.

Photoresponse investigation of polycrystalline gallium antimonide (GaSb) thin films

Thin films of polycrystalline gallium antimonide (GaSb) were grown on widely available mica substrates using the physical vapor deposition method. The as-grown films contain grains of nano-scale with regular symmetries, as identified by x-ray diffraction and scanning electron microscope analysis. Two-terminal devices with coplanar electrodes were fabricated from the polycrystalline GaSb films; thus, the time dependent photoresponse property of the films was investigated by measuring the current density–voltage characteristics of devices. A significant photoresponse of the device was revealed by the linear dependence of the applied bias. Additionally, the transient behavior of the GaSb thin films was used to optimize growth temperatures of the films. This study shows that polycrystalline GaSb thin films on mica at 500 °C are suitable for high photoresponse and low noise IR photodetectors, thus proving to be a low cost solution for IR photodetectors.

Next generation low temperature polycrystalline materials for above IC electronics. High mobility n- and p-type III–V metalorganic vapour phase epitaxy thin films on amorphous substrates

We report on the growth and electronic properties of polycrystalline III–V semiconductors, which to date have not been discussed in depth in the literature. III–V polycrystalline semiconductor thin films were grown by metalorganic vapour phase epitaxy in the temperature range 410 °C–475 °C, which is compatible for integration into the Back-End-Of-Line (BEOL) silicon based integrated circuits. The thickness of the films in this study is in the range of tens to a few hundreds of nanometers, and deposited on amorphous substrates (either smart-phone-grade glass or Si/SiO2) and, also, on oxidised GaAs epi-ready wafers. Extensive AFM, SEM and TEM analyses show interlinked-to-continuous polycrystalline III–V films based on In(Al)As or GaSb. Hall-van der Pauw measurements return results of high mobility and controllable charge density for n- and p-type field effect transistors. In the GaAs/In(Al)As system, electron density ranging from 1 × 1016 to 1 × 1019 cm−3 (n) was achieved, with room temperature mobility values in the range of 100–150 cm2 V−1 s−1 and hole mobility values in the range of 1–10 cm2 V−1 s−1 have been measured in Zn doped samples. Polycrystalline GaSb films demonstrated p-type behaviour (1 × 1017 cm−3) with remarkably high room temperature hole mobility values up to 66 cm2 V−1 s−1 for the films grown on Si/SiO2 substrate (and 300 cm2 V−1 s−1 for the GaAs substrate where an epitaxial process is actually in place). Materials could be stacked into heterostructures, providing a promising platform for complex devices enabling compatible n- and p- hetero-layers for 3D integration formed at temperatures ≤480 °C.

Synthesis, properties and structures of gallium(III) and indium(III) halide complexes with neutral pnictine coordination

A series of Group 13 halide complexes of SbnBu3, [GaX3(SbnBu3)] and [InX3(SbnBu3)] (X = Cl, Br, I) have been prepared by reaction of the appropriate trihalide with SbnBu3 in n-hexane or CH2Cl2 solution, and characterised by microanalysis, IR, 1H, 13C{1H} and 71Ga NMR spectroscopy. X-ray crystal structures are reported for [InX3(SbnBu3)] (X = Cl, Br) and [GaX3(SbnBu3)]. Similar pseudo-tetrahedral complexes of AsEt3, [GaCl3(AsEt3)], [InCl3(AsEt3)] and the five-coordinate [InCl3(AsEt3)2] were also obtained and their structures determined. Attempts to use [InCl3(SbR3)] and [GaCl3(SbR3)] (R = nBu, Et) as single source precursors for low pressure CVD growth of InSb or GaSb films were unsuccesful, instead producing elemental antimony, while [GaCl3(AsEt3)] and [InCl3(AsEt3)] failed to produce any deposition under similar conditions.

Влияние кристаллографической ориентации пленок GaSb на их структурные свойства при гетероэпитаксии на вицинальных подложках Si(001) методом молекулярно-лучевой эпитаксии

GaSb films were grown by molecular beam epitaxy using AlSb/As/Si transition layers on vicinal Si (001) substrates deflected 6 to the (111) plane. The influence of the GaSb films crystallographic orientation on their structural properties and surface morphology is investigated. It was found that GaSb(001 ̅)/Si films are characterized by better structural perfection, lower concentration of point defects and more planar and isotropic surface topography, compared with GaSb(001) films. Possible reason for the observed differences between GaSb films with different orientations is increased density of antiphase domains in GaSb(001) films. The morphological features of the grown films are caused by the terraces edges basically and by the anisotropy of the incorporation of Ga adatoms into the terraces edges, to a lesser extent.

Fabrication and characterization of n-ZnO/p-GaSb heterojunction diode

PurposeThe purpose of this paper is to examine the growth and characterization of the two different compound semiconductors, namely, n-zinc oxide (ZnO) and p-gallium antimonide (GaSb). In this paper, fabrication and characterization of n-ZnO/p-GaSb heterojunction diode is analyzed.Design/methodology/approachThermo vertical direction solidification (TVDS) method was used to synthesize undoped GaSb ingot from high purity Ga (5N) and Sb (4N) host materials. Thermal evaporation technique is used to prepare a film of GaSb on glass substrate from the pre-synthesized bulk material by TVDS method. Undoped ZnO film was grown on GaSb film by sol–gel method by using chemical wet and dry (CWD) technique to fabricate n-ZnO/p-GaSb heterojunction diode.FindingsThe formation of crystalline structure and surface morphological analysis of both the GaSb bulk and film have been carried out by x-ray diffraction (XRD) analysis and scanning electron microscopy analysis. From the XRD studies, the structural characterization and phase identification of ZnO/GaSb interface. The current–voltage characteristic of the n-ZnO/p-GaSb heterostructure is found to be rectifying in nature.Originality/valueGaSb film growth on any substrate by thermal evaporation method taking a small piece of the sample from the pre-synthesized GaSb bulk ingot has not been reported yet. Semiconductor device with heterojunction diode by using two different semiconductors such as ZnO/GaSb was used by this group for the first time.