GaSb Films Research Articles

Strain relief and AlSb buffer layer morphology in GaSb heteroepitaxial films grown on Si as revealed by high-angle annular dark-field scanning transmission electron microscopy

The interfacial misfit (IMF) dislocation array of an epitaxial GaSb film on a Si substrate has been imaged with high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The mismatch strain accommodation through dislocation formation has been investigated using geometric phase analysis (GPA) on HAADF-STEM images with atomic resolution to probe the defects’ local strain distribution. These measurements indicate that the lattice parameter of the epitaxial film recovers its bulk value within three unit cells from the interface due to the relaxation through IMF dislocations. The atomic number contrast of the HAADF-STEM images and energy dispersive x-ray spectrometry illustrate the formation of islands of AlSb buffer layer along the interface. The role of the AlSb buffer layer in facilitating the GaSb film growth on Si is further elucidated by investigating the strain field of the islands with the GPA.

Crystallization behaviors of an ultra-thin Ga–Sb film

Upon decreasing ultra-thin Ga16Sb84 films from 10 to 3 nm, the exponential increase in crystallization temperature and electrical resistance ratio are attributed to increased specific interface-energies and inhomogeneous interfacial strain at the interfaces. The specific interface-energies and strain also stabilize the Sb(Ga) phase and suppress phase-separation of the GaSb phase.

Effect of Sb template layer on GaSb thin films grown on Si(111) substrate by molecular beam epitaxy

AbstractGaSb thin films using an Sb template layer on Si(111) substrates were grown by MBE to investigate the effect of the Sb template on the crystalline quality of the GaSb films. Structural properties were compared with those of the GaSb films grown on Si(111) substrates using an AlSb initiation layer and a GaSb film directly grown on Si(111) substrate. For the GaSb thin films prepared using an Sb template layer, streaky RHEED patterns were observed throughout growth of GaSb layer and a typical surface RMS roughness value of 7.4 nm was obtained.The results of θ‐2θ scan XRD investigations indicated that GaSb film on Sb template is nearly unstrained. The φ‐scan XRD measurements with respect to {422} reflection peaks of GaSb films and Si(111) substrates did not show any sound evidence of alignment upon rotation by 30° and rather suggest two domain growth of the GaSb films. The smaller percentage of the domain which is rotated by 60° suggests that the GaSb film grown using an Sb template is more single crystal than the one grown using an AlSb initiation layer. These structural comparisons indicated that the Sb template layer is favorable in obtaining good GaSb epitaxial films. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Molecular beam epitaxy of GaSb on GaAs substrates with AlSb/GaSb compound buffer layers

GaSb films with AlSb/GaSb compound buffer layers were grown by molecular beam epitaxy on GaAs (001) substrates. The crystal quality and optical properties were studied by high resolution transition electron microscopy and low temperature photoluminescence spectra (PL), respectively. It was found that the AlSb/GaSb compound buffer layers can restrict the dislocations into GaSb epilayers. The intensity of PL spectra of GaSb layer becomes large with the increasing the periods of AlSb/GaSb superlattices, indicating that the optical quality of GaSb films is improved.

Structural and Optical Properties of GaSb Films Grown on AlSb/Si (100) by Insertion of a Thin GaSb Interlayer Grown at a Low Temperature

layers showed that the surface had uniformly-sized quantum dots with a low defect density. The surface roughness of a GaSb film with a thin GaSb interlayer grown at a low temperature was decreased by a factor of about 5 compared with the roughness of the GaSb film without the thin GaSb interlayer. In addition, double-crystal X-ray diraction and photoluminescence results showed that the structural and the optical properties of the GaSb layer with the GaSb interlayer were improved significantly. We suggest that the significant reduction of the dislocation density in the GaSb film was due to the dislocations being prevented from propagating into the GaSb overlayer by the thin GaSb interlayer.

GaSb film growth by liquid phase epitaxy

AbstractDoped GaSb (Gallium Antimonide) films on p‐GaSb substrates have been obtained by means of a low‐cost and fast‐growth method: the liquid phase epitaxy (LPE) technique. The growth temperature was 400 °C, and the growth time was varied between1 and 5 min. Characterization of the films was performed by means of high resolution X‐ray Diffraction, low temperature‐photoluminiscence and current‐voltage curve measurements. The X‐ray diffraction pattern confirms a zincblende‐type crystal structure with a high‐thin peak centred at 30.36°. The PL spectra at 27 K allowed to confirm the band‐gap energy to be 0.8 eV and the I‐V curves presented a PN junction behavior which corresponds to the obtained structured. Metal contacts of Au‐Zn and Au‐Ge were placed to perform electrical characterization (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth and characterization of GaSb/AlSb multiple quantum well structures on Si(111) and Si(001) substrates

For the purpose of investigating their structural and optical properties, GaSb thin films and GaSb/AlSb multiple quantum well (MQW) structures were grown on Si(111) substrates. A GaSb/AlSb MQW structure was also grown on Si(001) substrate as a control sample. Surface morphologies and a XRD measurements of GaSb films grown on Si(111) substrates showed that the GaSb film with a 5 nm thick AlSb initiation layer has good crystal quality. Observation of the RHEED patterns of both MQWs suggests that both GaSb films are under tensile strain at growth temperature. In-plane XRD measurement of MQW on Si(111) showed that the (111) face of the GaSb film is aligned to the Si(111) surface upon rotation by 30°. Photoluminescence (PL) spectra consisting of two peaks at 1250∼1400 nm were observed for both MQWs.

Void Formation and Structure Change Induced by Heavy Ion Irradiation in GaSb and InSb

Void formation and structure change by heavy ion irradiation were investigated in GaSb and InSb thin films. The voids were formed after irradiation in both materials. The average diameter of the voids was about 15 nm in GaSb and 20 nm in InSb irradiated with 60 keV Sn þ ions to a fluence of 0:25 � 10 18 ions/m 2 at room temperature. The void size in InSb is larger than that in GaSb. The large void size is quantitatively explained by the amount of induced vacancies obtained by the SRIM code simulation. The Debye-Scherrer rings were observed in the SAED patterns on both materials. The structure changes into a polycrystal by ion irradiation. Additionally, the 200 superlattice reflections in the [001] net pattern were almost absent, and the streak pattern along the h110i direction was observed in InSb. It is considered that the anti phase domains of different lengths are formed by ion irradiation. Ion irradiation transforms the structure of InSb from chemical ordering to chemical disordering via the formation of anti phase boundaries. [doi:10.2320/matertrans.M2010037]

Impact of ZnTe buffer on the electrical properties of n-type GaSb:Te films

We have investigated on the molecular beam epitaxy (MBE) of Te-doped GaSb films on ZnTe buffer. Te-doped GaSb (GaSb:Te) films with and without ZnTe buffer were grown on (0 0 1) GaAs substrates. GaSb:Te/ZnTe/GaAs film revealed higher mobility (=631 cm 2/V s) in comparison to GaSb:Te/GaAs film (=249 cm 2/V s). To explain the higher mobility of GaSb:Te on ZnTe buffer, dislocation density and temperature dependence of Hall measurement results were analyzed. Temperature dependence of Hall measurement shows strong influence of the dislocation scattering, which indicates that dislocation reduction by the ZnTe buffer enhances the carrier mobility of GaSb films.

Heteroepitaxial III–V films on fianite substrates and buffer layers

GaAs, GaSb, AlGaAs, and InGaAs epitaxial films and multilayer AlGaAs/InGaAs/GaAs heterostructures for PHEMT field-effect transistors have been obtained on fianite substrates by metal-organic vapour phase epitaxy. Films of different III–V compounds, including GaN, were grown on Si and GaAs substrates with a simple single buffer layer (fianite) and double buffer layer (fianite on porous Si and GaAs). It is established that the use of a two-layer buffer improves the structural quality and homogeneity of III–V films. A possibility of controlling the phase composition of GaN films using a corresponding buffer layer is shown. It is found that the use of a two-layer buffer increases the electrical homogeneity and decreases the electrical activity of defects in GaN films.

Molecular Beam Epitaxy of GaSb on GaAs Substrates with AlSb Buffer Layers

We investigate the molecular beam epitaxy growth of GaSb films on GaAs substrates using AlSb buffer layers. Optimization of AlSb growth parameter is aimed at obtaining high GaSb crystal quality and smooth GaSb surface. The optimized growth temperature and thickness of AlSb layers are found to be 450° C and 2.1 nm, respectively. A rms surface roughness of 0.67nm over 10 × 10 μm2 is achieved as a 0.5μm GaSb film is grown under optimized conditions.

Comparison of structural and optical properties of GaSb/AlGaSb quantum well structures grown on different oriented Si substrates

We report on the molecular beam epitaxy (MBE) of GaSb films and GaSb/AlGaSb multiple quantum well (MQW) structures grown on Si(1 1 1) and Si(0 1 1) substrates using an AlSb initiation layer. The structural and optical properties of the films on the different oriented Si substrates were characterized by cross-sectional transmission electron microscopy (TEM), high-resolution X-ray diffraction (HRXRD), atomic force microscopy (AFM), and photoluminescence (PL) measurements. The GaSb films and the MQW structures grown on Si(0 1 1) were found to have rather rough surfaces and of poor crystallinity under the present growth condition with the AlSb initiation layer. In contrast, the films grown on Si(1 1 1) indicated a mirror surface, definite MQW structures, and HRXRD patterns. The PL emissions within the 1.3–1.5 μm for the MQW structures on Si(1 1 1) and Si(0 1 1) were observed at the temperatures up to 300 and 200 K, respectively. We found that the PL peak energy, around 1.5 μm, of the MQW structures grown on Si(1 1 1) is almost temperature independent up to ∼120 K and exhibits a smaller variation with increasing temperature compared to those of the samples grown on Si (0 0 1) substrates. In the case of the MQW on Si (0 1 1), the PL peak energy as a function of temperature showed an intermediate behavior between those grown on Si(1 1 1) and Si(0 0 1) substrates.

Characterization of GaSb thin films from tailor-made single-source precursors

We investigated the growth and surface properties of GaSb thin films on a Si(0 0 1) substrate prepared using a tailor-made fully alkyl-substituted heterocyclic single-source precursor. The precursor properties were monitored during the evaporation process by residual gas analysis (RGA). The initial film growth was monitored by Auger electron spectroscopy (AES). Using a high-vacuum cold wall reactor, dense GaSb films could be produced and were characterized by AES, AFM and synchrotron X-ray photoelectron spectroscopy (S-XPS). The results are discussed in terms of a correlation of the electronic and geometrical properties with the composition and structure of the films.

Tailor-made precursors for the deposition of Sb-containing materials by the MOCVD process

Crystalline GaSb films were deposited using the tailor-made single-source precursor [ t-Bu 2GaSbEt 2] in a specifically designed MOCVD reactor under HV conditions at low temperatures. In addition, tetraethyldistibine Sb 2Et 4 has been successfully used as the precursor for the deposition of crystalline antimony films at low temperatures.

Growth and characterization of GaSb heteroepitaxial layers on Si(111) substrates

AbstractWe investigated the growth of GaSb layers and GaSb/‐AlGaSb multiple quantum well (MQW) structures using an AlSb initiation layer on Si(111) substrates. The entire growth was monitored using reflection high‐energy electron diffraction (RHEED). The GaSb epitaxial films and MQWstructures were characterized by X‐ray diffraction (HRXRD), atomic force microscopy (AFM) and photoluminescence (PL) spectroscopy.Our results suggest that high‐quality (111)‐oriented GaSb films with a mirror surface can be obtained using the present growth condition. The PL peak energy of the MQWs on Si(111) substrates is almost temperature independent up to ∼120 K and exhibits relatively smaller variation with temperature compared to that of the MQWs grown on Si(001) substrates. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Elastically induced coexistence of surface reconstructions

Scanning tunneling microscopy of Sb-capped GaAs shows the coexistence of different surface reconstructions. The majority of the surface consists of an $\ensuremath{\alpha}2(2\ifmmode\times\else\texttimes\fi{}4)$ reconstruction typically observed for GaAs(001) surfaces. At step edges, an $\ensuremath{\alpha}(4\ifmmode\times\else\texttimes\fi{}3)$ reconstruction, common for GaSb(001), is observed. We argue that strain couples the surface reconstruction to the film morphology. Density functional theory calculations show that the $(2\ifmmode\times\else\texttimes\fi{}4)$ reconstruction is stabilized in GaSb films when the lattice parameter is constrained to that of GaAs, as happens in the middle of a terrace, while the $(4\ifmmode\times\else\texttimes\fi{}3)$ reconstruction is stabilized when the lattice parameter is allowed to relax toward that of GaSb at step edges. This result confirms the importance of elastic relaxation in the coexistence of surface reconstructions.

Molecular beam epitaxy of GaSb on ZnTe/GaAs: Influence of the chemical composition of ZnTe surface

We have studied the molecular beam epitaxy (MBE) of GaSb films on GaAs (0 0 1) substrates by using ZnTe as a new buffer layer. GaSb films were grown on two distinct ZnTe surfaces and the influence of surface chemical composition of ZnTe on the morphological and structural properties of GaSb films has been investigated. Initial 2-dimensional (2D) growth of GaSb films is obtained on Zn-terminated surface consequently smooth morphology and high crystal quality GaSb films are achieved. The thin GaSb film (0.4 μm) grown on Zn-terminated ZnTe surface reveals considerably narrow X-ray diffraction linewidth (113 arcsec) along with small residual strain, which strongly supports the availability of ZnTe buffer for the growth of high-quality GaSb film.

Investigation of crystallographic tilting in GaSb/GaAs heteroepitaxial structure by high-resolution X-ray diffraction

GaSb epilayers were grown on GaAs(0 0 1) vicinal substrate misoriented towards (1 1 1) plane by solid-source molecular beam epitaxy (MBE). The relative tilt between GaSb epilayer and GaAs substrate was studied using high-resolution X-ray diffraction (HRXRD). It was demonstrated that the tilt of the 30 nm thick GaSb film was 0.32°, which was a simple geometrical consequence of 7.8% lattice mismatch. For the 1000 nm thick film, tilt rose to 0.45°, and the increase of tilt was the result of the forming of 60° misfit dislocations (MDs). In contrast to the phenomenon in low-misfit heteroepitaxy system, tilts induced by 60° MDs in our samples were positive (i.e. away from the surface normal) and we attributed the diversity to the different formation mechanisms of 60° MDs. The tilt study gave us another way to investigate the type and the formation mechanism of the MDs.

Optical investigation of GaSb thin films grown on GaAs by metalorganic magnetron sputtering

Metalorganic magnetron sputtering (MOMS) technology has been applied to the growth of epitaxial GaSb layers on GaAs (001). Optical studies are performed on a series of GaSb/GaAs samples grown under different growth conditions. Raman scattering measurements indicated the improvement of the crystalline quality of the GaSb thin film from the interface toward the surface with decreasing substrate growth temperature from 480 °C to 400 °C. Fourier transform infrared (FTIR) reflectance revealed the possible existence of an intermixed GaSb–GaAs layer near the interface. In UV reflectance spectra, the shapes of the high energy transition bands were found to be associated with the GaSb film quality.

Strucrural Properties of GaSb Layers Grown on InAs, AlSb, and GaSb Buffer Layers on GaAs (001) Substrates

The strain-relief and the structural properties of GaSb films with thin InAs, AlSb, and GaSb buer layers grown on GaAs (001) substrates at low temperature (LT) by molecular beam epitaxy were investigated using atomic force microscopy, transmission election microscopy, and X-ray diraction. The strain arising from depositing the thin buer layer onto the GaAs substrate was relieved by a periodic array of 90 misfit dislocations with a Burgers vector of 1/2a for the AlSb/GaAs and the GaSb/GaAs systems, but by both 60 and 90 misfit dislocations for the InAs/GaAs system. The 90 misfit dislocation arrays at the AlSb/GaAs and GaSb/GaAs interface had average spacing of 4.80 nm and 5.59 nm, respectively. The mean roughnesses and the full widths at half maximum of the rocking curves of the GaSb films on the thin AlSb and GaSb buer layers were found, respectively, to be less than 1 nm and about three times lower than the corresponding values for the system with an InAs buer layer. These results clearly demonstrate that the presence of a thin, low-temperature AlSb or GaSb buer layer is very useful for improving the quality of GaSb crystals grown on GaAs substrates.