Sb-rich GaSb Research Articles

Ion irradiation effects on Sb-rich GaSb films

Here we show the formation of amorphous, non-stoichiometric GaSb films by magnetron sputtering and the ion irradiation effects on the films. GaSb films in the 20–300 nm thickness range were deposited by magnetron sputtering on SiO2/Si substrates at room temperature and subsequently irradiated with 17 MeV Au+7 ions at different fluences. Structural, compositional, and morphological characterizations were performed by means of x-ray diffraction, Rutherford backscattering spectrometry, x-ray photoelectron spectroscopy, scanning electron microscopy and x-ray absorption fine structure analyses. We could verify that, throughout the above-mentioned thickness range, films were amorphous, with excess Sb to the ratio 1:2 (Ga:Sb). The initially compact films attained a foam-like structure after irradiation, with significant swelling that is dependent on the initial film thickness: the thicker the film, the more it swelled. The excess Sb attained different oxidation states depending on film thickness and this influenced the final density of the films, thus influencing the swelling. The local atomic structure around Ga atoms was also investigated, revealing a decrease in Ga–Sb scattering contribution with increasing irradiation fluence, at the same time as the increase in Ga–O scattering for irradiation fluence above 1 × 1014 at/cm2 (inclusive).

The high-thermal stability and ultrafast phase change memory based on Ge1.6Te-GaSb nano-composite alloys

Solving the contradictory between data retention and switching speed has been the subject of numerous investigations on phase change materials. Towards this end, Ge1.6Te-GaSb nano-composite is proposed, which combines advantages of fast crystallization speed and high thermal stability. The characterization results elucidate that doped materials exhibit a high crystallization temperature due to the enhanced stability of the amorphous state associated with the generated larger energy barrier. Furthermore, the reversible electrical switching capability of the phase-change devices is improved in terms of an ultrafast speed of 5 ns with Sb-rich GaSb addition. A good endurance of 20 K and long data retention are achieved simultaneously, indicating that Sb-rich GaSb incorporation into Ge1.6Te alloy is a promising material for high-temperature performance applications.

In-situ crystallization of GeTe\GaSb phase change memory stacked films

Single and double layer phase change memory structures based on GeTe and GaSb thin films were deposited by pulsed laser deposition (PLD). Their crystallization behavior was studied using in-situ synchrotron techniques. Electrical resistance vs. temperature investigations, using the four points probe method, showed transition temperatures of 138 °C and 198 °C for GeTe and GaSb single films, respectively. It was found that after GeTe crystallization in the stacked films, Ga atoms from the GaSb layer diffused in the vacancies of the GeTe crystalline structure. Therefore, the crystallization temperature of the Sb-rich GaSb layer is decreased by more than 30 °C. Furthermore, at 210 °C, the antimony excess from GaSb films crystallizes as a secondary phase. At higher annealing temperatures, the crystalline Sb phase increased on the expense of GaSb crystalline phase which was reduced. Extended X-ray absorption fine structure (EXAFS) measurements at the Ga and Ge K-edges revealed changes in their local atomic environments as a function of the annealing temperature. Simulations unveil a tetrahedral configuration in the amorphous state and octahedral configuration in the crystalline state for Ge atoms, while Ga is four-fold coordinated in both as-deposited and annealed samples.

Unusual crystallization behavior in Ga-Sb phase change alloys

Combined in situ X-ray scattering techniques using synchrotron radiation were applied to investigate the crystallization behavior of Sb-rich Ga-Sb alloys. Measurements of the sheet resistance during heating indicated a reduced crystallization temperature with increased Sb content, which was confirmed by in situ X-ray diffraction. The electrical contrast increased with increasing Sb content and the resistivities in both the amorphous and crystalline phases decreased. It was found that by tuning the composition between Ga:Sb = 9:91 (in at.%) and Ga:Sb = 45:55, the change in mass density upon crystallization changes from an increase in mass density which is typical for most phase change materials to a decrease in mass density. At the composition of Ga:Sb = 30:70, no mass density change is observed which should be very beneficial for phase change random access memory (PCRAM) applications where a change in mass density during cycling is assumed to cause void formation and PCRAM device failure.

Phase change characteristics of Sb-rich Ga–Sb–Se materials

Abstract In this paper, phase change characteristics of Sb-rich Ga–SbSe materials were systematically investigated for ultralong-retention and high-speed phase change memory (PCM). Sb-rich Ga–Sb–Se materials possess crystallization temperature higher than 225 °C and activation energy of crystallization above 3.0 eV, which leads to outstanding data retention ability in excess of 135 °C for 10 years. The film thickness reductions of Ga 9 Sb 71 Se 20 and Ga 10 Sb 60 Se 30 are about 2.6% and 3.8%, respectively, which are smaller than that of Ge 2 Sb 2 Te 5 during the amorphous-to-crystalline phase transition. Ga 10 Sb 60 Se 30 film exhibits a reversible phase change under irradiation of optical pulse. The fast crystallization is due to the precipitation of Sb crystallites acting as a template to accelerate the crystallization.

Crystallization Kinetics of Amorphous Ga-Sb Films Extended for Phase-Change Memory

Performance of phase-change materials based on Ga-Te-Sb was found getting better with decreasing Te content in our earlier studies. We concerned much properties of Te-free, Sb-rich binary Ga-Sb, which has been known to possess extremely fast crystallization behavior. Non-isothermal and isothermal crystallization kinetics of amorphous Sb-rich Ga-Sb films were explored by temperature dependent electrical resistance measurements. The crystallization temperature (183 to 261 degrees C) increases with decreasing Sb content (91 to 77 at%). The activation energy and rate-factor vary with Sb contents and reach the maximum at Ga19Sb81. The kinetic exponent is smaller than 1.5 at Sb < 85 at% denoting that the mechanism is one-dimensional crystal-growth from nuclei. The temperature corresponding to 10-year data-retention, evaluated from films, is 180 degrees C (Ga19Sb81) and 137 degrees C (Ga13Sb87), respectively. We verified memory performance using test-devices made of Ga16Sb84 working at voltages with 100 ns pulse-width.

Spontaneous Formation of Surface Antisite Defects in the Stabilization of the Sb-Rich GaSb(001) Surface

This Letter solves the long-standing puzzle [Phys. Rev. Lett. 79, 693 (1997)] of why GaSb(001) apparently violates the electron counting rule (ECR) in forming a reconstruction featuring long Sb-dimer chains, rather than the c(4x4) reconstruction found in all other arsenide and antimonide III-V compounds in the V-rich regime. We find that an alternative strategy, that in fact satisfies the ECR, is followed by the Sb-rich GaSb(001) surface, whereby long Sb-dimer chains are stabilized by randomly distributed subsurface Ga antisite defects. The excess of surface Sb drives the defect formation that in turn stabilizes the surface in a metastable phase. The transition to the c(4x4) reconstruction, where the ECR is instead satisfied through missing dimers, is therefore inhibited. Our conclusions are supported by ab initio simulations of experimental reflectance anisotropy spectra.

Study of arsenic for antimony exchange at the Sb-stabilized GaSb(001) surface

In this paper we present a first-principle study on the energetics of a single As2 molecule on GaSb(0 0 1) reconstructed surface. In order to shed light into the mechanisms of anion exchange at the Sb-rich GaSb(0 0 1) surface, we studied firstly As2 adsorption and then As for Sb exchange. We identify a surface region where both the processes are energetically favored. The results of this twofold analysis can be combined to derive possible reaction paths for the anion exchange process.

Indium inhomogeneity in In xGa 1− xSb ternary crystals grown by floating crucible Czochralski method

The distribution coefficients and the activity coefficients of In and Ga were calculated and used for growing In x Ga 1− x Sb crystals with x=0.01−0.10. The In compositional profiles were investigated by EPMA measurements along and across the section of crystals grown by Czochralski method. A floating crucible method has been developed to grow homogeneous In x Ga 1− x Sb crystals. By growing In 0.02Ga 0.98Sb crystals from In–Ga–Sb solution in an inner crucible floating in Sb-rich Ga–Sb melt the In compositional profiles were improved.

Low concentration GaSb grown from Sb-rich solutions by liquid phase epitaxy in the presence of erbium

In this article, we report the growth of GaSb layers by introducing the rare earth element Er into Sb-rich GaSb liquid phase epitaxy solutions. We find that the carrier concentration of GaSb layers can be effectively lowered due to the gettering of residual impurities and the suppression of complex acceptor defects in the presence of Er. Three intense sharp lines consisting of free exciton (FE) and excitons bound to neutral acceptors (BE3 and BE4) dominate the low temperature photoluminescence spectra of Er-doped GaSb. Zn-diffused Er-doped GaSb diodes exhibit higher contact resistances and breakdown voltages due to lower carrier concentration than for equivalent undoped diodes.