Chemical nature of the anion antisite in dilute phosphide GaAs1−xPx alloy grown at low temperature (original) (raw)
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Localization and anticrossing of electron levels in GaAs1-xNx alloys
Physical Review B, 1999
The electronic structure in nitrogen-poor GaAs 1Ϫx N x alloys is investigated using a plane-wave pseudopotential method and large supercells. Our calculations give a detailed description of the complex perturbation of the lowest conduction band states induced by nitrogen substitution in GaAs. The two principal physical effects are ͑i͒ a resonant impurity state a 1 (N) above the a 1 (⌫ 1c ) conduction band minimum ͑important at ''impurity'' concentrations, xϳ10 17 cm Ϫ3 ) and ͑ii͒ the creation of a 1 (L 1c ), and a 1 (X 1c ) states due to the splitting of the degenerate L 1c and X 1c GaAs levels ͑important at alloy concentrations, xϳ1% or ϳ10 21 cm Ϫ3 ). We show how the interaction of a 1 (N), a 1 (⌫ 1c ), a 1 (L 1c ), and a 1 (X 1c ) provides a microscopic explanation for the origin of the experimentally observed anomalous alloy phenomena. ͓S0163-1829͑99͒50440-2͔
DEFECTS AND ARSENIC DISTRIBUTION IN LOW-TEMPERATURE-GROWN GAAS
Applied Surface Science, 1995
We have used X-ray photoelectron spectroscopy (XPS) and variable energy positron beam spectroscopy (VEPBS) to study the excess arsenic and related defects in GaAs grown by molecular beam epitaxy at low temperatures (LT-GaAs). XPS shows about 1.3% excess arsenic in as-grown LT-GaAs and a non-uniform depth profile of arsenic concentration in the annealed LT-GaAs. From the S parameter, we obtain a non-uniform depth profile of defects in annealed LT-GaAs. From similarity between depth profiles of the S parameter and As concentration, we conclude that the positrons are trapped in vacancy complexes associated with arsenic dusters in the annealed LT-GaAs.
Arsenic antisite defects as the main electron traps in plastically deformed GaAs
Applied Physics A Solids and Surfaces, 1983
It is found from DLTS measurements that plastic deformation of GaAs single crystal creates a new kind of electron traps with an activation energy of 0.37 eV, and gives rise to an increase in the concentration of main electron traps with an energy of 0.80 eV. By comparing the concentrations of the main electron traps before and after deformation with analogous concentrations of As6a paramagnetic centers, found by EPR experiments, it is concluded that the centers observed in both cases are of the same origin. A nonstandard feature of the main traps is discovered: linear dependence of the DLTS-peak amplitude on the logarithm of the filling-pulse duration time. This feature can be explained in terms of the barrier-limited capture rate, assuming the traps are arranged in rows.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1999
Nanometer-scale compositional structure in InAs x P 1Ϫx /InN y As x P 1ϪxϪy //InP heterostructures grown by gas-source molecular beam epitaxy and in InAs 1Ϫx P x /InAs 1Ϫy Sb y /InAs heterostructures grown by metalorganic chemical vapor deposition has been characterized using cross-sectional scanning tunneling microscopy. InAs x P 1Ϫx alloy layers are found to contain As-rich and P-rich clusters with boundaries formed preferentially within ͑111͒ and ͑111͒ crystal planes. Similar compositional clustering is observed within InN y As x P 1ϪxϪy alloy layers. Imaging of InAs 1Ϫx P x /InAs 1Ϫy Sb y superlattices reveals nanometer-scale clustering within both the InAs 1Ϫx P x and InAs 1Ϫy Sb y alloy layers, with preferential alignment of compositional features in the ͓112͔ direction. Instances are observed of compositional features correlated across a heterojunction interface, with regions whose composition corresponds to a smaller unstrained lattice constant relative to the surrounding alloy material appearing to propagate across the interface.
Angle-resolved XPS structural investigation of GaAs surfaces
Journal of Crystal Growth, 2008
Angle-resolved X-ray photoelectron spectroscopy (ARXPS) analysis has been performed on GaAs (1 0 0) surfaces in different conditions as naturally oxidized, Ar + ion sputtering (E ¼ 1-5 keV) and chemical etching in H 2 SO 4 /H 2 O 2 /H 2 O (3:1:1). The most sensitive angle to the surface compositional changes was the take-off angle (TOA): 251. Native oxide phases on GaAs consist of a mixture of Ga 2 O 3 , As 2 O 3 and As 2 O 5 . Ar + ion sputtering procedure modifies the surface composition, in the altered layer where the concentration ratio C Ga /C As tends to 1.5-1.6. Wet chemical etching removes the oxide layer and the As-rich region from the surface. In the experiment combining chemical etching with Ar + ion sputtering for cleaning purpose, the native oxides are removed from the surface and C Ga /C As tends to stoichiometry. The experiment on native oxide reconstruction after storage in high-vacuum conditions (p$10 À8 Torr) provides evidence of the high reactivity of GaAs (1 0 0) surfaces. We have observed the presence of an As oxide (BE ¼ 43 eV) within a concentration range of 2-3%. r
Geometry and electronic structure of the arsenic vacancy on GaAs(110)
Physical Review Letters, 1994
Tunneling microscopy and spectroscopy, in conjunction with tight-binding molecular dynamics, provide compelling evidence that the "missing As" defect on GaAs(l10) is indeed an As vacancy. Neighboring Ga atoms relax upward by about 0.7 A, but do not rebond. The defect is positively charged and most likely in a +2 state. Both the relaxation and the preponderance of As vacancies on p-GaAs are explained by the energetics of the defect levels. The essential features of the observations can be understood from qualitative arguments based on hybrid orbitals.
Anion-Antisite defects in GaAs: As and Sb
International Journal of Quantum Chemistry, 1990
We present results of selfconsistent, first-principles calculations of total energies for A k a and Sb,, in GaAs. We confirm that both impurities in the substitutional T d site behave as double donors, and the first internal excitation appears at around 1 eV. For the neutral systems we obtain a metastable minimum in the total energy surface in a configuration with the impurity atom displaced toward the interstitial site; the transformation to this metastable configuration, however, is not expected to be operative for the Sb,, defect.
Low temperature scanning tunneling microscopy and spectroscopy of undoped LT-GaAs
2018
Using molecular beam epitaxy, we study self-assembled InAs quantum dots (QDs) grown on GaAs (001) substrates by lowtemperature scanning tunneling microscopy. We compare two different growth processes, the well-known Stranski-Krastanow mode and the more recently studied droplet epitaxy mode. We show that, for the same amount of deposited indium, the shape of the dots shows similar anisotropic tendency, but the InAs coverage dependence of the density shows that the growth mechanisms are different at the initial stage of the QD formation. By scanning tunneling spectroscopy at low temperature, we succeed in mapping the local density of states (LDOS) of a single quantum dot grown by the droplet epitaxy. Maps of LDOS are consistent with those previously reported for the Stranski-Krastanow mode; however, energy spectrum of our QDs shows different peak structures.
Scanning tunneling microscopy and spectroscopy: theory, techniques, and applications
Scanning tunneling microscopy is used to study low temperature grown (LTG) InGaAs, with and without Be doping. The Be-doped material is observed to contain significantly fewer AsGa antisite defects than the undoped material, with no evidence found for Be-As complexes. Annealing of the LTG-InGaAs forms precipitates preferentially in the undoped material. The previously observed dependence of the optical response time on Be-doping and annealing is attributed to changes in the As antisite concentration and the compensation effect of the Be. Low temperature grown (LTG) III-V semiconductor materials are known to contain excess arsenic. This change in the stoichiometry leads to several interesting properties such as a fast absorption recovery time or a high resistivity when the materials are subsequently annealed. Although most of the LTG semiconductor materials studies to date have been performed on GaAs, the possibility of producing devices having a subpicosecond return to equilibrium dynamic in the 1.55 µm wavelength region has produced a growing interest in LTG-InGaAs and InGaAs/InAlAs multiquantum well structures.[1,2] Compared to LTG-GaAs, the concentration of As-based deep centers is smaller in LTG-InGaAs,[3] resulting in a longer absorption recovery time in undoped material.[4] When LTG-InGaAs is doped with beryllium, the photoexcited free-carrier lifetime becomes shorter and comparable to that of LTG-GaAs (subpicosecond electron lifetimes have been observed [5]). Whereas annealing of undoped material is found to dramatically slow the absorption recovery time,[6] Be doping maintains the fast recovery time. To explain this effect, the presence of midgap states has been proposed, arising from complexes between Be dopants and the excess As introduced during growth.[1,2,4,5] The direct compensation effect of the Be has also been suggested.[4] In this work, we report a study of undoped and Be-doped LTG-InGaAs layers by scanning tunneling microscopy and spectroscopy. The scanning tunneling microscope (STM) has been previously used to observe defects in LTG-GaAs.[6] As for that case, we observe in LTG-InGaAs the presence of arsenic antisites. We find a significantly lower concentration of antisites in the asgrown Be-doped material compared to the undoped material (with the difference being much great