Arsenic Tetramers Research Articles

Corrugation reduction in periodically inverted GaAs by molecular beam epitaxy growth using arsenic dimers

Molecular beam epitaxy (MBE) regrowth of GaAs on periodically inverted GaAs(100) substrates using arsenic dimers (As2) was studied. We found that we can reduce corrugations on the regrown GaAs by MBE growth using As2 at considerably higher substrate temperatures (∼450 °C) than in the case of growth using arsenic tetramers (∼300 °C). This result indicates that As2 MBE regrowth can be used to fabricate highly efficient GaAs/AlGaAs wavelength conversion waveguiding devices owing to a reduction in the propagation losses caused by interface corrugations. We also estimated the diffusion lengths of Ga atoms coexisting with As2 on GaAs(100) surfaces from experimental thickness variations on the basis of a diffusion equation analysis.

First-principles study of arsenic impurity clusters in molecular beam epitaxy (MBE) grown HgCdTe

The understanding of the microstructures of the arsenic tetramer ( As t ) , dimer ( As d ) , and singlet ( As s ) of HgCdTe is important to explain the high electrical compensation of molecular beam epitaxy (MBE) samples and the conversion to p -type behavior. The stable configurations were obtained from the first-principles calculations for the arsenic cluster defects [ As n ( n = 1 , 2, and 4)] in as-grown HgCdTe. According to the defect formation energies calculated under Te-rich conditions, the most probable configurations of As t , As d , and As s have been established. For the optimized As t and As d the energy is favorable to combine in a nearest neighboring mercury vacancy ( V Hg ) , and the corresponding configurations can be used to explain the self-compensated n -type characteristics in as-grown materials. As t is likely to be more abundant than As d in as-grown materials, but arsenic atoms are more strongly bounded in As t than in As d , thus more substantial activation energy is needed for As t than that for As d . The atomic relaxations as well as the structural stability of the arsenic defects have also been investigated.

Microscopic Origin of Electrical Compensation in Arsenic-Doped HgCdTe by Molecular Beam Epitaxy: Density Functional Study

The understanding of the configurations of the arsenic tetramer (As t ), dimer (As d ), and singlet (As s ) is important to explain the high electrical compensation of molecular beam epitaxy (MBE) samples and the conversion to p-type behavior. In this work, the possible configurations were optimized from density functional calculations for arsenic defects As n (n = 1, 2, and 4) in as-grown HgTe. According to the dominant electronic contribution to the defect formation energies, which was calculated under Te-rich conditions, the most probable configurations for As t , As d , and As s have been established. The above discussion applies to the neutral arsenic defects. A further study is necessary to consider the entropy contribution to the defect formation energy.

The Influence of Arsenic Incorporation on the Optical Properties of As-doped GaN Films Grown by Molecular Beam Epitaxy Using Arsenic Tetramers

We have studied the influence of the incorporation of As on the optical properties of As-doped GaN layers grown by plasma-assisted molecular beam epitaxy (PA-MBE) using arsenic tetramers. The doping level of arsenic was determined by secondary ion mass spectrometry. The arsenic concentration is uniform throughout the layers. There is a sub-linear dependence of the arsenic incorporation on the flux with a log–log slope of about 0.1. The photoluminescence from the As-doped GaN films consists of UV excitonic emission at 3.4 eV, UV emission at 3.2 eV and a strong blue band centred at 2.6 eV. The intensity of the blue band centred at 2.6 eV increases more rapidly with arsenic flux than the concentration of arsenic in the bulk, and has a log–log slope of about 0.49. This suggests an approximately fourth-power dependence of the intensity of the blue emission on the concentration of arsenic in the GaN films.

InAs yP 1− y/InP quantum wells grown by solid source molecular beam epitaxy using As 2 and As 4

Strained InAs y P 1− y ( y: 0.3–0.75)/InP multiple quantum wells were grown on InP substrates by solid source molecular beam epitaxy using arsenic tetramer (As 4) and dimer (As 2). X-ray diffraction measurement and simulation reveal the high structural quality of the samples regardless of the arsenic species used, while the incorporation efficiency of As 2 is found to be higher than that of As 4. Room temperature and 10 K photoluminescence (PL) measurements were performed to optically examine the samples. The room temperature PL properties in the whole composition range inspected are obviously improved for the samples grown using As 2 instead of As 4, but the 10 K PL properties are comparable.

Correlation of arsenic incorporation and its electrical activation in MBE HgCdTe

The behavior of arsenic for p-type doping of MBE HgCdTe layers has been studied for various annealing temperatures and arsenic doping concentrations. We have demonstrated that arsenic is in-situ incorporated into HgCdTe layers during MBE growth. The carrier concentration has been measured by the Van der Pauw technique, and the total arsenic concentration has been determined by secondary ion mass spectroscopy. After annealing at 250°C under an Hg over pressure, As-doped HgCdTe layers show highly compensated n-type properties and the carrier concentration is approximately constant (∼mid 1015 cm−3) until the total arsenic concentration in the HgCdTe layers approach mid 1017 cm−3. The source of n-type behavior does not appear to be associated with arsenic dopants, such as arsenic atoms occupying Hg vacancy sites, but rather unidentified structural defects acting as donors. When the total arsenic concentration is above mid 1017 cm−3, the carrier concentration shows a dependence on the arsenic concentration while remaining n-type. We conjecture that the increase in n-type behavior may be due to donor arsenic tetramers or donor tetramer clusters. Above a total arsenic concentration of 1∼2×1018 cm−3, after annealing at 300°C, the arsenic acceptor activation ratio rapidly decreases below 100% with increasing arsenic concentration and is smaller than that after annealing at 450°C. The electrically inactive arsenic is inferred to be in the form of neutral arsenic tetramer clusters incorporated during the MBE growth. Annealing at 450°C appears to supply enough thermal energy to break some of the bonds of neutral arsenic tetramer clusters so that the separated arsenic atoms could occupy Te sites and behave as acceptors. However, the number of arsenic atoms on Te sites is saturated at ∼2×1018 cm−3, possibly due to a limitation of its solid solubility in HgCdTe.

GeAs as a novel arsenic dimer source for n-type doping of Ge grown by molecular beam epitaxy

GeAs is successfully applied as a new arsenic dimer source for efficient n-type doping of Ge grown by molecular beam epitaxy. The arsenic fluxes emanating from GeAs Knudsen cells are not composed of arsenic tetramers, but only of arsenic dimers. High electron concentrations of up to 1.1×1020 cm−3 are achieved with GeAs, which is much larger than any ever obtained in antimony-doped Ge. The electron concentration in the arsenic-doped Ge films depends on the GeAs cell temperature with an activation energy of 2.5 eV, which coincides with that of the arsenic dimer beam flux generated from GeAs. Moreover, it is found that the electron and arsenic concentrations in the arsenic-doped Ge layer are identical. These results indicate that arsenic atoms are incorporated into Ge from the arsenic dimer beam, and that a very high electrical activation of the incorporated arsenic atoms is obtained.

Modulated-beam mass spectrometry studies of the MOMBE growth of (100) GaAs and In 0.1Ga 0.9As

Modulated-beam mass spectrometry has been used for the first time to study the MOMBE growth of (100) GaAs and In 0.1Ga 0.9As using appropriate combinations of triethyl gallium, triethyl indium and arsenic tetramer sources. The GaAs MOMBE growth process has been monitored as a systematic function of substrate temperature, V : III flux-ratio and growth rate. These experiments indicate that rapid thermal decomposition of triethyl gallium takes place with increasing substrate temperature (80–350°C) to generate an increasing concentration of desorbing diethyl gallium. For substrate temperatures greater than 350°C, progressively increasing thermal decomposition of the diethyl gallium occurs at the substrate surface, and GaAs growth commences. Three specific subsequent growth regions are then identified as a function of increasing substrate temperature. The data obtained as a function of the different growth variables is then used to explain previously reported GaAs MOMBE growth rate results, and implications for the existing models of MOMBE growth processes are described. Finally, preliminary modulated-beam mass spectrometry data obtained during the MOMBE growth of In 0.1Ga 0.9As is described and correlated with previously reported In x Ga 1 − x As MOMBE growth studies.

Arsenic-induced intensity oscillations in reflection high-energy electron diffraction measurements

A technique of arsenic-induced RHEED intensity oscillations has been used to accurately measure arsenic incorporation rates as a function of substrate temperature during the homoepitaxial growths of both GaAs and InAs by molecular beam epitaxy (MBE). Measurements were made at growth temperatures from 350 to 650 °C and at arsenic fluxes of 0.1 to 10.0 monolayer/s. The method measures only the arsenic actually incorporated into the growing film and does not include the arsenic lost in splitting the arsenic tetramers or lost by evaporation from the sample.