Oxygen In GaAs Research Articles

Oxygen in GaAs and its relation to the EL3 defect investigated by TSC and PICTS

Thermally stimulated current (TSC) and photo induced current transient spectroscopy (PICTS) were used to investigate deep traps in oxygen-rich medium resistivity GaAs. We observed an abnormal behaviour of the TSC signal at a temperature of about 200 K. where the TSC current is lower than the dark current. This results in a negative peak occurring in the temperature range where the signal of the well known EL3 defect in undoped semi-insulating GaAs is present. For verification. comparative PICTS-measurements were performed, which exhibit the same negative peak at similar temperatures. The activation energy for this negative peak was determined to be ∼ 0.6 eV (TSC). This is in good agreement with published values for the EL3 ranging from 0.56 to 0.68 eV. Furthermore, we illustrate that the depth of the peak increases with increasing oxygen content. Our results support the assumption, that oxygen on an arsenic site the so called off centre oxygen oc-O As should be the origin of the EL3.

Vibrational Absorption of Hydrogen Bonded to Interstitial Oxygen in GaAs and GaP

In LEC-grown GaAs and GaP with an oxygen content larger than 1015 cm—3, two sharp vibrational absorption lines are investigated located at 3108.0 as well as 3235.0 cm—1 for GaAs and 3106.0 as well as 3250.9 cm—1 for GaP. These lines are due to the stretching modes of hydrogen bonded to interstitial oxygen in two different centres (Oi–H)I and (Oi–H)II as proved by the detection of the isotopically shifted lines in material doped additionally with deuterium. Centre (Oi–H)I is a single hydrogen atom bonded to oxygen and is in GaAs photosensitive at temperatures lower than 100 K. (Oi–H)II is a di-hydrogen centre with the two hydrogen atoms being on equivalent positions around O.

Behavior of Oxygen in Ga-As Melts with the Range of As Content up to 5 mass% Equilibrated with B<SUB>2</SUB>O<SUB>3</SUB> Flux

The equilibrium between Ga-As melt, containing arsenic up to 5 mass%, and B 2 O 3 flux was investigated from 1273 to 1523 K in a silica ampoule. The effect of arsenic on equilibrium contents of oxygen, boron and silicon in the melt was investigated. The results were analyzed using interaction parameters. The equilibrium distribution ratio of oxygen between Ga-As melt and B 2 O 3 flux decreased with the increase of temperature, Ga 2 O 3 content in the flux and arsenic content in the melt. The activity of Ga 2 O 3 in the B 2 O 3 flux was determined in the temperature range from 1273 to 1523 K, which is relevant to the practical process of crystal growth of GaAs.

Structural properties and energetics of oxygen impurities in GaAs

We investigate the structural properties, formation energies, and electronic structure of oxygen impurities in GaAs using first-principles total-energy calculations. Five charge states of oxygen occupying an arsenic site $({\mathrm{O}}_{\mathrm{As}})$ and various interstitial sites $({\mathrm{O}}_{i})$ were considered. For the ${\mathrm{O}}_{\mathrm{As}}$ defect in negative charge states we find off-center configurations with ${C}_{2v}$ symmetry as reported experimentally. Our results for the formation energies reveal a negative-$U$ behavior for the ${\mathrm{O}}_{\mathrm{As}}$ defect, in which the paramagnetic $2\ensuremath{-}$ charge states is never stable. For the ${\mathrm{O}}_{i}$ defect, we find three equilibrium configurations for the O atom, which are present in all the charge states investigated. The stable configuration for the neutral defect shows the O atom between an As-Ga pair forming the As-O-Ga structure. However, for the negative charge states, the stable configuration shows the O atom exactly at the tetrahedral interstitial site, bonding with four gallium first neighbors. Further, we find that the $1\ensuremath{-}$ charge state is never stable, suggesting that the interstitial defect also exhibits a negative-$U$ behavior. Based on our results, we suggest that the $A, {B}^{\ensuremath{'}},$ and B bands of the local-vibrational-mode absorption spectrum of oxygen in GaAs are due to the off-center ${\mathrm{O}}_{\mathrm{As}}$ defect. Also we show that this spectrum cannot be associated with an interstitial-oxygen configuration as previously proposed.

Diffusion and stability of oxygen in GaAs and AlAs

We investigated various basic properties of oxygen in GaAs and AlAs by using first-principles calculations and considering the charge states and Fermi-level effect. For GaAs, the obtained stable atomic configurations and their stability showed good agreement with experimentally obtained results. We found that many features, such as a stable site, a negative-U nature, a charge-state-dependent diffusion path, and a rather high diffusion barrier height in the negatively charge state, are similar between GaAs and AlAs. Some features, however, were dependent on the host. We found that an asymmetry effect during the diffusion is pronounced in p-type host in both GaAs and AlAs, but the effect shows different characters depending on the host. O is more stable in AlAs than in GaAs. All of the obtained basic properties can be explained by three characteristics: the large electron negativity of oxygen, the strong O-Al bond, and the large polarization of AlAs hosts. From our theoretical study, the experimentally observed higher O concentration for AlAs layers in GaAs/AlAs systems can be clearly explained.

Real-space Green's-function approach applied to the phonon spectra of isolated impurities.

It is shown how the real-space Green's-function approach to the calculation of densities of state for large systems can be used in studying the behavior of isolated impurities on crystals. The local Green's function associated with the impurity configuration can be obtained by coupling the impurity configuration with the Green's function of the host lattice surrounding the impurity configuration. The case of substitutional Si in GaAs illustrates the approach. The unusual case of isolated oxygen in GaAs is studied in detail. It is shown that the picture of oxygen forming isolated ${\mathrm{Ga}}_{2}$O molecules needs modification in that interactions with all four nearest-neighbor sites must be included to reproduce the experimental spectrum. Sources of the individual peaks in the multiplets are identified and the appearance of a transient four-component multiplet is explained. \textcopyright{} 1996 The American Physical Society.

The paramagnetic charge state of substitutional oxygen in GaAs

In oxygen-rich GaAs the optical absorption of substitutional oxygen (OAs) in the near infrared was investigated by measuring its magnetic circular dichroism (MCDA). An MCDA was discovered which originates from a paramagnetic ground state. By investigating its thermal decay kinetics and its dependence on optically induced recharging processes involving EL2 defects and by comparison with analogous local vibrational mode measurements, it could be shown that the MCDA is due to the metastable B′ charge state of the OAs centers. The B′ state is thus identified as the paramagnetic charge state of the OAs center.

The effect of boron, oxygen, and fluorine in ion implanted GaAs

Effects of boron, fluorine, and oxygen in GaAs have been investigated by electrical characterization using current-voltage, capacitance-voltage and deep level transient spectroscopy techniques. Ion implantation at 100 keV energy was conducted with doses of 1011 and 1012/cm2. Carrier compensation was observed in each implanted sample. The compensation effect strongly depended on ion implantation condition and ion species. More free carriers were compensated for higher dose and heavier species; however, severe surface damage would also be induced that degrade electrical performance. Rapid thermal annealing treatment showed the heavier ion implanted samples to be more thermally stable. Defect levels for each implanted species were compared and identified. A native shallow defect E4 was easily removed by ion implantation. In higher dose and heavier ion implantation, both electron and hole traps were induced. However, in some cases, heavier ion implantation also removed native defects. Acceptor-type surface states were created by implantation that degrade material electrical characteristics and also reduce the effect of compensation. The damage induced traps were mostly point-defects or point-defect/impurity complexes as evidenced by sensitivity to heat treatment.

Influence of the negative-U OAs defect in GaAs on the isolation behavior of oxygen-implanted AlGaAs/GaAs heterostructures

The isolation behavior of oxygen implants in AlGaAs/GaAs modulation-doped heterostructures has been studied in comparison to boron implants. After annealing between 400 and 550 °C a thermally activated compensation mechanism in addition to damage-induced deep levels is observed in the case of oxygen. Infrared absorption spectroscopy shows local vibrational modes of off-center substitutional oxygen in GaAs at wave numbers of 721 and 734 cm−1 in the implanted surface region after annealing. The substitutional oxygen acts as a deep electron trap and causes a chemical-induced compensation.

Improved quantification and detection limits for oxygen analysis in AlxGa1−x As/GaAs multilayers with secondary ion mass spectroscopy

The different contributions to the oxygen background signal in secondary ion mass spectroscopy measurements on AlGaAs and GaAs are investigated. The instrumental parameters for obtaining the lowest detection limits are established. The advantage of a heated sample holder, which reduces the oxygen background quickly after sample introduction in combination with the liquid-nitrogen cryoshield is demonstrated. A complete quantification procedure for oxygen in AlGaAs/GaAs multilayer structure is presented. Even at a conventional vacuum pressure 1×10−9 Torr and a primary current density allowing good depth resolution, a detection limit of oxygen in GaAs of 5×1015 cm−3 could be achieved, increasing with Al content to 1×1017 cm−3 in AlAs.

Determination of carbon and oxygen in GaAs by means of 3He-activation

Traces of carbon and oxygen (ppm and below-ppm levels) have been determined in GaAs by means of 3 He-activation. The excitation functions of the 3 He-induced nuclear reactions on 69 Ga, 71 Ga and 75 As have been determined in the energy region between 6 and 12 MeV in order to optimize the irradiation conditions and minimize the interference due to the matrix activation effects. The determination of the above mentioned contaminants by 3 He-activation is, because of matrix activation effects, possible only using projectile energies below 6 MeV.

Analysis of carbon and oxygen in GaAs using a secondary ion mass spectrometer equipped with a 20 K-cryopanel pumping system

The detection of carbon and oxygen in GaAs has been investigated by secondary ion mass spectrometry (SIMS). A reduction in carbon and oxygen background is achieved by means of a local pumping system using a 20 K-cryopanel placed around the sample. Detection limits are 4×1015 atoms/cm−3 for carbon, and 8×1015 atoms/cm−3 for oxygen.

Redistribution of implanted oxygen in GaAs

We show that implanted oxygen in GaAs has two different thermal behaviours depending on the implantation dose. In the case of low doses, below 1014 oxygen-cm−2 oxygen diffuses very quickly at 900°C. In the case of high doses, above 1014 oxygen-cm−2, oxygen piles up around its projected range during annealing. This should be due to the formation of precipitates. The presence of substrate impurities in the nucleation process is not suspected.

Contribution of activation analysis with low energy charged particles to studies on GaAs

It is shown that the instrumental analysis of carbon and oxygen in GaAs, at trace level, can be achieved by irradiation with low energy deuterons and tritons (3 MeV). The experimental sensitivities are 6 ppb/weight for the16O(13H,n)18F reaction and 25 ppb/weight for the12C(12H,n)13N reaction. Applications related to the metallurgy of GaAs are described.

Quantitative analysis of oxygen in thin epitaxial layers of GaAs by SIMS

This paper reports the quantitative analysis of oxygen in GaAs epitaxial layers by a CAMECA IMS 300 secondary ion mass spectrometer. It is shown that the residual oxygen pressure of the apparatus (∼1×10 −7 torr) does not affect the analysis. On the basis of standard samples analysed by activation with tritons [ 16O(T,n) 18F] the limit of detection of oxygen in GaAs is found to be ∼0.01 ppm.at. Some results on oxygen depth profiling in epitaxial layers are presented.

Pseudopotential calculations of the effect of displacement upon the impurity levels introduced by deep donor oxygen in GaAs, GaP, Si and nitrogen in diamond

Calculations of the effect of displacement upon deep donor levels suggest significant differences between groups IV and III–V semi-conductors. We conclude that oxygen in GaAs and GaP should possess tetrahedral symmetry and predict a large trigonal distortion for substitutional nitrogen in diamond. Our results indicate that the level due to N in diamond occurs in the upper half of the band gap.

The Influence of Oxygen on the Properties of GaAs Grown by Liquid Phase Epitaxy

Epitaxial layers of GaAs are grown from Ga solution. The effects of oxygen in achieving high purity GaAs layers are investigated. From the experimental results of doping with Ga2O3, the growth temperature dependence of carrier concentration and the impurity profile are explained by the temperature dependence of the distribution coefficient of oxygen in GaAs grown by liquid phase epitaxy. The distribution coefficients of oxygen are 6.5×10-4 at 700°C, 1.8×10-4 at 750°C and 5.1×10-5 at 800°C, respectively.

Nachweis und diffusion von Sauerstoff in GaAs

The oxygen content of GaAs single crystals grown under a protective B 2O 3 melt by the liquid encapsulation technique was determined by mass spectrometry, deuteron and neutron activation analysis and was found to be 10 19 –10 20 atoms cm -3. Crystals grown from the melt by other techniques as well as vapour- and solution-grown epitaxial layers were found to have concentrations of the same order of magnitude. An estimate from mass-spectrometric data yields an effective diffusion coefficient of oxygen in GaAs of D eff = 2 × 10 -3 exp (-1.1 eV.kT) cm 2 s -1 between 700 and 900°C.