M. Valladon

SEARCH FOR THE INFLUENCE OF CHEMICAL EFFECT ON THE STOPPING POWER: THE CASE OF OXIDES

Abstract Influence of possible chemical effects on the stopping power of BeO, Al 2 O 3 , TiO 2 , ZnO, Nb 2 O 5 and Ta 2 O 5 was studied between 0.5 and 0.7 MeV amu −1 for BeO and at ≅2.5 MeV amu −1 for the other oxides. The method of study was the “average stopping power method”. No chemical effect is detected at 2.5 MeV amu −1 . For BeO, energy dependant deviations from Bragg-Kleemans rule are observed.

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

Abstract 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 [ 16 O(T,n) 18 F] 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.

The problem of diffusion during charged particle activation analysis; the case of18F in pure germanium single crystals

During ion bombardment, thermal diffusion and radiation enhanced diffusion of atoms occur. These phenomena may be a source of error in ion beam analysis, particularly in radioactivation analysis if contaminant surface atoms are present. It is shown here that penetration of18F (derived from surface oxygen by nuclear reaction) in germanium single crystals, does not extend appreciably farther than the maximum range of the recoiling18F nuclei. Since the analyzed depth is over an order of magnitude larger than the recoil, the validity of charged particle activation analysis at the ppb level in the present case (oxygen→18F in germanium), is clearly demonstrated.

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.

Study of the incorporation and repartition of boron and carbon in Czochralski grown GaAs using charged particles activation

Charged particles activation methods were developed to study the incorporation and the repartition of B and C at trace level in GaAs ingots grown by the Czochralski method with liquid B2O3 encapsulation. The 10B(d, n)11C and 12C(d, n)13N reactions were used for the analysis of boron and of carbon. Radiochemical separations of 11C and of 13N after irradiation were necessary. For the separation of 11C the samples were oxidized in a mixture of B2O3 and Pb3O4, and CO2 was trapped in KOH. For the separation of 13N, the samples were fused under argon in a graphite crucible, and N2 trapped on titanium at 900°C. Detection limits were ∼1014 at./cm3 for carbon and 3×1014 at./cm3 for boron. Important (factors ⋍ 50) concentration variations could be correlated to the growth conditions, particularly the percentage of water in B2O3. A segregation of B and C in the ingots was also observed. B concentrates at the tail end, and C concentrates at the seed end.

Determination of residual impurities in InP grown by the Czochralski method, using charged particle activation analysis

InP samples were analyzed by charged particle activation analysis. Proton activation at 12 MeV permits the nondestructive survey of 30 elements. The main impurities are Ti, Fe, Ga and Zn (1015 to 2·1016 at/cm3). Oxygen was analyzed separately by triton activation at 3 MeV; the oxygen concentration is normally less than 1016 at/cm3.

Studies on Polycrystalline Silicon for Solar Applications, including Characterization of Trace Elements B, C and Al by Charged Particles Activation Analysis

Nuclear methods of analysis were used to study the behaviour of trace elements during the metallurgy of polycrystalline silicon for solar applications: these impurities may have an influence on the efficiency of the solar photocells made out of this silicon. The ingots were prepared in a graphite boat by the Bridgman method without seed, using electronic grade silicon as a starting material. Most impurities were determined by neutron activation, the global level being low: ¿ 3.1015 at/cm3. Charged particles were used to determine B, C and Al. For boron, the 10B (d,n)11C reaction with subsequent chemical separation of 11C was used; for carbon, we used non-destructive analysis and the 12C(d,n)13N reaction. For low levels of aluminum in silicon no suitable method existed; we could solve this problem using fast neutrons from the 9Be (d,n)10B reaction and the reaction 27A1 (n,¿)24 Na. Interferences from Mg (undetected) and from Si itself were negligible, the detection limit being 5.1014 at/cm3 in ultra pure silicon. High Carbon levels were found close to the solubility limit (2.1018 at/cm3); there is a significant segregation at the top, at the edges and at the bottom of the ingots. Activation results were used to calibrate infrared absorption at low temperature for the determination of carbon in silicon. Residual B and Al concentrations are low. Ingots doped with B or Al were analyzed, the doping with Al being inefficient. Boron was homogeneously distributed, while Al segregated at the top and at the grain boundaries.

Characterization of Semiconductor Materials by Charged Particle Activation

Results obtained during the past few years by research groups working on joint projects, mainly in view of a better knowledge of GaAs, are summarized here. The procedures of radioactivation analysis with charged particles (deuterons and tritons) are described to some extent. Finally, some important aspects of charged particle activation analysis, namely : calibration, etching after irradiation and diffusion during irradiation, are discussed.

The study of stopping powers by the method of the average stopping power

It is shown that the average stopping power method, at first developed to obtain accurate results in analysis by irradiation with charged particles, can be used to measure relative stopping powers with high accuracy. The basis for the study of deviations from Bragg—Kleemanns rule in the case of compounds is established; the case of several oxides is investigated experimentally.

Recent progress in the study of semiconductors using charged particle activation

Several examples of improvements or of new developments in the field of charged particle activation analysis applied to the study of semiconductors are described: determination of carbon at the sub-ppb level in GaAs, use of 20 to 30 MeV protons for trace analysis in InP, study of radioactivation with 12 MeV tritons, and use of channeling to study the lattice location of carbon atoms at trace level in GaAlAs.