High-temperature positron diffusion in Si, GaAs, and Ge

Soininen, E.; Mäkinen, J.; Beyer, Dirk; Hautojärvi, P.

doi:10.1103/physrevb.46.13104

Cited by 73 publications

(50 citation statements)

References 62 publications

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“…The transmission probability qT for the projectile particles as a function of the distance z can be approximated as Table I. Soininen et al (1992) Nieminen, 1984. "Soininen et al , 1992.…”

Section: Fig 4 Transmission Probabilities For Positrons and Electronsmentioning

confidence: 99%

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Theory of positrons in solids and on solid surfaces

1994

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Various experimental methods based on positron annihilation have evolved into important tools for researching the structure and properties of condensed matter. In particular, positron techniques are useful for the investigation of defects in solids and for the investigation of solid surfaces. Experimental methods need a comprehensive theory for a deep, quantitative understanding of the results. In the case of positron annihilation, the relevant theory includes models needed to describe the positron states as well as the different interaction processes in matter. In this review the present status of the theory of positrons in solids and on solid surfaces is given. The review consists of three main parts describing (a) the interaction processes, {b) the theory and methods for calculating positron states, and {c)selected recent results of positron studies of condensed matter. CONTENTS

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“…The transmission probability qT for the projectile particles as a function of the distance z can be approximated as Table I. Soininen et al (1992) Nieminen, 1984. "Soininen et al , 1992.…”

Section: Fig 4 Transmission Probabilities For Positrons and Electronsmentioning

confidence: 99%

“…In the Debye approximation (Perkins and Carbotte, 1970;Nieminen and Oliva, 1980;Jensen and Walker, 1990) temperatures. The scattering of positrons by ionized impurities has been studied in the case of phosphorus-doped silicon (Soininen et al , 1992). In this scattering process, a charged impurity causes a long-range Cou1ombic perturbation.…”

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confidence: 99%

Theory of positrons in solids and on solid surfaces

1994

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“…L ϩ is ϳ200 nm in GaAs free from positron trapping at defects. 28 The positron lifetime depends mainly on the electron density and provides direct information on the defect size. 8 Therefore, positron lifetime spectroscopy gives additional information on defects in comparison to Doppler broadening which is sensitive to the momentum distribution.…”

Section: B Positron Annihilationmentioning

confidence: 99%

Defect identification in GaAs grown at low temperatures by positron annihilation

Gebauer¹,

Börner

Krause‐Rehberg

et al. 2000

Journal of Applied Physics

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We use positron annihilation to study vacancy defects in GaAs grown at low temperatures ͑LT-GaAs͒. The vacancies in as-grown LT-GaAs can be identified to be Ga monovacancies, V Ga , according to their positron lifetime and annihilation momentum distribution. The charge state of the vacancies is neutral. This is ascribed to the presence of positively charged As Ga ϩ antisite defects in vicinity to the vacancies. Theoretical calculations of the annihilation parameters show that this assignment is consistent with the data. The density of V Ga is related to the growth stoichiometry in LT-GaAs, i.e., it increases with the As/Ga beam equivalent pressure ͑BEP͒ and saturates at 2ϫ10 18 cm Ϫ3 for a BEPу20 and a low growth temperature of 200°C. Annealing at 600°C removes V Ga . Instead, larger vacancy agglomerates with a size of approximately four vacancies are found. It will be shown that these vacancy clusters are associated with the As precipitates formed during annealing.

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“…This value, however, is believed to be less than the true phonon limited value, due to the effect of shallow trapping that occurs on negatively charged acceptor impurities [6]. Recently Soininen, et al [20] in some of the most accurate and systematic work so far, have measured positron diffusion lengths in GaAs above room temperature (where shallow trapping is not anticipated to be important), and quote a value for D+ of 1.6 _+ 0.2 cm 2 s -1 at 300 K, corresponding to a/~+ value of 62 + 8 cm 2 V -1 s -x. These authors found that the D+ temperature dependence was in accord with the positron scattering from polar optical as well as acoustic phonons as predicted by theory.…”

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confidence: 93%

Semi-insulating GaAs: A possible substrate for a field-assisted positron moderator

Shan

Ling

et al. 1994

Appl. Phys. A

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Abstract. Positron lifetime spectroscopy measurements have been carried out for semi-insulating GaAs with applied electric fields in the samples directed towards, and away from the positron injecting contact. The lifetime spectra have been decomposed into two components, the longer of which (~ 400 ps) is characteristic of open volume defects at the metal-semiconductor interface through which positrons are injected. The interesting feature of these experiments is the large increase in the intensity of this interface component as the field is directed towards the contact. We show that this increase is caused by a significant fraction of implanted positrons drifting under the influence of a strong electric field produced by a layer of space-charge formed adjacent to the positron injecting contact. The general trend of the intensity variation is well explained by the proposed model. Experiments involving the application of an ac bias to the samples strengthen the suggestion that the space charge region is largely formed from ionized EL2 donors. The results of the present work indicate that semi-insulating GaAs possesses properties that make it a suitable material for the fabrication of a high efficiency (~ 10%) room-temperature field-assisted positron moderator. The extraction of positrons from the GaAs substrate into the vacuum through a thin metalization is discussed based upon available positron affinities for the GaAs and various elemental metals. These data suggest that a few monolayers of a strongly electronegative metal such as Au or Pd may allow vacuum emission through quantum tunneling. These studies are important in their own right as a means of checking mechanisms of carrier transport in materials. They also have more direct technological relevance in that materials exhibiting large positron diffusivities/mobilities can often be employed as efficient moderators for low energy positron beams [7]. The motivation behind the present work on SI (Semi-Insulating) GaAs was initially in the former category, the intention being to make #+ measurements using the lifetime spectroscopy technique previously used for Si [8]. However, the unexpected results obtained, together with their lack of sensitivity towards #+, have led us to conclude that the relevance of the present study may be more in the second category; namely that SI-GaAs may be a good material from which to form an efficient FA (Field-Assisted) moderator of positrons.FA moderation is the name given to a particular type of process for slowing fi+ radiation, by which a significant fraction of positrons are, after implantation into either an insulator or semiconductor stressed with an electric field, enabled to avoid annihilation by drifting through the material into the vacuum. Since positron drift distances in an electric field can exceed typical thermal diffusion distances by approximately two orders of magnitude, the FA moderator has ultimately greater potential for super-efficient generation of slow positrons [9]. Calculations show that such moderators c...

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High-temperature positron diffusion in Si, GaAs, and Ge

Cited by 73 publications

References 62 publications

Theory of positrons in solids and on solid surfaces

Theory of positrons in solids and on solid surfaces

Defect identification in GaAs grown at low temperatures by positron annihilation

Semi-insulating GaAs: A possible substrate for a field-assisted positron moderator

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