Positron Studies of Defects in III–V Semiconductor Compounds

Positron annihilation lifetime spectroscopy and Doppler broadening annihilation line-shape measurements have been carried out in 40-MeV alpha-irradiated n-type GaAs. After irradiation, the sample has been subjected to an isochronal annealing over temperature region of 25-800°C with an annealing time of 30 min at each set temperature. After each annealing, the positron measurements are taken at room temperature. Formation of radiation-induced defects and their recovery with annealing temperature are investigated. The lifetime spectra of the irradiated sample have been fitted with two lifetimes. The average positron lifetime s avg = 244 ps at room temperature after irradiation indicates the presence of defects, and the value of s 2 (262 ps) at room temperature suggests that the probable defects are mono-vacancies. Two distinct annealing stages in s avg at 400-600°C and at 650-800°C are observed. The variations in line-shape parameter (S) and defect-specific parameter (R) during annealing in the temperature region 25-800°C resemble the behaviour of s avg indicating the migration of vacancies, formation of vacancy clusters and the disappearance of defects between 400 and 800°C.

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“…The value agrees well with the bulk value as obtained in several previous observations [20,[26][27][28].…”

Section: As-grown Samplesupporting

confidence: 92%

Positron annihilation measurements in high-energy alpha-irradiated n-type Gallium Arsenide

et al. 2015

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“…Positron annihilation techniques have proved to be valuable for non-destructively detecting vacancy defects in metals [1] and semiconductors [2]. A sub-class of such measurements are those in which the freedom of positron motion is observed either through measuring the diffusion constant D+ or the mobility #+ [3].…”

mentioning

confidence: 99%

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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“…Experimental evidence shows that positrons can get trapped at neutral and negative vacancies, which result in a change of their annihilation characteristics, e.g. , in an increase of their lifetime above the free recombination value [3]. Lifetimes can be related to the size of the vacancies, whereas angular correlations of annihilation radiation (ACAR) yield information about the momentum distribution of the electrons seen by the positron [4].…”

mentioning

confidence: 99%

“…A detailed interpretation of positron annihilation experiments is very delicate in semiconductors where, at variance with metals, vacancies can have different charge states. Binary semiconductors pose special problems since vacancies can be formed in both sublattices, and negatively charged antisite defects may act as shallow positron traps [3]. For example, the identification of vacancy charge states in GaAs has been the subject of different interpretations over the past few years [5,6].…”

mentioning

confidence: 99%