Field effect on positron diffusion in semi-insulating GaAs

Abstract

An energy-tunable monoenergetic positron beam was used to study positron diffusion in the space-charge region of an Au/GaAs͑SI͒ ͑semi-insulating͒ Schottky contact, where the electric field reaches ϳ10 5 V cm Ϫ1 by reverse biasing the diode. An analytical solution of the time-dependent positron drift-diffusion model under an electric field was obtained for the case of a semi-infinite body with a capturing boundary, and explains the experimental results well. A positron diffusion coefficient of 1.8Ϯ0.2 cm 2 s Ϫ1 , and a positron mobility of 70Ϯ10 cm 2 V Ϫ1 s Ϫ1 in GaAs͑SI͒ at 300 K, were obtained independently. This result is consistent with the Einstein relation. The dependence of the positron current density at the Au/GaAs interface on the electric field shows that GaAs͑SI͒ is a possible candidate for the fabrication of the field-assisted positron moderator. ͓S0163-1829͑96͒04428-1͔

Low-temperature positron transport in semi-insulating GaAs

“…The interface S value can be obtained by fitting the S-E curve. 19 For incident energies of 18 and 26 keV, positrons are mainly implanted into the bulk region close to the interface. Consequently, a large amount of positrons will diffuse to the interface and annihilate there.…”

“…The drift-diffusion equation can be solved with proper boundary and initial conditions. 19 By integrating the positron current density at the Au/GaAs interface, the fraction of positrons reaching this interface (zϭ0) can be obtained as 19,29 …”

“…17,18 Soininen et al reported a diffusion coefficient of 1.6͑2͒ cm 2 s Ϫ1 in semi-insulating ͑SI͒ GaAs at 300 K. 15 More recently, a diffusion coefficient of 1.8͑2͒ cm 2 s Ϫ1 and a mobility of 70Ϯ10 cm 2 V Ϫ1 s Ϫ1 in GaAs ͑SI͒ were obtained independently at room temperature. 19 Measurements of the temperature effect on positron diffusion showed that scattering from acoustic phonons is predominant in cubic metals ͑20-1400 K͒, 7 Ge (Ͼ500 K͒, 14 and Si ͑30-500 K͒. 14,20,21 The diffusion coefficient follows the T Ϫ1/2 power law.…”

On Approach of Estimation Time Scales of Relaxation of Concentration of Charge Carriers In High-Doped Semiconductor

“…Traditional way to determine time scales of charge carrier transport required determination non-stationary solution of appropriate mass transport equation. If parameters of semiconductor (charge carrier diffusion coefficients and mobilities et al) and strength of electric field in semiconductor material are independent on coordinate, mass transport equation could be easily solved [11,12]. In the common case of dependence of the above parameters and the electric field on coordinate exact solution of mass transport equation is unknown.…”

Investigation of electric fields in B‐implanted Si by positron beam spectroscopy

“…In addition to its powerful role in the field of defect studies, variable-energy positron annihilation spectroscopy (VEPAS) has been evolved to study electric fields and their influence on positron diffusion. Electric fields applied to Au/Si and Au/GaAs systems [1][2][3] were shown to drift positrons back to the metal-semiconductor interface. Internal electric fields have been found to act as barriers against positron diffusion in Si, in which no positron traps could be detected [4].…”