Berlin 2001 – wissenschaftliches Programm

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MS: Massenspektrometrie

MS 7: Techniques and New Developments

MS 7.4: Vortrag

Donnerstag, 5. April 2001, 18:00–18:15, EB 202

Silicon concentrations in silicon doped gallium arsenide single crystals — •B. Wiedemann¹, J. D. Meyer¹, D. Jockel², H. C. Freyhardt², B. Birkmann³, and G. Müller³ — ¹Institute for Nuclear Physics, University of Frankfurt, D-60486 Frankfurt am Main, Germany — ²Centre for Advanced Materials Development, D-37073 Goettingen, Germany — ³Department of Materials Science VI, University of Erlangen-Nuernberg, D-91058 Erlangen, Germany

The assessment of silicon concentrations in doped vertical gradient freeze GaAs is presented. SSMS measurements of the silicon concentration [Si] of singly and multiple charged silicon ions, Si⁺, Si²⁺, and Si³⁺, and Hall measurements of the electron carrier density n show a linear relation between [Si] and n in a broad region of concentration. It is concluded from the slope that most of the silicon atoms are incorporated into GaAs as donors and approximatly 0.8 electrons per silicon atom are contributed. In state of the art silicon doped GaAs single crystals concentrations between 5.5·10¹⁷ and 3.1·10¹⁸ cm⁻³ were measured. In this material the electron carrier densities increase in the range between 1.8·10¹⁷ and 2.2·10¹⁸ cm⁻³, whereas electron mobilities µ_n are found to be decreasing between 2.7·10³ and 1.8·10³ cm²V⁻¹s⁻¹. The concentration [Si] measured versus the g factor, the frozen part of the crystal, is consistent with the Scheil equation [Si] = 1.43·10¹⁸(1-g)^−0.85 cm⁻³ for the distribution coefficient k = 0.15 (1-k = 0.85, k·[Si]₀ = 1.43·10¹⁸ cm⁻³ with [Si]₀, the initial value in the melt). Differential interference contrast microscopic measurements show low defect densities on slices from the front to the tail of the crystal with increasing silicon concentrations until a concentration of approximately 3·10¹⁸ cm⁻³ is reached.