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Hier finden Sie wissenschaftliche Publikationen aus den Fraunhofer-Instituten. # The calibration of the strength of the localized vibrational modes of silicon impurities in epitaxial GaAs revealed by infrared absorption and raman scattering.

Kalibrierung der Intensität von lokalisierten Schwingungsmoden von Silizium in epitaktischem GaAs gemessen mit Infrarot-Absorption und Ramanstreuung

**Abstract**

N-type silicon-doped epitaxial layers of gallium arsenide grown by molecular-beam epitaxy (MBE) or metal-organo chemical vapor deposition (MOCVD) have been investigated by measurements of the Hall effect and the strengths of the localized vibrational modes (LVM) of silicon impurities using both Fourier transform absorption spectroscopy and Raman scattering at an excitation energy of 3 eV close to the E sub 1 band gap. Lines from Si(Ga) donors, Si(As) acceptors, Si(Ga)-Si(As) pairs, and Si-X, a complex of silicon with a native defect, were detected and correlated for the two techniques. The maximum carrier concentration (n) found for samples grown under standard conditions was 5.5 x 10 high 18 cm high minus 3. At higher doping levels Si-X becomes dominant and acts as an acceptor, so reducing (n). An integrated absorption of 1 cm high minus 2 in the Si(Ga) LVM line corresponds to 5.0 plus minus 4 x 10 high 16 atoms cm high minus 3: a similar calibration applies to the Si(As) line, but fo r Si-X, an absorption of 1 cm high minus 2 corresponds to only 2.7 plus minus 1.0 x 10 high 16 defects cm high minus 3. Possible structures for Si-X are discussed but a definitive model cannot yet be proposed. MBE samples grown at 400 degree C had values of (n) close to 10 high 19 cm high minus 3, and a negligible concentration of Si-X. On annealing, (n) decreased and Si-X defects were produced together with site switching of Si(Ga) to Si(As). These results are important to the understanding of the mechanism of silicon diffusion at low temperatures. The infrared absorption and Raman measurements are complementary. Absorption measurements made at a resolution of 0.1 cm high minus 1 require layers greater than or equal to 1 mym in thickness doped to a level of 3 x 10 high 17 cm high minus 3 but require the prior elimination of free-carrier absorption. Raman measurements can be made on as-grown layers only 10 nm in thickness doped to a level of 2 x 10 high 18 cm high minus 3, but with a s