Structural and defect characterization of GaAs and AlxGa1−xAs grown at low temperature by molecular beam epitaxy

Abstract

We have investigated the structural and defect characteristics of GaAs and Al x Ga 1Ϫx As grown at low substrate temperature ͑250°C͒ by molecular beam epitaxy. Using x-ray diffraction we have observed an increase in lattice parameter for all as-grown layers, with the Al x Ga 1Ϫx As layers showing a smaller expansion than the GaAs layer. However, infrared absorbtion measurements revealed that the concentration of neutral arsenic antisite defect, ͓As Ga ͔ 0 , was not significantly affected by aluminum content (x), with only a small reduction for xϭ0.36. Positron beam studies showed that the low temperature layers had a higher concentration of vacancy-related defects ͑ϳ10 17 cm Ϫ3 ͒ than the semi-insulating substrate, with the Al x Ga 1Ϫx As layers having the highest values. After annealing ͑600°C, 15 min͒ the lattice constants relaxed to those of conventionally grown material and ͓As Ga ͔ 0 was reduced in all cases, with the smallest reduction occurring for the xϭ0.36 layer, indicating that the Al atoms strengthen the lattice against excess arsenic incorporation and hold the arsenic antisite atoms more strongly in position. X-ray photoelectron spectroscopy showed that arsenic diffused out of the surface region and was replaced by oxygen, possibly due to an insufficient overpressure of forming gas during the anneal. This oxygen penetration was greater for the GaAs layer than for the Al x Ga 1Ϫx As layers. Extra Raman peaks at 200 and 257 cm Ϫ1 confirmed that the surface was very disordered. There was, nevertheless, a large increase ͑4%͒ in the positron S parameter in the bulk of the annealed layers, suggesting the formation of vacancy clusters, whereas in the surface region we find evidence that As Ga diffusion proceeded at a faster rate in the xϭ0.36 than the xϭ0.2, in agreement with the vacancy-enhanced As Ga diffusion model.

Defect identification in GaAs grown at low temperatures by positron annihilation

“…Similar values of L ϩ in LT-GaAs were reported by Fleischer et al 40 The decrease of L ϩ is directly visible in the S(E) variation at low energies: the faster the transition from surface to bulk annihilation is, the shorter is L ϩ . A short diffusion length is indicative for a high density of positron traps ͓Eq.…”

“…This is in accordance to the assumptions in the earlier PAS studies. [9][10][11]40,49 Due to the combination of different techniques in conjunction with theoretical calculations in the present study, the identification of V Ga can now be considered to be well established. Positron lifetime spectroscopy showed that the defects are monovacancies, whereas the conventional S -W analysis shows that they belong to the Ga sublattice.…”

Defect identification in semiconductors with positron annihilation: Experiment and theory

“…Thermal annealing experiments have been performed to elucidate vacancy formation mechanisms and the role of copper in determining the vacancy distribution in GaAs crystals (Elsayed et al, 2008(Elsayed et al, , 2011. LT-MBE GaAs is typically grown in conditions that favor the formation of Ga sublattice defects: Ga vacancies and As antisites (Bliss et al, 1992;Keeble et al, 1993;Störmer et al, 1996;Fleischer et al, 1997;Gebauer et al, 1997;Laine et al, 1999). The Ga vacancy-related defects follow the growth stoichiometry and compensate the n-type doping.…”

Effect of column III vacancy on arsenic precipitation in low-temperature grown III–V arsenides

“…It is then natural to question whether there is any interaction between excess As and vacancies upon annealing? Recently, Fleischer et al 11 have shown that vacancies play a role in As precipitation, and a vacancy-assisted antisite As diffusion model has been proposed to explain the defect-removal mechanism. 12 However, there still lacks a complete model on the role of point defects which may explain and predict the formation of As precipitates and the relationship between doping and composition.…”