ABSTRACT
It is well known that annealing of nitrogen containing structures enhances the PLintensities [7]. So these samples were annealed at 700°C for 15min. HRXRD and SIMS measurements did not reveal a significant difference between as grown and annealed GaNAs structures. After annealing PL spectra of these structures clearly showed for all samples an enhanced GaNAs signal, which was not detectable from the as grown samples with high nitrogen concentrations. The PL-wavelength of the annealed GaNAs signal versus the nitrogen content y is plotted in figure 3. A strong bowing is clearly observed and is described for y < 0.06 by
where the GaAs PL-bandgap Eg,GaAs is 1.42 eV, a=17 eV and b=148 eV. This composition dependence is in good agreement with the results of Sik et al. using a=17 eV and b=200eV [8],
4. Nitrogen and indium incorporation In a second series we have used the growth parameters of the GaNAs sample with the highest nitrogen content of y=0.055 and studied the incorporation of indium with increasing TMI-flux of 60 - 70 nm thick Ga(i.X)InxNyAs(i.y) epilayers. All GalnAs reference structures are compressivly strained and the amount of strain varies linearly with the indium composition (see triangles in figure 4). For the nitrogen containing (GaIn)(NAs) epilayers the strain is tensile for low indium content and becomes compressive for samples with xi„ > 0.10 (shown as diamonds in figure 4). The strain difference between these nitrogen containing structures and the GalnAs reference structures with 0< xi„ <0.17 is investigated. It is clearly seen that the strain difference reduces with increasing indium content. This phenomenon is not observed in MBE growth [4]. The indium content of the GalnAs and (GaIn)(NAs) layers have been confirmed by RBS. Within the error limits of RBS (< 3% of the measured indium content) we could not observe an altered indium incorporation in the (GaIn)(NAs) samples compared to the nitrogen free reference samples. From the reduction of strain with increasing indium content we can conclude, that the nitrogen content is reduced from 5.5 % to 1.4 % for an indium content up to 16%. These results will be investigated by FTIR and further SIMS measurements.
