Vibrational modes introduced by the incorporation of N into GaAs and GaInAs have been studied by Raman spectroscopy on samples grown by molecular-beam epitaxy using a rf nitrogen plasma source. When proceeding from GaAs(1-x)N(x) to Ga(1-y)In(y)As(1-x)N(x) with x<=0.04 and y<=0.12, the nitrogen-induced vibrational mode near 470 cm(exp -1) observed in GaAsN was found to broaden and to split into up to three components with one component at a frequency higher than that of the Ga-N mode in GaAsN. This observation shows that the incorporation of In into GaAsN strongly affects the local bonding of the N atoms by changing the local strain distributions as well as the formation of a significant fraction of In-N bonds. The resonant enhancement in the scattering cross section of the Ga-N vibrational mode, observed in low N-content GaAs(1-x)N(x) (x about 0.01) for incident photon energies matching the mostly N-related E(+) transition at around 1.8 eV, was found to broaden significantly upon increasing N content as well as upon the addition of In to form GaInAs
The bonding of nitrogen in low N-content AlxGa1−xAs1−yNy with x⩽0.05 and y⩽0.04 has been studied by Raman spectroscopy. Upon the addition of Al to GaAsN, additional vibrational modes are observed at around 450 cm−1, which is below the GaN-like longitudinal optical (LO) phonon mode centered at 470 cm−1. These modes are attributed to the formation of Al and N containing complexes with Al-to-N bonding. With increasing Al content the Al–N related modes gain intensity at the expense of the GaN-like mode, and they become the dominant N-related feature for an Al-content of 5% at a fixed N content of 1%. On the other hand, increasing the N content from 0% up to 4% at a constant Al concentration of 5% results first in the appearance and eventual saturation in intensity of the AlN-like modes, accompanied by a steep increase in intensity and eventual dominance of the GaN-like vibrational mode. Simultaneously the AlAs-like LO2 phonon mode shows a drastic decrease in intensity for N contents exceeding 2%. All these observations strongly indicate that there is a preferential formation of Al–N bonds in low N- and Al-content AlGaAsN, which is in direct contrast to GaInAsN, where even after thermal annealing the GaN-like mode remains dominant in the Raman spectrum compared to the InN-like modes.
Dilute InAs(1-y)N(y) and high In-content Ga(1-x)In(x)As(1-y)N(y) layers with y lt = 0.012 and x gt= 0.92 were grown by rf-nitrogen plasma source molecular-beam epitaxy on InP substrates using a metamorphic GaInAs buffer layer. The bonding of nitrogen in these alloys was analyzed by Raman spectroscopy, showing that nitrogen is incorporated in dilute InAsN as isolated N(As) for a nitrogen content of y = 0.005; two additional nitrogen-related modes were found to appear at higher nitrogen contents (y=0.012), possibly due to the formation of higher-order di-nitrogen In-N complexes. The addition of a small amount of Ga to the InAsN ([Ga] lt = 8%) was found to lead to an almost complete change from pure In-N bonding to a preferential bonding of the substitutional nitrogen to at least one Ga neighbour. Further, the effect of nitrogen incorporation on the higher-lying E(ind 1) and E(ind 1) + delta(ind 1) interband transitions of InAsN has been studied by spectroscopic ellipsometry, revealing a high-energy shift of both interband transitions with increasing nitrogen content at a rate similar to that reported for dilute GaAsN
We report here the first observation of the cyclotron resonance Landau splitting for low density electron inversion layers in Al Ga& As-GaAs heterojunctions.Even at temperatures close to 100 K electron-electron interactions couple the electrical dipole transitions from the ground and first excited Landau levels, with a coupling strength comparable to the one found at liquid helium temperatures. The experiment can be explained only in a single-particle approximation at sufficiently low densities and/or magnetic field strengths where the resonant polaron effect is important. PACS numbers: 73.20.Dx, 78.20.Ls Cyclotron resonance (CR) in a translational invariant system is a center-of-mass motion and independent of the electron-electron interaction. This famous result, known as Kohn's theorem [1], has been an important guideline
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