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Room temperature CER and low temperature PL spectra of n-type GaNxAs1−x layers of various nitrogen concentrations.
Standard DLTS spectra of n-type GaNxAs1−x layers of various nitrogen concentrations obtained with a reverse bias of −4 V, filling pulse duration of 1 ms, pulse height of −0.5 V, and a sampling rate window of 50 s−1.
Arrhenius plots obtained from LTDLS measurements of the thermal emission rates. The determined parameters for electron traps can be found in Ref. 10.
Sketch of N-related changes in the position of conduction band (ΔECB), the energy of deep donor trap (EDT), and the activation energy (Ea) for this trap in GaNAs alloys. The deep donor trap is described by a short range potential V(r) (R is the order of 1-2 lattice constants a, i.e., 2-4 nearest-neighbor environments for the point imperfection which is the source of deep donor trap). Because of the short range character of V(r) potential, it can be assumed that the energy of deep donor traps of the same microscopic nature almost does not change relative to the valence band edge with the incorporation of a small amount of nitrogen atoms into GaAs host, i.e., this change (ΔEDT) is much smaller than the N-related shift of the conduction band. Therefore, the activation energy for deep donor trap of the same nature should decrease with the increase in nitrogen concentration according to relation: Ea(GaNAs) ≈ Ea(GaAs) − ΔECB. The average distance between nitrogen atoms in GaNAs alloys with N < 1.25% is much larger than the scale of localizing potential V(r). It is at least 9 nearest-neighbor environments between N atoms versus 2-4 environments for the short range potential V(r). It means that most of GaAs-like deep donor traps in GaNAs alloy have purely GaAs-like environment but their activation energies cannot be the same as in GaAs host since N atoms shift the conduction band towards the deep donor trap EDT as shown in the sketch.
GaNAs band diagram plotted together with activation energies of electron traps (open diamonds for GaNAs layers and a solid diamond for the reference sample) obtained from LTDLS measurements. Horizontal dashed lines represent GaAs-like (black color) and N-containing (red color) electron traps in GaNAs. Electron traps in GaAs grown by molecular beam epitaxy14–17 are plotted by solid squares and the estimation of their positions in GaNAs is shown by horizontal dashed grey lines.
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