Deep-Level Structure of the Spin-Active Recombination Center in Dilute Nitrides

A gallium interstitial defect is thought to be responsible for the spectacular spin-dependent recombination in ${\mathrm{GaAs}}_{1-x}{\mathrm{N}}_x$ dilute nitrides. Current understanding associates this defect with at least two in-gap levels corresponding to the ($+/0$) and ($++/+$) charge-state transitions. Using a spin-sensitive photoinduced current transient spectroscopy, the in-gap electronic structure of a $x=0.021$ alloy is revealed. The ($+/0$) state lies $\approx 0.27\mathrm{eV}$ below the conduction band edge, and an anomalous, negative activation energy reveals the presence of not one but two other in-gap states. The observations are consistent with a ($++/+$) state $\approx 0.19\mathrm{eV}$ above the valence band edge, and a ($+++/++$) state $\approx 25\mathrm{meV}$ above the valence band edge.

Figure 1

Room-temperature PL spectra of ${\mathrm{GaAs}}_{0.979}{\mathrm{N}}_{0.021}$ excited with a $\pi$ (black) and a $\sigma$ (red) pump. The larger $\sigma$ pump PL intensity is due to SDR [8]. The insets show the allowed capture processes (electrons with solid lines, holes with dotted lines) under the two pump polarizations. The minimum band gap is $E_{\mathrm{g}\text{−}\mathrm{LH}}=1.09\mathrm{eV}$.

Figure 2

Typical PICTS sequence with a $\sigma$ pump (red) or $\pi$ pump (black). The SDR appears as an increase in the PC measured under a $\sigma$ pump. PC transients measured over 700 ms after the filling pulse show nonexponential behavior (inset).

Figure 3

Boxcar signals obtained with $\pi$ (black) and $\sigma$ (red) polarized filling pulses. The polarization-dependent peak is associated with electron emission from the $N_2$ state (see text). The low temperature peak exhibits an anomalous shift to higher temperatures as the rate window is shifted to lower rates. The insets show the allowed emission processes following $\pi$- (black) and $\sigma$- (red) polarized filling pulses.

Figure 4

Arrhenius plots generated from the boxcar (a) and inverse Laplace transform (b) analyses for $\pi$- (black) and $\sigma$- (red) polarized filling pulses. Activation energies obtained from the line slopes are shown.

Figure 5

Temperature variation of the emission rates given in Eqs. (3) and (5) using the estimated activation energies. The rates $e_{n2}$ and $e_{\mathrm{eff}}$ appearing in the rate window range (gray zone) are measured in the experiment (black lines). The negative slope of $e_{\mathrm{eff}}$ corresponds to an effective negative activation energy. The other rates, in green, fall outside the rate window range. To the right a schematic representation of the electronic structure of the ${\mathrm{Ga}}_{\mathrm{i}}$ center is shown.