Huge electron-hole exchange interaction in aluminum nitride

Optical spectroscopy is performed for $c$-plane homoepitaxial aluminum nitride (AlN) films. The temperature dependence of the polarization-resolved photoluminescence spectra reveals the exciton fine structure. The experimental results demonstrate that the electron-hole exchange interaction energy ($j$) in AlN is $j=6.8\text{meV}$, which is the largest value for typical III-V and II-VI compound semiconductors. We propose the effective interatomic distance as the criterion of the electron-hole exchange interaction energy, revealing a universal rule. This study should encourage potential applications of excitonic optoelectronic devices in nitride semiconductors similar to those using II-VI compound semiconductors.

Figure 1

Electronic band or exciton fine structure of AlN, $j<0$ (left), $j=0$ (center), and $j>0$ (right). ${\Gamma }_1$ and ${\Gamma }_5$ are dipole-allowed states (solid lines) for $E\parallel c$ and $E\perp c$, respectively. ${\Gamma }_2$ and ${\Gamma }_6$ are dipole-forbidden states (broken lines).

Figure 2

Typical PL spectrum of our $c$-plane homoepitaxial AlN films taken under the excitation power density of $6\text{kW}/{\text{cm}}^2$ at 10 K. Experimental geometry is Config. (a).

Figure 3

Temperature-dependent PL spectra for the $c$-plane homoepitaxial film (a) under Config. (a) and (b) under Config. (b). Respective excitation power densities are $72\text{kW}/{\text{cm}}^2$ and $238\text{kW}/{\text{cm}}^2$. At only the PL spectrum at 300 K in Fig. 3b, excitation power density is $714\text{kW}/{\text{cm}}^2$ due to the low S/N ratio and the spectrum is divided by 3.

Figure 4

Arrhenius plots of each peak, ${\text{D}}^0\text{X}$, $\text{X}$, and $\text{FX}$.

Figure 5

Effective interatomic distance vs the electron-hole exchange interaction energy in typical III-V and II-VI compound semiconductors.