Si-doped GaN∕AlN quantum dot superlattices for optoelectronics at telecommunication wavelengths

Abstract

We report on the controlled growth by molecular beam epitaxy of 20-period Si-doped GaN∕AlN quantum dot (QD) superlattices, in order to tailor their intraband absorption within the 1.3–1.55μm telecommunication spectral range. The QD size can be tuned by modifying the amount of GaN in the QDs, the growth temperature, or the growth interruption time (Ostwald ripening). By adjusting the growth conditions, QDs with height (diameter) within the range of 1–1.5nm (10–40nm), and density between 1011 and 1012cm−2 can be synthesized, fully strained on the AlN pseudosubstrate. To populate the first electronic level, silicon can be incorporated into the QDs without significant perturbation of the QD morphology. All the samples exhibit strong p-polarized intraband absorption at room temperature. The broadening of the absorption peak remains below 150meV and can be as small as ∼80meV. This absorption line is attributed to transition from the s ground level of the QD to the first excited level along the growth axis, pz. The peak energies of both photoluminescence emission and intraband absorption are consistent with the QD structural characteristics, and with their evolution by changing the growth conditions. Tuning of the intraband absorption from 0.740eV (1.68μm)to0.896eV (1.38μm) is demonstrated. Finally, we show that the AlN buffer layer can be replaced by a conductive AlxGa1−xN (x=0.35 and 0.6) ternary alloy without significant modification of the intraband properties of the QD stack.