Sub-250nm room-temperature optical gain from AlGaN/AlN multiple quantum dot structures

There are many pressing but yet unrealized applications for optoelectronic materials and devices that can function well into the deep-UV. Group-III nitrides, in particular AlGaN, are particularly suited to cover UV spectral ranges. An intense research effort is targeting the investigation and demonstration of deep-UV lasing from these materials. We developed AlGaN/AlN MQWs by Molecular Beam Epitaxy under a novel growth mode that introduces band structure potential fluctuations and high-density of nanocluster-like features within the AlGaN wells. A characterization of this material will be presented. The Variable-Stripe Length technique, a well-established methodology for measuring optical gain coefficient, is applied for a detailed quantification of the gain properties and polarization. We demonstrate optical gain in AlGaN nanostructures down to 230 nm at room temperature with a maximum net modal gain value of 118 $\pm$ 9 cm-1 at the highest excitation fluence of 15 $\mu$J/cm2. The optical gain threshold was measured to be 5 $\pm$ 1 $\mu$J/cm2 from which we estimate the density of optically excited carriers at the threshold to be 1.4 x 10$^{17}$ cm-3, which is two orders of magnitude lower than what currently achieved by quantum well structures. Moreover, we demonstrate that gain is TE-polarized.