Optical polarization control of photo-pumped stimulated emissions at 238 nm from AlGaN multiple-quantum-well laser structures on AlN substrates

We demonstrate the capability to control the optical polarization of room-temperature stimulated emissions (SEs) at 238–239 nm from optically pumped AlGaN multiple-quantum-well (MQW) heterostructures on bulk AlN. The results of structural and optical characterizations provided evidence that altering the strain state in the pseudomorphically grown MQW laser structures enabled the switching of the polarization direction of the SE from predominantly transverse electric (TE) at 238 nm to predominantly transverse magnetic (TM) at 239 nm. The SE observed at 238 nm represents the shortest peak wavelength with TE polarization yet reported for AlGaN materials grown on any type of substrate.