Stimulated emission, photoluminescence, and localisation of nonequilibrium charge carriers in ultrathin (monolayer) GaN/AlN quantum wells

The stimulated emission and photoluminescence of ultrathin GaN quantum wells with a nominal thickness of 1.5–2 monolayers (MLs) and AlN barrier layers 4–6.66 ML thick, obtained by plasma-activated molecular beam epitaxy on c-sapphire substrates, are studied. The stimulated emission of TE polarisation in ultrathin GaN/AlN quantum wells is obtained under pumping directly into quantum wells. The wavelength of stimulated emission varied from 262 to 290 nm, depending on the thickness of the wells and barriers. It is shown that stimulated emission is achieved on localised GaN states with a thickness of 2 and 3 ML in ultrathin quantum wells with a nominal thickness of 1.5 and 2 ML, respectively. The minimum excitation threshold of stimulated emission was 700 kW cm^-2 at λ = 270 nm.