Near-infrared stimulated emission from indium-rich InGaN layers grown by plasma-assisted MBE

We report on the stimulated emission (SE) in the near-infrared range from the planar InGaN epitaxial layers grown on sapphire substrates. By varying the indium content from 100% to 75%, the emission wavelength is tunable from 1.65 to 1.1 μm and minimum threshold intensities of 20–30 kW/cm2 at T = 77 K were obtained for layers with an 80%–90% indium fraction emitting around 1.3 μm. We suggest that at low temperatures, limitations for observation of SE from heavily doped InN and InGaN layers are mostly imposed by strong losses due to free-carrier absorption approaching material gain at residual electron concentrations in excess of several 1019 cm−3 and not directly by Auger recombination of non-equilibrium charge carriers. At higher temperatures, Shockley–Read–Hall (SRH) recombination sets on as a dominant nonradiative process, which determines temperature quenching of stimulated emission at Tmax ∼ 190–210 K in a way very similar to that observed earlier for InN layers with a much lower background doping level of about 3 × 1017 cm−3. Thus, different defect centers are expected to provide free electrons for InN and InGaN layers under consideration and to contribute to the SRH recombination rate, which affects SE at high temperatures.