Comparative study of near-threshold gain mechanisms in GaN epilayers and GaN/AlGaN separate confinement heterostructures

摘要

Abstract: We report the results of an experimental study on near- threshold gain mechanism in optically pumped GaN epilayers and GaN/AlGaN separate confinement heterostructures (SCHs) over the temperature range of 10 to 300 K. We show that in GaN epilayers the near-threshold gain mechanism is inelastic exciton-exciton scattering for temperatures below approximately 150 K, whereas at elevated temperatures an electron-hole plasma is the dominant gain mechanism. An analysis of the relative shift between the spontaneous emission and lasing peaks in SCH samples, combined with the temperature dependence of the lasing threshold, reveals that exciton-exciton scattering is the dominant gain mechanism leading to low-threshold ultraviolet lasing in the GaN/AlGaN SCH over the entire temperature range studied. Strongly polarized (TE:TM $GRT 300:1) lasing peaks were observed in a wavelength range of 358 - 367 nm. We found that high finesse lasing modes originated from self-formed microcavities in the AlGaN and GaN layers. The lasing threshold was measured to be as low as 15 kW/cm$+2$/ at 10 K and 105 kW/cm$+2$/ at room temperature. Based on our results we suggest ways for the realization of GaN-active-medium UV laser diodes.!30