Observation of hot luminescence and slow inter-sub-band relaxation in Si-doped GaN∕AlxGa1−xN (x=0.11, 0.25) multi-quantum-well structures

Abstract

We report on the growth, structural, electronic, and optical properties of Si-doped GaN∕AlxGa1−xN (x=0.11, 0.25) multiple-quantum-well structures grown on SiC by plasma-assisted molecular-beam epitaxy. We have demonstrated that the use of In as a surfactant during growth improves the structural and optical properties of these layers. Photoluminescence studies have made possible the identification of the fundamental and excited electronic levels by comparison with simulations of the electronic structure. Temperature dependence studies reveal an anomalous behavior of the photoluminescence intensity, which is the quenching of the e1−hh1 line, while the e2−hh1 and e3−hh1 transitions become dominant at room temperature in the samples with 11% and 25% Al in the barrier, respectively. This behavior can be explained by the population of the e2 and e3 electronic states by thermally excited carriers, and by the higher oscillator strength of e2−hh1 and e3−hh1 transitions compared with e1−hh1, due to the intense electric field in the quantum wells. Long inter-sub-band (ISB) relaxation times (40–100ps) have been measured in GaN∕AlGaN multiple quantum wells, as a consequence of the quenching of the longitudinal optical (LO)-phonon emission when the ISB transition energy is below the LO-phonon energy.

Recombination in Polar InGaN/GaN LED Structures with Wide Quantum Wells

“…It could be, however, that these technologically costly alternative routes need not be taken at all if a smart structure or device design could be found in which the internal fields, for example, could be disabled or compensated for. It seems possible that so‐called “thick” or “wide QWs,” [ 2,3 ] that is, QWs with a thickness of d QW ≥ 10 nm, in our particular case 25 nm, represent just such an alternative. [ 4–6 ]…”

“…It could be, however, that these technologically costly alternative routes need not be taken at all if a smart structure or device design could be found in which the internal fields, for example, could be disabled or compensated for. It seems possible that so-called "thick" or "wide QWs," [2,3] that is, QWs with a thickness of d QW ≥ 10 nm, in our particular case 25 nm, represent just such an alternative. [4][5][6] This Letter addresses the kinetics of the emission of such "wide QWs" after impulsive excitation, which is initially surprisingly very fast with decay time constants of 1.5 and 8 ns at 6 and 300 K, respectively.…”

On intrinsic Stokes shift in wide GaN/AlGaN polar quantum wells

“…The samples were grown at a substrate temperature of 720 °C, under Ga excess and without growth interruptions. More details on the sample growth can be found in [29]. The aluminum content was measured by Rutherford backscattering on 130 nm thick AlGaN reference layers deposited under the same growth conditions.…”

III-nitride semiconductors for intersubband optoelectronics: a review

“…An alternative to the above-described GaN growth conditions is the use of a surfactant to promote 2D growth [54]. Indium has been reported to behave as a surfactant for the PAMBE growth of (Al,G)aN, since it favors 2D growth under slightly N-rich conditions [41,44,[55][56][57]. The utility of this growth method to synthesize GaN/AlN QWs displaying ISB absorption has been demonstrated [28].…”