The carrier dynamics in InGaN layers and InGaN multiquantum-well (MQW) structures were studied by employing the degenerate pump and probe, time-resolved photoluminescence (PL), and white-light pump and probe measurements. The results from degenerate pump and probe measurements showed that the internal field existed in undoped in InGaN but then was screened by the electrons supplied by the Si atoms in Si-doped InGaN. The rise time of Pl in InGaN MQW obtained using the upconversion method was very fast, below 1ps, the mechanism of which is due to the carrier-carrier interaction enhanced by the residual electrons. The ΔOD spectra in InGaN MQW observed in white-light pump and probe measurements indicated that the carrier temperature was substantially higher than the lattice temperature even at 40ps after pulsed photo-pumping.
Static, field-mounted and time-resolved spectroscopic measurements were carried out to compare the electronic structures between AlGaN/GaN binary and GaN/InGaN ternary single quantum wells (SQWs). The internal field exits across the quantum well (QW) naturally induces quantum-confined Stark effects, namely the redshift of the QW resonance energy and separation of electron-hole wavefunction overlap. Thus AlGaN/GaN SQWs exhibited a weak luminescence peak due to the presence of nonradiative channels. However, optical absorption and degenerate pump-probe measurements revealed that excitonic character still remains for the thin QWs having the well width nearly the same as the bulk free exciton Bohr radius even under high electric field as high as 0.73 MV/cm. A slightly In-alloyed InGaN SQW exhibited bright luminescence peak in spite of the pronounced effective bandgap inhomogeneity in the QW, which was confirmed by the point excitation and monochromatic cathodoluminescence mapping methods to have the lateral potential interval smaller than 40 nm. Therefore the light emitting area of the potential minima has the size defined as 'quantum-disk'. Carriers generated in the InGaN QWEs are effectively localized in these regions to form localized QW excitons exhibiting highly efficient spontaneous emissions.
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