Excitation power dynamics of photoluminescence in InGaN∕GaN quantum wells with enhanced carrier localization

Abstract

Excitation-power dynamics of near-band-edge photoluminescence (PL) peak position in In x Ga 1−x N / GaN multiple quantum wells ͑x ϳ 0.15͒ was analyzed as a function of well width. The analysis was based on energy reference provided by photoreflectance (PR) spectra. The difference in spectral position of the PR feature and low-excitation PL band (the Stokes Shift) revealed carrier localization energy, which exhibited a remarkable sensitivity to the well width, increasing from 75 meV in 2 nm wells to about 250 meV in 4 nm wells. Meanwhile collating of the PR data with the flat-band model for the optical transition energy in quantum wells rendered a relatively weak ͑0.5 MV/ cm͒ built-in piezoelectric field. The blueshift of the PL peak position with increasing photoexcitation power density was shown to be in qualitative agreement with the model of filling of the band-tail states with some contribution from screening of built-in field in the thickest ͑4 nm͒ wells. Increased incident photon energy resulted in an additional blueshift of the PL peak, which was explained by a nonthermalized distribution of localized carriers and/or carrier localization in the interface region. Our results are consistent with a concept of emission from partially relaxed large In-rich regions with internal band potential fluctuations, which are enhanced with increasing the growth time.

Influence of quantum well inhomogeneities on absorption, spontaneous emission, photoluminescence decay time, and lasing in polar InGaN quantum wells emitting in the blue-green spectral region

“…1). Usually the difference between the energy of SE and CER transition (i.e., the Stokes shift) is evidence of the localized character of SE [20][21][22][23]. However, such a comparison is more complex for polar QWs due to the large built-in electric field related to polarization effects.…”

Comparative study of polar and semipolar (112¯2) InGaN layers grown by metalorganic vapour phase epitaxy

“…6 The red-shift of the (11 22) InGaN NBE might be also due to the stronger carrier localization. 33 It is worth noting that recently we compared the RT-PL peak emission wavelength (244 nm and 325 nm excitation sources) of InGaN materials grown on different ð11 22Þ GaN templates (emission wavelength % 460-560 nm) that have a low and high density of BSFs. The ð11 22Þ GaN templates with the low BSF density (<4 Â 10 3 cm À1 ) were grown on patterned r-plane sapphire substrates.…”

“…The blue-shift might be due to the screening of the built-in electric field and the filling of the band-tail localized states. 33 The PE strongly affects luminescence position of very small structures, e.g., quantum wells and dots, and its effect rapidly decreases with increasing thickness. For the 25-30 nm thick InGaN layers, residual PE exists in the strained and partially relaxed layers, and hence may induce the shift of luminescence.…”

“…Consequently, the band filling in the localized states induces the blue-shift of the PL peak emission wavelength of the ð11 22Þ InGaN layers due to the increase of carrier concentration caused by the increase of excitation power. 33 In this section, the PL properties of the InGaN samples were studied by different excitation wavelengths. At RT, only the fully strained (0001) InGaN layers show clear NBE luminescence when the layers were excited by the 266 nm excitation source.…”

“…33 Carrier localization effects might be derived from selforganized indium-rich InGaN regions (i.e., deviations from randomness). Carrier localization can prevent carriers from reaching defects, leading to a reduction of non-radiative recombination rates.…”