The effects of crystallographic orientation and strain on the properties of excitonic emission from wurtzite InGaN/GaN quantum wells

Abstract

We have examined in detail crystal orientation effects on the properties of excitonic emission from wurtzite In x Ga 1−x N/GaN quantum wells (QWs) with piezoelectric polarization using exciton binding and transition energy calculations based on a single-band effective-mass theory. We show numerical results for the bandgaps, effective heavy-hole masses, piezoelectric polarizations and fields, exciton wavefunctions, exciton binding and transition energies and radiative lifetimes of excitonic emission as a function of the QW crystallographic growth planes. Band-edge and effective-mass parameters for a continuum of GaN crystallographic orientations, on which InGaN/GaN QWs are grown, were obtained from In-composition-and strain-dependent k • p calculation for wurtzite In x Ga 1−x N, using the 6 × 6 k • p Hamiltonian in appropriate {hkil} representations. We have performed calculations for a continuum of technologically relevant QW growth planes {hh0l} oriented at various angles θ relative to the (0001) c-plane. The excitonic ground-and first-excited-state energies and wavefunctions were calculated using an effective potential method. A strong reduction of average in-plane heavy-hole effective mass and normal to the plane piezoelectric polarization and field is observed as θ varies from θ = 0 • (i.e. the c-axis direction) to θ = 49.5 • , where the piezoelectric polarization and electric field reverse their orientation with respect to the plane of the QW. The decrease of the electric field in the InGaN/GaN QW growth direction leads to an increased exciton transition energy and oscillator strength, which results in the increase of the exciton binding energy and decrease of the excitonic radiative lifetime. For angles θ > 49.5 • only small variations on the order of ∼10% in the exciton binding and transition energies and excitonic radiative lifetime are observed for narrow In 0.12 Ga 0.88 N/GaN QWs that have widths less than ∼ 3.5 nm. The average in-plane heavy-hole effective mass reaches its minimum for θ = 90 • , i.e. m-plane {1100} growth. These results indicate that InGaN/GaN QW structures grown on non-(0001)-oriented planes in a wide variety of angles 49.5 • θ 90 • can be used for optimized operation of optoelectronic devices.

Carrier-density-dependent recombination dynamics of excitons and electron-hole plasma in m -plane InGaN/GaN quantum wells

“…In addition, the ABC model only describes the dynamics of e-h pairs recombination. In our case, the exciton binding energy E b is estimated to be larger than 26 meV due to quantum confinement [24]. As a consequence, even at room temperature (k B T ≈ 26 meV), the influence of excitons needs to be taken into account.…”

“…where E b0 is the exciton binding energy at low carrier density [24] and n Mott is the 2D critical Mott density, which is about 10 12 cm −2 for GaN-based QWs [20,31]. Since we investigate InGaN QWs with a relatively low In content (<10%), we assume that the critical Mott density remains unchanged.…”

Free chargesversusexcitons: photoluminescence investigation of InGaN/GaN multiple quantum well nanorods and their planar counterparts

“…With incident light excitation, the excitons effectively form in the InGaN MQW nanorods as the binding energy is significantly larger than the thermal energy. 22 These excitons can diffuse and arrive at the sidewall surface of the nanorods. It has been reported that excitons effectively dissociate at the various heterogeneous interfaces, such as organic semiconductors and perovskites.…”

“…There has been a significant debate in the community on the carrier recombination dynamics of InGaN quantum wellswhether it originates from free electron-hole 19 or excitonic recombination. 20,21 Given the large exciton binding energy in InGaN quantum wells due to a strong quantum confinement effect, 22 the presence of both free carriers and excitons should be considered in density dependent carrier dynamics studies, which has recently been suggested. 12,23,24 Even at room temperature, a rapid formation of excitons results in a significant exciton fraction in the total carrier population in InGaN quantum wells, as quantitatively calculated by Hangleiter et al 24 Blancon et al recently 25 proposed that the lower energy states at the layer edges/surface area of perovskite nanoplatelets could directly facilitate exciton dissociation.…”

High spatial uniformity of photoluminescence spectra in semipolar (202¯1) plane InGaN/GaN quantum wells

“…The influence of the random cation distribution on the inhomogeneous broadening has been theoretically investigated by Lee and Bajaj for excitons in AlGaAs at low temperature. 29 In 3 nm semipolar InGaN QWs, the exciton binding energy is about 40 meV, 30 considerably larger than the room temperature k B T. Thus, it is reasonable to assume that at low and moderate carrier densities PL at room temperature is dominated by the exciton recombination. Recent studies on AlGaN and InGaN QWs support this assumption.…”