Effect of stacking faults on the photoluminescence spectrum of zincblende GaN

Abstract

The photoluminescence spectra of a zincblende GaN epilayer grown via metal-organic chemical vapour deposition upon 3C-SiC/Si (001) substrates were investigated. Of particular interest was a broad emission band centered at 3.4 eV, with a FWHM of 200 meV, which extends above the bandgap of both zincblende and wurtzite GaN. Photoluminescence excitation measurements show that this band is associated with an absorption edge centered at 3.6 eV. Photoluminescence time decays for the band are monoexponential, with lifetimes that reduce from 0.67 ns to 0.15 ns as the recombination energy increases. TEM measurements show no evidence of wurtzite GaN inclusions which are typically used to explain emission in this energy range. However, dense stacking fault bunches are present in the epilayers. A model for the band alignment at the stacking faults was developed to explain this emission band, showing how both electrons and holes can be confined adjacent to stacking faults. Different stacking fault separations can change the carrier confinement energies sufficiently to explain the width of the emission band, and change the carrier wavefunction overlap to account for the variation in decay time.

Investigation of stacking faults in MOVPE-grown zincblende GaN by XRD and TEM

“…when a (-1-11) SF intersects with a (111) SF, there are three possibilities: (a) the two SF lines annihilate each other, (b) one of the SF lines is annihilated while the other propagates through the intersection point, or (c) both of the SF lines propagate, as indicated by the yellow arrows in Figure 6. It is possible that each line consists of more than one SF, since the minimum separation between SFs that can be resolved from the TEM images shown here is 4 nm, and SF separations less than this have been observed in zb-GaN epilayers by high-resolution TEM data previously 11 . Hence for Using our SF propagation and annihilation model, we simulated a 400 nm thick and ~ 3.5 µm wide GaN epilayer, with a total of 720 SFs that have a mean separation of 4.78 nm parallel to the GaN/SiC interface (equal to a total SF density of about 2.6 × 10 6 cm -1 ) and the variance of the separations is 0.40 nm.…”

“…SF distribution in the [110] zoneFirst, we consider the SF distribution in the [110] zone, in which the inclination angle for both the (-111) and(1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11) SFs is 55° with respect to the GaN/SiC interface and is not affected by the substrate miscut.…”

Cathodoluminescence studies of the optical properties of a zincblende InGaN/GaN single quantum well

“…These stripes are interrupted by regions of low CL intensity, indicating the presence of non-radiative recombination centres. Non-radiative recombination can occur at point defects, threading dislocations or SFs [20,[30][31][32][33][34][35][36][37]. Even though there are dark regions in the image, these are not regions of zero emission but of relatively low emission intensity compared to the surrounding material.…”

“…As discussed earlier, in the panchromatic CL images the regions associated with the pale stripes in the SE images appear dark. This can be explained by the optical properties of SFs in zb-GaN, which are significantly different from SFs in wz-GaN [31,36,40]. As a simplified picture, one can consider a SF in wz-GaN as a monolayer-wide zb insertion and vice versa.…”

Stacking fault-associated polarized surface-emitted photoluminescence from zincblende InGaN/GaN quantum wells

“…This may be due to variation in the size and indium content of the quantum wires, and variation in the degree of CB filling. Furthermore, it is thought that the SFs will alter the local electric fields in the structure due to spontaneous polarisation effects 21 . Variation in the SF distribution is therefore another mechanism for increased inhomogeneity in the samples.…”