Cathodoluminescence mapping of epitaxial lateral overgrowth in gallium nitride

Abstract

The dislocation arrangements in gallium nitride (GaN) films prepared by lateral epitaxial overgrowth (LEO) have been studied by cathodoluminescence mapping and transmission electron microscopy. A very low density of electrically active defects (<10−6 cm−2) in the laterally overgrown material is observed. Individual electrically active defects have been observed that propagate laterally from the line of stripe coalescence into the overgrown material. Additionally, by mapping wavelength-resolved luminescence in an InGaN quantum well grown on top of the overgrown material, these defects are shown to be limited to the underlying material and do not propagate normal to the surface, as in other GaN films. In the seed region, threading dislocation image widths are seen to be nearly identical in the quantum well and the underlying GaN, indicating a comparable upper limit (∼200 nm) for minority carrier diffusion length in InGaN and GaN. Additionally, it is shown that, through processing variation, these lateral defects can be avoided in LEO films and that wavelength-resolved cathodoluminescence is an excellent large-area method for rapidly and quantitatively observing variations in process development.

Cathodoluminescence study of micro-crack-induced stress relief for AlN films on Si(111)

“…3c and 3d, as has previously been observed in GaN. 20,21 A considerable variation in the density of dark spots in the CL imaging of the AlN near-band-edge emission was observed throughout the sample, as demonstrated by the large variation in contrast observed between Fig. 3c and 3d.…”

Micro-Raman study of electronic properties of inversion domains in GaN-based lateral polarity heterostructures

“…27,28 However, recent studies by Rosner et al show that electrically active threading dislocations do indeed affect the recombination characteristics in GaN. 29,30 Threading dislocations act as nonradiative recombination centers in GaN and behave as deep level acceptors for n-type GaN. Coulomb scattering will occur since filled acceptor-like traps are negatively charged.…”

High-Efficiency Nitride-Based Solid-State Lighting

“…This CL characteristic has been observed in polar GaN LEO stripes. [16][17][18] The mottled area extends across the entire width of the [0001 ] stripe, which corresponds to the TEM observation of dislocation bending into the laterally overgrown regions for this stripe orientation. Even though the [0001 ] stripe shown in Fig.…”

“…The active region consists of an Al 0.1 GaN quantum well surrounded by Al 0. 16 GaN barriers, as well as Al 0.3 GaN hole-and electron-blocking layers to prevent carrier overflow out of the active region. A short-period alloy superlattice (SPASL) was used in both the n and p-type cladding regions to reduce the vertical resistivity.…”