Identification of subsurface damage in freestanding HVPE GaN substrates and its influence on epitaxial growth of GaN epilayers (original) (raw)
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Residual impurities in GaN substrates and epitaxial layers grown by various techniques
Journal of Crystal Growth, 2007
Low-temperature/high-resolution photoluminescence spectra of thick freestanding hydride vapor-phase epitaxial GaN substrates show intense sharp lines in the near bandedge spectral region, which has been previously assigned to recombination processes associated with the annihilation of excitons bound to neutral Si and O donors. Similar studies carried out on unintentionally doped (UID) and Sidoped homoepitaxial films grown by molecular beam epitaxy and metalorganic chemical vapor deposition methods, respectively, supports the previous identification of Si and O as the dominant shallow donors in UID GaN. The chemical nature of these background impurities and dopants were verified by high sensitivity secondary ion mass spectroscopy. The present work confirms Si and O as the pervasive dominant shallow donors in UID GaN and demonstrate the usefulness of photoluminescence as a non-destructive technique to identify impurities in GaN. r (J.A. Freitas Jr.), hyunhyun7@korea.ac.kr (J. Kim).
MRS Proceedings, 2001
ABSTRACTStructural, electrical and optical properties of free-standing 200-μm thick GaN films grown by hydride vapor phase epitaxy (HVPE) have been investigated. After laser lift-off, the GaN substrates were mechanically polished on both Ga and N-sides and dry etched only on the Ga- side to obtain a smooth epi-ready surface. Hot H3PO4 chemical etching on both surfaces was used to reveal the defect sites, which appeared as hexagonal pits. The etched surfaces were then examined by atomic force microscopy. A few seconds of etching was sufficient to smooth the N- face surface and produce etch pits with a density of ≈ 1×107 cm−2. In contrast, a 50 minute etching was needed to delineate the defect sites on the Ga-face which led to a density as low as 5×105 cm−2. From plan-view and cross-sectional transmission electron microscopy (TEM) analysis, we have estimated that the dislocation density is less than about 5×106 cm−2 and ≈ 3×107 cm−2 for the Ga and N-faces respectively. The full-width ...
Applied Physics Letters, 2000
A free-standing 300-μm-thick GaN template grown by hydride vapor phase epitaxy has been characterized for its structural and optical properties using x-ray diffraction, defect delineation etch followed by imaging with atomic force microscopy, and variable temperature photoluminescence. The Ga face and the N face of the c-plane GaN exhibited a wide variation in terms of the defect density. The defect concentrations on Ga and N faces were about 5×105 cm−2 for the former and about 1×107 cm−2 for the latter. The full width at half maximum of the symmetric (0002) x-ray diffraction peak was 69 and 160 arc sec for the Ga and N faces, respectively. That for the asymmetric (10–14) peak was 103 and 140 arc sec for Ga and N faces, respectively. The donor bound exciton linewidth as measured on the Ga and N faces (after a chemical etching to remove the damage) is about 1 meV each at 10 K. Instead of the commonly observed yellow band, this sample displayed a green band, which is centered at about...
Impurity effects on photoluminescence in lateral epitaxially overgrown GaN
Journal of Electronic Materials, 2003
Using a two-photon laser-scanning microscope (LSM), the spectral and intensity variations of photoluminescence (PL) in a lateral epitaxially overgrown GaN film were mapped with submicron resolution. The PL results are correlated with the carrier-density variation obtained by confocal-Raman microscopy and the surface Fermi-level positions measured by scanning Kelvin-force microscopy. Near-bandgap emission spectra taken in the wing regions provide support for the previously proposed, compensated-impurity band, which arises from the incorporation of a high concentration of impurities, resulting in a carrier density of ϳ10 20 cm Ϫ3 .
Microscopic emission properties of nonpolar a-plane GaN grown by HVPE - art. no. 612106
Gallium Nitride Materials and Devices, 2006
We have studied the emission distributions in nonpolar a-plane GaN thick films grown by HVPE using different nucleation schemes. The emission spectra show in addition to the near band edge emission band, also defect related bands due to different structural defects being enhanced/reduced to different extent in samples grown on different templates. Spatially resolved cathodoluminescence imaging reveals the in-plane distributions of the respective emission bands, which allows us to correlate the emissions with particular stacking fault structural defects independently revealed by plan-view transmission electron microscopy. In addition, emission distributions were visualized in vicinity of largescale defects like surface triangle pits, depressions and cracks attributed to prevailing defect formation and/or impurity incorporation.
Journal of Crystal Growth, 2009
The nucleation of HVPE GaN on misoriented sapphire substrates and the transition from the nucleation layer to an epitaxial film were investigated. After a KOH/NaOH eutectic etch of the approximately 45 mm thick GaN layer, grown on sapphire using a low temperature nucleation, high temperature epitaxy process, the cross-sections revealed columnar structures, up to roughly 1 mm above the sapphire substrate. Photoetching of the thick GaN layers revealed inhomogeneous defect distributions along the cross-sections, which appeared to be related to the numerous pinholes originating at the GaN/sapphire interface. We present a model explaining the formation of pinholes by the coalescence of the GaN nuclei during the epitaxial overgrowth.
Giant traps on the surface of hydride vapor phase epitaxy-grown free-standing GaN
Journal of Electronic Materials, 2006
Extended defects on the top surface of a 250-mm-thick free-standing GaN sample, grown by hydride vapor phase epitaxy (HVPE), were studied by deep level transient spectroscopy (DLTS) and scanning surface potential microscopy (SSPM). For comparison, similar studies were carried out on as-grown HVPE-GaN samples. In addition to the commonly observed traps in as-grown HVPE-GaN, the DLTS measurements on free-standing GaN reveal a very high concentration of deep traps (;1.0 eV) within about 300 nm of the surface. These traps show nonexponential capture kinetics, reminiscent of those associated with large defects, that can accumulate multiple charges. The SSPM measurements clearly reveal the presence of charged microcracks on the top surface of the sample. It appears that the ''giant traps'' may be associated with these microcracks, but we cannot rule out the involvement of other extended defects associated with the near-surface damage caused by the polishing/etching procedure.