Characterization of free-standing hydride vapor phase epitaxy GaN

Abstract

A free-standing GaN template grown to a thickness of 300 µm by hydride vapor phase epitaxy (HVPE) has been characterized for its structural properties by transmission electron microscopy (TEM). The TEM investigation was augmented by X-ray diffraction, defect delineation etching process followed by imaging with atomic force microscopy (AFM), and variable temperature photoluminescence (PL). Convergent Beam Electron Diffraction (CBED) was employed to determine the polarity of the free surface and the side juxtaposed to substrate before separation. The substrates side was confirmed to the N-face indicating a growth in the [0001] direction from Ga to N. The density of dislocations near the N-face was determined to be, in order, 3 ± 1 x 10 7 , 4 ± 1 x 10 7 , and about 1 x 10 7 cm -2 as determined by cross-sectional TEM, plan-view TEM and a defect revealing etch, respectively. Identical observations on the Ga-face revealed the defect concentration to be, in order, less than 1 x 10 7 cm -2 by plan-view TEM, 5 x 10 5 cm -2 by cross-sectional TEM, and 5 x 10 5 cm -2 by defect revealing hot H 3 PO 4 acid, respectively. The full width at half maximum (FWHM) of the symmetric (0002) X-ray diffraction peak was 69 and 160 arcsec for the Ga and N-faces, respectively. That for the asymmetric (1014) peak was 103 and 140 arcsec for Ga-and N-faces, respectively. The donor bound exciton linewidth as measured on the Ga and N-face (after the removal of the damage) is about 1 meV each at 10K. Instead of the commonly observed yellow band, this sample displayed a green band, which is centered at about 2.44 eV.

Ga vacancies as dominant intrinsic acceptors in GaN grown by hydride vapor phase epitaxy

“…The depth profile of Ga vacancies in Fig. 3 is very similar to those reported earlier for dislocations, [1][2][3][4] O impurities, 5,6 optical properties 1,6-8 and deep defect levels.…”

“…The quality of these layers improves drastically with thickness, making them interesting candidates for substrates of GaN homoepitaxy. For example, the dislocation densities decrease from the very high values of Ͼ10 11 cm Ϫ2 close to GaN/sapphire interface to less than 10 8 cm Ϫ2 in films which are thicker than 50 m. [1][2][3][4] The impurity concentrations, 5,6 electrical and optical properties, 1,[5][6][7][8] and deep level defects 2,9 have also qualitatively similar depth profiles. The atomic structures of the dominating point defects, however, have not been identified and their role as electrically active centers has not been quantitatively estimated.…”

Deep electron and hole traps in freestanding n-GaN grown by hydride vapor phase epitaxy

“…4,5 Studying such crystals is also very interesting from a purely scientific viewpoint because it provides access to reasonably low dislocation density material which makes it possible to separately study the impact of point defects and dislocations on the electrical and recombination properties of n-GaN. Preliminary measurements of electrical properties ͑e.g., Schottky barrier height͒, 6 deep level spectra, 6 defect structure by transmission electron microscopy ͑TEM͒, 4 and luminescence properties 7 have shown the existence of interesting differences in characteristics of the upper, low-dislocation-density Ga side, and the lower, higher-dislocation-density N side. Moreover, they have revealed the presence of thin damaged layers at both surfaces caused by the sample preparation routines.…”

Bending in HVPE GaN free‐standing films: effects of laser lift‐off, polishing and high‐pressure annealing

“…Such free-standing HVPE-GaN 2" wafers are now offered on the market, although still very expensive and having a few critical problems that need to be resolved. Several groups have reported a significant improvement of the quality of the films with increasing thickness, manifested in a strong reduction of dislocations, impurities, native defect densities and strain along the thickness of the HVPEGaN films [1][2][3][4]. However, this inhomogeneous defect distribution is believed to lead to a significant wafer bending [5] and consequently may contribute to the cracking [6], the latter being the most crucial problem, hampering the development of the HVPE free-standing quasi-substrate material and increasing the production cost.…”