A Nonpolara-Plane GaN Grown on a Hemispherical Patternedr-Plane Sapphire Substrate

Improvement of crystal quality and optical property in (11−22) semipolar InGaN/GaN LEDs grown on patterned m-plane sapphire substrate

“…The NBE emission from the HPSS semipolar GaN was approximately one order of magnitude stronger than that from the planar semipolar GaN layer. This result also suggests that the regrowth process on the surface with the array of hemispheres reduced the defects (such as BSFs and perfect dislocations) and improved the extraction efficiency when compared with the direct growth on the planar substrate [16,20,21]. Two additional emission bands at 3.42 eV and 3.32 eV are observed in both samples, which are attributed to the luminescences from the BSFs and the PDs, respectively [22,23].…”

“…It was reported that none of the BSFs were visible under on-axis (11 À22) x-ray rocking curves (XRCs), but their associated partial dislocations (PDs) can broaden on-axis (11-22) XRCs [12]. Therefore, the result showing no considerable difference between the FWHMs of the on-axis (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) indicates that the density of PDs is similar for the planar sapphire and the HPSS.…”

“…The surface morphology of the GaN layer was observed using atomic force microscopy (AFM). A triple-axis X-ray diffractometer (PANalytical X'-Pert PRO MRD) was employed to evaluate the crystal quality of the (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) semipolar GaN films. The state of the BSFs in the GaN layer was observed using crosssectional transmission electron microscopy (TEM).…”

“…Typical TD density is caused by the mismatch of the lattice constant and the thermal expansion coefficient between the GaN layer and sapphire substrate [4,5]. Until now, the most interesting results on (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) GaN-based layers have been obtained on semipolar free-standing GaN substrates. In that case, GaN substrates were sliced from thick c-plane-oriented GaN boules grown by hydride vapor phase epitaxy.…”

“…However, the limited size ($ a few mm 2 ) and the very high price of these substrates are serious drawbacks for industrial applications [6]. For these reasons, many researchers have tried to grow the (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) GaN layers on a sapphire substrate by defect reduction techniques such as epitaxial lateral overgrowth, the interlayer technique, and regrowth on a porous GaN layer [7][8][9].…”