In this paper, the potential of the high growth rate hydride vapor phase epitaxy technique and laser lift-off for the fabrication of large-area (2″) free-standing GaN substrates is revealed. Structural and optical properties of 250-μm-thick GaN layer grown on a MOVPE epitaxial lateral overgrown GaN template have been investigated employing different analytical experimental techniques.
A low value of dislocation density of ∼1×107 cm−2 on the Ga-terminated face of the free-standing material was determined from AFM images. X-ray diffraction (XRD), Raman scattering measurements, and low-temperature photoluminescence (PL) were exploited to assess the structural and optical quality of the GaN. The full-width at half-maximum value of XRD ω -scans of the free-standing GaN material was determined to be 264 arcsec for the (10-14) reflection. The XRD and low-temperature PL mapping measurements consistently proved the good crystalline quality and lateral homogeneity and small residual stress inside the material. Hence, the free-standing GaN achieved is highly advantageous for a lattice-constant and thermal-expansion-coefficient matched substrate for additional strain-free homoepitaxy of III-nitrides-based device heterostructures.
Source:Physica B: Condensed Matter