Large-area free-standing GaN substrate grown by hydride vapor phase epitaxy on epitaxial lateral overgrown GaN template
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 (1014) 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.
Fig. 1. An optical microscope image revealing the sample surface morphology.
Source: Physica B: Condensed Matter