Abstract:
Two-inch-diameter sapphire (0001) substrates were used for the growth of AlGaN/GaN
structure by hydride vapor phase epitaxy (HVPE). The two-dimensional electron gas
(2DEG) structure consisted of a 2 mm undoped GaN layer substrate, followed by 30 nm
thick Al0.3Ga 0.7N layer. Structural and optical properties of GaN layer were
characterized by high resolution X-ray diffraction, transmission electron microscopy
(TEM) and photoluminescence (PL) measurements. TEM images showed the
dislocation density in the GaN layer was ~ 9 ´ 109 /cm2 . The full width at half
maximum (FWHM) values of the x-ray rocking curve for GaN (0002) was 0.156 deg.
PL spectra of our sample exhibited a predominant band-edge emission of the wurzite
GaN epilayer near 3.36 eV with FWHM = 45 meV at 50 K and 75 meV at room
temperature, respectively. The Hall effect measurements gave a sheet electron
concentration of 7.8´1012 cm-2 and a mobility of 850 cm2/Vs at 300K. The experimental
data indicated that the HVPE grown GaN layers exhibited superior quality compared to
GaN layers grown by metal organic chemical vapor deposition in prior art literatures.