High-quality III-nitride films on conductive, transparent (2̅01)-oriented β-Ga2O3 using a GaN buffer layer

Abstract

We demonstrate the high structural and optical properties of InxGa1−xN epilayers (0 ≤ x ≤ 23) grown on conductive and transparent (01)-oriented β-Ga2O3 substrates using a low-temperature GaN buffer layer rather than AlN buffer layer, which enhances the quality and stability of the crystals compared to those grown on (100)-oriented β-Ga2O3. Raman maps show that the 2″ wafer is relaxed and uniform. Transmission electron microscopy (TEM) reveals that the dislocation density reduces considerably (~4.8 × 107 cm−2) at the grain centers. High-resolution TEM analysis demonstrates that most dislocations emerge at an angle with respect to the c-axis, whereas dislocations of the opposite phase form a loop and annihilate each other. The dislocation behavior is due to irregular (01) β-Ga2O3 surface at the interface and distorted buffer layer, followed by relaxed GaN epilayer. Photoluminescence results confirm high optical quality and time-resolved spectroscopy shows that the recombination is governed by bound excitons. We find that a low root-mean-square average (≤1.5 nm) of InxGa1−xN epilayers can be achieved with high optical quality of InxGa1−xN epilayers. We reveal that (01)-oriented β-Ga2O3 substrate has a strong potential for use in large-scale high-quality vertical light emitting device design.

Fabrication and optical characterization of GaN waveguides on (−201)-oriented β-Ga_2O_3

“…XRD RC results indicated low threading dislocation density (TDD), dominated by screw and mixed type dislocations [13]. The TDD and the type of dislocations were confirmed by atomic force microscopy (AFM) and transmission electron microscopy (TEM) analysis (TDD was on the order of 108 cm 2 [13,14]). To the best of our knowledge, this is the best RC FWHM value for GaN obtained for materials grown on a Ga 2 O 3 substrate.…”

“…The photoluminescence study reported in [13] has confirmed that the GaN on Ga 2 O 3 wafer has higher photoluminescence yield than GaN grown on Al 2 O 3 . AFM measurements have shown the root mean square (RMS) surface roughness as low as ∼ 0.3 nm over 400 µm 2 , and ∼ 0.17 nm over 25 µm 2 , indicating a significantly smoother surface compared to that of the commercial state-of the-art GaN grown on sapphire [13,14]. The XRD, TEM and AFM results indicated that the (−201) β − Ga 2 O 3 is the best orientation for GaN growth.…”

“…The XRD rocking curve (RC) showed a superior GaN quality with a small full width at half maximum (FWHM = 330 arcsec), which is a typical FWHM value of high quality GaN wafer [14]. XRD RC results indicated low threading dislocation density (TDD), dominated by screw and mixed type dislocations [13].…”

“…A detailed comparison of the material properties of the resulting wafer and commercially available GaN grown on Al 2 O 3 (Sapphire) has been reported in [13,14]. The XRD rocking curve (RC) showed a superior GaN quality with a small full width at half maximum (FWHM = 330 arcsec), which is a typical FWHM value of high quality GaN wafer [14].…”

“…These defects act as non-radiative recombination centers [12], thus deteriorating the optical quality of the epitaxially grown GaN layer. Recent studies have shown that GaN grown on (−201) β − Ga 2 O 3 has a much lower lattice mismatch of 4.7% as compared to 14% for GaN grown on Sapphire (Al 2 O 3 ) [13,14].…”