Epitaxial growth and characterization of cubic GaN on BP/Si(100) substrates
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Epitaxial growth and characterization of cubic GaN on BP/Si(100) substrates Suzuka Nishimura1, 2, Muneyuki Hirai1 and Kazutaka Terashima2 1 Solartes Lab., 2009-3 Endo, Fujisawa, Kanagawa 2520816, Japan 2 Shonan institute of technology, 1-1-25 Tsujido Nishikaigan, Fujisawa, Kanagawa 251-8511, Japan ABSTRACT We have focused to grow cubic GaN (c-GaN) on Si(100) substrates using boronmonophosphide (BP) buffer crystals. The growth of GaN was carried out by MOVPE on BP/Si(100) substrate of 2 inches in diameter. By the several evaluations, it was recognized that when the growth temperature is around 750˚C, c-GaN was dominant. The typical growth rate was about 0.5μm/h. We obtained c-GaN layer over 2.5μm thick without cracking. INTRODUCTION Cubic GaN, which is a semi stable structure, has a small piezoelectric constant compared with wurtzite GaN. It means c-GaN has a small fluctuation of oscillation wavelength due to internal stress. It has been reported to grow GaN on GaAs and 3C-SiC substrates [1, 2]. However, the large lattice mismatch made the high concentrated defect in grown GaN crystals. In addition the chemical reaction between GaN and the substrates makes many problems. On the other hand, Si substrates are the most useful materials with large diameter and high crystal perfection. We tried to grow c-GaN on Si(100) substrate using BP as a buffer. BP and c-GaN have the same crystal structure and the lattice mismatch is about 0.7%. The growth and evaluation of GaN crystal on the BP/Si(100) substrates have been investigated [3, 4]. We grew GaN by MOVPE technique. The crystals obtained were evaluated by Field Emission Scanning Electron Microscope (FE-SEM), X-ray diffraction (XRD) and Photoluminescence measurement (PL). This paper describes the growth and evaluations of GaN on 2 inches diameter BP/Si(100) substrates. EXPERIMENT The growth of GaN was carried out by MOVPE on BP/Si(100) substrate of 2 inches in diameter. The close coupled showerhead reactors produced by AIXTRON SE was used to grow GaN. Trimethylgallium (TMGa) and monomethylhydrazine (MMHy) were used for the gas sources of Gallium and Nitrogen, respectively with V/III ratio of 10. BP/Si substrates were heated at 1100˚C before growing GaN. Then the GaN buffer layer about 50nm thick was grown at low temperature around 550˚C. After that the GaN layer was grown 1 hour at 700˚C, 725˚C, 750˚C and 800˚C, respectively. In the case of 750˚C growth temperature, growth times are 1 hour for sample A and 2 hours for sample B. FE-SEM operating at 2kV, was used to study the surface morphology and thickness of the samples by cross sectional observation.
DISCUSSION Growth temperature dependence of GaN surface morphology is shown in figure 1(a) to (d). When the growth temperatures are 700˚C and 725˚C, the surface of GaN is rough and wurtzite structure is mixed. A gap is found when the growth temperature is 800˚C. While the growth temperature is 750˚C, the surface of GaN is quite smooth and there is no gap. We chose 750˚C for the GaN growth temperature.
(a) 700˚C
(b) 725˚C
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