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Notes: InN has been expected to be a suitable material for electronic devices such as high mobility transistors because of its small effective mass compared to other nitrides. Heteroepitaxial InN films were grown by metalorganic vapor-phase epitaxy. The films have been structurally characterized by triple-axis x-ray diffraction (XRD) analysis in terms of lattice-mismatch dependence and InN film thickness dependence, and Hall measurements have been performed. In the XRD measurement, ω and ω–2θ scans were used, and the degree of tilting (the linewidth of x-ray signal, Δωc) [(0002) reflection] and that of twisting (Δωa) [(101¯0) reflection] have been separated. In addition, the degree of distribution of lattice constant c (Δ2θc) [(0002) reflection] of InN films has been assessed. For study of the lattice-mismatch dependence, growth of InN films on GaN, AlN and directly on sapphire substrates was performed, and accordingly, Δωc was found to range from about 500 to 4000 arcsec, and Δ2θc from about 400 to 700 arcsec. Among those three kinds of samples, InN films grown on GaN showed the smallest Δωc and Δ2θc values. Observation of c- and a-lattice parameters has shown that the InN on GaN is affected by the residual strain. On the other hand, InN thickness dependence of XRD showed that Δωc was changed from about 700 to 500 arcsec, and Δ2θc from about 600 to 300 arcsec with increasing InN thickness from 400 to 2400 Å. In accordance with the thickness of InN, Δωa was found to change from about 2500 to 1700 arcsec. Moreover, it was found that the InN film less than 1200 Å thick is composed of grain islands with different crystalline orientation and that the growth mode changes at a thickness of about 1200 Å—and screw dislocations occur. It is found that the residual strain in InN films over 1200 Å thick is gradually released, resulting in almost the same orientation. This is reflected in the reduction of the mosaicity, the proceeding of relaxation and the surface morphology. Selection of GaN for the underlying layer of the InN film has been shown to lead to structural improvement of the epitaxial InN film. In fact, InN film with a thickness of 2400 Å grown on GaN has a Hall mobility of about 700 cm2/V s even at an electron carrier concentration of 5×1019 cm−3. This value corresponds to that for GaAs at the same impurity concentration. © 1999 American Institute of Physics.

Notes: We have observed photoluminescence of Al1−xInxN films. The films were grown on GaN by atmospheric pressure metalorganic vapor phase epitaxy. GaN was grown on a c-plane sapphire substrate with a low-temperature deposited AlN buffer layer. Photoluminescence, absorption, and x-ray diffraction measurements have shown that each spectral peak shifts with alloy composition x and that Al1−xInxN heteroepitaxial films are not macroscopically in phase separation and are constituted in the wurzite structure. © 1998 American Institute of Physics.

Notes: We have identified piezoelectric fields in strained GaInN/GaN quantum well p-i-n structures using the quantum-confined Stark effect. The photoluminescence peak of the quantum wells showed a blueshift with increasing applied reverse voltages. This blueshift is due to the cancellation of the piezoelectric field by the reverse bias field. We determined that the piezoelectric field points from the growth surface to the substrate and its magnitude is 1.2 MV/cm for Ga0.84In0.16N/GaN quantum wells on sapphire substrate. In addition, from the direction of the field, the growth orientation of our nitride epilayers can be determined to be (0001), corresponding to the Ga face. © 1998 American Institute of Physics.

Notes: We studied the effect of isoelectronic In doping on the crystalline and optical properties of GaN grown on sapphire with H2 or N2 carrier gas by metalorganic vapor phase epitaxy. The relationship between lattice constants c and a obtained by x-ray diffraction analysis showed that with increasing trimethylindium (TMI) flow during growth, the strain in GaN decreased, and accordingly, the tilting and the twisting components of crystalline mosaicity also decreased. In addition, the Raman shift, the excitonic photoluminescence peak energy, and the its linewidth shifted in accordance with the magnitude and the sign of the strain in GaN, regardless of the carrier gas used. These results revealed that for a smaller TMI flow region, In was incorporated so that the crystallinity of GaN improved, and for a larger TMI flow region, In substituted for Ga so that alloying formation might have occurred. © 1999 American Institute of Physics.