Alx Ga1-x NGaN (x∼0.3) heterostructures with and without a high-temperature (HT) AlN interlayer (IL) have been grown on sapphire (Al2 O3) substrates and AlN buffer/ Al2 O3 templates by metal organic chemical vapor deposition. The effects of an AlN buffer layer (BL) grown on an Al2 O3 substrate and an AlN IL grown under the AlGaN ternary layer (TL) on structural, morphological, and optical properties of the heterostructures have been investigated by high-resolution x-ray diffraction, spectroscopic ellipsometry, atomic force microscopy, and photoluminescence measurements. The AlN BL improves the crystal quality of the AlGaN TL. Further improvement is achieved by inserting an AlN IL between GaN BL and AlGaN TL. However, experimental results also show that a HT AlN IL leads to relatively rough surfaces on AlGaN TLs, and an AlN IL changes the strain in the AlGaN TL from tensile to compressive type. In addition, an AlN BL improves the top surface quality of heterostructures. © 2007 American Institute of Physics

The strain-stress analysis of Al x Ga 1)x N/GaN (x = 0.3) heterostructures with and without a high-temperature HT-AlN interlayer (IL) grown on sapphire (Al 2 O 3 ) substrates and AlN buffer/Al 2 O 3 templates via metal organic chemical vapour deposition (MOCVD) was carried out based on the precise measurement of the lattice parameters by using high-resolution X-ray diffraction (HRXRD). The a-and c-lattice parameters were measured from the peak positions that were obtained by rocking the theta axis at the vicinity of the symmetric and asymmetric plane reflection angles, followed by the in-plane and out-of-plane strains. Then, the biaxial and hydrostatic components were extracted from the total strain values that were obtained and were then discussed in the present study as the effect of the HT-AlN buffer and IL. The AlN buffer layer (BL) affects the strain values of the AlGaN ternary layer (TL). A further effect was realized by inserting an AlN IL between GaN BL and AlGaN TL. However, the experimental results also show that an AlN IL changes the strain behaviour in the a-and c-directions of the AlGaN TL from the tensile to compressive and the compressive to tensile type, respectively. These similar behaviours were observed in hydrostatic strain, biaxial strain and stress. Their reasons are explained with an effective a-lattice parameter, post-growth cooling and lattice and thermal mismatches. PACS: 61.05.cp, 68.55,ag, 81.15.Gh, 78.55.Cr KEY WORDS: high electron mobility transistors, high-resolution X-ray diffraction, metal organic chemical vapour deposition, strain Ó

We present surface properties of buffer films (AIN and GaN) and Al0.3Gao.zN/Al2O3-High Electron Mobility Transistor (HEMT) structures with/without AIN interlayer grown on High Temperature (HT)-AIN buffer/Al2O3 substrate and Al2O3 substrate. We have found that the GaN surface morphology is step-flow in character and the density of dislocations was about 10(8)-10(9) cm(-2). The AFM measurements also exhibited that the presence of atomic steps with large lateral step dimension and the surface of samples was smooth. The lateral step sizes are in the range of 100-250 nm. The typical rms values of HEMT structures were found as 0.27, 0.30, and 0.70 nm. HT-AIN buffer layer can have a significant impact on the surface morphology of Al0.3Ga0.7N/Al2O3-HEMT structures.

The structural and optical properties of an In x Ga 1Àx N/GaN multi-quantum well (MQW) were investigated by using X-ray diffraction (XRD), atomic force microscopy (AFM), spectroscopic ellipsometry (SE) and photoluminescence (PL). The MQW structure was grown on c-plane (0 0 0 1)-faced sapphire substrates in a low pressure metalorganic chemical vapor deposition (MOCVD) reactor. The room temperature photoluminescence spectrum exhibited a blue emission at 2.84 eV and a much weaker and broader yellow emission band with a maximum at about 2.30 eV. In addition, the optical gaps and the In concentration of the structure were estimated by direct interpretation of the pseudo-dielectric function spectrum. It was found that the crystal quality of the InGaN epilayer is strongly related with the Si doped GaN layer grown at a high temperature of 1090°C. The experimental results show that the growth MQW on the high-temperature (HT) GaN buffer layer on the GaN nucleation layer (NL) can be designated as a method that provides a high performance InGaN blue light-emitting diode (LED) structure.

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