AlGaN on sapphire

In this formula, Eg, x and b are the optical bandgap, AIN molar fraction and bowing parameter, respectively. In order to determine this relationship, not only precise characterisation of Eg by the optical method but also precise determination of alloy composition x is quite important. The optical bandgap of AlGaN on sapphire in the whole compositional range was first reported by Yoshida et al [2] in 1982. They used optical absorption edge for determination of Eg, and x was determined by electron... 

FIGURE 4 RLMs of (a) AlGaN about 0.1 im thick, and (b) GalnN about 40 nm thick on GaN grown by OMVPE on sapphire using LT-A1N buffer layer. 

The compositions of the ternary layers were evaluated from the lattice parameters measured using X-ray diffraction (see Datareview A1.2) and from the positions of the photoluminescence peaks. Both methods gave the same results, if the bowing parameters of 3.2 eV and 0.1 eV, for InGaN and AlGaN, respectively, were used (as proposed by Takeuchi et al [25] for strained layers on relaxed GaN on sapphire). 

FIGURE 2 L-I characteristic of the InGaN/AlGaN LED on sapphire under DC operation at 30°C. The inset shows the ageing result under a constant current density of 60 A/cm2 (30 mA) at 30°C. 

S. Shur, M. A. Khan, Migration enhanced MOCVD (MEMOCVE/ ) buffers for increased carrier lifetime in GaN and AlGaN epilayers on sapphire and SiC substrate, physica status solid (c) Volume 2, Issue 7, 2095-2098 (2005). 

H. Hirayama, S. Fujikawa, N. Noguchi, J. Norimatsu, T. Takano, K. Tsubald, N. Kamata, 222-282 nm AlGaN /and InAlGaN-based deep-UV LEDs fabricated on high-quality AIN on sapphire. Phys. Status SoUdi A206, 1176-1182 (2009)... 

Figure 5.17 Electron mobility at room temperature of n-type Si-doped a-plane GaN grown on r-plane sapphire. Planar GaN grown on AlGaN/AiN intermediate layer is indicated by Template (circles). SELO indicates GaN grown with the SELO process (squares). That of c-plane GaN grown on sapphire using a low-temperature buffer layer is also shown for comparison (cf Color Plate XXVI).

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