The strain free Al_xGa_1-xN(x= 0.23) and partially strained Al_xGa_1-xN(x= 0.27) have been grown on GaN/sapphire template using MOCVD. The composition of Al in AlGaN layer has been determined from the ω-2Θ scan. Figure.1 shows the ω-2Θ scan for Al_0.27Ga_0.73N /GaN layer.   The Reciprocal space mapping (RSM) of (105) reflection has been carried out for Al_xGa_1-xN(x= 0.23 and 0.27)/GaN layers and the in-plane strain of the Al_xGa_1-xN epilayers with respect to GaN has been estimated. Figure.2 illustrates the RSM of (105) reflection for Al_0.27Ga_0.73N /GaN layer. Figure .3 shows the band edge emissions at 320 nm and 312 nm corresponding for Al_0.23Ga_0.77N and Al_0.27Ga_0.73N respectively, whereas the 362 nm emission is for GaN.  The root mean square (RMS) surface roughness of Al_0.23Ga_0.77N and Al_0.27Ga_0.73N   has been estimated as 0.37 nm and 0.30 nm respectively using atomic force microscopy.

Ti/Al/Ni/Au: 200/1000/400/500 Å metal layers were deposited onAl_xGa_1-xN(x= 0.23) and Al_xGa_1-xN(x= 0.27) layers by E-beam evaporation technique. The samples were annealed with two step annealing in rapid thermal annealing system at optimum conditions of 550 ˚C under N2 ambient for 60 s and at 780 ˚C for 30 s.

 In addition the schottky behavior of Ni/Au: 400/1500 Å contacts on the strain free Al_xGa_1-xN(x= 0.23) and partially strained Al_xGa_1-xN(x= 0.27) layers have been studied using current -voltage (I-V) and capacitance-voltage(C-V) measurements. The device characteristics have been correlated with the structural quality of Al_xGa_1-xN layers.

 REFERNCES:

[1]  P. Gay, P. B. Hirsch and A. Kelly, Acta Metall. 1, 315 (1953).

[2]  C. G. Dunn and E. F. Koch, Acta Metall. 5, 548 (1957).

[3]  G. S. Huang, T. C. Lu, H. H. Yao, H. C. Kuo, and S. C. Wang, Appl. Phys. Lett. 88, 061904, (2006).

[4] B. Jacobs, M.C.J.C.M. Kramer , E.J. Geluk, F. Karouta, Journal ofCrystal Growth, Vol. 241, pp. 15, 2002.

[5]  L.F. Lester, J.M. Brown, J.C. Ramer, L. Zhang, S. D. Hersee, J.C. Zolper, Applied Physics Letters, Vol. 69,No. l8,p. 2737, 1996.     

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1. Studies on dislocation and surface morphology of Al_xGa_1-xN/GaN heterostructures grown by MOCVD
2. Structural and optical characterization of AlGaN/GaN layers
3. Effect of nucleation islands coalescence on determining the quality of AlN layers grown by MOCVD