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HL: Fachverband Halbleiterphysik

HL 81: Focus Session: Extended defects in semi- and nonpolar GaN II

HL 81.9: Talk

Thursday, March 14, 2013, 17:15–17:30, H13

Determination of In mole fraction and strain state in semi- and nonpolar InGaN layers by XRD — •Martin Frentrup, Simon Ploch, Tim Wernicke, and Michael Kneissl — TU Berlin, EW 6-1, Institut für Festkörperphysik, Hardenbergstr. 36, 10623 Berlin, Germany

In wurtzite semiconductor heterostructures with semi- and nonpolar orientation the anisotropic lattice mismatch leads to a triclinic distortion. The distortion can be described by introduction of two new lattice parameters δ₁ and δ₂ describing the deviation of the basis angles α (β) and γ from 90^∘ and 120^∘ respectively. This must be taken into account for the determination of ternary alloy composition by XRD.
In this paper, we will compare different XRD algorithms to determine the composition. With the method of Young et al.^[1] the position of the symmetric reflection is used to estimate the strain state and composition, assuming a relaxation mechanism by layer tilt.
Alternatively one can determine all parameters of the triclinic lattice (a, c, δ₁, δ₂) by measurement of several X-ray reflexes in ω-2θ-scans. This method is more accurate, since the exact strain state can be determined without making assumptions on the specific mechanism.
We will discuss the advantages and disadvantages of both methods regarding the determination of stoichiometry for (2021) oriented InGaN. These results will be used for comparison of the In incorporation efficiencies and relaxation in (1122) and (0001) orientated InGaN layers.

[1] E. Young, A. Romanov, J. Speck; APEX, 4 (2011), 061001