Lattice Parameters a-, c-, Strain-Stress Analysis and Thermal Expansion Coefficient of InGaN/GaN Solar Cell Structures Grown by MOCVD

Structural properties of InGaN/GaN solar cells (SCs) grown by metal organic chemical vapor deposition (MOCVD) technique are investigated by high resolution X-ray diffraction (HR-XRD) method. It is noticed that a- and c- lattice parameters of the structures showed small differences according to examined (hkl) planes. Fault percentage of the a- and c- lattice parameters are also calculated. It is seen that fault percentage is smaller than %2 for all samples. Investigations have been made for three different samples. Differences in crystal quality caused by growth conditions are seen in all three samples. At the same time, properties such as crystal size, strain and stress are determined. During determination of stress, two different methods including elastic constants, Young module and Poisson ratio are used. Results gained from these two methods are compared with each other.  Thermal expansion coefficients of InGaN are calculated for (002), (004), (006) and (121) planes for 100 o C temperature difference (300-400 o C). It is seen that peak positions gained from HR-XRD are nearly the same with the ones in database. All the results obtained from calculations are given in tables in the following sections of this article. It can be seen that all these results are in accordance with previous works done by different authors and with the real values.