XRD Measurement And Analysis Of Strain Distribution In GaN Material Along Surface Normal

So far, Gallium nitride(Ga N) is mainly prepared by heteroepitaxial growth on substrates such as sapphire, silicon carbide and silicon by Metal-organic Chemical Vapor Deposition(MOVCD), Molecular Beam Epitaxy(MBE) or Hydride Vapor Phase Epitaxy(HVPE). However, the Ga N epilayer always undergoes strain caused by lattice mismatch and thermal expansion mismatch between Ga N and the substrate. To investigate the formation and release mechanisms of strain, or to detect the distribution of strain in single crytal epilayers, two effective approaches have been put forward. One approach is to detect the strain along the corss section of samples by using Raman scattering, the other is by using Rutherford back scattering.As one of the most important methods to analyze the crystalline property of single crystal semiconductor and low dimension heterojunction materials, high resolution X-ray diffraction(HRXRD) can be used to detect the strain precisely. Compared with the two approaches mentioned above, HRXRD is widely accepted because of its lower cost and non-destructive measurement. However, the result of strain measured with conventional HRXRD method is exactly a weighted average value over the whole detected part of the epilayer, which cannot present the distribution of strain in material. On this background, the present paper investigates the methods to obtain the depth distribution of strain in polar Ga N(in-palne isotropic) and non-polar Ga N(in-plane anisotropic) using HRXRD. The main research results are as follows:1. It presents a method to obtain the information of strain distribution along the surfacenormal in polar Ga N based on HRXRD. Measurements of the Ga N epilayers grown on cone-shaped patterned sapphire and Si(111) substrate are carried out and the obtained strain is consistent with that measured by conventional HRXRD. The strain porfile result is further compared with that measured by Raman spectroscopyand it proves the method is effective.2. A method to obtain the information of strain distribution along the normal of the surface of non-polar Ga N epilayers based on HRXRD is presented. It is applied to measure the a-plane Ga N grown on r-plane sapphire, and the strain distribution in a-plane Ga N is estimated. The feasibility of the strain profile measurement of m-plane Ga N is also proven theoretically.