UC Santa Barbara

ABSTRACT

The Bowing Parameter of Low Indium Content InGaN

by

Camille Y. Pivard

The bandgap bowing parameter of indium gallium nitride (InGaN) semiconductor alloy is of great interest. Simulations of locally disordered InGaN material such as the ones used in an application of the Landscape theory of localization require a reliable bowing parameter value for low indium content InGaN. However, current scientific literature demonstrates a wide variation1-9 in the value of the InGaN bowing parameter. The current study aims to use well adapted experimental and data analysis techniques to obtain a sound result. High quality thin-film InGaN light emitting diode (LED) structures with varying indium content are grown by metal organic chemical vapor deposition (MOCVD). Their composition and the thicknesses of cap GaN and InGaN layers are determined via a Rigaku high-resolution X-ray diffractometer (HRXRD). The optical transmittance (OT) is obtained using a Shimadzu UV-Vis-NIR Spectroscopy. To ensure the dependability of the result, the experimental procedure uses a mask to expose the same small and localized area of the sample structures for both X-ray and optical measurements. The OT measurement technique avoids the Stoke shift induced error in the bandgap determination. Such error most likely occurs in emission-based measurement techniques. The experimental data are then analyzed using the transfer matrix method (TMM) for the InGaN absorption coefficient. The latter allows for bandgap determination using Tauc plots. The resulting low indium content (8%≤x≤15%) fully strained InGaN bowing parameter is 2.55 eV. In the same composition range, the InGaN strain corrected bowing parameter is 3.65 eV. An alternative InGaN absorption coefficient extraction method is also used for comparison. The single slab approximation method assumes that the multilayer structure can be considered as a single slab with infinite internal reflections and only the InGaN layer is effectively absorbing. This method yields the bowing parameters of 2.15eV and 3.2eV for fully strained and strain corrected InGaN structures respectively. The TMM is concluded to be the superior method for absorption coefficient extraction of the InGaN multilayer heterostructure. Ideas for future work are discussed.