• PDF / 411,925 Bytes
• 6 Pages / 432 x 648 pts Page_size
• 93 Downloads / 217 Views

DOWNLOAD

REPORT

---

MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.49

Modelling of III-Nitride Epitaxial Layers Grown on Silicon Substrates with Low Dislocation-Densities Khaled H. Khafagy1,2, Tarek M. Hatem1,3, Salah M. Bedair2 1 Centre for Simulation Innovation and Advanced Manufacturing, The British University in Egypt, ElSherouk City, Cairo 11837, Egypt

2 Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, NC 27695, USA.

3 Faculty of Energy and Environmental Engineering, The British University in Egypt, El-Sherouk City, Cairo 11837, Egypt.

ABSTRACT Large lattice and thermal expansion coefficients mismatches between IIINitride ሺ‫ܰܫܫܫ‬ሻ epitaxial layers and their substrates inevitably generate defects on the interfaces. Such defects as dislocations affect the reliability, life time, and performance of photovoltaic (PV) devices. High dislocation densities in epitaxial layer generate higher v-shaped pits densities on the layer top surface that also directly affect the device performance. Therefore, using an approach such as the embedded void approach (EVA) for defects reduction in the epitaxial layers is essential. EVA relies on the generation of high densities of embedded microvoids (~10 8/cm2), with ellipsoidal shapes. These tremendous number of microvoids are etched near the interface between the ‫ ܰܫܫܫ‬thinfilm and its substrate where the dislocation densities present with higher values. This article used a 3-D constitutive model that accounts the crystal plasticity formulas and specialized finite element (FE) formulas to model the EVA in multijunction PV and therefore to study the effect of the embedded void approach on the defects reduction. Mesh convergence and 2-D analytical solution validation is conducted with accounting thermal stresses. Several aspect and volume ratios of the embedded microvoids are used to optimize the microvoid dimensions.

755

Downloaded from https://www.cambridge.org/core. University of Texas Libraries, on 06 Jul 2019 at 11:53:02, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/adv.2019.49

INTRODUCTION As the III-Nitride ሺ‫ܰܫܫܫ‬ሻ epitaxial layers cannot be grown on lattice matched substrates because of the cost constraints, ‫ ܰܫܫܫ‬epitaxial layers have been grown on substrates with large lattice and thermal expansion coefficients (TEC) mismatches such as Silicon ሺܵ݅ሻ and Sapphire [1-2]. Therefore, the growth of ‫ ܰܫܫܫ‬such as Indium Gallium Nitride ሺ‫ܰܽܩ݊ܫ‬ሻ on Si substrates is inherently difficult and leads to generate defects such as dislocations with high densities [3]. Such defects act as scattering centers that impact the minority carrier lifetime, reduce thermal conductivity, and form easy pathways for impurity diffusion [4-6]. Furthermore, generation of high dislocation densities in the interfaces between ‫ ܰܫܫܫ‬layers and their substrates lead to higher generation of V-shaped pits densities on the top layer surface [7-9]. While, these v-pits are gene