Absorption of Light in Finite Semiconductor Nanowire Arrays and the Effect of Missing Nanowires

Nicklas Anttu

doi:10.3390/sym13091654

Abstract

When modelling the absorption in semiconductor nanowire (NW) arrays for solar cell and photodetector applications, the array is typically assumed to be infinitely periodic such that a single unit cell suffices for the simulations. However, any actual array is of a finite extent and might also show varying types of localized defects such as missing or electrically non-contacted individual NWs. Here, we study InP NWs of 2000 nm in length and 180 nm in diameter, placed in a square array of 400 nm in period, giving a rather optimized absorption of sunlight. We show that the absorption in the center NW of a finite N × N array converges already at N = 5 close to the value found for the corresponding infinite array. Furthermore, we show that a missing NW causes an enhanced absorption in neighboring nanowires, which compensates for 77% of the absorption loss due to the missing NW. In other words, an electrically non-contacted NW, which absorbs light but cannot contribute to the external short-circuit current, is a four times worse defect than a missing NW.

Highlights

III–V semiconductor nanowire (NW) arrays have shown promise for applications where light is absorbed such as solar cells and photodetectors [1,2,3,4,5]
The absorption in an NW array of a given material depends on the geometrical parameters including the length and diameter of the NWs and the array period [4,6,7,8,9]
More than two NWs away from the edge of a finite array or from the missing NW, the absorption recovers to values very close to those in the infinite array

Summary

Introduction

III–V semiconductor nanowire (NW) arrays have shown promise for applications where light is absorbed such as solar cells and photodetectors [1,2,3,4,5]. The optical properties of NW arrays can be optimized through electromagnetic optics modelling where the scattering and absorption of incident light is described with the Maxwell equations [9]. In such modelling, the nanowire array is usually assumed to be perfectly periodic and of an infinite extent in the transverse x-y plane [9]. It is sufficient to model a single unit cell of the periodic system and repeat this unit cell periodically thanks to the discrete translational symmetry Such a highly symmetric problem gives typically a low numerical burden for the simulations, allowing the scanning of a large range of varying geometry configurations [9]. Domain in the x-y plane to give, for the normally incident light, a periodic repetition of the supercell [14]

FEM Simulation Settings

Absorption Cross-Section and Short-Circuit Current

Results

Discussion