Carrier-induced refractive index change in InN

Abstract

Rapid development of InN technology demands comprehensive assessment of the electronic and optoelectronic potential of this material. In this theoretical work the effect of free electrons on the optical properties of the wurtzite phase of InN is investigated. The blue shift of the optical absorption edge by the free-carrier band filling is known as the Burstein-Moss effect for which InN offers to be a very suitable candidate as has been recently demonstrated experimentally. Due to well known Kramers-Kronig relations, a change in absorption is accompanied by a change in the index of refraction. Considering n-type InN samples with free electron concentrations ranging from 5x10 17 to 5x1020 cm-3, and employing a nonlocal empirical pseudopotential band structure, it is shown that this leads to a few percent change of the index of refraction. These carrier-induced refractive index changes can be utilized in optical switches, futhermore it needs to be taken into account in the design of InN-based optical devices such as lasers and optical modulators.