Studies on the refractive index modulation in tunnel-coupled quantum-confined active regions of AlGaAs/GaAs semiconductor heterostructures by the p–n junction electric field

Abstract

Experimental studies of the influence of the parameters of the quantum-confined active regions of GaAs (QW)/ Al 0.35 Ga 0.65 As (barrier) semiconductor heterostructures, fabricated by the MOCVD technique, on the modulation of the refractive index and the optical absorption by the field of the reverse-biased p-n junction were carried out. It is shown that the use of thin quantum-confined active regions is mission-critical for obtaining a large modulation of the refractive index in the spectral region with low optical losses. It is shown that the use of structures with two thin tunnel-coupled GaAs quantum wells 3-nm-thick each compared to a single GaAs quantum well, can significantly increase the modulation amplitude of the refractive index and reduce internal optical losses at the operating wavelength. It is experimentally demonstrated that a higher value of the refractive index modulation amplitude in samples based on double-well system is provided by unipolar modulation of the absorption spectrum due to the effect of the transition from the 'coupled quantum wells' state at moderate electric fields to the 'uncoupled quantum wells' state at strong electric fields. It is demonstrated that there is an increase of the refractive index modulation with an increase in coupling of quantum wells for electrons by reducing the barrier thickness from 6.5 to 4 nm. For a double-well system with 3-nm-thick GaAs QW and 4-nm-thick Al 0.35 Ga 0.65 As barrier, a value of 0.000 148 for the modal refractive index change is achieved at internal optical loss α1 cm -1 , originated from residual absorption in the quantum-confined active region, and it provides a material refractive index modulation of 0.0181.