Excitonic properties of strained wurtzite and zinc-blende GaN/Al(x)Ga(1-x)N quantum dots

TL;DR

This study provides a theoretical analysis of excitonic properties in strained GaN/AlN quantum dots with different crystal structures, highlighting the effects of strain and piezoelectric fields on energy levels and radiative decay times.

Contribution

It offers new insights into how strain and crystal structure influence excitonic behavior in GaN quantum dots, aiding in the design of optoelectronic devices.

Findings

Piezoelectric field dominates excitonic properties in WZ GaN/AlN quantum dots.

Red shift of exciton ground state energy occurs in larger WZ GaN/AlN quantum dots.

Radiative decay time varies significantly with quantum dot height and structure.

Abstract

We investigate exciton states theoretically in strained GaN/AlN quantum dots with wurtzite (WZ) and zinc-blende (ZB) crystal structures, as well as strained WZ GaN/AlGaN quantum dots. We show that the strain field significantly modifies the conduction and valence band edges of GaN quantum dots. The piezoelectric field is found to govern excitonic properties of WZ GaN/AlN quantum dots, while it has a smaller effect on WZ GaN/AlGaN, and very little effect on ZB GaN/AlN quantum dots. As a result, the exciton ground state energy in WZ GaN/AlN quantum dots, with heights larger than 3 nm, exhibits a red shift with respect to the bulk WZ GaN energy gap. The radiative decay time of the red-shifted transitions is large and increases almost exponentially from 6.6 ns for quantum dots with height 3 nm to 1100 ns for the quantum dots with height 4.5 nm. In WZ GaN/AlGaN quantum dots, both the radiative decay time and its increase with quantum dot height are smaller than those in WZ GaN/AlN quantum dots. On the other hand, the radiative decay time in ZB GaN/AlN quantum dots is of the order of 0.3 ns, and is almost independent of the quantum dot height. Our results are in good agreement with available experimental data and can be used to optimize GaN quantum dot parameters for proposed optoelectronic applications.