Structure asymmetry effects in the optical gain of piezostrained InGaN quantum wells

We investigate the effects of structural asymmetry on the electronic and optical properties of indium gallium nitride (InGaN) quantum wells (QW's). Using a pulsed current excitation technique, spectral blue shift as large as 80 meV is observed in a strained 3.0-nm In0.2Ga0.8N QW as the pulsed current increases from 1 mA to 1A. Based on a self-consistent calculation, we are able to quantify a gain competition process among the interactions of piezoelectricity, many-body, charge screening, and band filling effects. Such interactions are shown to provide a mechanism for shaping the QW confined potential such that superior carrier confinement and charge screening of the piezoelectric field can be obtained in the asymmetric InGaN QW. At high carrier injection of Ninj > 2 × 1019 cm-3, a tenfold increase in the TE-polarized optical gain can be achieved by using the asymmetric GaN-InGaN-AlGaN QW instead of the symmetric InGaN-AlGaN QW. Due to the diminishing of piezoelectricity-induced quantum-confined Stark effect, the calculated optical gain spectra of the asymmetric InGaN QW exhibit a spectral blue shift with respect to those of the symmetric InGaN QW.