Direct evidence for self localization of barrier state electrons in 1500 nm MQW lasers

Investigations of MQW lasers usually concentrate on the properties of the confined (2D) carriers which contribute to gain. The effect of the unconfined (3D) barrier state carriers is usually considered since they influence the density and the properties of the confined carriers. This paper highlights the role of the barrier state (3D) electrons whose density may be large at high injection which causes Coulomb enhanced localization. We demonstrate this localization by observing a proper lasing transitions between the self-localized 3D electrons and confined (HH2) holes. This switches the laser wavelength between ~ 1500 nm and 1340 nm. We emphasize that the localization is exclusively due to the internal Coulomb fields since the laser structure can not support by itself any degree of localization. The lasers we used contain four 6 nm wide InGaAs quantum wells separated by 12 nm wide InGaAsP barriers