Effect of non-uniform carrier injection on two-state lasing in quantum dot microdisks with split electrical contact

In this papaer, the emission characteristics of InAs/InGaAs quantum dot (QD) microdisk lasers, of different cavity diameters, with a top split electrical contact formed using the focused ion beam technique are investigated. The dependences of the threshold currents of two-state lasing (i.e. currents corresponding to the start of the ground- and excited-state lasing) for microdisks of 24 and 28 mu m diameters on the electrical contact area are presented. The contact area was found to influence the threshold currents of two-state lasing in microdisks. It is shown that a decrease in the area of the injected electrical contact leads to a decrease in the current corresponding to the start of the excited-state lasing, while the ground-state (GS) lasing threshold remains virtually unchanged. The temperature evolution of the threshold currents for two-state lasing was also studied in microdisks with different electrical contact areas. We demonstrate that the use of contacts of different areas is a method of controlling the threshold currents of two-state lasing and can be used in engineering of QD lasers intended, for example, for multi-level signal transmission with wavelength multiplexing by switching from the GS to excited-state lasing.