Toward Nonepitaxial Laser Diodes

Thin-film organic, colloidal quantum dot, and metal halideperovskitesemiconductors are all being pursued in the quest for a wavelength-tunablediode laser technology that does not require epitaxial growth on atraditional semiconductor substrate. Despite promising demonstrationsof efficient light-emitting diodes and low-threshold optically pumpedlasing in each case, there are still fundamental and practical barriersthat must be overcome to reliably achieve injection lasing. This reviewoutlines the historical development and recent advances of each materialsystem on the path to a diode laser. Common challenges in resonatordesign, electrical injection, and heat dissipation are highlighted,as well as the different optical gain physics that make each systemunique. The evidence to date suggests that continued progress fororganic and colloidal quantum dot laser diodes will likely hinge onthe development of new materials or indirect pumping schemes, whileimprovements in device architecture and film processing are most criticalfor perovskite lasers. In all cases, systematic progress will requiremethods that can quantify how close new devices get with respect totheir electrical lasing thresholds. We conclude by discussing thecurrent status of nonepitaxial laser diodes in the historical contextof their epitaxial counterparts, which suggests that there is reasonto be optimistic for the future.