Continuous-Wave Amplified Spontaneous Emission and High-Current-Density Operation from a Transparent Perovskite LED Architecture

Metal halide perovskites are excellent candidates for the gain material in thin film laser diodes. They exhibit high optical gain, low amplified spontaneous emission (ASE) thresholds, and a wide emission wavelength tunability. These attributes have facilitated notable advancements such as optically-pumped pulsed and continuous-wave (CW) lasing from a large library of optical cavities, operating under both room-temperature and cryogenic conditions. The successful development of perovskite laser diodes and their prospective heterogeneous integration into photonic circuits would pave the way for a multitude of applications in domains such as sensing, ranging, data communication, and miniaturized displays.<br/> <br/>However, achieving a current-injection perovskite laser, a promising yet complex feat, remains elusive due to the inherent complexity of the optoelectronic design challenges. Firstly, there is the necessity for high internal quantum efficiency (IQE) at extreme current densities ranging from hundreds to thousands of A/cm². This demands effective strategies for mitigating Joule heating, a problem magnified by perovskites' inherent low thermal conductivity and diminished stability at such high current densities. Secondly, the device stack must be optimized in terms of its optical design to maximize the net modal gain. This imposes stringent criteria on the thickness and conductivity of the layers comprising the device stack. In particular, the key challenge stems from the presence of conductive metal electrodes in the vicinity of a gain layer. It's essential, on the one hand, that electrodes inject kA/cm² current densities into the device. On the other hand, these highly conductive layers contribute to substantial free-carrier optical absorption, thereby increasing ASE threshold and current density necessary for ASE/lasing. In the last step toward a laser, a high quality-factor optical cavity has to be integrated into the perovskite LED (PeLED) without compromising the device performance and reliability.<br/><br/>In this work, we embed a perovskite waveguide stack, optimized for high-current density operation, into a scaled (50 um in diameter) transparent LED architecture with reduced optical losses. We reliably operate this miniaturized PeLED in a sub-µs pulsed mode above 3 kA/cm² without irreversible degradation. At these current densities, the device delivers EQEs above 1% at 77 K. Moreover, we achieve low ASE thresholds (&lt; 10 µJ/cm²) from this fully contacted electrical structure at 77 K using 3-ns optical pumping. This PeLED allows us to achieve several crucial milestones towards injection lasing: 1) ASE enhancement at synchronized photo-electrical co-excitation; 2) optically-pumped CW ASE when excited with 1-µs-long optical pulses; 3) electroluminescence brightness levels close to half of the brightness produced by CW optical pumping at ASE threshold. These milestones set us within reach of realizing a perovskite-based thin-film laser diode. Finally, we will also discuss novel concepts of integrating a fully functional PeLED with optical cavities for future thin-film perovskite laser diodes.