Semiconductor laser diodes are vital to a wide array of technologies, including fiber optic networks, medical diagnostic tools, and remote sensing systems. Commercial laser diodes are based on epitaxially grown III-V semiconductors, which require lattice-matched substrates and high growth temperatures. In the past three decades, successful demonstrations of light-emitting diodes (LEDs) and optically pumped lasers based on non-epitaxially processed semiconductors, including organics, colloidal quantum dots (CQDs), and halide perovskites, has prompted interest in creating a laser diode from these materials, yet even today, this remains an insurmountable challenge.

As compared to organics and CQDs, perovskites have the unique advantage of long-range crystal structure and delocalized carrier wavefunctions, enabling greater mobilities and alleviating non-radiative loss pathways that plague organics and CQDs. However, perovskites suffer from rapid degradation induced by thermal, electrical, and chemical stresses, rendering high-current density operation difficult. Like early GaAs laser diodes, the first non-epitaxial injection lasers will likely require cryogenic temperatures to achieve lasing, as colder temperatures substantially reduce gain thresholds and thermal stresses. This brings about a new obstacle, as perovskite LEDs feature organic charge transport layers whose conductivities decrease exponentially with decreasing temperature.

We aim to augment the traditional perovskite LED architecture by replacing organic charge transport layers with inorganic materials, particularly metal oxide semiconductors. To this end, we investigate the potential for metal oxide deposition on perovskite, starting with an examination of the chemical, electronic, and structural degradation of perovskite during atomic layer deposition (ALD). We then fabricate perovskite LEDs with various metal oxide transport layers, and develop a novel method of fine-tuning charge injection balance, using a few atomic layers of Al₂O₃ to facilitate tunneling-mediated electron injection into the perovskite. We show that this device structure offers a substantial improvement in low-voltage operation at cryogenic temperature as compared to a traditional structure. Finally, we probe the causes of efficiency roll-off, which poses a significant challenge to injection lasing, in our LED structure. This research contributes new knowledge of perovskite device processing and behavior, which may bring the development of a perovskite laser diode closer to reality.

Adviser: Barry Rand