Trap-Free Field Effect Transistors based on Epitaxial Single-Crystal Perovskites

Lead-halide perovskites have emerged as important semiconducting materials suitable for a variety of optoelectronic applications. Further advances in the field will rely on establishing the basic properties of these materials. We report the first experimental realization of the <i>intrinsic</i> (not dominated by defects) charge conduction regime in metal-halide perovskite field-effect transistors (FETs). The advance has been enabled by: i) a new vapor-phase epitaxy technique that results in large-area single crystalline all-inorganic cesium lead bromide (CsPbBr₃) films with excellent structural and surface properties, including atomically-flat surface morphology, essentially free from defects and traps at the level relevant to device operation; ii) an extensive materials analysis of these films using a variety of thin film and surface probes certifying the chemical and structural quality of the material; iii) the fabrication of nearly ideal (trap-free) FETs with textbook FET characteristics superior to any reported to date. These devices have allowed the investigation of the intrinsic carrier mobility as a function of temperature via both FET and gated Hall-effect measurements. The intrinsic mobility of our CsPbBr₃ FETs was found to increase on cooling from ~ 30 cm²V^-1s^-1 at room temperature to ~ 250 cm²V^-1s^-1 at 50 K. The combination of photo-Hall, gated Hall, and FET measurements reveal the intrinsic band transport occurring in these devices, with the mobility limited only by phonon scattering. The outstanding quality of these devices is largely due to the atomically flat, single crystalline morphology of the epitaxial CsPbBr₃ films achieved over macroscopic length scales, as confirmed by comprehensive structural, morphological and surface analysis.<br/>The epitaxial CsPbBr₃ FETs exhibit no degradation over a long-term storage in air (as tested for up to several months) or during extended electric measurements (that sometimes run for several weeks on end), with the exceptions of driving the FETs into a saturation regime or micro crack formation at low temperatures. While the encapsulation of the perovskite in parylene may have contributed to the excellent operational stability of our FETs, our as-grown uncoated perovskite films did not exhibit noticeable degradation during a prolonged storage in the regular laboratory air (ranging in duration from days to weeks).<br/>Establishing the intrinsic (phonon-scattering limited) mobility can not only serve as a rigorous test for theoretical models of carrier transport but can also reveal the ultimate fundamental limits of mobility in these materials, as well as point to a path for future innovation to still newer and improved perovskite systems. Additionally, our findings suggest that epitaxial perovskites offer an ideal platform for fundamental studies on charge transport in this class of materials. The robust, simple, and effective method for fabricating perovskite FETs that exhibit stable and ultimately efficient intrinsic charge transport paves a way for a plethora of new perovskite-based devices, such as light emitting FETs, electrically pumped injection lasers, better radiation detectors, sensors and memories.<br/><b>Reference:</b><br/>Bruevich, V., Kasaei, L., Rangan, S., Hijazi, H., Zhang, Z., Emge, T., Andrei, E. Y., Bartynski, R. A., Feldman, L. C., Podzorov, V., Intrinsic (Trap-Free) Transistors Based on Epitaxial Single-Crystal Perovskites. Adv. Mater. 2022, 34, 2205055. https://doi.org/10.1002/adma.202205055