The surface structure and chemistry of semiconductor single crystals are crucial to optoelectronic and nanoelectronic devices. Unfortunately, little is known about the native surfaces of perovskite single crystals grown by solution-based methods. Here, we found that a textured surface with characteristic striations and pyramidal pits is often present on the native surface of MAPbI3 single crystal (SC), both of which result from an unexpected etching process due to the unsaturated solution residing at the surface. The striations reflect the instantaneous fluctuations of the vicinal growth planes for a particular growth sector. The etch pits originate from the outcrops of the edge dislocations and are featured with a rectangle pyramidal shape at the (100), (010), and {112} faces as well as a square pyramidal shape at the (110) surface plane. Such two characteristic features, especially for the etch pits that could derive the dislocation density (around 104–105 cm–2 for MAPbI3 SC at the (100) surface), could be used as standard methods to evaluate the quality of organic–inorganic halide perovskite SCs. The native surface morphology with the presence of both striations and pits is strongly dependent on the details of the SC taken-out process from the growth solution and the quality of the as-grown SC, which could be the main reason for wide variations in different reported surface morphologies and hence electrical properties of SC devices.

Time of flight (ToF) transient current method is an important technique to study the transport characteristics of semiconductors. Here, both the (direct current) DC and pulse bias ToF transient current method were employed to investigate the transport properties and electric field distribution inside the MAPbI3 single crystal detector. Due to the almost homogeneous electric field built inside the detector during pulse bias ToF measurement, the free hole mobility can be directly calculated to be about 22 cm2V-1s-1, and the hole lifetime is around 6.5-17.5 μs. Hence, the mobility-lifetime product can be derived to be 1.4-3.9×10-4 cm2V-1. The transit time measured under the DC bias deviates with increasing voltage compared with that under the pulse bias, mainly arising from the inhomogeneous electric field distribution inside the perovskite. The positive space charge can then be deduced to increase from 3.1×1010 cm-3 to 6.89 ×1010 cm-3 in the bias range of 50-150 V. The ToF measurement can provide us a facile way to accurately measure the transport properties of the perovskite single crystals, and is helpful to obtain a rough picture of the internal electric field distribution as well.

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