Polar-Induced Selective Epitaxial Growth of Multijunction Nanoribbons for High-Performance Optoelectronics

Semiconductor heterostructures are basic building blocks for modern electronics and optoelectronics. However, it still remains a great challenge to combine different semiconductor materials in single nanostructures with tailored geometry and chemical composition. Here, a polar-induced selective epitaxial growth method is reported to alternately grow CdS and CdS _xSe_{1- x} heterostructure nanoribbons (NRs) side by side in the lateral direction, with the heterointerface (junction) number to be well controlled. Transmission electron microscopy (TEM) and spatial-resolved μ-PL spectra are employed to characterize the heterostructure NRs, which indicate that the achieved NRs are high-quality heterostructures with sharp interfaces. Kelvin probe force microscopy (KPFM) and femtosecond pump-probe characterizations further confirm the efficient charge-transfer process across the interfaces in the multijunction NRs. Photodetectors based on the achieved NRs are realized and systematically investigated, demonstrating junction number-dependent optoelectronic response behaviors. NRs with more junctions exhibit more superior device performances, reflecting the important roles of the high-quality interface regions. Based on this multijunction NRs device, high on-off ratio (10⁷) and remarkable responsivity (1.5 × 10⁵ A/W) are demonstrated, both of which represent the best results compared to the reported CdS, CdSe, and their heterostructures. These novel multijunction NRs may find broad applications in future integrated photonics and optoelectronics devices and systems.