Van der Waals Epitaxy of HgCdTe Thin Films for Flexible Infrared Optoelectronics

Abstract

performance, such as fast response, tailorable bandgap over the 1-30 µm range, and high quantum efficiency, HgCdTebased IR photodetectors grown on latticematched Cd 0.96 Zn 0.04 Te (CZT) substrates and associated focal plane arrays (FPAs) dominate the high-performance end of IR applications. [1] The further development of IR applications requires the future HgCdTe IR detectors to have new features of lower cost, larger array format size, higher operating temperature, larger field of view (FOV), and multiband detection. [2] Over the past 10-20 years, significant progress has been achieved in these areas. For example, alternative substrates (Si, Ge, GaAs, and GaSb) instead of the traditional CZT substrates were researched for growing HgCdTe IR materials in order to fabricate nextgeneration IR imaging FPAs with lower cost and larger array format. [3][4][5] Recently curved imaging FPAs have been proposed as a feasible approach for achieving larger FOV with simpler and flatter lenses in comparison to conventional planer FPAs. [2] The conventional development pathway of these curved imaging FPAs relies on substrate thinning and FPA bending, which is inherently limited due to complex device processing, low yield, and high cost. Note that II-VI HgCdTe materials are more vulnerable to damage during the substrate-thinning processes because they are much more fragile and sensitive to chemical/mechanical damage in comparison to conventional Group IV and III-V semiconductors. In addition, the process does not remove the substrate completely due to the variability limits of array alignment on the polishing tool. Consequently, both the flexibility of the thinned FPA and the feasibility of monolithic integration are also limited in comparison to what could be achieved if transferable and/or free-standing HgCdTe device active layer of thickness <10 µm was available.Two-dimensional (2D)-layered materials such as graphene and mica have the potential to serve as substrates for growing high-quality three-dimensional (3D) semiconductor thin films through van der Waals epitaxy (vdWE) techniques such as molecular beam epitaxy (MBE) and MOCVD. [6] For vdWE growth, the stringent requirement of matched lattice constants for highquality heterostructure growth in traditional semiconductor epitaxy is mitigated. This is because the 2D-layered substrates have naturally passivated surfaces and strong chemical bonding is not required at the interface. In this way, the generation of dislocations at the interface can be effectively suppressed. [7,8] Van der Waals epitaxial (vdW) growth of semiconductor thin films on 2D layered substrates has recently attracted considerable attention since it provides a potential pathway for realizing monolithically integrated devices and flexible devices. In this work, direct growth of epitaxial HgCdTe (111) thin films on 2D layered transparent mica substrates is achieved via molecular beam epitaxy. The full width at half maximum of the ω-mode X-ray diffraction peak is measured to be around 306 arc sec. Mid-wave in...