Growth of LiGa5O8 Single Crystal Thin Films and Their Conductive Mechanism by the Mist-CVD Method

doi:10.16553/j.cnki.issn1000-985x.2025.0002

Abstract

Abstract: The phenomenon of facile n-type doping and the challenges associated with p-type doping are frequently observed in wide-bandgap oxide semiconductors. LiGa₅O₈ is an innovative oxide semiconductor material which is theoretically amenable to bipolar doping. Remarkable properties are exhibited by LiGa₅O₈， positioning it as a promising candidate in the realm of oxide semiconductor optoelectronics， with the potential to advance the development of high-performance PN homojunctions and other bipolar devices. In this study， unintentionally doped high-quality single crystal LiGa₅O₈ thin films were synthesized by the mist-chemical vapor deposition （mist-CVD） method， and their quality， optical and electrical properties were meticulously measured and characterized. The experimental results indicate that the synthesized LiGa₅O₈ thin films exhibit excellent quality and crystallinity， with a thickness of 484 nm， small surface roughness （Rq=2.48 nm， Ra=1.73 nm）， and an optical bandgap of 5.22 eV， with a chemical composition ratio of Li， Ga， and O approximately 1∶5∶8. The films are characterized by n-type conductivity， with conductivity diminishing as lithium content increases， while p-type conductivity is not observed. The photodetectors prepared using the obtained LiGa₅O₈ thin films demonstrate favorable I-V and I-t characteristics under 254 nm illumination. Theoretical calculations of the band structure suggest that achieving p-type doping in LiGa₅O₈ is more challenging than n-type doping. By analyzing the intrinsic defects GaLi and LiGa in the oxygen-rich conditions of LiGa₅O₈， it is found that the formation energy of GaLi defects is exceptionally low， introducing shallow donor energy levels， thus resulting in the n-type conductive characteristics of the films； simultaneously， as the proportion of Li increases， Ga_Li defects compensate for Li acceptors， leading to negligible conductivity in the films. Future endeavors will encompass doping with elements such as Si， Ge and P， with the objective of obtaining higher carrier concentration LiGa₅O₈ crystal thin film materials.

Key words: wide-bandgap oxide semiconductor; LiGa₅O₈ single crystal film; mist-CVD method; n-type conduction; intrinsic defect

CLC Number:

ZHAO Hao, YU Bowen, LI Qi, LI Guangqing, LIU Yiyuan, LIN Na, LI Yang, MU Wenxiang, JIA Zhitai. Growth of LiGa₅O₈ Single Crystal Thin Films and Their Conductive Mechanism by the Mist-CVD Method[J]. Journal of Synthetic Crystals, 2025, 54(6): 997-1004.

Figures/Tables 7

Fig.1 XRD pattern of the LiGa5O8 thin film grown on c-Al2O3 substrate

Fig.2 SEM and AFM images of the LiGa5O8 thin film

Fig.3 Ultraviolet and infrared spectra of the LiGa5O8 thin film. （a） Ultraviolet transmittance spectrum；（b） ultraviolet Tauc plot；（c） infrared transmittance spectrum

Fig.4 XPS of the LiGa5O8 thin film

Fig.5 Photodetector performance of the LiGa5O8 thin film （n（Li）∶n（Ga） = 0.21）. （a） Structure of the photodetector device；（b） I-V curves of dark and photocurrent under 254 nm illumination；（c） I-t curve of photoresponse time at a 10 V bias

Fig.6 Calculated band structures of intrinsic Li and Ga substitution defects in LiGa5O8. （a） Band structure of a perfect LiGa5O8 lattice， solid line represents PBE calculation， dotted line represents GW calculation；（b） band structure with GaLi defects， n（Li）∶n（Ga）=0.185；（c） band structure with LiGa（8） defects， where Li substitutes 8-coordinated Ga， n（Li）∶n（Ga）=0.215；（d） band structure with LiGa（4） defects， where Li substitutes 4-coordinated Ga， n（Li）∶n（Ga）=0.215

Fig.7 Formation energies of GaLi and LiGa defects in LiGa5O8 （solid line represents the formation energy of GaLi defects， dotted line represents the formation energy of LiGa defects）

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Growth of LiGa₅O₈ Single Crystal Thin Films and Their Conductive Mechanism by the Mist-CVD Method

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