Growth And Properties Of GaN/MoS₂ Heterojunctions On Metallic Molybdenum Substrates

In recent years,the graphene-like layered two-dimensional?2D?material molybdenum disulfide?MoS₂?has attracted wide attention,due to its good photoelectric and mechanical properties.It is expected to be one of the candidates for the development of next-generation microelectronic devices and optoelectronic devices.Gallium nitride?GaN?is a Group III nitride semiconductor material with a forbidden band width that includes the entire visible spectrum?Eg=3.39 eV?.It has high electronic drift speed,high temperature resistance,good thermal conductivity and other characteristics,so it is widely used in semiconductor lasers?LD?,semiconductor light-emitting diodes?LED?and detectors,etc,and has also played an important role in the preparation of high-frequency,high-temperature and high-power devices.The GaN/MoS₂ heterojunction was studied in this paper.Since the lattice mismatch between MoS₂ and GaN is small?0.8%?and the thermal expansion coefficient is similar,low dislocation growth of GaN can be achieved.It is possible to realize 3D/2D heterojunction devices,reduce the cost of device fabrication,and expand the development of 3D semiconductors.In this paper,a chemical vapor deposition high vacuum tube furnace?Kejing OTF-1200X?is used,and sulfur powder?S?and molybdenum trioxide?MoO₃?powder are used as raw materials,and argon?Ar?is used as a carrier gas.The MoS₂ film was grown on a metal Mo substrate under a certain temperature and pressure.The structure,morphology and electrical properties of MoS₂ films with different growth temperatures and different MoO₃ dosages were characterized by different detection methods.The results showed that the optimum conditions for the growth of MoS₂ were as follows:reactant MoO₃ powder was 1.6g,S powder was 0.6 g,growth temperature was 925?,and Ar flow rate was 50 sccm.Under these conditions,the MoS₂ film preferentially grows in the?002?direction,with a maximum grain size of 76.4nm and a minimum roughness of 41.6 nm.Mo substrate and MoS₂ exhibit certain Schottky contact characteristics.Based on the synthesis of MoS₂ film,a second-generation electron cyclotron resonance plasma enhanced metal organic chemical vapor deposition?ECR-PEMOCVD?reactor was used to to grow GaN epitaxial film.The effects of different growth temperatures on the structure,morphology and photoelectric properties of GaN films were investigated.The results showed that the optimum growth conditions for the GaN/MoS₂ heterojunction are:buffer layer temperature of 500?,trimethylgallium?TMGa?flow rate of 0.8 sccm,nitrogen?N₂?flow rate of 100 sccm;growth layer temperature of 700?,TMGa flow rate of 0.8 sccm and the N₂ flow rate of 100 sccm.Under this condition,the GaN film is preferentially grown along the?002?direction,and the grain size is large.And the c-axis tensile stress exists on the surface of the GaN film,and the tensile stress is-1.73 GPa.The current-voltage?I-V?test results show that the GaN and MoS₂ exhibit near-Schottky contact,and the GaN surface defects are relatively small.Photoluminescence spectroscopy?PL?tests showed a blue shift in the edge-emitting peak.This is mainly due to the c-axis tensile stress of the GaN film and the quantum size effect of the small grains.