Fabircations Of P-type Delafossite Oxide Thin Films And Its Heterojunctions

High-performance p-type oxide semiconductor,as an inevitable component of transparent electronics and bipolar oxide devices,have been a much sought after goal for materials scientists during the past decades.But,converting oxides to p-type via element acceptor doping is extremely difficult owing to the strong localization behavior of the valnce band for oxides.For this purpose,Hosono and co-works proposed the concept of "chemical valence band modification"(CMVB)in 1997 and successfully prepared p-type CuAlO2 thin films with a delafossite structure,which sparks an extensive exploration of p-type oxide semiconductor films and devices based on Cu-and Ag-based delafossites.However,there are still some problems to be solved urgently.1)the preparation process for the film is relatively complicated.2)the conductivity needs to be improved.3)Heterojunction devices are more difficult to construct.Thus,we selected the delafossite Ag-based AgCrO2 and Cu-based CuRhO2 as the main research objects and successfully constructed heterojunction devices based on p-type AgCrO2 films and obtained p-type CuRhO2 films with a high conductivity by chemical solution deposition method.The main research contents are included as follows:(1)Investigations of the preparation process for AgCrO2 film and its heterojunction with self-rectifying resistive switching behavior:We prepared p-type delafossite AgCr1-xMgxO2 thin films onto n-Si substrates by using chemical solution deposition method and constructed a p-n heterojunction based on AgCrO2/n-Si.The resistive switching behavior was also investigated by substituting Cr with Mg elements.The results show that bipolar RS with self-rectifying behaviors are observed in the p-n heterojunction and the AgCr0.92Mg0.08O2/n-Si heterojunction shows the best performance.The intrinsic rectifying behavior in the low resistance state is attributed to the existence of a Schottky-like barrier at the interface.The RS behavior originates from the modification of the barrier,which is induced by the trapping/detrapping of charge carriers in oxygen vacancies at the interface.(2)Investigations of the fabrication of a transparent AgCrO2/In2O3 heterojunction and its backward diode rectifying behavior:we constructed a transparent p-n heterojunction based on nondegenerate p-type AgCrO2 and n-type In2O3 semiconductor films by chemical solution deposition and investigated its rectifying behavior.The results show that the AgCrO2/In2O3 heterojunction exhibits a backward diode rectifying behavior.The decrease of grain boundary in the In2O3 film can improve the backward diode rectifying performance.The optimized heterojunction exhibits a very high reverse rectification ratio that exceeds 103.The backward diode rectifying behavior originates from the electron band-to-band tunneling(BTBT)current in the reverse voltage region,which is induced by type-? band alignment.(3)Investigations of the preparation process for p-type CuRhO2 films and their electrical transport properties:Thirdly,we prepared high-quality c-axis oriented CuRhO2 series films by chemical solution deposition for the first time and investigated their electrical transport properties by substituting Rh with Mg element.The results show that the resistivity decreases rapidly with the introduction of Mg doping.When the Mg doping content x increases to 0.10,the room temperature resistivity will be the lowest value and metallic conduction behavior appears.The analyses of the transport mechanism at different temperature regions for the CuRhO2 film show that a three-dimensional variable-range hopping mechanism(3D-VRH)is dominated at the lower temperature region and a thermal activation model is dominated at the higher temperature region,and the hole carriers and its transport path are located in the Cu layer.After Mg doping,a three-dimensional variable-range hopping mechanism(3D-VRH)dominated at the lower temperature region,but a Fermi-liquid behavior dominated at the higher metallic conduction behavior temperature region.The CuRh0.90Mg0.10O2 film with a thickness of 150 nm has the highest room-temperature conductivity up to 735 S cm-1 compared to that of other p-type delafosstie films.(4)Investigations of the transparent and conducting properties for the p-type CuRh0.90Mg0.10O2 films:we prepared CuRh0.90Mg0.10O2 series films with different thicknesses by chemical solution deposition and investigated their transparent conducting properties.The results show that the resistivity and sheet resistance both decrease gradually with the increase of the film thickness.Upon increasing the film thickness to 40 nm,the surface morphology for the film is dense and uniform,and the carrier concentration and mobility remain basically stable.By calculating and comparing the Figure of Merit(FOM)of the films,the performance of transparency and conductivity for the films with thicknesses between 25 and 90 nm is optimal.