Performance Research And Optimization Of Cu/GaN Triboelectric Nanogenerator

Triboelectric nanogenerator（TENG）can convert high-entropy friction loss energy and random discrete mechanical energy into electrical energy.Since its first proposal in 2012,it has attracted extensive attention from numerous applications and has been used in energy collection,small self-driving electronic devices,medical technology,and other fields.Traditional polymer insulator/metal TENG generates alternating current based on the coupling of contact electrification and electrostatic induction.The high internal impedance（MΩ～GΩ）of the polymer insulator leads to low current density（n A/cm²～μA/cm²）and high voltage（V～k V）of the system.With the miniaturization and co-integration with conventional electronic devices,TENG energy source needs to provide higher current in parallel circuits.Recently,the metal-semiconductor direct current triboelectric nanogenerator（MSDC-TENG）based on Schottky contact was proposed.When the metal slides on the semiconductor,the interface ultra-high electric field will accelerate the interface electrons again,forming hot electrons and hot holes for high current output.When the friction region is in micrometer or nanometer size,a more satisfactory output power density（100-1000 W/m²）can be obtained.However,TENG with micro contact have poor stability issues.Subsequently,researchers found that when the size of the friction contact area of TENG is above the centimeter level,the stability of TENG can be effectively improved.On the other hand,it is an effective means to improve the output performance through surface engineering（lithography,soft lithography,ultrafast laser patterning,etc.）or surface modification technology（ion implantation,doping nanomaterials in triboelectric materials,embedding composite materials into friction materials,etc.）This paper reports the epitaxial growth of Ga/N polar GaN semiconductor materials with hexagonal structure on a traditional sapphire substrate using MOCVD technology.Using silane（Si H₄）and magnesium ferrocene（Mg（C₅H₅）₂）as N-type and P-type dopants.We mainly studied the performance of Cu/GaN TENG.Attempt to improve the performance of the generator through two directions:surface engineering and structural engineering.At the same time,during the experiment,the influence of controllable variables（pressure,acceleration,etc.）on the output performance of the generator and how to improve the stability of the generator were also studied.The main content is as follows:（1）Improving carrier concentration on GaN wafer surface through Si/Mg doping,the performance of Cu/GaN TENG in small area（1.5×1.5 mm²）contact was significantly improved.When the carrier concentration on the surface of P-type GaN wafers is 1×10¹⁸cm^-3,the Cu/P-type GaN TENG achieves the best performance(compared to the performance of the initial Cu/GaN TENG:open circuit voltage(V_oc)increased from 5.6 V to 14.2 V,short-circuit current(I_sc)density increased from 0.5 A/m²to 25.5 A/m²,and power density increased by 120 times).When the carrier concentration on the surface of P-type GaN wafers is 1×10¹⁸cm^-3,the measured maximum load current density is 12.8 A/m²,and the maximum load output power is 102.4W/m².It can be applied to small autonomous driving electronic devices.The experimental result provides a new approach for the current regulation of MSDC-TENG.（2）We investigated the corrosion process of GaN wafers with different polarities（N/Ga）in molten KOH and the effect of molten KOH corrosion on the performance of Cu/P type GaN TENG.performance of Cu/P type GaN TENG in centimeter scale（1.5×1.5 cm²）area contact was reported.Using molten KOH to corrode the surface of Ga polarized GaN wafers,and during the corrosion process,more defects and dangling bonds will be generated on the wafer surface.The performance of Cu/P-type GaN TENG composed of the best corroded Ga polarity GaN wafer（at a corrosion temperature of 220 ^oC and a corrosion time of 15 min）and Cu sheet is compared with that of Cu/P type GaN TENG composed of uncorroded Ga polarity GaN wafer and Cu sheet.Open circuit power increased by 14 times(I_scincreased from 20μA to 80μA;V_ocincreased from 8 V to 29 V.The maximum load power density obtained is 0.28W/m².The Cu/P type GaN TENG based on centimeter level Schottky contacts reported in this study exhibited a good I_scdensity of 36μA/cm².The experiment demonstrated a surface corrosion method to enhance the performance of generators in an extremely simple,low-cost,and efficient way.（3）Chosing Cu/P-type GaN TENG as the research object(GaN wafer surface carrier concentration of 1×10¹⁷cm^-3,friction contact area of 1.5×1.5cm²)to explore the effect of built-in electric field on the performance of TENG.The experiment introduces heterojunctions in the P-type GaN wafer structure to regulate the free diffusion of electrons in the built-in electric field and the strength of the built-in electric field,thereby improving the performance of Cu/P-type GaN TENG.The experimental results show that the performance of Cu/P-type GaN TENG composed of GaN（GaN/Al GaN/P-type GaN）and Cu sheets in heterojunction structure is significantly better than that of GaN（GaN/U GaN/P-type GaN）and Cu/P-type GaN TENG composed of Cu sheets in homojunction structure.Specifically,I_scincreased from 20μA to 30μA.V_ocincreased from 8 V to 15 V.（4）Explored the effects of different electrode preparation processes on the performance of Cu/P-type GaN TENG.Electrodes were prepared on the surface of P-type GaN wafers using a soldering iron welding/electron beam evaporation process in the experiment.Under both preparation processes,the electrode material all can form good ohmic contact with the surface of GaN wafers.The performance of Cu/P-type GaN TENG using soldering iron welding/electron beam evaporation process is I_sc～20μA;V_oc～8 V/I_sc～18μA;V_oc～6 V。The surface of GaN wafers was roughened using inductively coupled plasma（ICP）etching technology and explored the effect of etching process on the performance of Cu/P-type GaN TENG.Comparing the performance of Cu/P type GaN TENG before and after etching,the performance of Cu/P-type GaN TENG was effectively improved after etching:I_scincreased from 20μA to40μA;V_ocincreased from 10 V to 22 V.