The Photochemical Photocurrent Ambipolar Behavior Of α/β-Ga₂O₃ Phase Junction And Its Solar-Blind Ultraviolet Adjustable Logic Device

Devices of Photoelectrochemical（PEC）are the most artificial devices similar to a nervous system.They can solve the problems of complex computer/nervous system interface and multifunctional integration in the Post-Moore era,and obtain a neurosimulation system that integrates sensing,computing,and storage.However,as an important degree of freedom,the polarity of photocurrent has been neglected in the past research.The direction of photocurrent（positive or negative）in photoelectric chemical devices can be adjusted by changing the wavelength of incident light or by applying a bias voltage.This phenomenon is called Photoelectrochemical Photocurrent Switching（PEPS）phenomenon.Ga₂O₃is a kind of ultra-wide-band gap semiconductor,which has the advantages of more ideal band gap,more suitable energy level position and more stable physical and chemical properties compared with the mainstream Ti O₂photocurrent ambipolar composites in the past.The ultra wide band gap of Ga₂O₃4.9e V makes it photosensitive only to solar blind deep ultraviolet light with wavelength less than 280 nm,showing the advantages of no interference from ambient light and high accuracy.Higher base of conduction band and lower top of valence band indicate stronger REDOX characteristics.A small dielectric constant corresponds to a larger solid/liquid interface barrier.It has good thermal and chemical stability and can work stably in acidic or alkaline solutions.Based on the significant material advantages of Ga₂O₃in PEPS optoelectronic devices,the ambipolar photocurrent behavior of Ga₂O₃based PEC devices have been studied in this paper.The main research results are as follows:1.Growth and crystal phase regulation of porous Ga₂O₃ nanorod arrays.By increasing the contact area between the semiconductor material and the electrolyte solution to increase the rapid separation of more photo-generated carriers,and designing the nanorod arrays structure to improve the light capture capability.The spongy porous Ga OOH nanorod arrays was obtained by the traditional hydrothermal method using Ga（NO₃）₃as growth solution on the FTO substrate for 12 h at 150℃.Theα-Ga₂O₃nanorod arrays can be obtained by annealing at 450℃andβ-Ga₂O₃nanorod arrays can be obtained by annealing at 700℃.Scanning electron microscopy（SEM）results show that the average height of Ga₂O₃nanorod arrays prepared by this method is 1.72μm,the tip section is diamond shaped,and the diameter is 100～300 nm.The samples were characterized by X-ray Diffractometry（XRD）,Raman Spectroscopy（Raman）,Fourier Transform Infrared Spectroscopy（FTIR）and X-ray Photoelectron Spectroscopy（XPS）,further proving that we have prepared Ga₂O₃nanocrystals with different crystalline phases.2.Regulation of electrolyte/crystal phase Ga₂O₃ PEPS effect and its logic device.The effects of different electrolyte environments（acidic solution,neutral solution and basic solution）on PEC devices constructed byα-Ga₂O₃have been studied.It was found that in H₂SO₄solution,the device has a negative photocurrent phenomenon,but the positive photocurrent phenomenon is imperceptible.In Na₂SO₄solution,the device exhibits a constant forward photocurrent.In Na OH solution,the device exhibited obvious negative photocurrent phenomenon when the applied bias negative potential（-0.6～0 V）,and obvious positive photocurrent phenomenon when the applied bias positive potential（0～0.6 V）,showing bipolar photocurrent phenomenon as a whole.This is becauseα-Ga₂O₃has different conduction band levels in different electrolyte environments,so that the redox process of photogenerated electrons in solution is different.At the same time,the effect of Ga₂O₃PEPS can be regulated by different crystal phases.In Na OH solution,PEC devices constructed withα-Ga₂O₃show ambipolar photocurrent behavior,with ambipolar switching point at 0 V,while PEC devices constructed withβ-Ga₂O₃show constant positive photocurrent phenomenon.The difference in ambipolar behavior between the two is attributed to the fact thatα-Ga₂O₃has more oxygen vacancies and surface states at the semiconductor/electrolyte interface,and its conduction band electrons are more likely to enter the solution.Based on the ambipolar photocurrent behavior ofα-Ga₂O₃,we construct an adjustable Boolean logic gate device（OR/XOR）using 0.2 V/-0.2 V and 255 nm/310 nm light as input sources,respectively.3.Regulation ofα/βphase junction on Ga₂O₃ PEPS effect and its logic device.The switching logic gate based onα-Ga₂O₃ambipolar behavior takes advantage of the photoelectric effect of FTO,and the wavelength of the control light source is 255nm/310 nm,not all of solar blind light,which makes the working process of the device easy to be interfered by the ambient light.At the same time,the PEPS effect switch point of the device is fixed,which greatly limits the application range of Ga₂O₃based PEPS effect devices.Therefore,high qualityα/βphase junction Ga₂O₃nanorod array were prepared at 700℃by rapid thermal annealing without changing the structure of the nanorod arrays.The outer layer is coated withβ-Ga₂O₃material,and the inner is composed ofα-Ga₂O₃nanorod array.In Na OH solution,as the thickness ofβ-Ga₂O₃nanometer coating increases gradually,the PEPS switching point of the device gradually moves in the negative direction until a constant positive photocurrent phenomenon appears.This is due to there are fewer oxygen vacancies on the surface of theβ-Ga₂O₃nanorod array located in the outer layer,and the barrier generated at the solid-liquid interface is larger,which makes it difficult for electrons to enter the solution and produce negative photocurrent phenomenon.Based on the solar blind characteristics ofα/β-Ga₂O₃nanorod arrays,we fabricated pure solar-blind UV controlled adjustable Boolean logic gate devices（OR/XOR）using 0.15 V/-0.11 V and265 nm/225 nm light as input sources,respectively.In addition,a half adder and a simple four-terminal input XOR gate device are fabricated based on the adjustable PEPS effect switching point ofα/β-Ga₂O₃nanorod arrays.It provides a new research idea and direction for the application of Ga₂O₃in PEC devices..