| In recent years,due to its low background noise and high sensitivity,the solar-blind photodetector has played an irreplaceable role in optoelectronic technologies.Ga2O3,a new wide bandgap oxide semiconductor material having a band gap of 4.45.3 eV,is highly transparent in the visible region while extremely sensitive to ultraviolet light with a high absorption coefficient in the ultraviolet band.Meanwhile,Ga2O3 also holds a series of advantages such as excellent thermal and chemical stability,being easy to prepare,low cost,etc.,which makes it an ideal material for solar-blind photodetectors.However,up to now,Ga2O3-based solar-blind photodetection is still in the laboratory-research stage due to some problems that need to be solved,for instance,the long response and decay time,and the low dark current accompanied by the low photo-responsivity.In this regard,in this thesis,we aim to prepare and optimize the device with fast response and high photo-responsivity by regulating the properties of the Ga2O3 thin film materials.In this thesis,Ga2O3 thin films with different crystal states and crystal phase structure were prepared on a-Al2O3?112?0?and m-Al2O3?303?0?substrates by the pulsed laser deposition?PLD?technology at different temperatures and oxygen pressures.The main research results are as follows:?1?The PLD technology was used to prepare Ga2O3thin films at different substrate temperatures.Firstly,the effect of substrate temperature on the crystallization characteristics of the thin films was studied.Then the influence of the crystallization characteristics of Ga2O3 thin films on the response behavior of the devices was analyzed.As the substrate temperature increases,the Ga2O3 thin film changes from amorphous to crystalline.For a-Al2O3?112?0?and m-Al2O3?303?0?substrates,the critical crystallization temperature of Ga2O3 films are 450°C and550°C,respectively.It has been found that the photodetector by using this critical crystalline Ga2O3 film has a very high responsivity.Since the critical crystalline Ga2O3 thin film is composed of amorphous and dominated nanocrystals,the internal gain mechanism is attributed to the tunneling mechanism inside the film and high density interfacial states.?2?The critical crystal state Ga2O3 film was further optimized by changing the growth oxygen pressure in order to regulate the oxygen vacancy concentration in the film,decrease the dark current and improve the device responsivity.The results show that when the oxygen pressure is 0.02 Pa and 4.0 Pa,the dark current of the device is as low as 10-910-10 A.Meanwhile,the responsive speed was the fast,however,the too low or too high oxygen pressure would cause the device's photo-responsivity to drop sharply to 10-2 A/W.When the oxygen pressure is among 0.52.0 Pa,it is easy to obtain a high responsivity.A maximum responsivity of 403.9 A/W was achieved as the oxygen pressure is 2.0 Pa.?3?The Ga2O3 thin films and devices with different crystal phase structures were prepared by adjusting the growth oxygen pressure at a high temperature of 650°C.The effects of crystal phase structure on the response characteristics of the devices were investigated.When the oxygen pressure is below 1.0 Pa,the Ga2O3 film has a mixed phase structure in which the?phase and the?phase coexist,and the internal gain in the film due to the high density interfacial states endows the device an increased responsivity.At the same time,the crystalline Ga2O3 film device exhibit a dark current as low as 10-710-10 A,which can be ascribed to the low carrier concentration and strong interfacial scattering effect at the grain boundaries.The high temperature is favorable for forming chemical bonds between the Ga and O atoms,and therefore the oxygen vacancy concentration is significantly reduced,yielding fast respond rates in all the devices. |
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