Preparation Of The Alloy Semiconductor Epitaxial Film Based On SnO₂ And Its Application In Deep Ultraviolet Detection

SnO₂is a typical direct band-gap semiconductor material and its band-gap is 3.6 e V,so it has a high transmittance in the visible light range.Moreover,compared with other wide band-gap semiconductor materials,the SnO₂has many advantages,such as more stable physical and chemical properties,higher mechanical strength and greater electronic mobility.In addition,the SnO₂thin films rely on the special electrical and optical properties that have been widely used in many fields such as transparent conductive thin films,thin film based gas sensors,short-wave photoelectric devices and so on.Especially in recent years,the increasing demand for short-wave photoelectric devices has greatly promoted the development of ultraviolet light-emitting diodes and ultraviolet photo detectors,and also made people take more and more attention on the SnO₂.For example,many new type SnO₂-based ultraviolet detectors have been successfully fabricated in the ultraviolet detection field.However,there are some obvious performance short comings of these SnO₂-based ultraviolet detectors.Firstly,these detectors are still unable to meet the needs of deep ultraviolet wavelength detection.Secondly,the dark current of these detectors are very large,so it takes serious negative impact on the detection rate and sensitivity of light response.Furthermore,the light response speed of these SnO₂-based detectors is slower and the response time is very longer.The key to the further development of SnO₂-based ultraviolet detectors is whether these problems can be solved successfully.Therefore,the research on this topic focuses on these problems and hopes to find a perfect solution to solve them successfully.In order to fabricate SnO₂-based ultraviolet detectors with excellent performances in all aspects,we propose a method of doping pure SnO₂to construct multi component alloy semiconductors and expect this way could increase the band gap of pure SnO₂to meet the band-gap requirements of deep ultraviolet detectors.Then we prepared a series of SnO₂and Zr_xSn_1-xO₂and Hf_xSn_1-xO₂epitaxial thin films with different doping content-based by pulsed laser deposition.Subsequently,we utilize these annealed epitaxial thin films to fabricate the MSM structure deep ultraviolet photo detectors.In addition,the performance of the detectors was systematically tested and characterized.Generally speaking,our work of the research mainly consists of these following aspects:(1)Firstly,the pure SnO₂and a series of Zr_xSn_1-xO₂and Hf_xSn_1-xO₂for sputtering ceramic targets with different doping content were sintered.Then SnO₂,Zr_xSn_1-xO₂and Hf_xSn_1-xO₂epitaxial thin films were successfully prepared on C-plane sapphire by pulsed laser deposition at 700^oC and under the growth condition of the oxygen pressure is 3Pa.The results show that for Zr_xSn_1-xO₂ternary alloy system,pure tin-rich phase films can be obtained when the solid solubility of zirconium is less than 36%,while for Hf_xSn_1-xO₂ternary alloy system,pure tin-rich phase films can be obtained when the solid solubility of hafnium is less than43%,and the average FWHM of two different types of tin-rich phase ternary alloy semiconductor epitaxial films is only about 0.05^o.The results show that the crystal plane is flat and the orientation is good.In addition,the?-scan results further show that the epitaxial relationship between SnO₂and C-plane sapphire is SnO₂(100)||Al₂O₃(0001),SnO₂[010]||Al₂O₃[11-20].The optical and electrical measurements show that the optical band gaps of the two alloy semiconductor films increase with the increase of doping content,and the resistance also increases rapidly with the increase of doping amount.(2)SnO₂and a series of Zr_xSn_1-xO₂and Hf_xSn_1-xO₂thin films with different doping contents were annealed in a tube furnace with high purity oxygen for two hours,then cooled slowly and naturally.After anneal,these thin films were systematically tested and characterized.It was found that the Zr_xSn_1-xO₂and Hf_xSn_1-xO₂ternary alloy semiconductor thin films with pure tin-rich phase still exist after anneal.The film still has no phase separation and keeps a single tin-rich phase structure,which indicates that the tin-rich phase structure of the two ternary alloys is equilibrium structure and can exist stably.Moreover,the optical and electrical measurements show that the optical band-gap of the films hardly changes before and after annealing,while the resistance of pure SnO₂and low doping concentration Zr_xSn_1-xO₂and Hf_xSn_1-xO₂films increases significantly after annealing.(3)MSM-structured ultraviolet detectors were fabricated by vacuum evaporation on annealed SnO₂,Zr_xSn_1-xO₂and Hf_xSn_1-xO₂thin films coated with high purity aluminium parallel electrodes with a spacing of 10 microns.The performance of the detectors was systematically tested and characterized.It was found that the dark current of pure SnO₂-based ultraviolet detector was very large,which makes the light gain ratio smaller and also make the persistent photoconductivity phenomenon obvious that results in a very slow light response speed.The performance of the Zr_xSn_1-xO₂and Hf_xSn_1-xO₂thin film-based ultraviolet detectors with lower doping content has been significantly improved,but the dark current of the devices is still large.At the same time,the dark current of the multi phase-coexistencece Zr_xSn_1-xO₂and Hf_xSn_1-xO₂thin film-based detectors with high doping content is very small,but the optical gain is not obvious,so there is a close relationship between the performance of the device and the doping concentration.For the Zr_xSn_1-xO₂ternary alloy system,the comprehensive performance of the Zr_0.36Sn_0.64O₂thin film based detectoris excellent.The dark current is about 0.8 p A at 20 volt bias voltage,the light-dark ratio is thousands of times,the light response time is about 20 ms,the peak responsibility is 6.02A/W under the 270nmdepth ultraviolet radiation;For the Hf_xSn_1-xO₂ternary alloy system,the Hf_0.38Sn_0.62O₂film-based detector has a excellent performance.The dark current is about 0.2 p A at the 20 volts bias voltage,and the light-dark current ratio is more than one thousand times,the light wave rejection ratio is more than 4,000 times,the response time is several tens of milliseconds,the peak response is 0.44 A/W,and the cutoff wavelength is about 290 nm.