Study On Chemical Bath Deposition And Sensitization Process Of PbSe Photoelectric Film

Infrared radiation is a form of electromagnetic radiation with wavelengths ranging between those of visible light and microwaves,and is not visible to the human eyes.In order to detect the presence and magnitude of infrared radiation,it must be converted into a signal that can be perceived by human sensory organs or technological devices,such as visible light or an electrical signal.This is achieved through the use of infrared detectors,which play a pivotal role in enabling the exploration of the infrared radiation.With the development of internet of everything（Io E）and artificial intelligence（AI）,the infrared detectors can combine with AI to achieve intelligent recognition and control,and integrate with sensor networks and cloud computing technology to acquire and analyze the real-data,greatly improving production efficiency and quality of human life.Currently,infrared detectors are widely used in various fields,such as military,security,medical,industrial,environmental monitoring,and consumer electronics.In particular,the rapid growth of infrared detectors in the civilian field has imposed new requirements on manufacturing cost,stability,compatibility with CMOS and MEMS technology,and other aspects.At room temperature,the lead selenide（PbSe）processes some advantages,such as a low direct bandgap（0.27 eV）,a large exciton Bohr radius（46 nm）,high carrier mobility and small effective mass for both electrons and holes.Hence,the PbSe film detector can maintain excellent infrared responsiveness at room temperature,especially in the mid-infrared region which has higher application value.However,the detectivity and responsivity of the domestic PbSe detectors are much lower than similar foreign products,which is attributed to the outdated preparation process,short development time and blockade of technology.Therefore,it is urgent to solve this critical problem.Within this research,the PbSe films were successfully to deposited by CBD using high concentration of ammonia（NH₃·H₂O）or potassium hydroxide（KOH）as complexing agent.The nucleation and growth mechanism and the effects of process parameters on the structures,electrical and optical properties of PbSe films were studied.At the same time,the effects of the vacuum heat treatment before sensitization,sensitization in Ar and secondary sensitization in I₂+N₂ on the structure and photoelectric properties of optimal PbSe film were also investigated.The main results are as follows:（1）The PbSe films of 60–160 nm thick were fabricated on the glass substrate by CBD using the high concentration ammonia as complexing agent,and the effects of deposition time and HF treatment time of glass substrate on structure and properties of PbSe film were investigated.With the deposition time increase from 1 h to 5 h,the grain size decreased firstly and then increased,and the spherical particles transformed to cubic particles,due to the transformation of deposition mechanism.It was demonstrated that the 10%HF treatment can effectively promote the thickness and grain size of PbSe film.The optical sample（HF treated for 10min and deposited for 4 h）possessed an optical band gap of 1.36 eV,carrier concentration of 7.48×10¹⁷/cm³,carrier mobility of 34.9 cm²/V·s and resistivity of 0.238Ω·cm.（2）The effects of deposition time（2-5 h）and deposition temperature（65-75℃）on structure and properties of PbSe films deposited by CBD using KOH as complexing agent were investigated.With the increase of the deposition time,the thickness of the PbSe film gradually increased,the Pb/Se ratio approached to 1,the carrier mobility increased and the optical band gap decreased.The increase of deposition temperature can accelerate the transformation of deposition mechanism from cluster mechanism to ion-by-ion mechanism,resulting in the increase of grain size,thickness and carrier mobility of PbSe film,and the decrease of Pb/Se ratio and optical band gap.The optical sample deposited at 75℃ for 5 h possessed the grain size of 55.3 nm,thickness of 1.65μm and optical band gap of 0.31 eV.（3）The porous PbSe film with a grain size of～0.5μm was firstly transformed from flaky pastry-like plumbonacrite(Pb₁₀O（OH）₆（CO₃）₆)precursor film by ion exchange process,where the precursor film was prepared by a low-toxicity CBD process.The variations of phase composition,surface morphology,and binding state of main surface elements,as well as the optical properties of films with immersion time were mainly investigated.The experimental results showed that the flaky pastry-like Pb₁₀O（OH）₆（CO₃）₆ film can be fully converted to cubic PbSe film as the immersion time is over 1.5 h,and the grain size of PbSe was further increased with the immersion time prolonging from 1.5 to 2.5 h,improving optical properties of PbSe films in the mid-infrared region.It was demonstrated that the optical absorption of the composite PbSe film combined dense and porous PbSe film was enhanced by 60%compared with the dense PbSe film,while the optical reflection was decreased by 55%,in the wavelength range from 450 to 5000 nm.（4）The vacuum heat treatment before sensitization of PbSe film can not only further develop the grains and increase the grain size in the recrystallization process,but also reduce defects,increase carrier concentration and mobility.The PbSe films before and after vacuum heat treatment were sensitized in I₂+O₂ atmosphere,showing that the best sensitization time of the PbSe film without heat treatment was 30 min,and the highest detectability（D*） and responsivity（R）were 8.83×10⁷ Jones and 0.455 m A/W respectively;The optimum sensitization time of the heat-treated PbSe thin film was 1 h,and the highest D* and R were1.77×10⁸ Jones and 6.58 m A/W,respectively.（5）In this work,the PbSe film was firstly sensitized at high temperatures（773-848 K）in argon atmosphere.The optimal PbSe film sensitized at 823 K processes the average grain size of～520 nm,carrier concentration of 9.9×10¹⁶ cm^-3,carrier mobility of 13.9 cm²/V·s,and D* of 2.31×10⁹ Jones for 1550 nm laser radiation（active area is 1×1 mm² and basic voltage is 50 V）.In particular,the optimized PbSe film displayed high reproducibility,fast response and excellent high frequency stability.A potential barrier model was proposed to explain the highest optoelectronic performance,where the evaporation of the Se at grain boundaries can generate n-type semiconductor area and the diffusion of O into PbSe grain lattice contributes to inhibit the recombination of carriers.（6）The PbSe film sensitized by Ar at high temperature was secondary sensitized in I₂+N₂ at 613 K.The first-principles calculation and potential barrier model were proposed to explain the improvement of optoelectronic performance after secondary sensitization.After secondary sensitization,the grain size and dark current decreased,while D^* increased significantly.When the volume of I₂+N₂ was 2 L（the partial pressure is 135.21 Pa and standard atmospheric pressure,respectively）,the carrier concentration and carrier mobility of sensitized PbSe were 1.68×10¹⁴cm^-3and 2.37 cm²/V·s respectively.The D^* and R of the PbSe film were 1.12×10⁹ Jones and 25.1 m A/W（active area is 2×2 mm² and basic voltage is 30 V）,respectively,which was about 64.37%and 132.8% of the D^* and R of a similar PbSe infrared detector from Trinamix.