Time and temperature dependent breakdown characteristics of ZnS:Mn films obtained by rf-magnetron sputtering

Breakdown delay times (t_del) for films of managanese-doped zinc sulfide (ZnS:Mn) were measured in the range 10^–6–10^–1 s. The maximum value was t_del=10^–3–10^–2 s. The electrical strength (E_br) was found to increase as the voltage pulse duration was reduced, the more so the thinner the ZnS:Mn film. The temperature dependence of E_br exhibited a weak reduction in E_br as the temperature was raised to roughly 80°C and a sharp reduction in E_br for T>130°C. A maximum in E_br was observed at T130°C which is presumably explained by a structural modification of the ZnS:Mn film. The experimental results obtained are explained in terms of a combined electronic and thermal breakdown mechanism.State Academy of Control Systems and Radioelectronics, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 3–6, April, 1994.     

Electrical breakdown of dysprosium oxide films

The principal laws governing the electrical breakdown of dysprosium oxide films in silicon metal — insulator — semiconductor structures are investigated. The dependence of the breakdown field E_br on the rise rate of the voltage on the structure K_v, the temperature, the material and area of the electrode, and the humidity of the environment is studied. The dependence of the time delay of breakdown on the amplitude of a rectangular voltage pulse is investigated. It is established that the breakdown field increases linearly with log K_v for all insulator thicknesses, and the saturation of E_br is observed at K_v>10⁵ V/sec. It is found that E_br does not depend on the electrode material and decreases as the area of the electrode or the temperature is increased. The maximum breakdown field is determined: E _br ^max =14 MV/cm. The mechanism of the precursory stage of breakdown, i.e., the period of transient buildup of critical charge in the insulator, is discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 95–101, August, 1995.     

Temperature dependence of the dielectric strength of zinc sulfide films

The temperature dependence of the dielectric strength E_pn of ZnS:Mn films produced by high-frequency magnetron sputtering was investigated in the range T=20–200°C. It is shown that processes associated with removal of adsorbed water from the ZnS:Mn films are responsible for the maximum on the E_pn=f(T) curve. Data on the temperature dependence of the capacitance and loss-angle are given for thin-film systems based on ZnS:Mn. Tomsk State Academy of Control Systems and Radioelectronics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 91–94, June, 1966.     

The Kinetics of Destruction of Piezoceramics under the Electric-Field Action

The electrical durability (time since the application of a constant voltage up to the breakdown) as a function of the electric field strength E and the breakdown field intensity E _br as a function of the rate of rise of the electric field strength E are measured on ferroelectric-piezoceramic disks. It is concluded that the destruction of ferroelectric-piezoceramics has a kinetic character.     

Temperature accelerated dielectric breakdown of PECVD low-k carbon doped silicon dioxide dielectric thin films

The dielectric breakdown strength of carbon doped silicon dioxide thin films with thickness d from 32 nm to 153 nm is determined at 25 °C, 50 °C, 100 °C, 150 °C and 200 °C, using I–V measurements with metal-insulator-semiconductor (MIS) structures. It is found that the dielectric breakdown strength, E_B, decreases with increasing temperature for a given film thickness. In addition, a film thickness dependence of breakdown is also observed, which is argued to show an inverse relation to thickness d in the form of E_B∝(d-d_c)^-n. The exponential parameter n and critical thickness limit d_c also exhibit temperature dependent behavior, suggesting a temperature accelerated electron trapping process. The activation energy for the temperature acceleration was shown to be thickness dependent, indicating a thickness dependent conduction mechanism. It is thereafter demonstrated that for relatively thick films (thickness >50 nm), the conduction mechanism is Schottky emission. For relatively thin films (thickness <50 nm), the Schottky conduction mechanism was obeyed at low field region while FN tunnelling was observed as a prevail one in the high field region. PACS 73.40.Qv     

Mechanism of photoluminescence excitation of Mn<Superscript>2+</Superscript> ions in ZnS crystals

The mechanisms of photoluminescence excitation of Mn²⁺ ions in ZnS crystals have been investigated on the basis of complex analysis of the temperature dependences of the photoluminescence and photoluminescence-excitation spectra of ZnS:Mn crystals. The activation energy of a manganese luminescence center was estimated at E_a = 0.17 ± 0.05 eV. It is shown that E_a represents an energy band with a width ΔE_a = 0.1 eV, within which a manganese luminescence center can experience radiationless recombination. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 6, pp. 788–793, November–December, 2005.     

Breakdown of thin films “cured” with tantalum oxide

Studies have been made of the temperature and time characteristics of breakdown in a thin Ta₂O₅ film produced by reactive evaporation with subsequent curing of the defect sites, with aluminum electrodes. The data obtained are explained from the viewpoint of classical thermal breakdown.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 120–124, April, 1977.In conclusion, we express our indebtedness to N. S. Mukhachev and N. R. Spiridonov for their assistance in measuring the temperature dependence of E_br.     

Chemical bath-deposited ZnS thin films: Preparation and characterization

Chemical bath deposition of ZnS thin films from NH₃/SC(NH₂)₂/ZnSO₄ solutions has been studied. The effect of various process parameters on the growth and the film quality are presented. The influence on the growth rate of solution composition and the structural, optical properties of the ZnS thin films deposited by this method have been studied. The XRF analysis confirmed that volume of oxygen of the as-deposited film is very high. The XRD analysis of as-deposited films shows that the films are cubic ZnS structure. The XRD analysis of annealed films shows the annealed films are cubic ZnS and ZnO mixture structure. Those results confirmed that the as-deposited films have amorphous Zn(OH)₂. SEM studies of the ZnS thin films grown on various growth phases show that ZnS film formed in the none-film phase is discontinuous. ZnS film formed in quasi-linear phase shows a compact and a granular structure with the grain size about 100 nm. There are adsorbed particles on films formed in the saturation phase. Transmission measurement shows that an optical transmittance is about 90% when the wavelength over 500 nm. The band gap (E_g) value of the deposited film is about 3.51 eV.     

SrS:Ce/ZnS:Mn-A di-band phosphor for near-UV and blue LED-converted white-light emitting diodes

The SrS:Ce/ZnS:Mn phosphor blends with various combination viz 75:25, 50:50 and 25:75 were assign to generate the white-light emission using near-UV and blue-light emitting diodes (LED) as an excitation source. The SrS:Ce exhibits strong absorption at 427 nm and the corresponding intense emission occurs at 480 and 540 nm due to electron transition from 5d(²D)−4f(²F_5/2, _7/2) of Ce³⁺ ion as a result of spin-orbit coupling. The ZnS:Mn excited under same wavelength shows broad emission band with λ_max=582 nm originates due to 3d (⁴G−⁶S) level of Mn²⁺. Photoluminescence studies of phosphor blend excited using near-UV to blue light confirms the emitted radiation varies from cool to warm white light in the range 430-600 nm, applicable to LED lightings. The CIE chromaticity coordinate values measured using SrS:Ce/ZnS:Mn phosphor blend-coated 430 nm LED pumped phosphors in the ratio 75:25, 50:50 and 25:75 are found to be (0.235, 0.125), (0.280, 0.190) and (0.285, 0.250), respectively.     

Red electroluminescent process excited by hot holes in SrGa2S4:Ce, Mn thin film

This paper reports the first observation of red electroluminescence (EL) in SrGa₂S₄:Ce, Mn thin film. The EL spectrum consists of single broad emission band having a peak wavelength of 665 nm. The dominant EL decay time was 31 μs. The relationship between the applied voltage and the EL waveform was measured in single insulating thin film electroluminescent (TFEL) devices. An asymmetric EL waveform was observed in SrGa₂S₄:Ce, Mn TFEL devices under a rectangular applied voltage. The polarity of the EL waveform in these devices was different from the waveform in manganese-activated zinc sulfide ZnS:Mn devices. This indicates that hot holes excite the Mn²⁺ ions to cause the red EL.     

Synthesis of robust water-soluble ZnS:Mn/SiO2 core/shell nanoparticles

Water-soluble Mn doped ZnS (ZnS:Mn) nanocrystals synthesized by using 3-mercaptopropionic acid (MPA) as stabilizer were homogeneously coated with a dense silica shell through a multi-step procedure. First, 3-mercaptopropyl triethoxy silane (MPS) was used to replace MPA on the particle surface to form a vitreophilic layer for further silica deposition under optimal experimental conditions. Then a two-step silica deposition was performed to form the final water-soluble ZnS:Mn/SiO₂ core/shell nanoparticles. The as-prepared core/shell nanoparticles show little change in fluorescence intensity in a wide range of pH value.     

X-Ray induced enhancement effect in electroluminescent zinc sulphides

Enhancement effect in electroluminescent emission from ZnS∶Cu, Cl and ZnS∶Cu, Mn, Cl luminophors under the concurrent action of sinusoidal electric field and x-radiation has been investigated. Variation of the enhancement ratioR=B _E+R/B_E+B_R whereB _E+R =Light output when both electric field and x-radiation are operative;B _E=Electroluminescent output;B _R=Photoluminescent output with frequency and voltage of the applied A.C. field and with x-ray intensity has been studied. A non-linear behaviour of the enhancement with voltage and x-ray intensity has been found, which is similar to that observed in the case of ultraviolet stimulated electroluminescent emission. R _max in both the species studied, is always found to be less than 4/3 in each case.     

Combustion synthesis and photoluminescence of ZnS:Mn particles

An efficient process based on a solid-state combustion technique has been developed to produce high crystalline and micrometer sized particles of ZnS:Mn⁺² phosphor with sphalerite structure. The precursor mixture of 0.915Zn+S+0.05Mn+0.035ZnCl₂+kNaCl composition (where k is the mole number of NaCl) was combusted under the argon atmosphere followed by post-heat treatment procedure at 700 °C. It was shown that photoluminescence (PL) intensity of ZnS sample can be easily controlled through adjusting NaCl concentration. In the optimized reaction conditions ZnS samples have showed PL intensity almost comparable to that of a commercial one, despite the relatively low purity of precursor materials used. Many interesting phenomena such as high luminescent efficiency, pure cubic ZnS formation after the post-heat treatment and strong influence of Cl⁻ ion on PL intensity have been observed and discussed.     

Photophysical and photoluminescence properties of co-activated ZnS:Cu,Mn phosphors

ZnS:Cu,Mn phosphors were prepared by conventional solid state reaction with the aid of NaCl-MgCl₂ flux at 900 °C. The samples were characterized by X-ray powder diffraction, UV-vis absorbance spectra and photoluminescence spectra. All samples possess cubic structure. Cu has a much stronger effect on the absorption property of ZnS than Mn. Incorporation of Mn into ZnS host only slightly enhances the light absorption, while addition of Cu remarkably increases the ability of absorption due to ground state Cu⁺ absorption. The emission spectra of the ZnS:Cu,Mn phosphors consist of three bands centered at about 452, 520 and 580 nm, respectively. Introduction of Mn significantly quenches the green luminescence of ZnS:Cu. The excitation energy absorbed by Cu is efficiently transferred to Mn activators non-radiatively and the Mn luminescence can be sensitized by Cu behaving as a sensitizer (energy donor).     

Luminescent thin ZnS : Mn films

Photo-, cathodo-, β-luminescence spectra of the ZnS : Mn films and electroluminescence spectra of highly efficient d.c. diodes with SnO_x-ZnS : Mn-Cu_xS-ZnS : Mn-Al structure have been investigated. Strong dependence of intensity and structure of the luminescence band on applied voltage has been found. Results suggest that collision cannot be the only process causing luminescence of the d.c. diodes investigated. The yield of Mn luminescence in ZnS is found to be strongly electric field-dependent.     

AlGaN/GaN场板结构高电子迁移率晶体管的场板尺寸优化分析

对不同场板尺寸的AlGaN/GaN 场板结构高电子迁移率晶体管进行了研究,建立简化模型分析场板长度对沟道电场分布的影响.结果表明,调整钝化层厚度和场板长度都可以调制沟道电场的分布形状,当场板长度较小时,随着长度的增大器件击穿电压随之增加,而当长度增大到一定程度后器件击穿电压不再增加.通过优化场板长度,器件击穿电压提高了64%,且实验结果与模拟结果相符. 关键词： AlGaN/GaN 击穿电压 场板长度     

MOCVD技术制备的ZnS:Mn电致发光薄膜结晶性及Mn2+分布

本文报导了用MOCVD技术制备的ZnS:Mn电致发光薄膜为立方晶相,结晶取向性好,颗粒大。从高倍率的扫描电镜拍摄的照片观察到薄膜的表面平滑。SIMS测量表明Mn2+在ZnS薄膜纵向分布均匀,但在两侧有起伏,可能的原因是在生长的初终阶段流量的突变使化合物的化学计量比偏离而产生位错,引起原子的局部堆积,并且由于初终阶段ZnS:Mn生长的衬底不同使原子堆积层厚度不同。     

Fast two-step microwave-activated synthesis of Mn doped ZnS nanocrystals: Comparison of the luminescence and doping process with thermochemical approach

In this work we report a fast two-step microwave activated synthesis of the ZnS:Mn nanocrystals. Zn(NO₃)₂ and Na₂S₂O₃ were used as the precursors and Mn(NO₃)₂ was employed as the source of the impurity. The aqueous synthesis was based on the heat sensitivity of Na₂S₂O₃, which releases some S species on heating. Consequently, the reaction was well activated under microwave irradiation resulting in formation of ZnS:Mn nanocrystals. Thioglycerol (TG) was also used as the capping agent and the catalyst of the reaction. The synthesis process was done in two steps, i.e. 1 min irradiation without TG and then injection of TG and continuation of irradiation. ZnS:Mn nanocrystals were quickly formed in the solution and luminescence was emerged in a few minutes. Optical transmission spectroscopy and X-ray diffraction analysis demonstrated formation of ZnS:Mn nanocrystals with a cubic crystalline structure and 3.0 nm average size. Photoluminescence measurements also showed some spectra with a Mn related peak located at 585 nm. The mentioned peak corresponds to ⁴T₁→⁶A₁ transition in Mn impurities and revealed the effective incorporation of Mn ions inside the nanocrystals. Evolution of the PL was also investigated and showed an increase in longer irradiation times. A qualitative model is also used to justify the necessity of using a two-step method as well as the PL emergence and increase in longer irradiation times. The model is based on separation between the nucleation and growth steps and significant role of TG in these stages. Finally, we present a comparison between the results of microwave activated method and two-step thermochemical approach. Although the synthesis time in microwave activated method was considerably short (less than 5 min), the luminescence properties were quite comparable with long time thermochemical approach. The doping process was also investigated for different Mn/Zn concentrations in two approaches. The results demonstrated that the doping occurred more effectively in the microwave activated synthesis.     

Luminescence enhancement of Mn doped ZnS nanocrystals passivated with zinc hydroxide

Mn-doped ZnS nanocrystals prepared by solvothermal method have been successfully coated with different thicknesses of Zn(OH)₂ shells through precipitation reaction. The impact of Zn(OH)₂ shells on luminescent properties of the ZnS:Mn nanocrystals was investigated. X-ray diffraction (XRD) measurements showed that the ZnS:Mn nanocrystals have cubic zinc blende structure. The morphology of nanocrystals is spherical shape measured by transmission electron microscopy (TEM). ZnS:Mn/Zn(OH)₂ core/shell nanocrystals exhibited much improved luminescent properties than those of unpassivated ZnS:Mn nanocrystals. The luminescence enhancement was observed with the Zn(OH)₂ shell thickening by photoluminescence (PL) spectra at room temperature and the luminescence lifetime of transition from ⁴T₁ to ⁶A₁ of Mn²⁺ ions was also prolonged. This result was led by the effective, robust passivation of ZnS surface states by the Zn(OH)₂ shells, which consequently suppressed nonradiative recombination transitions.     

Mechanoluminescence and thermoluminescence of Mn doped ZnS nanocrystals

This paper reports the synthesis of ZnS:Mn nanocrystals by the chemical route in which mercaptoethanol was used as the capping agent. The particle size of such nanocrystals was measured using XRD and TEM patterns and was found to be in between 3and 5 nm. It was found that the peak position of TL glow curve and the TL intensity of ZnS:Mn nanoparticles increases as the particle size is decreased. The isothermal decay technique is used to determine the trap-depth. The stability of the charge carriers in the traps increase with the decrease in size of the nanoparticles. The higher stability may be attributed to the higher surface/volume ratio and also to the increase in the trap-depth with decreasing particle size. When a ZnS:Mn nanocrystal is deformed the peak intensity I_m increases linearly with the increasing height of the load. After I_m, initially the ML intensity decreases at a fast rate, and later on it decreases at a slow rate. The ML in ZnS:Mn nanocrystals can be understood on the basis of the piezoelectrically induced electron detrapping model.