Electron ejection processes at insulator-semiconductor interfaces in ACTFEL display devices

Luminance, conduction current and threshold voltage of ZnS:Mn ac thin film electroluminescent display devices were measured as functions of device temperature (10 K-300 K) and risetime of the excitation voltage pulse (2 /spl mu/s-50 /spl mu/s). Results provided insight into the electron ejection mechanism at the insulator-phosphor interfaces. It was found that the distribution of interface state electrons at the beginning of the excitation voltage pulse varied substantially with device temperature. Pure tunneling is thought to be the dominant electron ejection mechanism at the beginning of the voltage pulse while phonon-assisted tunneling is responsible for altering the interface electron distribution during the interval between the pulses. A delay of several microseconds was observed in the build up of the transferred charge. It is attributed to the relatively small population of electrons available at the insulator-phosphor interface.<>     

A new low-voltage Si-compatible electroluminescent device

Thin film direct-current electroluminescent devices with ZnS:Mn as the active light-emitting layer have been fabricated on Si wafers. The devices incorporate a high-efficiency electron injector layer capable of passing high current densities (>10^-2A cm^-2dc) through the active layer. A useful luminance of 78 fL has been achieved at 48V, significantly lower voltage than for conventional ac thin film or dc powder electroluminescent devices. The structure also includes a potential energy step at the interface between SiO2and ZnS due to the difference in electron affinities which offers the possibility of hot electron injection into the active layer. The unique combination of efficient cathode emission and hot injection possible in these devices suggests that a solid state analogue of the cathode ray tube may be realizable.     

Thin film ZnS:Mn AC-electroluminescent device with a Ge layer

A new thin film electroluminescent device (indium tin oxide ITO-Y2O3- (ZnS:Mn)- Ge-Y2O3- Al) (type II) has been prepared, and is compared to the conventional structure (ITO- Y2O3- (ZnS:Mn) - Y2O3- Al) (type I). The optically active conduction charge is measured for both types in order to ascertain the effect of the Ge layer which is believed to act as a carrier injection source. We found that in this new structure, compared to type I, the amount of the conduction charge is larger, but the maximum luminance value is lowered by a factor of 2 to 3 and the breakdown voltage is slightly lowered. These results can be explained from the experimental observation that remarkable assymmetry of luminescence waveforms is present in the type II device, i.e., the Ge layer influences the electric field near the ZnS-Ge interface. The appearance of the type II display is improved compared to type I.     

Dependence of electroluminescence efficiency and memory effect on Mn concentration in ZnS:Mn ACTEL devices

We have studied experimentally the dependence of the electroluminescence efficiency and the memory effect on the Mn concentration in ZnS:Mn ac thin-film electroluminescence (ACTEL) devices. With other device parameters kept approximately constant, we find that both luminous efficiency and memory loop width (expressed as a percentage of threshold voltage) exhibit a maximum as a function of Mn concentration. In addition, the memory loop width was found to depend on the ZnS film thickness. Under 1-kHz sine-wave excitation, the peak luminous efficiency in these devices was ∼0.5 l/W and occurred at ∼0.2-wt % Mn, while the peak memory loop width was ∼11 percent of the threshold voltage and occurred at ∼1.1-wt % Mn. The luminous efficiency and memory loop width were found to depend on the frequency and waveform of the excitation. The optimum Mn concentration chosen far a ZnS :Mn memory device depends on a compromise between a high luminous efficiency and a wide memory loop width. A key new result is that the average threshold electric field for electroluminescence increases logarithmically with Mn concentration beyond ∼0.2-wt % Mn. The above results suggest that the Mn doping is modifying the carrier-conduction process in the ZnS:Mn thin film.     

Distribution of mobile ions in thin insulator films at the insulator-semiconductor interface

The influence of a semiconductor on the mobile ion distribution in insulator thin films at the insulator-semiconductor interface was considered. The degree of ion localization at the interface under the field effect in the film was calculated. The threshold of the ion delocalization with a decrease in the voltage applied to the structure was determined. The relation between the delocalization thresholds and ion current peaks in dynamic current-voltage characteristics of the system is discussed.     

A dual color basis tunable color EL device employing ZnS:Tb,F/ZnS:Mn stacked phosphor layers with color filters

A tunable color thin-film electroluminescent (EL) device having a stacked structure of ZnS:Tb, F/ZnS:Mn with red and green colored filters was developed. The obtained red and green emissions have high enough luminance to be considered as a practical tunable color display panel, though the color tone of the green emission approaches yellow-green. It was confirmed that varying the color between red and green can be easily done by changing the filters and applied voltage. This device should be useful for a wide variety of applications in such fields as active information display systems     

用MOCVD方法制备ZnS：Mn交流薄膜电致发光显示器

用ＭＯＣＶＤ方法制备ＺｎＳ：Ｍｎ交流薄膜电致发光显示器赵丽娟，钟国柱，杨宝钧，郑陈玮，赵国璋（中国科学院长春物理研究所１３００２１）（中国科学院激发态物理开放实验室）Ｚｎ：ＭｎＡｌｔｅｒｎａｔｉｖｅＣｕｒｒｅｎｔＴｈｉｎＦｉｌｍＥｌｅｃｔｒｏｌｕｍｉ...     

A novel TFEL device using a high-dielectric-constant multilayer ceramic substrate

A novel composite-structure ac EL device using thin films and a ceramic substrate has been developed. A light-emitting thin film (ZnS:Mn) and ITO electrodes are deposited on a multilayer ceramic substrate consisting of a very high-dielectric ceramic insulating layer (εs∼ 10⁴), internal printed electrodes, and a ceramic base plate. This device features low operating voltage (40-80 V), breakdown-failure-free operation, and high legibility.     

量子点电致发光器件发光层能级变化与驱动电压的关系研究

以量子点电致发光器件(QLED)中能级分布和载流子浓度的关系为理论基础,研究了QLED发光层能级变化与驱动电压的关系,建立了数学模型.以CdSe/ZnS核壳结构量子点为发光层,计算了器件正常发光时的阈值电压,分析了电流密度与量子点中电子准费米能级与空穴准费米能级之差的关系.结果表明,当驱动电压大于9.8V时,CdSe/ZnS中电子的准费米能级与空穴的准费米能级之差大于1.03 eV,量子点电致发光器件正常发光;理论模型证实由于电子在发光层与电子传输层界面的大量积聚,导致淬灭发生,降低发光效率.     

Monolithic thin-film photoconductor—AC EL structure with extrinsic memory by optical coupling

A novel memory ZnS:Mn ac thin-film EL device is described. The deposition of a photoconducting thin film of amorphous silicon on a conventional EL layer stack induces a hystereticL-Vcharacteristic. Operating characteristics are discussed. Outstanding features are a typical memory margin of 9V peak and electrical switching times (ON and OFF) shorter than 2 ms under 1-kHz CW excitation.     

Analysis of forward current-voltage characteristics of nonideal Ti/4H-SiC Schottky barriers

Forward current-voltage characteristics of nonideal Ti/4H-SiC Schottky contacts with an ideality factor n = 1.1–1.2 in the exponential portion of the characteristics have been analyzed. The nonideality was considered to be a result of the formation of a thin dielectric layer between the deposited titanium layer and 4H-SiC. The following electrical parameters of the contacts were determined from experimental current-voltage characteristics: energy barrier height, thickness of the intermediate dielectric layer, and energy distribution of the density of states at the insulator-semiconductor interface.     

Annealing and light effect on optical and electrical properties of ZnS thin films grown with the SILAR method

Zinc sulphide (ZnS) thin films were grown on glass substrates by the Successive Ionic Layer Adsorption and Reaction (SILAR) technique at room temperature and ambient pressure. Surface morphologies of grown films were characterized using scanning electron microscopy (SEM). The crystal structure and crystal size of the thin films were characterized by the X-ray diffraction (XRD) method and found that the films exhibit polycrystalline characterization. The optical absorption measurements were done as a function of the temperature at 10–320 K temperature range. Using absorption measurements, the band gap energies were calculated at 10 and 320 K, as 3.83 and 3.72 eV, respectively. The annealing temperature effect on optical band gap and the light effect on the electrical properties of ZnS thin films were investigated and it was found that the current increased with increasing light intensity. The annealed films were found have more resistance than the as-grown film.     

用XPS法研究硫化锌薄膜

运用ＸＰＳ法研究ＺｎＳ：Ｃｕ，Ｃｌ，Ｅｒ薄膜器件的界面态及所掺激活剂的纵向分布，认为氧吸附形成的ＺｎＳ薄膜的表面构态是产生薄膜界面态和界面陷阱能级的主要原因，对研究薄膜器件的激发过程有参考意义。     

Effect of Si nanoparticles on electronic transport mechanisms in P-doped silicon-rich silicon nitride/c-Si heterojunction devices

We successfully fabricated hetero-junction (H-J) devices from P-doped silicon-rich SiN_x embedded with Si nanoparticles on a p-type crystalline Si substrate at low temperature. High-resolution transmission electron microscopy (HRTEM) analysis indicates that the thin films contain nano-crystallites. The H-J devices showed a good rectification ratio at room temperature. Three distinct regions of temperature dependent J-V characteristics curve can be identified, where different current density variations are indicated. In the low voltage range, the current across the interface of H-J follows an ohmic behavior. In the intermediate range of voltage, the current transport mechanism shows a transition from the phosphorus diffusion to tunneling dominant due to the silicon nanoparticle size and interface of HJ device changed, while the space-charge-limited current (SCLC) dominates the conduction mechanism in the high voltage range and the density of trapping states also affects the electron transport proceeding. At last, the proper size of silicon nanoparticle can reduces the interface charge density of H-J, which is confirmed via the numerical C-V matching technique and we propose a new energy band diagram to fit the HJ device embedded by the silicon nanoparticles.     

粉末交流电致发光应用新领域—特殊波长光的暗室照明

根据不同的感光胶片对特种波长光感光灵敏度低和电致发光单色性的特点，研制出系列暗室照明光源和显示器件。研究方法是改变Ⅱ－Ⅵ族化合物半导体的禁带宽度和杂质能级深度。首先做出单色光，再加有机染料使光谱窄化，使达到安全照明与显示的目的。     

白色发光的电致发光显示器

在ZnS中加入Mn、Cu中心制备出白色发光的电致发光材料，发射光谱中可出现3个发光峰，分别是460nm、520nm和585nm。深入研究了Mn、Cu中心的分布和2个中心在不同激发条件下的相互作用，在低压区Mn中心受Cu中心的敏化，高压区Mn中心碰撞激发，利用两中心激发机理不同，适当选择合适条件，实现白光。     

Determination of the energy distribution of interface traps in MIS systems using non-steady-state techniques

Experimental techniques are described for determining the energy distribution of interface traps at the semiconductor-insulator interface of MIS devices. The device used here was an MNOS capacitor in which the semiconductor was n-type. The first technique which is described is that of measuring the thermally stimulated currents. The method consists of biasing the capacitor into the accumulation mode at a low temperature thereby filling the traps at the semiconductor oxide interface. The device is then biased into the deep-depletion mode in which state the traps remain filled because the temperature is too low to allow the electrons to be thermally excited out of the traps. The temperature of the device is then raised at a uniform rate, and the current associated with the release of electrons from the trap is monitored. The shape of the I?T characteristic is a direct image of the interface trap distribution is a broad peak with a maximum at 0·35 eV below the bottom of the conduction band, and of height approximately 6 × 10¹³ cm^?2eV^?1. The experiments were carried out at two heating rates (0·1°K/sec and 0·01°K/sec), and the trap densities so obtained were identical.The second method consists of biasing the device into the accumulation mode at a fixed temperature thereby filling the traps at the silicon-silicon oxide interface. It is then short-circuited and the non-steady state transient current associated with the release of electrons from the interface traps is monitored. The energy distribution of the interface traps in the upper half of the forbidden gap is shown to be readily obtained from the transient currents, and is found to be identical to that obtained using the thermal technique.     

An analytical model for electron transport and luminance in SrS:Cu,Ag ACTFEL display devices

An analytical model is developed to explain electron transport and luminance mechanisms in SrS:Cu,Ag ac thin film electroluminescent (ACTFEL) display devices. The model includes shallow and deep interface states, bulk traps, and impact excitation and ionization of activators. Mathematical expressions describing optoelectronic processes in the phosphor layer and interface states are written and numerical solutions for field, current and luminance are obtained. Results of calculations are compared with experimental data. The model is able to simulate the dominant features of the experimental luminance and current waveforms.     

Physical processes in insulated-gate field-effect transistors

The current-voltage characteristics of insulated-gate field-effect transistors have been calculated for arbitrary ratios of the gate insulator-semiconductor thickness. Comparison of the calculations to experimental results with CdS thin film transistors shows a good correspondence for both enhancement and depletion type units. It is found that the failure of experimental devices to show current saturation for drain voltages beyond pinch-off can be attributed to the presence of partially ionised donors at the CdS-SiO interface.