发光二极管中负电容现象的机理

为解释发光二极管（LEDs）中的负电容（NC）现象，提出了在有源区与局部强复合效应有关的新模型，首次通过对载流子连续性方程的求解导出了NC的解析表达式。理论结果表明，在一定的范围内激活区载流子复合速率越大，LEDs中的NC效应越显著，这与实验结果完全一致。它表明，LEDs中的NC是由其激活区载流子复合引起的，而非外部原因造成。     

发光二极管的低频电容特性

通过自建装置精确测试了发光二极管(LED)的低频(小于102Hz)电学特性。电学测量表明,所有LED在低频下都表现出明显的负电容(NC)现象,且频率越低NC现象越明显。调制发光测量表明,相对发光强度在低频下表现出明显饱和现象,并且随频率增加而减小。比较电学和光学的测量结果可以证实,辐射发光是产生NC现象的主要原因。通过对LED电学测量结果的详细分析得出了NC随电压和频率的变化关系式。     

GaN蓝光发光二极管的负电容现象研究

利用交流(a．c．)小信号法对GaN蓝光发光二极管(LEDs)的电容-电压特性进行了研究．观察到了GaN蓝光LEDs中的负电容现象．并且测试频率越低、正向电压越大．这种负电容现象就越明显。研究结果表明,这一现象产生的最主要原因是由于GaN蓝光LEDs有源区内注入载流子的辐射复合。     

纳米硅颗粒在多孔氧化铝中的光致荧光特性

采用阳极氧化方法制备了多孔硅（Ps），经过超声波充分粉碎PS层得到分散的si纳米颗粒（n-Si），利用高速离心旋转方法将n-si镶嵌到多孔氧化铝（Al2O3）模板中，得到nSi／Al2O3。复合体系。研究了PS、分散的n-Si和n-Si／Al2O3。的荧光（PL）光谱性质，观察到n-Si极强的蓝紫光发射。结果表明，在Al2O3模板中的n-Si，比起PS和丙酮中的发光峰值波长向短波方向“蓝移”，而且半峰全宽（FWHM）也相对变窄。实验现象表明，量子限制效应（QCE）对样品的PL性质有苇要作用，并用QCE对样品的发光“蓝移”现象进行了解释。     

一种利用发光光谱估计LED正向电压的方法

提出了一种通过发光光谱估计发光二极管(LED)正向电压的方法。推导了LED正向电压与结温的关系,探讨了利用发光光谱估计结温的方法,从而建立了发光光谱和正向电压的联系。本文方法不需要直接测量结温和理想因子等参数,只由发光光谱就可得到较为准确的LED正向电压值。实验结果表明,正向电压的光谱估计值和实际测量值能够较好的吻合。     

ZnS:Cu粉末交流电致发光器件特性研究

以商用ZnS：Cu交流电致发光粉作为发光层，以ITO作为电极制作了粉末交流电致发光器件。以交流脉冲方波为驱动电压，详细研究了外加电压的幅值，频率以及脉宽对其发光频谱及亮度的影响。实验结果表明当电压小于200V，发光亮度随着电压的升高而缓慢增强，当电压大于200V，随着电压的升高亮度准线性增强。随着驱动频率的增大，发光光谱的中心波长发生蓝移，从100Hz时的504nm（绿光）到100kHz时的450nm（蓝光），发光亮度随频率增加先快速增强然后逐渐趋于饱和，达到一个极值后开始减小。随着脉宽的增大，发光亮度线性增强。另外文章中对驱动频率影响发光光谱的原因进行了深入分析，这对进一步研究ZnS：Cu交流电致发光粉的发光机理有着重要的作用。     

有机发光器件中空穴注入对负电容的影响

对不同结构的有机发光器件(OLED)进行了电容-电压(C-V)特性测量,研究了不同空穴注入结构对OLED负电容的影响。结果表明,负电容的产生与OLED内部电场的分布有着密切的关系,负电容开始出现的频率与电压的平方根呈指数关系。与超薄的单层空穴注入层相比,掺杂的空穴注入层不仅能降低器件的驱动电压,而且其载流子传输特性和出现负电容时的初始电压对频率有着更强的依赖性。     

具有NPB:DPVBi掺杂层的有机白光器件的研究

制作了结构为ITO／NPB（50nm）／NPB；DPVBi（10：1，30nm）／Alqs（20nm）／LiF（1nm）／Al的有机白光器件。由于掺杂层NPB：DPVBi的引入，电子及空穴容易被DPVBi及NPB俘获，提高激子的复合，进一步提高监光的发光能力。发光区从Alq3的发光峰逐渐变为DPVBi的发光和NPB发光增强，从而发光峰值发生变化。该器件的最大亮度和效率分别为22V时4721cd／m^2和5V时0．80cd／A。     

脉冲激光沉积制备ZnO薄膜及其发光性质研究

采用脉冲激光沉积（PKD）技术，在Si（100）衬底上制备出高度C轴取向的ZnO薄膜。通过测量X射线衍射（XRD）谱、扫描电镜（SEM）和光致发光（PL）谱，研究了衬底温度改变对薄膜结构和PL的影响。实验结果表明，当衬底温度从400℃升到700℃时，薄膜的（002）衍射峰半高宽（FWHM）变窄，紫外（UV）发光强度在衬底温度为500℃达到最强。这可能是当衬底温度为500℃时，ZnO薄膜的化学配比较好，说明化学配比对UV发光的影响要大于薄膜微结构的影响。改变衬底温度对薄膜的表面形貌也有较大的影响。     

量子点发光显示器件

量子点发光二极管（QD—LEDs）是将有机小分子OLED与可发光无机量子点（QD）结合起来而形成的一种新技术。量子点LED既具有聚合物的可溶性，容易制造的优点。同时还具有潜在的类似于磷光材料的高发光效率。     

Experimental study of negative capacitance in LEDs

Light-emitting diodes(LEDs) have been widely usedin display,light and many other fields ,and thereforethey attract more and more attentions[1].However ,themain research ontheir performance focuses on the lightemission and dc current-voltage characteristics ,the accharacteristics are seldomreported.In fact ,the study offorward ac characteristics[2]is veryi mportant to the de-vices application andtothe devices mechanisms compre-hension.In this paper ,the light emission and capaci-tance-voltage …     

Mechanism of negative capacitance in LEDs

In order to explain the phenomenon of negative capacitance（NC） in light emitting diodes LEDs, we present a new model based on local strong recombination in active region and firstly deduce the analytic expression of NO from continuity equation. The theoretical result indicates that the NC effect becomes stronger when the carrier recombination rate increases in a certain range,which is consistent with the experimental result. Accordingly,we confirm that the NO is caused by carrier recombination in active reaion instead of by other exterior factors.     

Electrical Characteristics of GaN-Based Light-Emitting Diodes on Patterned Sapphire Substrates

Patterned sapphire substrate light-emitting diodes display obvious negative capacitance (NC) at large forward biases. This is measured using a method based on a small signal alternating current together with direct I–V plots. The NC in patterned sapphire substrate LEDs grows exponentially with the forward applied voltage. This observation is unexpected and in contrast with Shockley’s p–n junction theory, which only includes an increasing diffusion capacitance and not a NC. However, this result is in good agreement with conventional sapphire substrate LEDs. Furthermore, the negative terminal capacitance confirmed the prediction of Laux and Hess’ theory. The ideal factor of a patterned sapphire substrate LED is about 5, greatly exceeding the traditional theoretical value. The capacitance increased to a maximum and then gradually decreased, which was similar to the results for a p–n junction. Patterned sapphire substrate LEDs can withstand higher voltages than conventional sapphire substrate LEDs. This work could further confirm the existence of NC.     

Capacitance–voltage characteristics of P3HT:PCBM bulk heterojunction solar cells with ohmic contacts and the impact of single walled carbon nanotubes on them

Capacitance–voltage (C–V) characteristics of P3HT:PCBM devices of two different thicknesses are correlated with current density–voltage (J–V) characteristics. The rising portion of the C–V characteristics coincides with the exponential current density below the built-in voltage. The negative capacitance (NC) of these devices is a low frequency phenomenon and it occurs in trap-free space charge limited current (SCLC) regime. The onset frequencies of NC for devices with and without SWNTs also do not follow direct relation with effective mobility. The NC in thin devices has non-monotonic change with voltage for thin devices showing that interface state kinetics can be the reason for its occurrence. The NC of thick devices, on the other hand, increases monotonically with voltage showing that bulk properties dominate in these. Addition of SWNTs to these devices for efficiency improvement does not modify their built-in voltage. Also, the SWNTs do not affect the forward NC behaviour. However, the devices containing SWNTs show NC in reverse bias also which has different frequency dependence with voltage. The reverse bias NC is attributed to the large non-linear reverse current by charge injection into the additional energy levels introduced by SWNTs.     

Negative capacitance effect in semiconductor devices

Nontrivial capacitance behavior, including a negative capacitance (NC) effect, observed in a variety of semiconductor devices, is discussed emphasizing the physical mechanism and the theoretical interpretation of experimental data. The correct interpretation of NC can be based on the analysis of the time-domain transient current in response to a small voltage step or impulse, involving a self-consistent treatment of all relevant physical effects (carrier transport, injection, recharging, etc.). NC appears in the case of the nonmonotonic or positive-valued behavior of the time-derivative of the transient current in response to a small voltage step. The time-domain transient current approach is illustrated by simulation results and experimental studies of quantum well infrared photodetectors (QWIPs). The NC effect in QWIPs has been predicted theoretically and confirmed experimentally. The huge NC phenomenon in QWIP's is due to the nonequilibrium transient injection from the emitter caused by the properties of the injection barrier and the inertia of the QW recharging     

The source of negative capacitance and anomalous peak in the forward bias capacitance-voltage in Cr/p-si Schottky barrier diodes (SBDs)

The frequency and voltage dependence of capacitance–voltage (C–V) and conductance-voltage (G/ω−V) characteristics of the Cr/p-Si metal semiconductor (MS) Schottky barrier diodes (SBDs) were investigated in the frequency and applied bias voltage ranges of 10 kHz to 5 MHz and (−4 V)−(+4 V), respectively, at room temperature. The effects of series resistance (R_s) and density distribution of interface states (N_ss), both on C–V and G/ω−V characteristics were examined in detail. It was found that capacitance and conductance, both, are strong functions of frequency and applied bias voltage. In addition, both a strong negative capacitance (NC) and an anomalous peak behavior were observed in the forward bias C–V plots for each frequency. Contrary to the behavior of capacitance, conductance increased with the increasing applied bias voltage and there happened a rapid increase in conductance in the accumulation region for each frequency. The extra-large NC in SBD is a result of the existence of R_s, N_ss and interfacial layer (native or deposited). In addition, to explain the NC behavior in the forward bias region, we drew the C–I and G/ω−I plots for various frequencies at the same bias voltage. The values of C decrease with increasing frequency at forward bias voltages and this decrease in the NC corresponds to an increase in conductance. The values of N_ss were obtained using a Hill–Coleman method for each frequency and it exhibited a peak behavior at about 30 kHz. The voltage dependent profile of R_s was also obtained using a Nicollian and Brews methods.