基于空间电荷限制电流模型的FeCl3掺杂CBP的空穴迁移率研究

基于不同浓度FeCl3掺杂的4,4′-N,N′-二咔唑基联苯(CBP)设计制作了一系列的单空穴有机电致发光器件(OLED),采用空间电荷限制电流法估算了具有不同浓度FeCl3掺杂的CBP的空穴迁移率,并与OLED中常用的空穴传输材料N,N′-二苯基-N,N′-(1-萘基)-1,1′-联苯-4,4′-二胺(NPB)进行了比较研究。结果表明,FeCl3掺杂CBP可以极大地提高CBP薄膜的空穴迁移率,当FeCl3的浓度为12%时空穴迁移率最大,在电场强度为0.5MV/cm的条件下迁移率为4.5×10-5cm2/V·s,即使在零电场条件下迁移率依然高达2.2×10-5 cm2/V·s,近似为常用空穴传输材料NPB空穴迁移率的4倍。用CBP∶12%FeCl3做空穴传输层,制备了OLED器件,最大亮度为68468cd/m2,相对于采用NPB做空穴传输层的参比器件提高了97%,最大电流效率为31.28cd/A,比参比器件提高了23%。器件亮度和效率的提高归因于空穴传输性能的改善,使得器件中载流子的传输更为平衡,从而提高了激子形成的几率,且减少了激子-极化子之间的淬灭。     

影响空间电荷限制电流法测量钙钛矿迁移率的因素

讨论了离子迁移、介电常数依赖性、内建电场、陷阱、厚度与注入势垒等对空间电荷限制电流测量方法的影响.简要介绍了一些解决措施,例如针对离子迁移问题可以使用脉冲空间电荷限制电流法,针对缺陷问题可以使用不同的迁移率描述模型等.这为后续学者更加精确地使用空间电荷限制电流法测量钙钛矿迁移率提供参考.     

非晶GaN薄膜的空间电荷限制电流特性

采用直流磁控溅射技术制备了Si衬底上的非晶GaN薄膜. GaN肖特基二极管伏安曲线不能简单地用包含串联电阻和复合电流效应的热电子发射理论来解释，其他电流输运机制（空间电荷限制电流）起主要作用. 分析数据得到平衡时的电子浓度为1.1E4cm-3和位于EC-0.363eV的陷阱能级. 测量空间电荷限制电流可以用来研究宽带隙化合物非晶半导体GaN的深能级性质.     

非晶GaN薄膜的空间电荷限制电流特性

采用直流磁控溅射技术制备了Si衬底上的非晶GaN薄膜.GaN肖特基二极管伏安曲线不能简单地用包含串联电阻和复合电流效应的热电子发射理论来解释,其他电流输运机制(空间电荷限制电流)起主要作用.分析数据得到平衡时的电子浓度为1.1×104cm-3和位于Ec-0.363eV的陷阱能级.测量空间电荷限制电流可以用来研究宽带隙化合物非晶半导体GaN的深能级性质.     

非晶GaN薄膜的空间电荷限制电流特性

采用直流磁控溅射技术制备了Si衬底上的非晶GaN薄膜.GaN肖特基二极管伏安曲线不能简单地用包含串联电阻和复合电流效应的热电子发射理论来解释,其他电流输运机制(空间电荷限制电流)起主要作用.分析数据得到平衡时的电子浓度为1.1×104cm-3和位于Ec-0.363eV的陷阱能级.测量空间电荷限制电流可以用来研究宽带隙化合物非晶半导体GaN的深能级性质.     

OLED器件空间电荷限制电流模型的MATLAB分析计算

介绍了OLED器件空间电荷限制电流(SCLC)模型的MATLAB分析计算方法.SCLC模型可能是线性或非线性微分方程,将阳极与阴极之间的空间分割为一系列节点以后,SCLC模型可以通过有限差分方法整理为一个矩阵方程.对于线性模型,只需要调用一次MATLAB矩阵左除命令即可获得其数值解.对于非线性模型,可以通过牛顿法做矩阵迭代计算求出其数值解.介绍了确定电场函数的方法.给出了所用的MATLAB计算程序.该方法概念简单,使用方便,不需要花费较多精力编程即可以求解OLED器件的SCLC模型.     

有机发光二极管中空间限制电流的解析模型

文中指出了J-V的解析方程不是漂移方程和泊松方程的严格解,通过分析Pasveer文章中迁移率跟载流子浓度和电场强度的关系,发现载流子浓度的依赖关系是没有必要的。同时对目前流行的Poole-Frenkel模型进行近似化处理,得到了依赖于电场强度的迁移率关系,并在这个近似化处理后的依赖关系的基础上漂移方程和泊松方程能够被严格地解出来,通过把电流-电压方程(关系)的解析模型应用于半导体聚合物,很好地描述了伏安实验数据。     

高电子迁移率晶体管材料结构的制备及分析

针对高电子迁移率晶体管(HEMT)器件,分析了双δ掺杂 GaAs HEMT的结构组成,基于固源分子束外延方法制备了双δ掺杂 GaAs HEMT的缓冲层、沟道层、平面掺杂层和隔离层等多层材料结构。采用 X-ray射线衍射、透射电镜研究了多层材料的结构。范德堡霍尔测试结果表明, HEMT的2DEG测试浓度为1.82×1012 cm-3,电子迁移率大于6520 cm2·V-1·s-1。     

外加太赫兹场与磁场作用下的高电子迁移率晶体管电流特性

外加太赫兹(THz)场垂直入射高电子迁移率晶体管(HEMT),使得HEMT中产生的载流子激发沟道内的等离子振荡,振荡频率处于太赫兹范围.论文研究了外加磁场对该器件电流特性的影响.结果表明,随着外加磁场强度的增加,HEMT的响应率峰值发生蓝移.因此通过改变磁场能够对HEMT的振荡响应实现有效调谐.     

外加太赫兹场与磁场作用下的高电子迁移率晶体管电流特性

外加太赫兹(THz)场垂直入射高电子迁移率晶体管(HEMT),使得HEMT中产生的载流子激发沟道内的等离子振荡,振荡频率处于太赫兹范围.论文研究了外加磁场对该器件电流特性的影响.结果表明,随着外加磁场强度的增加,HEMT的响应率峰值发生蓝移.因此通过改变磁场能够对HEMT的振荡响应实现有效调谐.     

Estimation of electron mobility of n-doped 4, 7-diphenyl-1, 10-phenanthroline using space-charge-limited currents

The electron mobilities of 4, 7-diphenyl-1, 10-phenanthroline (BPhen) doped 8-hydroxyquinolinatolithium (Liq) at various thicknesses (50-300 nm) have been estimated by using space-charge-limited current measurements. It is observed that the electron mobility of 33 wt% Liq doped BPhen approaches its true value when the thickness is more than 200 nm. The electron mobility of 33 wt% Liq doped BPhen at 300 nm is found to be ～5.2 × 10~(-3) cm~2/(V·s) (at 0.3 MV/cm) with weak dependence on electric field, which is about one order of magnitude higher than that of pristine BPhen (3.4 × 10~(-4) cm~2/(V·s)) measured by SCLC. For the typical thickness of organic light-emitting devices, the electron mobility of doped BPhen is also investigated.     

Photoluminescence evaluation of pseudomorphic high electron mobility transistor device waters

Photoluminescence (PL) has been used for some time the evaluation of pseudomorphic high electron mobility transistor material structures. Among the results routinely obtained from these structures are estimates of electron sheet density in the InGaAs channel, either from empirical relationships or from first principles (from direct observation of the Fermi level). We present a semiempirical line shape model for the study of PL line shapes at low temperatures. We show that the primary source of error for optical measurement of the sheet density is in the filling of the channel by electrons injected by the incident laser. We also demonstrate the potential for extraction of structural parameters such as channel composition and thickness from careful observation of variations in PL transition energies.     

Effect of parasitics on electrochemical capacitance-voltage profiling of pseudomorphic high electron mobility transistor structures

The effect of parasitic series resistances on electrochemical capacitance-voltage (EC-V) profiling is simulated numerically for Al_xGaj_1-xAs/InyGa_1-yAs pseudomorphic high electron mobility transistor (p-HEMT) structures. The actual EC-V measurement is simulated numerically by reconstructing the charge distribution from an intrinsic distribution calculated from a self-consistent k p model. The calculated charge distribution then forms the basis for examining the possible profiles an EC-V measurement would produce when parasitics are taken into account. From a simple lumped-circuit model, it is shown that parasitic resistances distort the shape of the charge distribution by changing the relative heights of the 5-layer and channel charges. Hysteresis effects may also occur and may be accompanied by a change in material type from n to p even though the material is known to be n-type over the entire range of measurement. Additionally, an undesirable dependence of the charge profile on the probe signal frequency is found.     

A novel insulated gate technology for ingaas high electron mobility transistors using silicon interlayer based passivation technique

A novel insulated gate technology for InGaAs high electron mobility transistors (HEMT) is described. It utilizes a silicon interface control layer (Si ICL)-based passivation structure. By applying an HF surface treatment, the technology becomes applicable to the air-exposed surfaces of InGaAs and InAlAs. The basic metal-insulator-semiconductor structures were fabricated and characterized in detail by x-ray photoelectron spectroscopy analysis and capacitance-voltage measurements. The interface has been shown to be essentially free from interface states. InGaAs insulated gate HEMTs (IGHEMT) were then success-fully fabricated. The fabricated recessed gate IGHEMTs have good gate control of the drain current with good pinch-off characteristics. A highest effective mobility of 2010 cm²/Vs was obtained. The devices show extremely low gate leakage currents below lnA/mm.     

Electron mobility anisotropy in (Al,Ga)Sb/InAs two-dimensional electron gases epitaxied on GaAs (001) substrates

The electron mobility anisotropy in (Al,Ga)Sb/InAs two-dimensional electron gases with different surface morphology has been investigated. Large electron mobility anisotropy is found for the sample with anisotropic morphology, which is mainly induced by the threading dislocations in the InAs layer. For the samples with isotropic morphology, the electron mobility is also anisotropic and could be attributed to the piezoelectric scattering. At low temperature (below transition temperature), the piezoelectric scattering is enhanced with the increase of temperature, leading to the increase of electron mobility anisotropy. At high temperature (above transition temperature), the phonon scattering becomes dominant. Because the phonon scattering is isotropic, the electron mobility anisotropy in all the samples would be reduced. Our results provide useful information for the comprehensive understanding of electron mobility anisotropy in the (Al,Ga)Sb/InAs system.     

Electron mobility in two-dimensional electron gas in AIGaN/GaN heterostructures and in bulk GaN

We report on temperature dependencies of the electron mobility in the two-dimensional electron gas (2DEG) in AIGaN/GaN heterostructures and in doped bulk GaN. Calculations and experimental data show that the polar optical scattering and ionized impurity scattering are the two dominant scattering mechanisms in bulk GaN for temperatures between 77 and 500K. In the 2DEG in AIGaN/GaN heterostructures, the piezoelectric scattering also plays an important role. Even for doped GaN, with a significant concentration of ionized impurities, a large volume electron concentration in the 2DEG significantly enhances the electron mobility, and the mobility values close to 1700 cm²/Vs may be obtained in the GaN 2DEG at room temperature. The maximum measured Hall mobility at 80K is nearly 5000 cm²/Vs compared to approximately 1200 cm²/Vs in a bulk GaN layer. With a change in temperature from 300 to 80K, the 2DEG in our samples changes from nondegenerate and weakly degenerate to degenerate. Therefore, in order to interpret the experimental data, we propose a new interpolation formula for low field mobility limited by the ionized impurity scattering. This formula is valid for an arbitrary degree of the electron gas degeneracy. Based on our theory, we show that the mobility enhancement in the 2DEG is related to a much higher volume electron concentration in the 2DEG, and, hence, to a more effective screening.     

Dry etching of Hg1−xCdxTe using CH4/H2/Ar/N2 electron cyclotron resonance plasmas

An approach is presented which eliminates the problems caused by hydrocarbon polymer deposition during etching Hg_1-x Cd_xTe with CH₄/H₂ based plasmas. We find that the addition of N₂ to the plasma inhibits polymer deposition in the chamber and on the sample. We speculate that atomic nitrogen formed from N₂ in the plasma has several beneficial effects: the elimination of polymer precursors, the reduction of the atomic hydrogen concentration, and a potential increase of methyl radical concentration. Evidence for the reaction between the nitrogen and the polymer precursors is presented. It is also demonstrated that the addition of N₂ to CH₄/H₂ based electron cyclotron resonance (ECR) plasmas used to etch HgCdTe eliminates the roughness normally formed during etching and results in a steadier etch rate.     

Maximum entropy mobility spectrum analysis of HgCdTe heterostructures

We report on mobility spectrum analysis of p-type HgCdTe using a new maximum entropy algorithm termed full MEMSA (f-MEMSA). The algorithm is the first that separates the constraints on the transverse and longitudinal components of the conductivity tensor, which results in a higher resolution, compared to other MEMSA algorithms. Compared to the Lakeshore c-QMSA algorithm, f-MEMSA demonstrated a lower detection limit and smaller errors for estimations on synthetic data sets. f-MEMSA was applied to experimental data measured on p-type Hg_0.77Cd_0.23Te, measured between T=30 K and 300 K and for an applied magnetic field between μ₀H=0 T and 9 T. Despite the demonstrated high performance of f-MEMSA on synthetic data, we observed several nonphysical contributions, such as low mobility electrons and high mobility holes. A systematic study of different sample geometries and growth methods showed that the high mobility holes, so-called mirror peaks, can be attributed to finite contact size effects. It also indicated that the low mobility electrons appear in the mobility spectrum as a consequence of a limitation in the application of mobility spectrum analysis (MSA) to vacancy-doped HgCdTe, which is consistent with a magnetic freezeout of the holes at high magnetic fields.     

Influence of layer structure on performance of AlGaN/GaN high electron mobility transistors before and after passivation

Intentionally undoped and three different, doped layer structures are used to investigate properties of AlGaN/GaN high electron mobility transistors (HEMTs) before and after SiN passivation. For unpassivated devices, the drain current, transconductance, cutoff frequency, and microwave output-power increase with increased doping level, in spite of an increase in the gate-leakage current. After passivation, an overall performance improvement of all devices occurs. The passivation-induced sheet charge decreases from 2×10¹² cm⁻² in undoped structures to ∼0.7×10¹² cm⁻² in higher doped structures and performance improvement with passivation is less pronounced for higher doped devices. However, the output power of unpassivated and passivated devices on higher doped structures is much higher than that on the undoped-passivated counter-part. These results underline an advantage of the doped layer structure for the preparation of high-performance AlGaN/GaN HEMTs.     

Estimation of charge carrier mobility in amorphous organic materials using percolation corrected random-walk model

A computationally simple yet predictive multi-scale simulation scheme is introduced to estimate zero-field charge mobilities for amorphous OSC materials. A percolating charge model is utilized to describe inhomogeneity of hopping trajectories of carriers in amorphous media. The prediction scheme is composed of the following stages: quantum chemical calculation of Marcus inner sphere reorganization energies, molecular dynamics simulations of the amorphous condensed phase bulk structure, automated quantum chemical calculations of the electronic coupling for dimer pairs in the amorphous solid, and calculation of the Marcus theory charge hopping rates and an estimated bulk mobility using the Einstein relation, corrected for the inhomogeneous hopping network of the solid. Comparisons with independent experimental measurements of hole mobility for ten OSC compounds show that this approach gives good correlation between predictions and measurements suitable for ranking systems, and useful quantitative agreement. This low-cost model with minimal complexity is well-suited for incorporation into a virtual materials discovery framework for advanced OSC solutions.