Charge Carrier Mobility and Series Resistance Extraction in 2D Field-Effect Transistors: Toward the Universal Technique

2D semiconductor field-effect transistors (2D FETs) have emerged as a promising candidate for beyond-silicon electronics applications. However, its device performance has often been limited by the metal-2D semiconductor contact, and the non-negligible contact resistance (R_SD) not only deteriorates the on-state current but also hinders the direct characterization of the intrinsic properties of 2D semiconductors (e.g., intrinsic charge carrier mobility, μ_int). Therefore, a proper extraction technique that can independently characterize the metal-2D semiconductor contact behavior and the intrinsic properties of a 2D semiconducting layer is highly desired. In this study, a universal yet simple method is developed to accurately extract the critical parameters in 2D FETs, including characteristic temperature (T_o), threshold voltage (V_T), R_SD, and μ_int. The practicability of this method is extensively explored by characterizing the temperature-dependent carrier transport behavior and the strain-induced band structure modification in 2D semiconductors. Technology computer aided design simulation is subsequently employed to verify the precision of R_SD extraction. Furthermore, the universality of the proposed method is validated by successfully implementing the extraction to various 2D semiconductors, including black phosphorus, indium selenide, molybdenum disulfide, rhenium disulfide, and tungsten disulfide with top- and bottom-gated configurations.     

纤锌矿GaN低场电子迁移率解析模型

在GaAs低场电子迁移率解析模型的基础上得到了纤锌矿GaN低场电子迁移率的解析模型,该模型考虑了杂质浓度、温度和杂质补偿率对低场电子迁移率的影响.模拟结果和测量数据的比较表明该模型在10 16～10 2 0 cm-3的电子浓度、30～80 0K的温度和0～0 9的杂质补偿率范围内具有较好的一致性.该电子迁移率解析模型对于GaN器件的数值模拟和器件仿真设计具有很强的实用意义.     

Scalable Nanowire Photonic Crystals: Molding the Light Emission of InGaN

To date, there have been no efficient semiconductor light emitters operating in the green and amber wavelengths. This study reports on the synthesis of InGaN nanowire photonic crystals, including dot‐in‐nanowires, nanotriangles, and nanorectangles with precisely controlled size, spacing, and morphology, and further demonstrates that bottom‐up InGaN photonic crystals can exhibit highly efficient and stable emission. The formation of stable and scalable band edge modes in defect‐free InGaN nanowire photonic crystals is directly measured by cathodoluminescence studies. The luminescence emission, in terms of both the peak position (λ ≈ 505 nm) and spectral linewidths (full‐width‐half‐maximum ≈ 12 nm), remains virtually invariant in the temperature range of 5–300 K and under excitation densities of 29 W cm^?2 to 17.5 kW cm^?2. To the best of our knowledge, this is the first demonstration of the absence of Varshni and quantum‐confined Stark effects in wurtzite InGaN light emitters—factors that contribute significantly to the efficiency droop and device instability under high‐power operation. Such distinct emission properties of InGaN photonic crystals stem directly from the strong Purcell effect, due to efficient coupling of the spontaneous emission to the highly stable and scalable band‐edge modes of InGaN photonic crystals, and are ideally suited for uncooled, high‐efficiency light‐emitting‐diode operation.     

High-yield GaN nanowire synthesis and field-effect transistor fabrication

This letter describes a simple way to grow high-quality GaN nanowires in a specific area. The relationship between catalyst formation and nanowire growth was addressed. High-yield gallium nitride nanowire field-effect transistors were demonstrated successfully using a prealigned process: Ni catalysts with a diameter of 200 nm were deposited selectively at predetermined positions. GaN nanowires were then grown by vapor-liquid-solid mechanism in a chemical vapor deposition (CVD) reactor. Fabricated GaN nanowire FETs showed a high current density along with good saturation and pinch-off characteristics. These authors contributed equally to this work.     

Performance of commercial foundry-level AlGaN/GaN HEMTs after hot electron stressing

The performance degradation of commercial foundry level GaN HEMTs placed under a constant-power drain voltage step-stress test has been studied. By utilizing electroluminescence measurement techniques to optimize hot electron stress testing conditions (Meneghini, 2012), no significant permanent changes in saturation current (I_dss), transconductance (Gm), and threshold voltage (V_th) can be seen after stress testing of drain voltages from 30 V up to 200 V. We observe little permanent degradation due to hot electron effects in GaN HEMTs at these extreme operating conditions and it is inferred that other considerations, such as key dimensions in channel or peak electric field (Chynoweth, 1958; Zhang and Singh, 2001) [2,3], are more relevant to physics of failure than drain bias alone.     

AlGaN/GaN异质结构欧姆接触的研制

研究了 Ga N高温宽禁带半导体外延层上欧姆接触的制备工艺 ,讨论了几种测试方法的优缺点 ,并根据器件制作的工艺兼容性 ,在 n-Ga N样品上获得了 4× 1 0 - 6 Ω·cm2的欧姆接触 ,在 Al Ga N/Ga N异质结构样品上获得了 4× 1 0 - 4Ω· cm2 的欧姆接触。实验结果表明 ,Al Ga N/Ga N上低阻欧姆接触的制备及其工艺兼容性是Ga N HFET器件研制的技术难点     

Synthesis of GaN nanowires and nanorods via self-growth mode control

The synthesis of hexagonal wurzite one-dimensional (1D) GaN nanostructures on c-Al₂O₃ substrates was investigated using a thermal chemical vapor deposition (CVD) process. The diameter of the GaN nanostructures was controlled by varying the growth time using a mixture of GaN powder and Ga metal with the ammonia gas reaction. The morphologies of the GaN nanowires and nanorods were confirmed by field emission scanning electron microscopy. The micro-Raman spectroscopy and X-ray scattering measurements indicated that the GaN nanostructures had a hexagonal wurzite structure without any oxide phases. We investigated the difference in the structural properties between the GaN nanowires and nanorods. Deep-level emission bands were not observed in cathodoluminescence measurements from either the GaN nanowires or nanorods, indicating the incorporation of low-level impurities into our 1D GaN nanostructures.     

Characterization of Non-Alloyed Ohmic Contacts to Si-Implanted AlGaN/GaN Heterostructures for High-Electron Mobility Transistors

This paper reports results of a study of non-alloyed ohmic contacts on Si-implanted AlGaN/GaN heterostructures, obtained from current–voltage characteristics of transfer-length method (TLM) test structures. It is shown that the measured contact resistance from the Ti/Au/Ni metal contacts, deposited on Si-implanted regions, to the two-dimensional electron gas channel at the AlGaN/GaN heterointerface of the non-implanted region, is formed by three different components: (i) contact resistance between the metal␣and the semiconductor (0.60 ± 0.16 Ω mm), (ii) resistance of the implanted region (0.62 ± 0.03 Ω mm) and (iii) an additional resistance (0.72 ± 0.24 Ω mm) giving a total value of 1.9 ± 0.3 Ω mm. The specific ohmic contact resistance was determined to be (2.4 ± 0.5) × 10⁻⁵ Ω cm².     

栅槽刻蚀工艺对增强型GaN HEMT器件性能的影响

基于凹槽栅增强型氮化镓高电子迁移率晶体管(GaN HEMT)研究了不同的栅槽刻蚀工艺对GaN器件性能的影响。在栅槽刻蚀方面,采用了一种感应耦合等离子体(ICP)干法刻蚀技术与高温热氧化湿法刻蚀技术相结合的两步法刻蚀技术,将AlGaN势垒层全部刻蚀掉,制备出了阈值电压超过3 V的增强型Al_2O_3/AlGaN/GaN MIS-HEMT器件。相比于传统的ICP干法刻蚀技术,两步法是一种低损伤的自停止刻蚀技术,易于控制且具有高度可重复性,能够获得更高质量的刻蚀界面,所制备的器件增强型GaN MIS-HEMT器件具有阈值电压回滞小、电流开关比(I_ON/I_OFF)高、栅极泄漏电流小、击穿电压高等特性。     

沟道电场分布对AlN/GaN HFETs极化库仑场散射的影响

Based on the measured capacitance–voltage(C–V) curves and current–voltage(I–V) curves for the prepared differently-sized Al N/Ga N heterostructure field-effect transistors(HFETs), the I–V characteristics of the Al N/Ga N HFETs were simulated using the quasi-two-dimensional(quasi-2D) model. By analyzing the variation in the electron mobility for the two-dimensional electron gas(2DEG) with the channel electric field, it is found that the different polarization charge distribution generated by the different channel electric field distribution can result in different polarization Coulomb field(PCF) scattering. The 2DEG electron mobility difference is mostly caused by the PCF scattering which can reach up to 899.6 cm2/(V s)(sample a), 1307.4 cm2/(V s)(sample b),1561.7 cm2/(V s)(sample c) and 678.1 cm2/(V s)(sample d), respectively. When the 2DEG sheet density is modulated by the drain–source bias, the electron mobility for samples a, b and c appear to peak with the variation of the 2DEG sheet density, but for sample d, no peak appears and the electron mobility rises with the increase in the2 DEG sheet density.     

Metal-organic vapor phase epitaxy growth and characterization of AlN/GaN heterostructures

Low-pressure, metal-organic vapor-phase epitaxy (MOVPE) was used to grow AlN/GaN metal-insulator-semiconductor (MIS) heterostructures with AlN thickness between 3 nm and 30 nm. The Hall mobility was found to decrease with increasing AlN thickness, with optimal mobility measured at 5-nm AlN. By decreasing the ammonia flow during AlN growth (lower V/III ratio), surface and interface quality were greatly improved with a corresponding improvement in electrical properties. For the optimal V/III ratio, room-temperature (RT) mobility and sheet charge were 891 cm²/Vs and 2.15×10¹³ cm⁻², respectively. The best RT mobility, for both optimal V/III and thickness, was 1015 cm²/Vs with a sheet charge of 1.1×10¹³ cm⁻².     

寄生电感对低压增强型GaN HEMT开关行为的影响

寄生电感是影响功率管开关特性的重要因素之一,开关频率越高,寄生电感对低压增强型氮化镓高电子迁移率晶体管(GaN HEMT)的开关行为影响越深,使其无法发挥高速开关的性能优势。通过建立数学模型,理论分析了考虑各部分寄生电感后增强型GaN HEMT的开关过程,并推导了各阶段的持续时间和影响因素,然后通过建立双脉冲测试平台,对各部分寄生电感对开关特性的具体影响进行了实验验证。实验结果表明,寄生电感会使开关过程中的电流、电压出现振荡,影响开关速度和可靠性,并且各部分寄生电感对增强型GaN HEMT的开关过程影响程度不同,在实际PCB布局受到物理限制时,需要根据设计目标优化布局,合理分配各部分寄生电感以获得最优的开关性能。     

Plasma atomic layer etching of GaN/AlGaN materials and application: An overview

With the development of the third generation of semiconductor devices, it is essential to achieve precise etching of gallium nitride (GaN) materials that is close to the atomic level. Compared with the traditional wet etching and continuous plasma etching, plasma atomic layer etching (ALE) of GaN has the advantages of self-limiting etching, high selectivity to other materials, and smooth etched surface. In this paper the basic properties and applications of GaN are presented. It also presents the various etching methods of GaN. GaN plasma ALE systems are reviewed, and their similarities and differences are compared. In addition, the industrial application of GaN plasma ALE is outlined.     

Simulation on the effect of non-uniform strain from the passivation layer on AlGaN/GaN HEMT

High electron mobility transistors (HEMTs) based on the III-nitride material system have attracted interest for high-frequency electronic components operating at high-power levels. Nitride based HEMTs can achieve power, bandwidth and efficiency levels that exceed the performance of Si, GaAs or SiC based devices. At present, a major limitation of nitride HEMTs is their failure to achieve reliability on par with Si-LDMOS or GaAs pHEMT devices. The development of SiN_x passivation layers have largely mitigated the gate lag effect, however, this passivation layer introduces an additional strain that forms a non-uniform polarization induced charge. Furthermore, this excess strain can locally relax the film eliminating the piezoelectric induced charge in addition to forming defects that act as electron traps.     

GaN基高速蓝绿光光源的研究进展

随着射频通信频谱资源的逐渐饱和，局域范围内高速通信亟需开辟一条新的赛道，而可见光通信得益于光的大带宽本质和通信范围有限而频谱免许可，是传统通信的理想补充之一。GaN基蓝绿光发光光源近十年来的快速发展，特别是性能优良的小尺寸高速光源micro-LED的发展，使其成为“万物互联”的物联网时代终末端通信的重要促进力量。文章分蓝绿光micro-LED和带有谐振腔的GaN基蓝绿光光源(含超辐射发光二极管和激光器)两个主要类别，回顾了蓝绿光高速光源的发展历程和最新进展，主要包括micro-LED结构与阵列、面发射腔增强光源、边发射腔增强光源三个方面。     

InGaN/GaN多量子阱纳米线发光二极管制备及研究

用SiO2纳米图形层作为模板在以蓝宝石为衬底的n-GaN单晶层上制备了InGaN/GaN多量子阱纳米线,并成功实现了其发光二极管器件(LED).场发射扫描电子显微镜(FESEM)的测量结果表明,InGaN/GaN多量子阱纳米线具有光滑的表面形貌和三角形的剖面结构.室温下阴极射线荧光谱(CL)的测试发现了位于461 nm...     

Single Crystal Gallium Nitride Nanomembrane Photoconductor and Field Effect Transistor

Large‐area, free‐standing and single‐crystalline GaN nanomembranes are prepared by electrochemical etching from epitaxial layers. As‐prepared nanomembranes are highly resistive but can become electronically active upon optical excitation, with an excellent electron mobility. The interaction of excited carriers with surface states is investigated by intensity‐dependent photoconductivity gain and temperature‐dependent photocurrent decay. Normally off enhancement‐type GaN nanomembrane MOS transistors are demonstrated, suggesting that GaN could be used in flexible electronics for high power and high frequency applications.     

氮化镓基发光二极管的发光光谱和功率特性

用直流和脉冲电流的方法研究了氮化镓基紫色和蓝色发光二极管的发光光谱和功率特性.结果表明，紫色发光二极管的发光中心波长在直流情况下随电流的增加发生红移，在脉冲情况下随电流的增加发生蓝移；蓝色发光二极管的发光中心波长在直流和脉冲情况下都发生蓝移.两种发光二极管的功率在直流情况下会发生饱和，并随电流的进一步增加而急剧减小，以上现象可能是由于热效应和量子阱中的压电效应引起的.     

InGaN/GaN多量子阱LED电致发光谱中双峰起源的研究

研究了MOCVD生长的具有双发射峰结构的InGaN/GaN多量子阱发光二极管(LED)的结构和发光特性.在透射电子显微镜(TEM)下可以发现量子阱的宽度不一致,电致发光谱(EL)发现了位于2.45eV的绿光发光峰和2.81eV处的蓝光发光峰.随着电流密度增加,双峰的峰位没有移动,直到注入电流密度达到2×104 mA/cm2时,绿光发光峰发生蓝移,而蓝光发光峰没有变化.单色的阴极荧光谱(CL)发现绿光发射对应的发光区包括絮状区域和发光点,而蓝光发射对应的发光区仅包含絮状区域.通过以上的结果,我们认为蓝光发射基本上源于InGaN量子阱发光,而绿光发射则起源于量子阱和量子点的发光.