Ga-N熔体热力学性质及钠助熔剂法制备GaN单晶的研究进展

作为第三代半导体的关键材料之一,Ⅲ族氮化物在过去几十年中因其应用于光电子和微电子器件而得到了广泛的研究,如发光二极管(LED)、激光二极管(LD)和高电子迁移率晶体管(HEMT)。Na助熔剂法已成为生长高质量GaN晶体的重要技术之一。综述和讨论了Na助熔剂法GaN结晶的发展历程与最新技术,包括Ga-N的结晶热力学性质、熔体结构、助熔剂选择、单点籽晶技术、多点籽晶技术、孔隙与位错控制、形貌演化与生长条件优化等。最后,对比其他体GaN技术,展望了Na助熔剂法的挑战与机遇。

NH_(3)/N_(2)复合热退火技术改善高浓度Mg掺杂GaN材料性能

研究了NH_(3)/N_(2)复合热退火技术对高浓度Mg掺杂GaN材料晶体质量、发光性质及导电性能的影响。实验结果表明,相较于传统N_(2)氛围高温热退火后处理工艺而言,NH_(3)氛围高温热退火后处理工艺可以改善高浓度Mg掺杂GaN材料的晶体质量,同时可以增进Mg受主原子的有效掺杂,使得其光致发光谱中蓝光峰强度增强。采用NH_(3)氛围高温热退火结合N_(2)氛围低温热退火后处理工艺复合技术制备得到的高浓度Mg掺杂GaN材料内部背景电子浓度显著降低。这是由于在NH_(3)氛围高温热退火后处理工艺中,NH_(3)的热分解产物能够有效降低材料内N空位和间隙Ga原子等浅施主型缺陷浓度,最终改善高浓度Mg掺杂GaN材料的导电性能。

4H-SiC衬底上生长参数对AlGaN基深紫外多量子阱受激辐射特性的影响

SiC衬底是制备高性能AlGaN基深紫外激光器的良好候选衬底。采用金属有机化学气相沉积方法在4H-SiC衬底上生长了深紫外AlGaN/AlN多量子阱结构(MQWs),系统研讨了MQWs生长参数对深紫外激光结构自发辐射和受激辐射特性的影响规律。综合分析MQWs的表面形貌和发光性能后发现,随着NH_(3)流量增加和生长温度升高,MQWs表面粗糙度降低,内量子效率提升。经优化,MQWs的内量子效率达到74.1%,室温下的激射阈值光功率密度和线宽分别为1.03 MW/cm~2和1.82 nm,发光波长为248.8 nm。这主要归因于高的NH3流量和生长温度抑制了有源区中的碳杂质并入,载流子辐射复合效率和材料增益增加;同时生长速率降低,改善了MQWs结构的表面形貌,降低了界面散射损耗。采用干法刻蚀和湿法腐蚀的复合工艺制备了光滑陡直的谐振腔,激光器的腔面损耗降低,阈值光功率密度和线宽进一步降低至889 kW/cm~2和1.39 nm。

Hydride vapor phase epitaxy for gallium nitride substrate

Due to the remarkable growth rate compared to another growth methods for gallium nitride(GaN)growth,hydride vapor phase epitaxy(HVPE)is now the only method for mass product GaN substrates.In this review,commercial HVPE systems and the GaN crystals grown by them are demonstrated.This article also illustrates some innovative attempts to develop homebuilt HVPE systems.Finally,the prospects for the further development of HVPE for GaN crystal growth in the future are also discussed.

基于GaN的开关线性复合高速随动脉冲负载直流变换器

有源相控阵雷达发射机收发组件工作在高频脉冲负载模式,这对其供电电源的负载动态性能提出了很高要求。该文针对高速负载切换的二次DC-DC电源,提出开关线性复合并联结构的脉冲负载变换器及其相应的控制策略。基于器件级环路建模的方法有效提升了线性稳压电路的环路带宽,使其进行快速功率跟踪,并设计基于GaN的低阻抗交错并联Buck变换器,使其以较快的速度高效地提供主要脉冲功率。针对重复频率50 kHz、峰值功率120 W的高频模拟雷达脉冲负载,该文搭建脉冲电流上升下降时间50 ns以内的脉冲电源原理样机,输出电压跌落小于5%。实验结果表明所提方法能够有效改善脉冲电源的动态性能。

GaN载片式功率放大器质量提升研究

随着T/R组件集成度的不断提升,氮化镓(GaN)功放载片因其输出功率大、效率高、体积小的特点,成为功率放大器发展中的一种新形态。文中研究了一种新型的GaN功放载片可靠性和质量评价提升的方法,针对于GaN功放载片的特点,该方法将微波单片和分立器件的评价方法相结合,关注功率管芯、匹配电容等可靠性核心元件,通过细化筛选试验、加严质量一致性评价,辅以加速寿命试验的方式,在早期剔除不良品,控制产品的技术状态,提升产品的可靠性。利用两型GaN功放载片产品进行验证,两型产品在质量一致性评价时发现高功率管芯和匹配电容的问题,证明该方法可以显著提升GaN功放载片的质量。

Refractory Metal Nitride Schottky Contact on GaN

For thermally stable or high-temperature operating,Schottky contact utilizing refractory metal nitride,TiN,MoN and ZrN,on n-GaN were evaluated.The refractory metal nitride films were formed by reactive sputtering in Ar and N2 ambient.Current-voltage characteristics show that ideality factors of 1.09-1.22 and barrier heights of 0.66-0.75 eV was obtained for the three metal nitrides.For the ZrN contact,the ideality factor and barrier height of became 1.06 and 0.77 eV,respectively,after 800 ℃ annealing.AlGaN/GaN heterostructure FET with TiN gate was also investigated.No obvious degradation was found for the TiN-gate device even after thermal treatment at 850 ℃.This shows that Schottky contact utilizing refractory metal nitride on GaN has the potential for thermal stability or high-temperature operating.

Direct growth of graphene on gallium nitride by using chemical vapor deposition without extra catalyst

Graphene on gallium nitride （GaN） will be quite useful when the graphene is used as transparent electrodes to improve the performance of gallium nitride devices. In this work, we report the direct synthesis of graphene on GaN without an extra catalyst by chemical vapor deposition. Raman spectra indicate that the graphene films are uniform and about 5-6 layers in thickness. Meanwhile, the effects of growth temperatures on the growth of graphene films are systematically studied, of which 950 ℃ is found to be the optimum growth temperature. The sheet resistance of the grown graphene is 41.1 Ω/square, which is close to the lowest sheet resistance of transferred graphene reported. The mechanism of graphene growth on GaN is proposed and discussed in detail. XRD spectra and photoluminescence spectra indicate that the quality of GaN epi-layers will not be affected after the growth of graphene.

Damage evolution and removal behaviors of GaN crystals involved in double-grits grinding

Elucidating the complex interactions between the work material and abrasives during grinding of gallium nitride(GaN)single crystals is an active and challenging research area.In this study,molecular dynamics simulations were performed on double-grits interacted grinding of GaN crystals;and the grinding force,coefficient of friction,stress distribution,plastic damage behaviors,and abrasive damage were systematically investigated.The results demonstrated that the interacted distance in both radial and transverse directions achieved better grinding quality than that in only one direction.The grinding force,grinding induced stress,subsurface damage depth,and abrasive wear increase as the transverse interacted distance increases.However,there was no clear correlation between the interaction distance and the number of atoms in the phase transition and dislocation length.Appropriate interacted distances between abrasives can decrease grinding force,coefficient of friction,grinding induced stress,subsurface damage depth,and abrasive wear during the grinding process.The results of grinding tests combined with cross-sectional transmission electron micrographs validated the simulated damage results,i.e.amorphous atoms,high-pressure phase transition,dislocations,stacking faults,and lattice distortions.The results of this study will deepen our understanding of damage accumulation and material removal resulting from coupling between abrasives during grinding and can be used to develop a feasible approach to the wheel design of ordered abrasives.

Ultrathin GaN Film Derived from Amorphous Ga_(2)O_(3) Film

It remains a big challenge to synthesize two-dimensional(2D)GaN material for applications in power nanodevices.Traditional synthetic methods require complex equipment and processes and time consuming.Here,we reported a two-step route to prepare polycrystalline 2D GaN film.The amorphous ultrathin Ga_(2)O_(3)film was first exfoliated from the surface of liquid gallium.In a vapor phase reaction,2D Ga_(2)O_(3)film was then converted into 2D GaN film while maintaining the 2D morphology.Raman and high-resolution transmission electron microscope(HRTEM)analysis implies the successful synthesis of wurtzite-type GaN ultrathin film.This simple strategy proposed in this work will provide more opportunities for applications of GaN ultrathin film in many devices.

In-situ multi-information measurement system for preparing gallium nitride photocathode

We introduce the first domestic in-situ multi-information measurement system for a gallium nitride （GaN） photo- cathode. This system can successfully fulfill heat cleaning and activation for GaN in an ultrahigh vacuum environment and produce a GaN photocathode with a negative electron affinity （NEA） status. Information including the heat clean- ing temperature, vacuum degree, photocurrent, electric current of cesium source, oxygen source, and the most important information about the spectral response, or equivalently, the quantum efficiency （QE） can be obtained during prepa- ration. The preparation of a GaN photocathode with this system indicates that the optimal heating temperature in a vacuum is about 700 ~C. We also develop a method of quickly evaluating the atomically clean surface with the vacuum degree versus wavelength curve to prevent possible secondary contamination when the atomic level cleaning surface is tested with X-ray photoelectron spectroscopy. The photocurrent shows a quick enhancement when the current ratio between the cesium source and oxygen source is 1.025. The spectral response of the GaN photocathode is flat in a wavelength range from 240 nm to 365 nm, and an abrupt decline is observed at 365 nm, which demonstrates that with the in-si$u multi-information measurement system the NEA GaN photocathode can be successfully prepared.

Thermal stability of tungsten and tungsten nitride Schottky contacts to AlGaN/GaN

Thin tungsten nitride （WNx） films were produced by reactive DC magnetron sputtering of tungsten in an Ar-N2 gas mixture. The films were used as Schottky contacts on AlGaN/GaN heterostructures. The Schottky behaviours of WNx contact was investigated under various annealing conditions by current-voltage （I-V） measurements. The results show that the gate leakage current was reduced to 10-6 A/cm2 when the N2 flow is 400 mL/min. The results also show that the WNx contact improved the thermal stability of Schottky contacts, Finally, the current transport mechanism in WNx/AlGaN/GaN Schottky diodes has been investigated by means of I-V characterisation technique at various temperatures between 300 K and 523 K. ATE model with a Gaussian distribution of Schottky barrier heights （SBHs） is thought to be responsible for the electrical behaviour at temperatures lower than 523 K.

基于建模数据和最优化算法的GaN HEMT精确电热行为建模方法

为了实现对氮化镓高电子迁移率晶体管GaN HEMT(gallium nitride high electron mobility transistor)高速开关带来的开通过压、误导通、开关振荡和EMI噪声等问题展开定量的仿真分析,提出了一种基于建模数据和最优化算法的门极增强型GaN HEMT电热行为模型建模方法。相比较于常规GaN HEMT行为模型,所提出的建模方法采用2个简单的建模公式实现了对GaN HEMT在第一和第三象限宽工作温度范围内的电热特性进行准确的建模。同时采用一个紧凑的建模公式实现对GaN HEMT非线性寄生电容的精确建模。此外,提出了一种遗传算法和Levenberg-Marquardt算法组合的优化算法,基于该优化算法和建模数据实现了对建模参数的快速提取,在较大程度上减小了建模时间和工作量。仿真表明,所提出的建模方法能够实现对不同公司多个型号的GaN HEMT器件展开精确的建模。最后通过吻合的动态仿真和实验数据验证了所提建模方法的正确性和有效性。

Analysis and Characterization of Normally-Off Gallium Nitride High Electron Mobility Transistors

High electron mobility transistor(HEMT)based on gallium nitride(GaN)is one of the most promising candidates for the future generation of high frequencies and high-power electronic applications.This research work aims at designing and characterization of enhancement-mode or normally-off GaN HEMT.The impact of variations in gate length,mole concentration,barrier variations and other important design parameters on the performance of normally-off GaN HEMT is thoroughly investigated.An increase in the gate length causes a decrease in the drain current and transconductance,while an increase in drain current and transconductance can be achieved by increasing the concentration of aluminium(Al).For Al mole fractions of 23%,25%,and 27%,within Al gallium nitride(AlGaN)barrier,the GaN HEMT devices provide a maximum drain current of 347,408 and 474 mA/μm and a transconductance of 19,20.2,21.5 mS/μm,respectively.Whereas,for Al mole fraction of 10%and 15%,within AlGaN buffer,these devices are observed to provide a drain current of 329 and 283 mA/μm,respectively.Furthermore,for a gate length of 2.4,3.4,and 4.4μm,the device is observed to exhibit a maximum drain current of 272,235,and 221 mA/μm and the transconductance of 16.2,14,and 12.3 mS/μm,respectively.It is established that a maximum drain current of 997 mA/μm can be achieved with an Al concentration of 23%,and the device exhibits a steady drain current with enhanced transconductance.These observations demonstrate tremendous potential for two-dimensional electron gas(2DEG)for securing of the normally-off mode operation.A suitable setting of gate length and other design parameters is critical in preserving the normally-off mode operation while also enhancing the critical performance parameters at the same time.Due to the normallyon depletion-mode nature of GaN HEMT,it is usually not considered as suitable for high power levels,frequencies,and temperature.In such settings,a negative bias is required to enter the blocking condition;however,in the before-mentioned normally-off devices,the negative bias can be avoided and the channel can be depleted without applying a negative bias.

Modeling,simulations,and optimizations of gallium oxide on gallium-nitride Schottky barrier diodes

With technology computer-aided design(TCAD)simulation software,we design a new structure of gallium oxide on gallium-nitride Schottky barrier diode(SBD).The parameters of gallium oxide are defined as new material parameters in the material library,and the SBD turn-on and breakdown behavior are simulated.The simulation results reveal that this new structure has a larger turn-on current than Ga2O3 SBD and a larger breakdown voltage than Ga N SBD.Also,to solve the lattice mismatch problem in the real epitaxy,we add a Zn O layer as a transition layer.The simulations show that the device still has good properties after adding this layer.

Self-screening of the polarized electric field in wurtzite gallium nitride along[0001]direction

The strong polarization effect of GaN-based materials is widely used in high-performance devices such as white-lightemitting diodes(white LEDs),high electron mobility transistors(HEMTs),and GaN polarization superjunctions.However,the current researches on the polarization mechanism of GaN-based materials are not sufficient.In this paper,we studied the influence of polarization on electric field and energy band characteristics of Ga-face GaN bulk materials by using a combination of theoretical analysis and semiconductor technology computer-aided design(TCAD) simulation.The selfscreening effect in Ga-face bulk GaN under ideal and non-ideal conditions is studied respectively.We believe that the formation of high-density two-dimensional electron gas(2 DEG) in GaN is the accumulation of screening charges.We also clarify the source and accumulation of the screening charges caused by the GaN self-screening effect in this paper and aim to guide the design and optimization of high-performance GaN-based devices.

用于GaN基HEMT栅极金属TiN的ICP刻蚀工艺

GaN基高电子迁移率晶体管(HEMT)在射频(RF)通信及新能源汽车领域有着巨大的应用潜力。TiN材料因其良好的热稳定性、化学稳定性及工艺兼容性,可用作GaN基HEMT的栅极材料。采用ULVAC公司生产的NE-550型电感耦合等离子体(ICP)刻蚀设备对TiN材料进行了干法刻蚀工艺的研究。采用光刻胶作为刻蚀掩膜,Cl_(2)和BCl_(3)混合气体作为工艺气体,通过调整工艺参数,研究了ICP源功率、射频(RF)偏压功率、腔体压力、气体体积流量以及载台温度对TiN刻蚀速率和侧壁角度的影响。最后通过优化工艺参数,得到了TiN刻蚀速率为333 nm/min,底部平整且侧壁角度为81°的栅极结构。

Band Edge Emission Improvement by Energy Transfer in HybridⅢ-Nitride/Organic Semiconductor Nanostructure

GaN nanorods are fabricated using inductively coupled plasma etching with Ni nano-island masks. The poly [2- methoxy-5-（2-ethyl）hexoxy-l,4-phenylenevinylene] （MEH-PPV）/GaN-nanorod hybrid structure is fabricated by depositing the MEH-PPV film on the GaN nanorods by using the spin-coating process. In the hybrid structure, the spatial separation is minimized to achieve high-emciency non-radiative resonant energy transfer. Optical properties of a novel device consisting of MEH-PPV/GaN-nanorod hybrid structure is studied by analyzing photoluminescenee （PL） spectra. Compared with the pure GaN nanorods, the PL intensity of the band edge emission of GaN in the MEH-PPV/GaN-nanorods is enhanced as much as three times, and the intensity of the yellow band is suppressed slightly. The obtained results are analyzed by energy transfer between the GaN nanorods and the MEH-PPV. An energy transfer model is proposed to explain the phenomenon.

Structural,Morphological and Electrical Properties of In-Doped Zinc Oxide Nanostructure Thin Films Grown on p-Type Gallium Nitride by Simultaneous Radio-Frequency Direct-Current Magnetron Co-Sputtering

Zinc oxide （ZnO） is one of the most promising and frequently used semiconductor materials. In-doped nanos- tructure ZnO thin films are grown on p-type gallium nitride substrates by employing the simultaneous rf and dc magnetron co-sputtering technique. The effect of In-doping on structural, morphological and electrical properties is studied. The different dopant concentrations are accomplished by varying the direct current power of the In target while keeping the fixed radio frequency power of the ZnO target through the co-sputtering deposition technique by using argon as the sputtering gas at ambient temperature. The structural analysis confirms that all the grown thin films preferentially orientate along the c-axis with the wurtzite hexagonal crystal structure without having any kind of In oxide phases. The presenting Zn, 0 and In elements＇ chemical compositions are identified with EDX mapping analysis of the deposited thin films and the calculated M ratio has been found to decrease with the increasing In power. The surface topographies of the grown thin films are examined with the atomic force microscope technique. The obtained results reveal that the grown film roughness increases with the In power. The Hall measurements ascertain that all the grown films have n-type conductivity and also the other electrical parameters such as resistivity,mobility and carrier concentration are analyzed.

基于GaN器件的单相逆变器TCM控制策略研究

氮化镓(GaN)高电子迁移率晶体管具有开关速度快、器件损耗小的优点,在高频应用场合得到广泛应用。为了进一步提高变换器效率和功率密度,将三角电流模式(TCM)调制用于基于GaN器件的单相逆变器中,通过控制负向电流与死区时间实现了全范围零电压开关(ZVS),达到提高变换器效率和功率密度的目的。搭建了1台样机进行验证,实验结果表明,TCM调制在不同负载条件下均可实现软开关,最大开关频率可达300 kHz,峰值效率可达98.5%。