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。

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.

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.

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%。

Vertical Gallium Nitride Power Devices：Current Status and Prospects

A comprehensive review on the current status and prospects of vertical gallium nitride(GaN) power devices is presented.The paper starts with an introduction of the market potential for GaN power devices, and presents a comparison between lateral and vertical GaN power devices.Then, different high-performance vertical GaN power devices are introduced, including diodes and transistors on free-standing GaN substrates and low-cost Si substrates.The paper is concluded by elucidating the research and commercialization prospects in developing several key components of vertical GaN power devices.This relatively new area has only been explored for 3-5 years, but already seen the demonstration of a series of successful vertical power devices that outperformed lateral GaN power devices and conventional Si power devices.There are tremendous research opportunities regarding materials, physics, devices and system-level integrations of vertical GaN power devices.The vertical GaN power devices show great potential for >600 V level high-current,high-voltage and high-power applications.

P-GaN栅结构GaN基HEMT器件研究进展

增强型氮化镓(GaN)基高电子迁移率晶体管(high electron mobility transistor,HEMT)是高频高功率器件与开关器件领域的研究热点,P-GaN栅技术因具备制备工艺简单、可控且工艺重复性好等优势而成为目前最常用且唯一实现商用的GaN基增强型器件制备方法。首先,概述了当前制约P-GaN栅结构GaN基HEMT器件发展的首要问题,从器件结构与器件制备工艺这2个角度,综述了其性能优化举措方面的最新研究进展。然后,通过对研究进展的分析,总结了当前研究工作面临的挑战以及解决方法。最后,对未来的发展前景、发展方向进行了展望。

氮极性AlGaN基隧道结深紫外LED

针对AlGaN(Aluminum Gallium Nitride)基深紫外LED(Light Emitting Diode)发光效率低、工作偏压较大的问题,设计了一种带有n^(+)-GaN/Al_(0.4)Ga_(0.6)N/p^(+)-GaN隧道结的氮极性AlGaN基深紫外LED器件结构。该结构由n-Al_(0.65)Ga_(0.35)N电子提供层、 Al_(0.65)Ga_(0.35)N/Al_(0.5)Ga_(0.5)N多量子阱、组分渐变p-Al_(x)Ga_(1-x)N和n^(+)-GaN/Al_(0.4)Ga_(0.6)N/p^(+)-GaN隧道结构成。研究结果表明,相比于无隧道结的参考LED,隧道结LED具有更高的内量子效率和光输出功率,同时其具有更低的开启电压。隧道结LED光电特性的改善,归因于隧道结的引入提升了LED的空穴注入效率,提高了LED器件的电流扩展能力。通过模拟软件对半导体器件载流子输运、光电特性的模拟,有助于加深对半导体器件物理特性的理解。若在“半导体器件物理”学习课程加入对半导体器件模拟软件的学习,能有效提升学生对半导体器件物理知识的理解和探索。

多孔GaN阵列结构的制备及其光电性能

以硝酸钠溶液作为腐蚀液,通过电化学和紫外辅助电化学相结合的两步法腐蚀GaN薄膜,制备出了多孔阵列结构。采用扫描电子显微镜(SEM)表征了多孔阵列结构的形貌,结果表明多孔GaN阵列结构排列整齐,孔径分布均匀,其平均孔径为24.1 nm,孔隙密度为3.86×10^(10 )cm^(-2),深度为2μm。利用X射线衍射仪(XRD)和Raman光谱仪表征了多孔GaN阵列的晶体结构,与平面GaN薄膜相比,多孔GaN阵列结构的晶体质量更好,且具有较低的残余应力。使用光致发光(PL)光谱和紫外-可见光(UV-Vis)吸收光谱表征了GaN的光学性能,与平面GaN薄膜相比,多孔GaN阵列结构的光致发光强度和光吸收能力有较大提升。通过电化学工作站对多孔GaN阵列结构的光电性能进行测试,在1.23 V偏压下,多孔GaN阵列结构的光电流是GaN平面结构的约3.36倍,最大光电转化效率ηmax是平面GaN薄膜的约3.5倍。该研究为多孔GaN阵列结构的应用提供了一定的实验数据和理论指导。

GaN单晶的HVPE生长与掺杂进展

相比于第一代和第二代半导体材料,第三代半导体材料具有更高的击穿场强、电子饱和速率、热导率以及更宽的带隙,更适用于制备高频、大功率、抗辐射、耐腐蚀的电子器件、光电子器件和发光器件。氮化镓(GaN)作为第三代半导体材料的代表之一,是制作蓝绿激光、射频微波器件和电力电子器件的理想衬底材料,在激光显示、5G通信、相控阵雷达、航空航天等领域具有广阔的应用前景。氢化物气相外延(Hydride vapor phase epitaxy,HVPE)方法因生长设备简单、生长条件温和和生长速度快而成为制备GaN晶体的主流方法。由于普遍使用石英反应器,HVPE法生长获得的非故意掺杂GaN不可避免地存在施主型杂质Si和O,使其表现出n型半导体特性,但载流子浓度高和电导率低限制了其在高频大功率器件中的应用。掺杂是改善半导体材料电学性能最普遍的方法,通过掺杂不同掺杂剂可以获得不同类型的GaN单晶衬底,提高其电化学特性,从而满足市场应用的不同需求。本文介绍了GaN半导体晶体材料的基本结构和性质,综述了近年来采用HVPE法生长高质量GaN晶体的主要研究进展;对GaN的掺杂特性、掺杂剂类型、生长工艺以及掺杂原子对电学性能的影响进行了详细介绍。最后简述了HVPE法生长掺杂GaN单晶面临的挑战和机遇,并展望了GaN单晶的未来发展前景。