High-quality homoepitaxial layers grown on 4H-SiC at a high growth rate by vertical LPCVD

High quality,homoepitaxial layers of 4H-SiC were grown on off-oriented 4H-SiC（0001） Si planes in a vertical low-pressure hot-wall CVD system（LPCVD） by using trichlorosilane（TCS） as a silicon precursor source together with ethylene（C₂H₄） as a carbon precursor source.The growth rate of 25-30μm/h has been achieved at lower temperatures between 1500 and 1530℃.The surface roughness and crystalline quality of 50μm thick epitaxial layers（grown for 2 h） did not deteriorate compared with the corresponding results of thinner layers（grown for 30 min）.The background doping concentration was reduced to 2.13×10¹⁵ cm^-3.The effect of the C/Si ratio in the gas phase on growth rate and quality of the epi-layers was investigated.     

PVT法同质籽晶AlN晶体生长

为了获得高质量AlN晶体,通过物理气相传输(PVT)法,采用AlN籽晶进行AlN晶体生长,并通过双温区加热装置对衬底与原料之间的温差进行调节。研究结果表明,籽晶形核阶段,随着AlN籽晶与原料顶温差的减小,AlN的形核机制呈现三种模式,分别为岛生长模式、畴生长模式和螺旋位错生长模式;晶体生长阶段,通过增加AlN籽晶与原料顶温差来提高晶体生长速率,采用10℃/h的变温速率将温差从10℃增加为30℃时,AlN晶体生长模式不变,仍然保持螺旋位错生长模式,该生长模式下获得的AlN晶体结晶质量最高,(0002)面摇摆曲线半峰宽(FWHM)约为55 arcsec。     

GaN grown by hydride vapor phase epitaxy on p-type 6H-SiC layers

6H-SiC/GaN pn-heterostructures were grown by subsequent epitaxial growth of p-SiC by low temperature liquid phase epitaxy (LTLPE) and n-GaN by hydride vapor phase epitaxy (HVPE). For the first time, p-type epitaxial layers grown on 6H-SiC wafers were used as substrates for GaN HVPE growth. The GaN layers exhibit high crystal quality which was determined by x-ray diffraction. The full width at a half maximum (FWHM) for the ω-scan rocking curve for (0002) GaN reflection was ∼120 arcsec. The photoluminescence spectra for these films were dominated by band-edge emission. The FWHM of the edge PL peak at 361 nm was about 5 nm (80K).     

Selective area growth of GaN using gas source molecular beam epitaxy

Ammonia cracking efficiencies on various surfaces were examined. The following is an ordering of surfaces according to their ammonia cracking efficiencies: GaN (highest), Si₃N₄, SiO₂ (lowest). Selective area growth of GaN was performed over SiO₂ masks deposited on GaN previously grown on sapphire substrates using ammonia-based molecular beam epitaxy. GaN growth on patterned SiO₂/GaN is very selective at a growth temperature of 800°C. Good quality growth occurs in the window region with no deposits on the mask surface when growth is performed at 800°C, whereas some deposits on the SiO₂ masks accumulate when growth is performed at 700°C. The ratio of lateral growth rate to vertical growth rate is ≤1.     

Growth of CdS crystals by the physical vapor transport method

Based on the physical vapor transport (PVT) method, the growth of large-size CdS crystals inside a vertical semi-closed tube is studied. Firstly, in order to ensure 1D diffusion-advection transport, multi-thin tubes are used in the growth tube. The XRD spectra of the CdS crystal grown in this configuration indicates that the crystal quality has clearly been improved, where the FWHM is 58.5 arcsec. Secondly, theoretical and experimental growth rates under different total pressures are compared; the results show that the experiential growth rate equation is valid for our semi-tube growth, and it could be used to estimate the growth rate and maximum growth time under different total pressures.     

Model development of GaN MOVPE growth chemistry for reactor design

The metalorganic vapor phase epitaxy of GaN is complicated by the extensive and pervasive complex gas phase chemistry within the growth system. This gas phase chemistry leads to the high sensitivity of the material properties on the detailed fluid dynamics within the system. Computational fluid dynamics (CFD) based reactor modeling combined with gas phase kinetics studies was used to determine the transport and reaction behavior within a high performance vertical MOVPE reactor. The complexity of the growth chemistry model was increased in a step-wise fashion. At each step, the concentration profiles were determined using available recent kinetic data. The high gas flow rate typically employed in GaN MOVPE results in a very thin high-temperature flow sheet above the growth front, leading to an extremely high thermal gradient. Within this thin high-temperature flow sheet, a stratified chemical structure is formed as a result of the unique thermal fluid environment. This stratified structure is closely related to the transport and reaction behavior within GaN MOVPE processes and forms part of the engineering guidelines for GaN MOVPE reactor design.     

立方相GaN的高温MOCVD生长

利用MOCVD技术在提高生长温度(900℃)下生长出了高质量的立方相GaN,生长速度提高到1.6μm/h.高温生长的GaN样品近带边峰室温光荧光半高宽为48meV,小于在830℃下生长的GaN样品.在ω扫描模式下,X射线衍射表明高温生长的GaN具有较小的(002)峰半高宽21′.可以看出,尽管立方GaN是亚稳态,高生长温度仍然有利于其晶体质量的提高.本文对GaN生长中生长温度和生长速度之间的关系作了讨论.     

立方相GaN的高温MOCVD生长

利用MOCVD技术在提高生长温度(900℃)下生长出了高质量的立方相GaN,生长速度提高到1.6μm/h.高温生长的GaN样品近带边峰室温光荧光半高宽为48meV,小于在830℃下生长的GaN样品.在ω扫描模式下,X射线衍射表明高温生长的GaN具有较小的(002)峰半高宽21′.可以看出,尽管立方GaN是亚稳态,高生长温度仍然有利于其晶体质量的提高.本文对GaN生长中生长温度和生长速度之间的关系作了讨论.     

Mass spectroscopy study of GaN metalorganic chemical vapor deposition

Metalorganic chemical vapor phase deposition of GaN on (100) GaAs has been studied using mass spectroscopy. With increasing substrate temperature, the amount of decomposed trimethylgallium (TMGa) was observed to increase exponentially with a characteristic energy of 1.5 eV. The presence of NH₃ was found to suppress the production of CH₃ in the gas phase. This implies that CH₃ of TMGa reacts with the hydrogen atom of NH₃, forming CH₄ as a main gas product. Studies of nitrogen evaporation from the growth surface when TMGa flow was off lead to the conclusion that increased growth rate could result in decreased background electron concentration due to nitrogen vacancy. The presence of NH₃ significantly promotes the decomposition of TMGa. Desorption of excess Ga atoms from the growth surface at low NH₃ flow rates takes place as suggested by the increased ratio of peak intensity of Ga (m/e = 69) to that of DMGa ((CH₃)₂Ga, m/e- 99) with decreasing NH₃ flow rate.     

Seeded growth of GaN at high N2 pressure on (0 0 0 1) polar surfaces of GaN single crystalline substrates

GaN single crystals obtained by the high nitrogen pressure solution method without an intentional seeding, show strong growth anisotropy which results in their platelet shape. The attempts to enhance the growth into (0 0 0 1) directions by the increase of the integral supercooling in the solution, often lead to the growth instabilities on both Ga-polar and N-polar (0 0 0 1) surfaces. This can be avoided only by the precise control of the growth conditions at the crystallization front on the particular surface.The results of the seeded growth on both Ga- and N-polar (0 0 0 1) surfaces in configuration enabling such a control is reported. It is shown that dominating mechanisms of the unstable growth such as the cellular growth or edge nucleation can be suppressed. Differences in nucleation and growth in dependence on surface polarity are discussed.     

Plasma characteristics and the growth of group III-nitrides by metalorganic molecular beam epitaxy

Improved quality and controllability of growth processes are key issues for the maturation of III-N technologies. One of the most important concerns for the growth of III-N materials in ultra high vacuum is the ability to provide an effective nitrogen flux to the growth surface. This work has sought to correlate radio frequency (rf) plasma parameters and their impact on the growth of GaN by plasma-assisted metalorganic molecular beam epitaxy. Utilizing optical emission spectrometry, the atomic nitrogen production has been optimized as a function of rf power and N₂ flow rate. Growth experiments indicate that the abundance of atomic nitrogen alone does not control growth. Increasing energy per molecule in the rf source, with a constant level of atomic nitrogen, dramatically decreases the GaN growth rate. High levels of atomic nitrogen with a low energy per molecule resulted in restoration of the growth rate to ∼0.5 μm/h.     

8英寸Si衬底上高质量AlGaN/GaN HEMT结构的生长

在8英寸(1英寸=2.54 cm)的Si衬底上采用金属有机化学气相沉积(MOCVD)生长了高质量、无龟裂的GaN薄膜和AlGaN/GaN高电子迁移率晶体管(HEMT)结构.通过调节应力调控层的结构,厚度为5 μm的GaN膜层翘曲度低于50 μm.采用X射线衍射(XRD)对GaN薄膜的(002)和(102)衍射峰进行扫描,其半峰全宽(FWHM)分别为182和291 arcsec.透射电子显微镜(TEM)截面图显示GaN外延层的位错密度达到了3.5×107/cm2,证实了在大尺寸Si衬底上可以制作高质量的GaN薄膜.AlGaN/GaN HEMT结构的二维电子气浓度和载流子迁移率分别为9.29×1012/cm2和2 230 cm2/(V·s).基于这些半绝缘AlGaN/GaNHEMT结构所制作的功率电子器件的输出电流可达20 A,横向击穿电压可达1 200 V.     

Investigations on low temperature mo-cvd growth of GaAs

The growth conditions for the deposition at low temperatures of epitaxial layers of GaAs on (100) GaAs crystals using TMG and arsine are studied in detail. The films are grown at atmospheric pressure in a vertical reactor in which the arsine is fed in through the rf heated susceptor for precracking. The growth temperature was varied between 680°C and 450°C. In the whole temperature range epitaxial growth was obtained. The growth rate at temperatures below 600°C depends on the AsH₃ flow, suggesting that the availibility of As vapor species, not AsH₃ limits epitaxial growth in this temperature range. For a constant AsH₃ /TMG ratio of 8 the growth rate decreases by exp (-E/kT) with an activation energy of E = 1.5 eV. Growth rates as low as 0.5 um/h have been achieved. Unintentionally doped layers show semi-insulating behaviour at growth temperatures below 500° C, similar to the behaviour seen from MBE layers. However, n-type layers with reasonable mobilities can be grown in the low temperature range (450 ° C) using H₂ Se as the doping gas.     

Morphology and crystalline property of an AIN single crystal grown on AIN seed

AIN single crystal grown by physical vapor transport (PVT) using homogeneous seed is considered as the most promising approach to obtain high-quality AIN boule.In this work,the morphology of AIN single crystals grown under different modes (3D islands and single spiral center) were investigated.It is proved that,within an optimized thermal distribution chamber system,the surface temperature of AIN seed plays an important role in crystal growth,revealing a direct relationship between growth mode and growth condition.Notably,a high-quality AIN crystal,with (002) and (102) reflection peaks of 65 and 36 arcsec at full width at half maximum (FWHM),was obtained grown under a single spiral center mode.And on which,a high-quality AlxGa1-xN epitaxial layer with high Al content (x =0.54) was also obtained.The FWHMs of (002) and (102) reflection of AlxGa1-xN were 202 and 496 arcsec,respectively,which shows superiority over their counterpart grown on SiC or a sapphire substrate.     

Performance enhancement of GaN SB-MOSFET on Si substrate using two-step growth method

We have grown high quality GaN layers on (1 1 1)-oriented silicon substrate using a two-step growth method and fabricated high-performance normally-off n-channel GaN Schottky-barrier MOSFET (SB-MOSFET). Indium-tin-oxide (ITO) was used as Schottky-barrier contact for source and drain (S/D) because the work function of ITO is close to the electron affinity of GaN. Due to enhanced crystalline quality and reduced surface roughness of GaN layer grown by two-step process, the fabricated device exhibited much improved performances: sufficiently high threshold voltage of 3.75 V, subthreshold slope of 171 mV/dec, low specific on-resistance of 9.98 mΩ cm², and very high field-effect mobility of 271 cm²/V s. This is the highest mobility value among the GaN MOSFETs ever reported so far.     

Growth and fabrication of AlGaN/GaN HEMT based on Si(1 1 1) substrates by MOCVD

AlGaN/GaN high electron mobility transistor (HEMT) hetero-structures were grown on the 2-in Si (1 1 1) substrate using metal-organic chemical vapor deposition (MOCVD). Low-temperature (LT) AlN layers were inserted to relieve the tension stress during the growth of GaN epilayers. The grown AlGaN/GaN HEMT samples exhibited a maximum crack-free area of 8 mm×5 mm, XRD GaN (0 0 0 2) full-width at half-maximum (FWHM) of 661 arcsec and surface roughness of 0.377 nm. The device with a gate length of 1.4 μm and a gate width of 60 μm demonstrated maximum drain current density of 304 mA/mm, transconductance of 124 mS/mm and reverse gate leakage current of 0.76 μA/mm at the gate voltage of −10 V.     

在蓝宝石图形衬底上生长低穿透性位错的GaN薄膜

使用MOCVD外延系统,采用3D-2D生长模式在圆锥图形蓝宝石衬底上生长GaN薄膜。研究发现3D-2D生长模式能够有效的减少GaN薄膜的穿透性位错,其中3D GaN层的生长条件是关键：低V/III比,低温和高生长压力。为了进一步减少TD,3D GaN层的厚度应该与图形衬底上的图形高度接近。当3D GaN层生长结束时,3D GaN层把图形衬底的图形围在其中,具有倾斜的侧壁和（0001）向的上表面,而图形上基本没有沉积物。在接下来的2D生长过程里,GaN沿倾斜侧面快速生长,使得侧面上的穿透性位错产生弯曲,从而减少GaN薄膜的穿透性位错。经过对3D条件的优化,GaN薄膜的穿透性位错降低到1×108cm-2,XRD测试得到的（002）,（102）半宽分别达到211弧秒和219弧秒。     

昆明物理研究所大面积水平推舟液相外延碲镉汞薄膜技术进展

报道了近年来昆明物理研究所在富碲水平推舟液相外延碲镉汞外延薄膜制备技术方面的进展。2019年以来,突破了?120 mm碲锌镉晶体定向生长技术,使碲锌镉衬底沉积相和夹杂相密度≤5×103 cm－2,位错腐蚀坑密度（EPD）≤4.0×104 cm－2,?120 mm（111）晶圆衬底的Zn组份分布极差≤0.36%。基于碲锌镉衬底技术的进步,液相外延碲镉汞薄膜的最大生长尺寸达到了70 mm×75 mm,薄膜位错腐蚀坑密度均值为5×104 cm－2,X射线双晶回摆曲线半峰宽（DCRC-FWHM）≤35 arcsec,部分可控制到25 arcsec以下;50 mm×60 mm尺寸长波碲镉汞薄膜的厚度极差≤±1.25 μm,室温截止波长极差≤±0.1 μm,中波碲镉汞薄膜相应指标分别为≤±1 μm、≤±0.05 μm。材料技术的进展促进了制冷型碲镉汞探测器产能提升和成本的降低,也支撑了高性能长波/甚长波探测器、高工作温度（HOT）探测器以及2048×2048、4096×4096等甚高分辨率高性能探测器的研制。     

Direct growth of high-quality thick CdTe epilayers on Si (211) substrates by metalorganic vapor phase epitaxy for nuclear radiation detection and imaging

Direct growth of high-quality, thick CdTe (211) epilayers, with thickness up to 100 μm, on Si (211) substrates in a vertical metalorganic vapor phase epitaxy system is reported. In order to obtain homo-orientation growth on Si substrates, pretreatment of the substrates was carried out in a separate chamber by annealing them together with pieces of GaAs at 800–900°C in a hydrogen environment. Grown epilayers had very good substrate adhesion. The full-width at half-maximum (FWHM) value of the x-ray double-crystal rocking curve from the CdTe (422) reflection decreased rapidly with increasing layer thickness and remained between 140–200 arcsec for layers >18 μm. Photoluminescence measurement at 4.2 K showed high-intensity, bound excitonic emission and very small defect-related deep emissions, indicating the high crystalline quality of the grown layers. Furthermore, a CdTe/n⁺-Si heterojunction diode was fabricated that exhibited clear rectifying behavior.