High quality AIN and GaN grown on compliant Si/SiC substrates by gas source molecular beam epitaxy

Epitaxial layers of AlN and GaN were grown by gas source molecular-beam epitaxy on a composite substrate consisting of a thin (250 nm) layer of silicon (111) bonded to a polycrystalline SiC substrate. Two dimensional growth modes of AlN and GaN were observed. We show that the plastic deformation of the thin Si layer results in initial relaxation of the AlN buffer layer and thus eliminates cracking of the epitaxial layer of GaN. Raman, x-ray diffraction, and cathodoluminescence measurements confirm the wurtzite structure of the GaN epilayer and the c-axis crystal growth orientation. The average stress in the GaN layer is estimated at 320 MPa. This is a factor of two less than the stress reported for HVPE growth on 6H-SiC (0001).     

利用AlxGa1-xN在Si(111)上生长无裂纹GaN

利用LP-MOCVD技术在Si(111)衬底上,用不同Al组分的AlGaN做缓冲层,再在缓冲层上生长GaN薄膜,采用XRD技术和原子力显微镜(AFM)分析样品知,样品整体的结晶质量良好。通过分析外延层的拉曼谱得出GaN中存在应力,而且是张应力,通过计算得出,应力为0.23 GPa。     

<Emphasis Type="Italic">In Situ</Emphasis> Stress Measurements During GaN Growth on Ion-Implanted AlN/Si Substrates

In situ wafer curvature measurements were used in combination with postgrowth structural characterization to study the evolution of film stress and microstructure in GaN layers grown by metalorganic chemical vapor deposition on N⁺ ion-implanted AlN/Si (111) substrates. The results were compared with growth on identical unimplanted substrates. In situ stress measurements revealed that, for the unimplanted sample, the GaN initiated growth under compressive stress of −1.41 GPa which arose due to lattice mismatch with the AlN buffer layer. In contrast, GaN growth on the ion-implanted sample began at lower compressive stress of −0.84 GPa, suggesting a reduction in epitaxial stress. In both cases, the compressive growth stress was fully relaxed after ~0.7 μm and minimal tensile stress was generated during growth. During post-growth cooling, tensile stress was introduced in the GaN layer of both samples due to thermal expansion mismatch. Post-growth optical microscopy characterization, however, demonstrated that the ion-implanted sample had lower density of channeling cracks compared with the unimplanted sample. Cross-sectional transmission electron microscopy images of the sample grown on ion-implanted Si with no post-implantation nitrogen annealing revealed the formation of horizontal cracks in the implanted region beneath the AlN buffer layer. The weakened layer acts to decouple the GaN film from the Si substrate and thereby reduces the density of channeling cracks in the film after growth.     

引入GaN过渡层对Si（111）衬底上生长GaN外延的影响

本文研究了在Si(111)衬底上生长GaN外延层的方法。相比于直接在AlN缓冲层上生长GaN外延层,引入GaN过渡层显著地提高了外延层的晶体质量并降低了外延层的裂纹密度。使用X射线双晶衍射仪、光学显微镜以及在位监测曲线分析了GaN过渡层对外延层的晶体质量以及裂纹密度的影响。实验发现,直接在AlN缓冲层上生长外延层,晶体质量较差, X射线(0002)面半高宽最优值为0.686°,引入GaN过渡层后,通过调整生长条件,控制岛的长大与合并的过程,从而控制三维生长到二维生长过渡的过程,外延层的晶体质量明显提高, (0002)面半高宽降低为0.206°,并且裂纹明显减少。研究结果证明,通过生长合适厚度的GaN过渡层,可以得到高质量、无裂纹的GaN外延层。     

ScAlN缓冲层厚度对Si(100)衬底上GaN外延层的影响

采用脉冲直流磁控溅射方法在Si(100)衬底上制备了ScAlN薄膜。以溅射的ScAlN作为缓冲层,在Si(100)衬底上用金属有机化学气相沉积(MOCVD)技术外延了GaN薄膜。使用高分辨X射线衍射、原子力显微镜和拉曼光谱研究了ScAlN缓冲层的厚度对ScAlN缓冲层和GaN外延层的影响。研究结果表明,ScAlN缓冲层的厚度是影响GaN薄膜晶体质量的重要因素。随着ScAlN厚度的增加,ScAlN的(002)面X射线衍射摇摆曲线半高宽持续减小,GaN的(002)面X射线衍射摇摆曲线半高宽先减小后增大。当ScAlN缓冲层厚度为500nm时,得到的GaN晶体质量最好,其中GaN(002)面的X射线衍射摇摆曲线半高宽为0.38°,由拉曼光谱计算得到的张应力为398.38MPa。     

以金属为缓冲层在Si(111)上分子束外延GaN及其表征

用电子束蒸发方法在Si(111)衬底上蒸发了Au/Cr和Au/Ti/Al/Ti 两种金属缓冲层,然后在金属缓冲层上用气源分子束外延(GSMBE)生长GaN. 两种缓冲层的表面都比较平整和均匀,都是具有Au(111)面择优取向的立方相Au层. 在Au/Cr/Si(111)上MBE生长的GaN,生长结束后出现剥离. 在Au/Ti/Al/Ti/Si(111)上无AlN缓冲层直接生长GaN,得到的是多晶GaN;先在800℃生长一层AlN缓冲层,然后在710℃生长GaN,得到的是沿GaN(0001)面择优取向的六方相GaN. 将Au/Ti/Al/Ti/Si(111)在800℃下退火20min,金属层收缩为网状结构,并且成为多晶,不再具有Au(111)方向择优取向.     

SiC衬底AlN缓冲层的应变对GaN外延层质量的影响

在3英寸(1英寸=2.54 cm)SiC衬底上采用金属有机物化学气相沉积(MOCVD)法生长GaN外延材料。研究了AlN缓冲层的应变状态对GaN外延层应变状态和质量的影响。使用原子力显微镜和高分辨率X射线双晶衍射仪观察样品表面形貌,表征外延材料质量的变化,使用高分辨喇曼光谱仪观察外延材料应力的变化,提出了基于外延生长的应变变化模型。实验表明,GaN外延层的张应变随着AlN缓冲层应变状态的由压变张逐渐减小,随着GaN张应力的逐渐减小,GaN位错密度也大大减少,表面形貌也逐渐变好。     

溅射AlN技术对GaN基LED性能的影响

研究了在图形蓝宝石衬底(PSS)上利用磁控溅射制备AlN薄膜的相关技术,随后通过采用金属有机化学气相沉积(MOCVD)在相关AlN薄膜上生了长GaN基LED.通过一系列对比实验,分析了AlN薄膜的制备条件对GaN外延层晶体质量的影响,研究了AlN薄膜溅射前N2预处理功率和溅射后热处理温度对GaN基LED性能的作用机制.实验结果表明:AlN薄膜厚度的增加,导致GaN缓冲层成核密度逐渐升高和GaN外延膜螺位错密度降低刃位错密度升高;N2处理功率的提升会加剧衬底表面晶格损伤,在GaN外延膜引入更多的螺位错;AlN热处理温度的升高粗化了表面并提高了GaN成核密度,使得GaN外延膜螺位错密度降低刃位错密度升高;而这些GaN外延膜位错密度的变化又进一步影响到LED的光电特性.     

Formation of Semipolar Group-III-Nitride Layers on Textured Si(100) Substrates with Self-Forming Nanomask

Semiconductors - The epitaxial growth of AlN and GaN layers is investigated using metalorganic vapor-phase epitaxy on a Si(100) substrate, on the surface of which a V-shaped nanostructure with...     

Si(111)衬底上GaN外延材料的应力分析

对Si(111)衬底上GaN外延材料的应力随着低温AlN插入层数的变化进行了分析研究。通过喇曼散射谱在高频E2(TO)模式下的测试分析发现,随着低温AlN插入层数的增加,GaN材料的E2(TO)峰位逐渐接近体GaN材料的E2(TO)峰位(无应力体GaN材料的E2(TO)峰位为568cm-1),计算得出GaN材料的应力从1.09GPa减小到0.42GPa。同时,使用室温光荧光谱进行了分析验证。结果表明,Si衬底上GaN外延材料受到的是张应力,通过低温AlN插入层技术可以有效降低GaN材料的应力,并且最终实现了表面光亮的厚层无裂纹GaN材料。     

Specific features of the hydride vapor-phase epitaxy of nitride materials on a silicon substrate

Specific features of the growth of the GaN/AlN/Si heterocomposite in which layers of Group-III element nitrides are grown on a silicon substrate by hydride vapor-phase epitaxy are studied. The effect of the temperature at which the AlN buffer layer is grown on diffusion processes at the heterointerfaces and on the quality of the epitaxial layers being grown is considered. It is shown that, with the epitaxial technique used, the buffer layer should be grown at high temperatures (1080°C) because the thickness of the component-mixing region is minimized in this case and abrupt interfaces are formed in the GaN/AlN/Si heterocomposite. The double-stage growth of gallium nitride on the high-temperature AlN buffer layer with a thickness of 300–400 nm makes it possible to obtain GaN layers with thicknesses of up to 0.3 μm without crack formation.     

6英寸硅基GaN HEMT外延材料的制备

采用金属有机物化学气相沉积(MOCVD)方法,在6英寸(1英寸=2.54 cm)Si(111)衬底上,使用多层不同Al摩尔组分的AlGaN插入层技术,成功生长出厚度为2.9 μm无裂纹(扣除边缘2mm)的GaN外延层,解决了大尺寸外延片的翘曲度问题,并在此基础上生长了全结构的高电子迁移率晶体管(HEMT)外延片.采用X射线双晶衍射对外延材料结构进行了表征.Hall测试结果表明,HEMT外延材料的迁移率为2 080 cm2/(V·s),方块电阻为279.8 Ω/□,电荷面密度为1.07×1013 cm-2.采用喇曼光谱仪对GaN的应力进行了表征,GaN的喇曼E2(h)峰位于567.02 cm-1,表面受到的张应力为0.170 6 GPa,由于GaN外延层受到的张应力很小,说明插入多层AlGaN后应力已经释放.汞探针C-V测试二维电子气浓度较Hall测试结果偏低,可能是在C-V测试时肖特基势垒接触会降低载流子浓度.     

Si衬底上热壁外延制备GaAs单晶薄膜材料

报道了采用热壁外延（ＨＷＥ）技术,在Ｓｉ表面生长ＧａＡｓ薄膜。先通过活化剂活化Ｓｉ表面,再采取两步生长法外延ＧａＡｓ单晶薄膜,最后进行断续多层循环退火（ＩＭＣＡ）。经电子探针（ＥＰＭＡ）、Ｒａｍａｎ光谱、Ｈａｌｌ测量和荧光（ＰＬ）光谱测试分析,证实在Ｓｉ表面获得了的４μｍ厚的ＧａＡｓ单晶薄膜。     

基于AlN和GaN形核层的AlGaN/GaN HEMT外延材料和器件对比

使用金属有机物化学气相淀积(MOCVD)方法在蓝宝石衬底上分别采用AlN和GaN作为形核层生长了AlGaN/GaN高电子迁移率晶体管(HEMT)外延材料,并进行了器件制备和性能分析.通过原子力显微镜(AFM)、高分辨率X射线双晶衍射仪(HR-XRD)和二次离子质谱仪(SIMS)等仪器对两种样品进行了对比分析,结果表明采用AlN形核层的GaN外延材料具有更低的位错密度,且缓冲层中氧元素的拖尾现象得到有效地抑制.器件直流特性显示,与基于GaN形核层的器件相比,基于AlN形核层的器件泄漏电流低3个数量级.脉冲Ⅰ-Ⅴ测试发现基于GaN形核层的HEMT器件受缓冲层陷阱影响较大,而基于AlN形核层的HEMT器件缓冲层陷阱作用不明显.     

Flat GaN epitaxial layers grown on Si(111) by metalorganic vapor phase epitaxy using step-graded AlGaN intermediate layers

In this work, we report on the growth by metalorganic vapor phase epitaxy (MOVPE) of GaN layers on AlN/Si(111) templates with step-graded AlGaN intermediate layers. First, we will discuss the optimization of the AlN/Si(111) templates and then we will discuss the incorporation of step-graded AlGaN intermediate layers. It is found that the growth stress in GaN on high-temperature (HT) AlN/Si(111) templates is compressive, although, due to relaxation, the stress we have measured is much lower than the theoretical value. In order to prevent the stress relaxation, step-graded AlGaN layers are introduced and a crack-free GaN epitaxial layer of thickness >1 μm is demonstrated. Under optimized growth conditions, the total layer stack, exceeding 2 μm in total, is kept under compressive stress, and the radius of the convex wafer bowing is as large as 119 m. The crystalline quality of the GaN layers is examined by high-resolution x-ray diffraction (HR-XRD), and the full-width-at-half maximums (FWHMs) of the x-ray rocking curve (0002) ω-scan and (−1015) ω-scan are 790 arc sec and 730 arc sec, respectively. It is found by cross-sectional transmission electron microscopy (TEM) that the step-graded AlGaN layers terminate or bend the dislocations at the interfaces.     

Effects of high-temperature AIN buffer on the microstructure of AlGaN/GaN HEMTs

Effects on AlGaN/GaN high-electron-mobility transistor structure of a high-temperature AlN buffer on sapphire substrate have been studied by high-resolution x-ray diffraction and atomic force microscopy techniques. The buffer improves the microstructural quality of GaN epilayer and reduces approximately one order of magnitude the edge-type threading dislocation density. As expected, the buffer also leads an atomically flat surface with a low root-mean-square of 0.25 nm and a step termination density in the range of 10⁸ cm^?2. Due to the high-temperature buffer layer, no change on the strain character of the GaN and AlGaN epitaxial layers has been observed. Both epilayers exhibit compressive strain in parallel to the growth direction and tensile strain in perpendicular to the growth direction. However, an high-temperature AlN buffer layer on sapphire substrate in the HEMT structure reduces the tensile stress in the AlGaN layer.     

Effect of AlN buffer thickness on GaN epilayer grown on Si(1 1 1)

We studied the influence of high temperature AlN buffer thickness on the property of GaN film on Si (1 1 1) substrate. Samples were grown by metal organic chemical vapor deposition. Optical microscopy, atomic force microscopy and X-ray diffraction were employed to characterize the samples. The results demonstrated that thickness of high temperature AlN buffer prominently influenced the morphology and the crystal quality of GaN epilayer. The optimized thickness of the AlN buffer is found to be about 150 nm. Under the optimized thickness, the largest crack-free range of GaN film is 10 mm×10 mm and the full width at half maximum of GaN (0 0 0 2) rocking curve peak is 621.7 arcsec. Using high temperature AlN/AlGaN multibuffer combined with AlN/GaN superlattices interlayer we have obtained 2 μm crack-free GaN epilayer on 2 in Si (1 1 1) substrates.     

MOCVD Growth of Device—quality GaN on Sapphire

An AIN Layer grown by an ALE has been developed to improve the growth quality of GaN ON Al2O3 substrate by low-pressure metalorganic vapor phase epitaxy(LP-MOVPE).An ALE AIN layer grown on Al2O3 substrate has a high quality and the structure is similar to GaN, this AIN layer can release the stress between Al2O3 substrate and GaN epilayer.By using this method, the orientation of substrate is extended to GaN epilayer, and the column tilt and the twist are improved, so as to obtain the device-quality GaN.     

Compositional modulation in In(x)Ga(1-x)N: TEM and X-ray studies

Transmission Electron Microscopy (TEM) and X-ray diffraction (XRD) have been used to study compositional modulation in In(x)Ga(1-x) N layers grown with compositions close to miscibility gap. The samples (0.34 < x < 0.8) were deposited by molecular beam epitaxy using either a 200 nm thick AlN or GaN buffer layer grown on a sapphire substrate. Periodic compositional modulation leads to extra electron diffraction spots and satellite reflections in XRD in the theta-2theta coupled geometry. The ordering period delta measured along c-axis was about delta = 45 A for x = 0.5 and delta = 66 A for x = 0.78 for samples grown on AlN buffer layer. TEM and XRD determinations of delta were in good agreement. Compositional modulation was not observed for the sample with x = 0.34 grown on a GaN buffer layer. Larger values of delta were observed for layers with higher In content and for those having larger mismatch with the underlying AlN buffer layer. The possibility that the roughness of the AlN growth surface promotes strong In segregation on particular crystallographic planes leading to compositional modulation is considered.     

AlGaN/GaN HEMTs on resistive Si(111) substrate grown by gas-sourceMBE

Al_0.3Ga_0.7N/GaN high electron mobility transistor (HEMT) structures have been grown on resistive Si(111) substrate by molecular beam epitaxy (MBE) using ammonia (NH₃). The use of an AlN/GaN intermediate layer allows a resistive buffer layer to be obtained. High sheet carrier density and high electron mobility arc obtained in the channel. A device with 0.5 μm gate length has been realised exhibiting a maximum extrinsic transconductance of 160 mS/mm and drain-source current exceeding 600 mA/mm. Small-signal measurements show f_t of 17 GHz and f_max of 40 GHz