Optical properties of GaN epilayers grown on Si (111) and Si (001) substrates

We report the observation of bright photoluminescence (PL) emission from two types of GaN epilayers grown by molecular beam epitaxy (MBE). Wurtzite phase GaN/Si (111) epilayers are grown by gas source MBE process, whereas cubic phase GaN epilayers are grown on (001) Si covered by thin SiC film in the process of Si annealing in propane prior to the GaN growth. PL emissions are identified based on the results of detailed PL and time-resolved PL investigations. For the wurtzite phase GaN we observe an efficient up in the energy transfer from bound to free excitons. This process is explained by a large difference in the PL decay times for two types (free and bound (donor, acceptor)) of excitonic PL emissions. For cubic phase GaN we confirm recent suggestion that acceptors have smaller thermal ionization energies than those in the wurtzite phase GaN.     

Si基GaN紫外光探测器

报道了以Si(111)为衬底的GaN光导型紫钙探测器的制备及其光电流性质,探测器的光谱响应表明,这种GaN探测器在紫外波段250－360nm有近于平坦的光电流响应,36nm附近陡峭的截止边,在357nm波长处,测得5V偏压下的响应度高达6．9A／W。响应度随外加偏压的增加而增加,5V时达到饱和,通过拟合光电流响应随入射光调制频率的变化关系,得到GaN探测器的响应时间为4．8ms。     

Synthesis and characterization of heteroepitaxial GaN films on Si(111)

We report crack-free and single-crystalline wurtzite GaN heteroepitaxy layers have been grown on Si (111) substrate by metal-organic chemical vapor deposition(MOCVD). Synthesized GaN epilayer was characterized by X-ray diffraction(XRD), atomic force microscope (AFM) and Raman spectrum. The test results show that the GaN crystal reveals a wurtzite structure with the <0001> crystal orientation and XRD ω-scans showed a full width at half maximum (FWHM) of around 583 arcsec for GaN grown on Si substrate with an HT-AlN buffer layer. In addition, the Raman peaks of E₂^high and A₁(LO) phonon mode in GaN films have an obvious redshit comparing to bulk GaN eigen-frequency, which most likely due to tensile strain in GaN layers. But the AO phonon mode of Si has a blueshit which shows that the Si substrate suffered a compressive strain. And we report that the AlN buffer layer plays a role for releasing the residual stress in GaN films.     

氨化Si基Ga2O3/V薄膜制备GaN纳米线

为了制备高质量的GaN纳米结构,采用磁控溅射技术先在硅衬底上制备Ga2O3/V薄膜,然后在流动的氨气中进行氨化反应,成功制备出GaN纳米线.采用X射线衍射(XRD)、傅里叶红外吸收光谱(FTIR)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)对样品进行分析.研究结果表明,采用此方法得到了六方纤锌矿结构的GaN纳米线,且900℃时制备的纳米线质量最好,直径在60nm左右,长度达到十几微米.     

Si(111)衬底上HVPE GaN厚膜生长

在Si(111)衬底上,以MOCVD方法高温外延生长的AIN为缓冲层,使用氮化物气相外延(HVPE)方法外延生长了15Km的c面GaN厚膜.并利用X射线衍射(XRD)、光致发光谱(PL)、拉曼光谱(Raman)等技术研究了GaN厚膜的结构和光学性质.分析结果表明,GaN厚膜具有六方纤锌矿结构,外延层中存在的张应力较小,...     

氨化Si基Ga2O3/In制备GaN薄膜

研究了Ga2O3/In 膜反应自组装制备GaN薄膜,再将Ga2O3/In膜在高纯氨气气氛中氨化反应得到GaN薄膜,用X射线衍射(XRD),傅里叶红外吸收(FTIR),扫描电镜(SEM),原子力显微镜(AFM),透射电镜(TEM)对样品进行结构,形貌的分析.测试结果表明:用此方法得到了六方纤锌矿结构的GaN多晶膜,且900℃时成膜的质量最好.     

Single Crystalline GaN Tiles Grown on Si (111) Substrates by Confined Lateral Guided Growth to Eliminate Wafer Bowing

A novel concept termed confined lateral guided growth (CLGG) has been demonstrated to prepare single crystalline GaN microtiles with a goal to create high crystalline quality and strain‐free GaN on large‐sized Si (111) substrates. Uniform array of hexagonal GaN tiles has been created with a diameter of larger than 30 μm for each tile. As revealed by the surface pits density of around 2 × 10⁸ cm⁻², the density of dislocations in these GaN tiles has been significantly reduced compared with that obtained typically from a GaN heteroepitaxy on Si (111). The strain in GaN tiles has been dramatically reduced to nearly zero. This approach offers a route to eliminate wafer‐bowing for growing high crystalline quality GaN on Si, especially when the substrate size scales to 12 in and beyond. The growth behavior and mechanism within these confined growth masks are investigated by both finite element modeling and experimental studying, indicating that CLGG is dominated by gas phase diffusion.     

Growth of GaN on SiC/Si substrates using AlN buffer layer by hot-mesh CVD

GaN films were grown on SiC/Si (111) substrates by hot-mesh chemical vapor deposition (CVD) using ammonia (NH₃) and trimetylgallium (TMG) under low V/III source gas ratio (NH₃/TMG = 80). The SiC layer was grown by a carbonization process on the Si substrates using propane (C₃H₈). The AlN layer was deposited as a buffer layer using NH₃ and trimetylaluminum (TMA). GaN films were formed and grown by the reaction between NH_x radicals, generated on a tungsten hot mesh, and the TMG molecules. The GaN films with the AlN buffer layer showed better crystallinity and stronger near-band-edge emission compared to those without the AlN layer.     

氮化时间对扩镓硅基GaN晶体膜质量的影响

采用射频磁控溅射在扩镓硅基上溅射Ga2O3薄膜,然后氮化反应组装GaN晶体膜,并研究氮化时间对薄膜晶体质量的影响。测试结果表明：采用两步法生长得到六方纤锌矿结构的GaN多晶膜,扩镓硅层有效的抑制了硅衬底的氮化和弛豫了GaN与Si衬底的热失配。同时显示：在相同的氮化温度下,晶粒尺寸随氮化时间的增加而增大,薄膜的晶化程度相应的得到提高。     

Synthesis of hexagonal and cubic GaN thin film on Si (111) using a low-cost electrochemical deposition technique

Gallium nitride GaN thin films were deposited on Si (111) substrates using electrochemical deposition technique at 20 °C. SEM images and EDX results indicated that the growth of GaN films varies with the current density. XRD and Raman analyses showed the presence of hexagonal wurtzite and cubic zinc blende GaN phases with the crystallite size around 18-19 nm. Photoluminescence spectrum showed that the energy gaps of h-GaN/Si (111) and c-GaN/Si (111) were near 3.39 eV and 3.2 eV respectively at 300 K. Raman spectrum indicated the presence of mixed phonon modes of hexagonal and cubic GaN.     

Structure and optical spectrum of GaN nanorods produced on Si(111) substrates

A novel method is applied to prepare nanorods. In this method, nanorods have been successfully synthesized on Si(111) substrates through annealing sputtered Ga₂O₃/Nb films under flowing ammonia at 950 °C in a quartz tube. The as-synthesized nanorods are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectra. The results show that the nanorod is single-crystalline GaN. It has a diameter of about 200 nm and lengths typically up to several micrometers. Photoluminescence spectrum under excitation at 325 nm only exhibits a UV light emission peak is located at about 368.5 nm. Finally, the growth mechanism of nanorods is also briefly discussed.     

氨化Si基Ga2O3/In2O3制备GaN薄膜

研究了Ga2O3/In2O3 膜反应自组装制备GaN薄膜,再将Ga2O3/In2O3膜在高纯氨气气氛中氨化反应得到GaN薄膜,用X射线衍射 (XRD),傅里叶红外吸收(FTIR),扫描电镜(SEM)和透射电镜(TEM)对样品进行结构、形貌的分析.测试结果表明,用此方法得到了六方纤锌矿结构的GaN多晶膜,且900℃时成膜的质量最好.     

High-quality epitaxial Bi(111) films on Si(111) by isochronal annealing

Bi(111) films grown on Si(111) at room temperature show a significantly higher roughness compared to Bi films grown on Si(100) utilizing a kinetic pathway based on a low-temperature process. Isochronal annealing steps of 3 min duration each with temperatures up to 200 °C cause a relaxation of the Bi films' lattice parameter toward the Bi bulk value and yield an atomically flat Bi surface. Driving force for the relaxation and surface reordering is the magic mismatch of 11 Bi atoms to 13 Si atoms that emerges at annealing temperatures above 150 °C and reduces the remaining strain to less than 0.2%.     

以ZnO为缓冲层制备硅基氮化镓薄膜

用脉冲激光沉积法(PLD)先在600℃的Si(111)衬底上沉积ZnO薄膜,然后用磁控溅射法再沉积GaN薄膜。直接沉积得到的GaN薄膜是非晶结构,将样品在氨气氛围中在850、900、950℃下退火15min得到结晶的GaN薄膜。用X射线衍射(XRD)、傅立叶红外吸收谱(FTIR)、光致发光谱(PL)和扫描电子显微镜(SEM)研究了ZnO缓冲层对GaN薄膜的结晶和形貌的影响。     

氨化温度对氨化Si基Ga2O3/Cr膜制备GaN纳米结构的影响

采用磁控溅射的方法在Si(111)衬底上溅射沉积Ga2O3/Cr膜,并通过氨化的方法在Si(111)衬底上成功合成了六方纤锌矿GaN纳米结构材料,研究了不同的氨化温度对合成GaN纳米材料的影响.采用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、透射电子显微镜(TEM)、高分辨透射电子显微镜(HR-TEM)、傅里叶红外吸收(FTIR)光谱来检测样品的形态,结构和成分,并且讨论了GaN纳米结构的生长机理.研究结果表明,在Cr催化合成GaN纳米结构的过程中,氨化温度对其有重要影响,最佳温度是950℃.     

用MOCVD法在LiGaO2(001)上生长GaN的研究

LiGaO₂单晶是目前所知的GaN最为理想的衬底材料,本研究用金属有机物气相沉积法(MOCVD)在LiGaO₂(001)衬底上进行了外延生长GaN膜的试验,生长出了表面较为平整的GaN外延膜.应用原子力显微镜(AFM)、X射线粉末衍射(XRD)和高分辨X射线双晶衍射分别对衬底对外延膜和衬底材料进行了分析测试.结果表明,用MOCVD法可以在LiGaO₂(001)衬底上生长出较高质量的无掺杂GaN(0001)外延膜.但由于MOCVD法是在高温还原气氛中生长GaN外延膜的,LiGaO₂在这种气氛中不够稳定,实验发现衬底材料在生长过程中部分样品发生开裂,但没有发生相变.     

基于薄膜SOI材料的GaN外延生长应力释放机制

本文研究了SOI衬底上采用MOCVD方法生长GaN材料的应力释放机制.采用SIMOX工艺制备的具有薄膜顶层硅的SOI材料作为外延生长的衬底材料,采用MOSS在位检测系统以及拉曼测试作为GaN内部应力的表征手段.结果表明,SOI材料对硅基GaN异质外延中的晶格失配应力和热应力的释放都有显著作用.薄膜SOI材料通过顶层硅与外延层的界面滑移,将一部分晶格失配应力通过界面的滑移释放,并且通过柔性薄膜顶层硅自身的应力吸收作用,将一部分热失配应力转移到衬底,从而有效地降低了GaN外延层的张应力.     

AlN缓冲层对提高硅基GaN薄膜质量的作用机理及其研究进展

AlN作为中间层可以有效提高硅基GaN的晶体质量。本文对于AlN作为形核层和插入层提高GaN晶体质量的机理进行分析和总结，并给出AlN的最佳生长条件。     

Effect of high temperature AlGaN buffer thickness on GaN Epilayer grown on Si(111) substrates

Crack-free GaN epitaxial layer was obtained through inserting 80 nm graded AlGaN buffer layer between GaN epilayer and high temperature AlN buffer on 2-in Si(111) substrates by metal organic chemical vapor deposition. This paper investigated the influence of AlGaN buffer thickness on the structural properties of the GaN epilayer. It was confirmed from the optical microscopy and scanning electronic microscopy that the graded AlGaN buffer with optimized thickness had a remarkable effect on introducing relative compressive strain to the top GaN layer and preventing the formation of cracks. X-ray diffraction and atomic force microscopy analysis showed that AlGaN buffer with proper thickness could improve the crystal quality and surface morphology of the GaN film. Transmission electron microscopy analysis revealed that a significant reduction in threading dislocations was achieved in GaN epilayer by the insertion of graded AlGaN buffer.     

Growth of GaAs nanowhisker arrays by magnetron sputtering on Si(111) substrates

The growth of GaAs nanowhisker (NW) arrays on Si(111) substrates by magnetron sputtering is demonstrated. The characteristic NW length is proportional to the effective thickness of a deposited layer and inversely proportional to the transverse whisker size at the top. The results are explained in terms of the diffusion model of NW growth.