生长在图形化蓝宝石衬底上的GaN薄膜光学性质研究

图形化蓝宝石衬底（PSS）技术作为提高LED发光效率的方法之一,一直备受关注。研究了PSS上生长的GaN薄膜的表面形貌、吸收光谱、红外光谱、拉曼散射（Raman）和太赫兹光谱等,并与常规蓝宝石衬底上的GaN外延薄膜进行对比。结果表明,PSS上生长的GaN外延薄膜的表面形貌、光提取效率（LEE）得到明显改善。此研究成果对进一步提高GaN基短波（蓝/紫光）发光二极管（LED）的发光效率具有一定的借鉴意义,为进一步拓展PSS器件的太赫兹响应提供了依据。     

利用磁控溅射在GaN/蓝宝石衬底上生长ZnO薄膜

Zinc oxide (ZnO) thin films were grown on n-GaN/sapphire substrates by radio-frequency (RF) magnetron sputtering. The films were grown at substrate temperatures ranging from 400 to 700 ℃ for 1 h at a RF power of 80 W in pure Ar gas ambient. The effect of the substrate temperature on the structural and optical properties of these films was investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and photoluminescence (PL) spectra. XRD results indicated that ZnO films exhibited wurtzite symmetry and c-axis orientation when grown epitaxially on n-GaN/sapphire. The best crystalline quality of the ZnO film is obtained at a growth temperature of 600 ℃. AFM results indicate that the growth mode and degree of epitaxy strongly depend on the substrate temperature. In PL measurement, the intensity of ultraviolet emission increased initially with the rise of the substrate temperature, and then decreased with the temperature. The highest UV intensity is obtained for the film grown at 600 ℃ with best crystallization. oindent     

蓝宝石衬底上侧向外延GaN中的位错降低

采用侧向外延(ELOG)方法,在制作了条形掩膜图形的GaN衬底上用MOCVD生长高质量GaN.AFM,化学湿法腐蚀及TEM分析表明:采用两步法ELOG生长的GaN中,掩膜下方的缺陷被掩膜所阻挡,窗口区内二次生长的GaN的位错也大幅降低;在相邻生长前沿所形成的合并界面处形成晶界;化学湿法腐蚀无法得到关于合并界面处缺陷的信息.侧翼区域中极低的穿透位错使得ELOG GaN适用于在其上制作高性能的氮化物基激光器.     

用MOCVD在r面蓝宝石衬底上生长的a面GaN的独特电学性质研究

Nonpolar （1120） a-plane GaN films have been grown by low-pressure metal-organic vapor deposition on r-plane （1102） sapphire substrate. The structural and electrical properties of the a-plane GaN films are investigated by high-resolution X-ray diffraction （HRXRD）, atomic force microscopy （AFM） and van der Pauw Hall measurement. It is found that the Hall voltage shows more anisotropy than that of the c-plane samples; furthermore, the mobility changes with the degree of the van der Pauw square diagonal to the c direction, which shows significant electrical anisotropy. Further research indicates that electron mobility is strongly influenced by edge dislocations.     

在c面蓝宝石上生长的InN外延薄膜中位错与极性的TEM研究

有关GaN和富Ga的InGaN薄膜中的位错和极性已有TEM研究，而InN和富In的InGaN薄膜却少见报道。研究InN薄膜中的缺陷和极性对生长高质量的InN薄膜很有意义。本文用TEM研究在c面蓝宝石上分子束外延生长的InN（760nm）／GaN（245nm）／AlN（14nm）薄膜中的穿透位错和极性。     

蓝宝石衬底上HVPE-GaN厚膜生长

采用氢化物气相外延(HVPE)方法,以蓝宝石作衬底,分别在MOCVD-GaN模板和蓝宝石衬底上直接外延生长GaN.模板上的GaN生长表面平整、光亮,但开裂严重.其(0002)的双晶衍射半高宽最低为141″;蓝宝石衬底上直接生长GaN外延层质量较差,其双晶衍射半高宽为1688″,但不发生开裂.HCl的载气流量对预反应有很大的影响.应力产生于外延层和衬底之间的界面处,界面孔洞的存在可以释放应力,减少开裂.光致发光(PL)谱中氧杂质引起强黄光发射.     

蓝宝石衬底上HVPE-GaN厚膜生长

采用氢化物气相外延(HVPE)方法,以蓝宝石作衬底,分别在MOCVD-GaN模板和蓝宝石衬底上直接外延生长GaN.模板上的GaN生长表面平整、光亮,但开裂严重.其(0002)的双晶衍射半高宽最低为141″;蓝宝石衬底上直接生长GaN外延层质量较差,其双晶衍射半高宽为1688″,但不发生开裂.HCl的载气流量对预反应有很大的影响.应力产生于外延层和衬底之间的界面处,界面孔洞的存在可以释放应力,减少开裂.光致发光(PL)谱中氧杂质引起强黄光发射.     

前处理蓝宝石衬底上生长高质量GaN薄膜

采用化学方法腐蚀部分c面蓝宝石衬底,在腐蚀区域形成一定的图案,利用LP-MOCVD在经过表面处理的蓝宝石衬底上外延生长GaN薄膜.采用高分辨率双晶X射线衍射(DCXRD)、透射光谱分析GaN薄膜的晶体质量和光学质量.分析结果表明,GaN薄膜透射谱反映出的GaN质量与X射线双晶衍射测量的结果一致,即透射率越大,半高宽越小,结晶质量越好;对蓝宝石衬底进行前处理可以大大改善GaN薄膜的晶体质量和光学质量,其(0002)面及(1012)面XRD半高宽(FWHM)分别降低到208.80"及320.76"     

前处理蓝宝石衬底上生长高质量GaN薄膜

采用化学方法腐蚀部分c面蓝宝石衬底,在腐蚀区域形成一定的图案,利用LP-MOCVD在经过表面处理的蓝宝石衬底上外延生长GaN薄膜.采用高分辨率双晶X射线衍射(DCXRD)、透射光谱分析GaN薄膜的晶体质量和光学质量.分析结果表明,GaN薄膜透射谱反映出的GaN质量与X射线双晶衍射测量的结果一致,即透射率越大,半高宽越小,结晶质量越好;对蓝宝石衬底进行前处理可以大大改善GaN薄膜的晶体质量和光学质量,其(0002)面及(1012)面XRD半高宽(FWHM)分别降低到208.80"及320.76"     

预处理蓝宝石衬底上生长高质量 GaN 显示薄膜

采用化学方法腐蚀部分 c-面蓝宝石衬底,在腐蚀区域形成一定的图案,利用 LP-MOCVD 在此经过表面处理的蓝宝石衬底上外延生长 GaN 薄膜.采用高分辨率双晶X射线衍射(DCXRD)、光致发光光谱(PL)、透射光谱分析GaN薄膜的晶体质量和光学质量.分析结果表明,CaN 薄膜透射谱反映出的 CaN 质量与 X射线双晶衍射测量的结果一致,即透射率越大,半高宽越小,结晶质量越好;对蓝宝石衬底进行前处理可以大大改善GaN薄膜的晶体质量和光学质量,其(0002)面及(1012)面XRD半高宽(FWHM)分别降低到 208.80arcsec 及 320.76arcsec,而且其光致发光谱中的黄光带几乎可以忽略.     

锥形图形衬底上氮化镓薄膜生长和表征

GaN films are grown on cone-shaped patterned sapphire substrates(CPSSs)by metal-organic chemical vapor deposition,and the influence of the temperature during the middle stage of GaN growth on the threading dislocation(TD)density of GaN is investigated.High-resolution X-ray diffraction(XRD)and cathodeluminescence(CL)wereusedtocharacterizetheGaNfilms.TheXRDresultsshowedthattheedge-typedislocation density of GaN grown on CPSS is remarkably reduced compared to that of GaN grown on conventional sapphire substrates(CSSs).Furthermore,whenthegrowthtemperatureinthemiddlestageofGaNgrownonCPSSdecreases,the full width at half maximum of the asymmetry(102)plane of GaN is reduced.This reduction is attributed to the enhancement of vertical growth in the middle stage with a more triangular-like shape and the bending of TDs.The CL intensity spatial mapping results also showed the superior optical properties of GaN grown on CPSS to those of GaN on CSS,and that the density of dark spots of GaN grown on CPSS induced by nonradiative recombination is reduced when the growth temperature in the middle stage decreases.     

基于图形衬底生长的GaN位错机制分析

采用缺陷选择性腐蚀法结合光学显微镜及原子力显微镜(AFM)对金属有机化合物气相外延(MOVPE)在蓝宝石图形衬底(PSS)上生长的非掺杂GaN体材料的位错产生机制进行了研究,分析结果表明,位错来源于三个方面:一是"二步法"生长机制引入的位错;二是是由于图形衬底上不同区域GaN晶体相互连接时由于晶面不连续所造成的位错群;三是由于图形衬底制作工艺过程中引入的表面污染与损伤.     

Nucleation and growth behavior for GaN grown on (0001) sapphire via multistep growth approach

Formation and coalescence of GaN truncated three dimensional islands (TTIs) on (0001) sapphire are observed during growth of GaN using a close spaced metalorganic chemical vapor deposition reactor. To encourage formation of TTIs to occur uniformly over the buffer layer, growth conditions are chosen under which thermal desorption and/or mass transport of the buffer layer can be suppressed. During coalescence of TTIs, growth conditions that favor higher desorption of species on the GaN (0001) surface and incorporation on other planes are beneficial. Therefore, changing the growth conditions as the growth mode changes is effective to obtain both good crystallinity and flat surface morphology.     

A 4.69-W/mm output power density InAIN/GaN HEMT grown on sapphire substrate

We report high performance InAlN/GaN HEMTs grown on sapphire substrates.The lattice-matched InAlN/GaN HEMT sample showed a high 2DEG mobility of 1210 cm2/(V.s)under a sheet density of 2.6 ×1013 cm-2.Large signal load-pull measurements for a(2 × 100 μm)× 0.25 μm device have been conducted with a drain voltage of 24 V at 10 GHz.The presented results confirm the high performances reachable by InAlN-based technology with an output power density of 4.69 W/mm,a linear gain of 11.8 dB and a peak power-added efficiency of 48％.This is the first report of high performance InA1N/GaN HEMTs in mainland China.     

蓝宝石衬底上输出功率密度为4.69W/mm的InAlN/GaN HEMT

We report high performance InAlN/GaN HEMTs grown on sapphire substrates. The lattice-matched InAlN/GaN HEMT sample showed a high 2DEG mobility of 1210 cm²/(V·s) under a sheet density of 2.6 × 10¹³ cm^-2. Large signal load-pull measurements for a (2 × 100 μm) × 0.25 μm device have been conducted with a drain voltage of 24 V at 10 GHz. The presented results confirm the high performances reachable by InAlN-based technology with an output power density of 4.69 W/mm, a linear gain of 11.8 dB and a peak power-added efficiency of 48%. This is the first report of high performance InAlN/GaN HEMTs in mainland China.     

A 4.69-W/mm output power density InAlN/GaN HEMT grown on sapphire substrate

We report high performance InAlN/GaN HEMTs grown on sapphire substrates.The lattice-matched InAlN/GaN HEMT sample showed a high 2DEG mobility of 1210 cm²/（V·s） under a sheet density of 2.6×10¹³ cm^-2.Large signal load-pull measurements for a（2×100μm）×0.25μm device have been conducted with a drain voltage of 24 V at 10 GHz.The presented results confirm the high performances reachable by InAlN-based technology with an output power density of 4.69 W/mm,a linear gain of 11.8 dB and a peak power-added efficiency of 48%.This is the first report of high performance InAlN/GaN HEMTs in mainland China.     

基于蓝宝石纳米图形衬底上氮化镓生长的研究

利用两步生长法在蓝宝石纳米图形衬底（NPSS）上生长得到高质量的氮化镓薄膜。通过XRD和SEM对薄膜质量的表征和研究发现,为得到高质量的氮化镓（GaN）薄膜,在NPSS上生长时得到的最优缓冲层厚度为15nm,而在微米级尺寸的图形衬底（MPSS）上得到的最优缓冲层厚度远大于15nm。同时,在NPSS上生长氮化镓薄膜的过程中观察到一个有趣的现象,即GaN在NPSS上生长的初始阶段,氮化镓晶粒主要在图形之间的平面区域生长,极少量的GaN在衬底图形的侧面上聚集生长。这一有趣的现象明显不同于GaN在MPSS上的生长过程。接着,又在NPSS上生长了GaN基LED结构,并对其光电性能进行了研究。     

Investigation of light output performance for gallium nitride-based light-emitting diodes grown on different shapes of patterned sapphire substrate

GaN-based blue light-emitting diodes (LEDs) on various patterned sapphire substrates (PSSs) are investigated in detail. Hemispherical and triangular pyramidal PSSs have been applied to improve the performance of LEDs compared with conventional LEDs grown on planar sapphire substrate. The structural, electrical, and optical properties of these LEDs are investigated. The leakage current is related to the crystalline quality of epitaxial GaN films, and it is improved by using the PSS technique. The light output power and emission efficiency of the LED grown on triangular pyramidal PSS with optimized fill factor show the best performance in all the samples, which indicates that the pattern structure and fill factor of the PSS are related to the capability of light extraction.     

High-Quality GaN heteroepitaxial films grown by metalorganic chemical vapor deposition

In this paper, we describe the growth and characterization of high-quality GaN heteroepitaxial films grown on basal-plane sapphire substrates using metalorganic chemical vapor deposition. The quality of these films is analyzed by a variety of methods, including high-resolution x-ray diffraction, optical transmission spectroscopy, transmission electron microscopy (TEM), room temperature photoluminescence, and room-temperature Hall measurements. The x-ray diffraction full width at half maximum value of ΔΘ ～37 arc s is the narrowest reported to date for any III-V nitride film on any substrate. The x-ray rocking curves for ～0.48 μm thick GaN/Al₂O₃ heteroepitaxial layers exhibit Pendellösung fringes, indicating that even relatively thin films can be of high quality. High-resolution TEM lattice images further attest to the excellent structural quality, showing the films to be completely free of stacking faults. Furthermore, no evidence of columnar growth is observed.     

The effect of GaN and ain buffer layers on GaN film properties grown on both C-plane and A-plane sapphire

This paper presents a comparative study of the properties of GaN grown by organometallic vapor phase epitaxy, using both a GaN and A1N buffer layer, as a function of sapphire orientation (c-plane vs a-plane). Results are presented for varying the thickness of the buffer layer, varying the growth temperature of the GaN film, and also varying the ammonia/trimethylgallium mass flow ratio. The electron Hall mobilities of GaN films grown on an A1N buffer layer were, in general, higher compared to films grown using a GaN buffer layer. In addition, growth on a-plane sapphire resulted in higher quality films (over a wider range of buffer thicknesses) than growth on c-plane sapphire. The room temperature electron mobilities were also found to be dependent on, not only the growth temperature, but also the ammonia/trimethylgallium mass flow ratio.