分子束外延GaN薄膜的X射线光电子能谱和俄歇电子能谱研究

用XPS和AES电子能谱的方法对等离子体辅助分子束外延(MBE)生长的GaN薄膜进行了表面分析和深度剖析.发现红外分子束外延(RFMBE)生长的富镓GaN薄膜实际表面存在O和C吸附层,C主要为物理吸附,而O在GaN表面形成局域化学键产生氧络合物覆盖层,并形成一定的深度分布.杂质O在GaN带隙中导带底形成杂质带同时引入深受主能级,使得带隙变窄室温光吸收谱向低能方向移动,光致发光谱出现宽带发光峰.从而影响GaN薄膜的电学和光学性质 关键词： GaN薄膜 X射线光电子能谱 俄歇电子能谱 表面分析     

Si基GaN外延层光致发光光谱与二次离子质谱的研究

报道了在Si基上用简便的真空反应法制备出GaN外延层．光致发光光谱测试结果表明不同的生长温度和退火工艺会对GaN外延层的发光特性产生影响,在1050℃下生长的GaN外延层的发光强度高于其他温度下生长的发光强度,退火可以使GaN外延层的发光强度增强．二次离子质谱(SIMS)测试结果表明外延层中Ga和N分布均匀,在表面处Ga发生了偏聚,同时外延层中还存在Si,O等杂质,这使得外延层中背景电子浓度高达1.7×10¹⁸/cm³. SIMS测试结果还表明,在外延生长前采用 关键词：     

GaN:Zn发光的显微观察

利用扫描电子显微镜(SEM)观察了气相外延GaN:Zn晶片的表面形貌、Zn浓度分布和阴极射线发光微区光谱及其MIS结构的电致发光微区光谱。研究表明,Zn杂质掺入GaN可以形成四种能量位置的发光中心;它们的形成与Zn浓度和晶体的微区结构有关;二者的不均匀决定了发光的不均匀性。     

金属有机物化学气相沉积同质外延GaN薄膜表面形貌的改善

为了获得高质量的GaN薄膜材料,研究了金属有机物气相沉积系统中GaN插入层对GaN衬底同质外延层表面宏观缺陷和晶体质量的影响.研究发现,插入层生长温度是影响GaN同质外延膜表面形貌和晶体质量的关键因素.由于生长模式与插入层生长温度相关,随着插入层生长温度的降低,外延膜生长模式由准台阶流模式转变为层状模式,GaN同质外延膜表面丘壑状宏观缺陷逐渐减少,但微观位错密度逐渐增大.通过对插入层温度和厚度的优化,进一步调控外延层的生长模式,最终有效降低了外延层表面的宏观缺陷,获得了表面原子级光滑平整、位错密度极低的GaN同质外延膜,其X射线衍射摇摆曲线(002),(102)晶面半峰宽分别为125arcsec和85arcsec,表面粗糙度均方根大小为0.23nm.     

SiC/AlN上外延GaN薄膜的黄带发光与晶体缺陷的关系

利用室温光致发光(PL)技术研究了在6HSiC(0001)上用金属有机物化学汽相沉积(MOCVD)外延生长的GaN薄膜“黄带”发光(YL)特点,与扫描电子显微镜(SEM)、X射线衍射(XRD)技术得到的GaN薄膜的表面形貌质量和内部结晶质量的结果相对照,表明“YL”发光强度与GaN薄膜的扩展缺陷多少直接相对应通过二次离子质谱(SIMS)技术获取的GaN薄膜中Ga元素深度分布揭示出镓空位(V_Ga)最可能是“YL”发光的微观来源分析认为,虽然宏观扩展缺陷(丝状缺陷、螺形位错等)和微观点缺陷V_Ga及其与杂质的络合物(complexes)都表现出与“YL”发射密切相关,但V_Ga及其与杂质的络合物更可能是“YL”发射的根本微观来源室温下获得的样品“YL”发射强度和光谱精细结构可用于分析GaN薄膜缺陷和晶体质量.     

射频等离子体辅助MBE生长GaN及Mg掺杂的光致发光

采用射频等离子体辅助分子束外延(RF plasma-assisted MBE)系统生长非故意掺杂GaN和p型GaN,并且通过室温和低温光致发光(PL)谱测试研究了材料的发光特性及与杂质态的关系,对于GaN外延层出现的黄带发光进行分析。结果表明,富Ga条件下生长的GaN材料特性要优于富N生长的材料;非故意掺杂的富Ga样品中出现的黄带发光(YL)与GaN中生成能最低的氮空位(V_N)缺陷有关;不同的Mg掺杂浓度对样品的PL特性有较大的影响;结合Hall效应测量结果,认为在Mg重掺杂的样品中出现的黄带发光,与GaN的自补偿效应以及重掺杂导致的晶体质量下降有关。     

在GaN生长初期形貌发展的观察

报道了对GaN在生长初期形貌发展的观察和形貌的高度分布演化.形貌观察发现GaN外延层由分离的岛转化为连续的膜,形貌的发展显示GaN经历了横向生长的阶段.利用原子力显微镜有数字化记录的特点,从形貌的观察中也得到了外延层高度分布,发现高度分布可用单峰或多峰高斯分布拟合.通过与形貌特征的对比,发现宽而且不对称的分布对应着岛状的外延层形貌,可以用多峰高斯分布拟和;窄而且对称的分布则对应着比较连续的膜,可以用单峰高斯分布拟和.     

淀积在不同小倾角蓝宝石衬底的n型GaN的研究

采用金属有机物化学淀积技术在不同倾角（0°—03°）的蓝宝石衬底上外延n型GaN.通过原子力显微镜观察到n型GaN均呈台阶流生长模式,02°和03°倾角衬底的n型GaN表面台阶朝向相同、分布均匀,明显地看到在0°倾角衬底的n型GaN表面由台阶重构直接导致的台阶朝向随机分布、疏密不匀的形貌.电子背散射分析表明,在0°倾角衬底的n型GaN外延层的应力随外延厚度增加而增加,而02°和03°倾角衬底的n型GaN外延层的应力没有明显的变化.电学和光学特性研究表明,02°和03°倾角衬底的n型GaN有较高的电子浓度和较低的黄光带与近带边强度之比. 关键词： 金属有机物化学淀积 氮化物 原子力显微镜 光致发光     

GaN外延层中的缺陷对光学性质的影响

用金属有机化合物气相外延（ＭＯＶＥＰ）方法生长具有不同表面形貌的非掺杂ＧａＮ，并对部分样品的外延层表面进行镜面加工．用阴极射线发光、光散射和拉曼散射方法观察ＧａＮ中深能级发光、缺陷散射光分布和拉曼散射光频移．结果表明，缺陷不但影响ＧａＮ的发光和光散射，而且影响拉曼频移     

MOVPE低温生长的n型GaN电学特性研究

系统研究了采用金属有机物化学气相外延方法在740℃和900℃条件下生长的n型GaN的电学特性. 电化学电容-电压测试表明,在低温条件下采用三乙基镓作为Ga源生长有利于降低非故意掺杂n型GaN的背景杂质浓度. 另外,对重掺Si的n型GaN的霍耳效应测试表明,随着Si掺杂浓度增大,电子浓度相应线性增大,表现出杂质带导电特性,而迁移率则相应减小. 同时,原子力显微镜测试和X射线衍射测试均表明生长温度和掺杂浓度对外延材料的表面形貌和晶体质量有影响,特别是在高掺杂浓度的情况下,样品的表面形貌恶化更严重. 在所研究的 关键词： n型GaN 电子浓度 迁移率     

Luminescent properties of GaN films grown on porous silicon substrate

GaN films have been grown on porous silicon at high temperatures (800-1050 °C) by metal organic vapor phase epitaxy. The optical properties of GaN layers were investigated by photoluminescence (PL) and cathodoluminescence (CL) spectroscopy. PL spectra recorded at 5 K exhibit excitonic emissions around 3.36-3.501 eV and a broad yellow luminescence at 2.2 eV. CL analysis at different electron excitation conditions shows spatial non-uniformity in-depth of the yellow and the band-edge emissions. These bands of luminescence are broadened and red- or blue-shifted as the electron beam penetrates in the sample. These behaviors are explained by a change of the fundamental band gap due to residual strain and the local thermal effect. It was found that the use of AlN buffer layer improves the crystalline quality and the luminescence property of GaN.     

MOVPE 生长GaN薄膜的 光致黄带发光与激发光源的相关性

用四种不同光源作为激发光源,研究了蓝宝石衬底金属有机物汽相外延方法生长的氮化镓薄膜的光致发光特性。结果发现用连续光作为激发光源时,光致发光谱中除出现365 nm的带边发射峰外,同时观察到中心波长位于约550 nm 的较宽黄带发光;而用脉冲光作为激发光源时其发光光谱主要是365 nm附近的带边发光峰,未观察到黄带发光。氮化镓薄膜的光致发光特性依赖于所用的激发光源性质。     

Properties comparison of GaN epilayers deposited under different growth temperatures

Undoped GaN epilayers were grown on c-plane sapphire substrates under different growth temperatures by metalorganic chemical vapour deposition (MOCVD). The optical and structural characteristics of these grown samples were studied and compared. It was found that the crystalline quality of GaN film deposited at 1050°C was better that of other samples. Photoluminescence spectra showed that the intensities of yellow luminescence band of the samples decreased as the growth temperature increased. All above test results demonstrate that high temperature deposition can serve as a good method for high-quality GaN epilayer growth and there exists an optimal growth temperature.     

Carrier recombination under one-photon and two-photon excitation in GaN epilayers

Luminescence properties of 100-mum thick GaN epilayers grown by hydride vapor phase epitaxy (HVPE) over three different substrates: high-pressure grown n-type bulk GaN (HP-n-GaN), high-pressure bulk GaN doped with magnesium (HP-GaN:Mg), and free-standing HVPE lifted-off from sapphire (FS-HVPE-GaN), were compared by means of one-photon and two-photon excitations. The contribution of carrier capture to nonradiative traps was estimated by the analysis of luminescence transients with carrier diffusion taken into account. The estimated values of carrier lifetime of about 3ns and diffusion coefficient of 1cm(2)/s indicate the highest quality of GaN epilayers on FS-HVPE-GaN substrates.     

Temperature-dependent photoluminescence of GaN grown on β-Si3N4/Si (1 1 1) by plasma-assisted MBE

Photoluminescence (PL) of high quality GaN epitaxial layer grown on β-Si₃N₄/Si (1 1 1) substrate using nitridation-annealing-nitridation method by plasma-assisted molecular beam epitaxy (PA-MBE) was investigated in the range of 5-300 K. Crystallinity of GaN epilayers was evaluated by high resolution X-ray diffraction (HRXRD) and surface morphology by Atomic Force Microscopy (AFM) and high resolution scanning electron microscopy (HRSEM). The temperature-dependent photoluminescence spectra showed an anomalous behaviour with an ‘S-like’ shape of free exciton (FX) emission peaks. Distant shallow donor-acceptor pair (DAP) line peak at approximately 3.285 eV was also observed at 5 K, followed by LO replica sidebands separated by 91 meV. The activation energy of the free exciton for GaN epilayers was also evaluated to be ∼27.8±0.7 meV from the temperature-dependent PL studies. Low carrier concentrations were observed ∼4.5±2×10¹⁷ cm⁻³ by measurements and it indicates the silicon nitride layer, which not only acts as a growth buffer layer, but also effectively prevents Si diffusion from the substrate to GaN epilayers. The absence of yellow band emission at around 2.2 eV signifies the high quality of film. The tensile stress in GaN film calculated by the thermal stress model agrees very well with that derived from Raman spectroscopy.     

高质量氮化镓材料的光致发光研究

利用氨气源分子束外延（GSMBE）技术,在改型Ⅳ型分子束外延设备上生长高质量GaN单晶外延材料,并对样品进行了光致发光测量。分析室温和低温光致发光谱,系统地研究GaN的发光峰及其起源,并对常见的黄色发光带现象及其微结构起因进行探讨。     

Origin of yellow luminescence from reduced pressure grown bulk GaN crystals

Cathodoluminescence (CL) in the scanning electron microscope has been applied to study the luminescence emission of GaN single crystals grown by LPE methods. CL spectra show the presence of near band edge and of yellow emissions. The latter has been found to be mainly related to rows of hillocks formed at the growth steps. The origin of the yellow luminescence is discussed     

Improvement of interface properties of AlGaN/GaN heterostructures under gamma-radiation

The cathodoluminescence (CL) spectra of AlGaN/GaN heterostructures grown on sapphire substrate were studied before and after gamma irradiation treatment. The CL spectroscopy results reveal strong yellow and blue luminescence transformation under gamma radiation treatment. The changes in CL spectra are compared with changes in the electrical characteristics of two-dimensional gas in AlGaN/GaN heterostructures. The origins of the observed improvement in properties of AlGaN/GaN heterostructures after gamma radiation treatment with 1 × 10⁶ rad are discussed on the basis of compensation and structural ordering of native defects.