GaN外延层中的缺陷研究

采用阴极射线致发光法观察金属有机物汽相外延法生长的具有不同表面形貌的GaN外延层中黄色发光带的强度分布.结果表明六角金字塔形表面形貌对发光强度分布的测量有很大影响.测量和比较表面镜面加工样品的黄色发光带强度分布、原子序数衬度和X射线波谱发现,黄色发光带的强度在含有O和C等杂质缺陷附近较强.高分辨透射电子显微镜观察表明,杂质缺陷区的晶格结构不同于GaN基质,以及位错和裂缝等由应力引起的缺陷.认为此类缺陷可能是生长过程中,杂质在结晶小丘合并处的V形凹角中的沉积所产生. 关键词：     

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.     

Cathodoluminescence from deformed doped MgO crystals

The cathodoluminescence (CL) from indented Fe doped MgO single crystals has been studied with the scanning electron microscope and the results have been compared with the CL from undoped crystals. As in the undoped crystals, the iron doped crystals show in the deformed regions an enhanced luminescence emission but it has been found that iron acts as a quencher of luminescence. The results indicate that in the blue emission of the deformed crystals there is not a noticeable contribution of iron. From the evolution of CL with the irradiation time in the electron microscope it is concluded that the total Fe content influences the CL emission more than the Fe³⁺ content.     

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.     

Cathodoluminescence of oxyfluoride glass-ceramics

Tb, Ce, Eu activated oxyfluoride glass-ceramics with the composition SiO₂ · Al₂O₃ · Li₂O · LaF₃ have been studied by cathodoluminescence (CL). We compared CL intensities and decay times of the Tb, Ce, Eu activated glass-ceramic samples and observed that the Tb activated sample has the most intense luminescence, but the Ce activated sample has the shortest decay times. Induced optical absorption and thermostimulated luminescence have been observed after X-ray irradiation of samples.     

Cathodoluminescence mapping and spectroscopy of Te-doped InxGa1−xSb grown by the vertical Bridgman method under an alternating magnetic field

Cathodoluminescence (CL) in the scanning electron microscope and wavelength dispersive X-ray microanalysis (WDX) have been used to assess the homogeneity of a whole Te-doped In_xGa_1?xSb ingot grown by the vertical Bridgman method under an alternating magnetic field. In particular, WDX has been used to determine the chemical composition of the ingot along the growth axis and several radial directions, while CL has been used to investigate the effective incorporation of In into the alloy, the nature and distribution of extended defects influencing the luminescence of the material and the shape evolution of the growth interfaces along the growth axis. CL spectroscopy reveals that doping with Te influences the band gap energy of this ternary compound through the Moss–Burstein effect.     

Radiation-induced cathodoluminescent signatures in calcite

At ambient temperatures, a permanent change due to neutron irradiation has been identified in the luminescent properties of the common mineral calcite. Calcite is one of many ubiquitous minerals that are known to exhibit luminescence under electron bombardment, a process known as cathodoluminescence (CL). The UV–Visible spectra of individual calcite grains were measured with CL spectroscopy before and after neutron irradiation. Exposure to neutrons causes additional crystal lattice defects (beyond those naturally-occurring) that leave a permanent, readily-measurable CL signature in the 515 nm region of the spectrum. Dose response results following irradiation have been measured and a spectroscopic signature is described that increases proportionately to neutron dose. The CL measurements are complicated by a dependence on the orientation relative to direction of excitation. When taken into account, the total dose to the crystal can be estimated, and possibly even the direction of the neutron source can be determined. This signature could potentially be developed into a nuclear forensics tool to help identify locations where special nuclear materials have been stored.     

Dependence of optical properties on specific surface area and grain sizes in TiO2 powders

The diffuse reflectance (DR) spectra and the cathodoluminescence (CL) spectra in the range 0.34–2.10 μm and changes in the spectra after bombardment by accelerated electrons have been studied as a function of the specific surface area and the grain sizes of titanium dioxide (rutile) powders of different grades (P1, P2, P02, R10). It has been established that the diffuse reflection coefficient and the luminescence band intensity increase as the specific surface area decreases and the grain size of the powder increases. A smaller specific surface area of the powders means lesser initial flareup and subsequent “quenching” of the CL bands as a function of electron fluence. It has been shown that history-related differences between powders of different grades is a less significant factor than the specific surface area in determining the diffuse reflectance and luminescence and also the radiation resistance of the powders. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 1, pp. 73–77, January–February, 2006.     

Cathodoluminescence microscopic studies of α-HgI2 platelets and crystals

Cathodo Luminescence studies (CL) have been carried out on red mercuric-iodide (α-HgI₂) crystals and platelets grown by the vapor transport method. Panchromatic CL images revealed inhomogeneous distribution of growth-induced dislocations and terraces. The effect of prolonged KI (20%) treatment on the evolution of different CL bands has been investigated. CL spectra of the platelets at 80 K showed three luminescence bands at about 546, 567 and 624 nm. The intensity of the 567 nm band (band II) decreased after KI treatment, thus indicating the role of I vacancies on the evolution of this band. An additional band at about 555 nm is observed in as-grown crystals, but not revealed in platelets. Increase of the relative intensity of band III (624 nm) on prolonged KI treatment indicates the association of some surface states on this band along with the effect of impurities as reported earlier. Hg treatment causes an increase of total CL intensity and also the relative intensity of band II in platelets and crystals.     

化学气相沉积法制备β-Ga_2O_3纳米结构及其缺陷发光性质研究

利用化学气相沉积法(CVD),在不同压强下分别得到β-Ga2O3纳米线(NWs)和纳米带(NBs)。研究结果表明,获得的NWs与NBs均为单斜结构的β-Ga2O3,且NWs结晶质量优于NBs。在阴极射线发光(CL)光谱中,发现NWs与NBs在近紫外和蓝光波段有较强的发光。对比NWs与NBs的CL光谱,推断β-Ga2O3在374 nm和459 nm的近紫外和蓝色发光峰分别来自于Ⅰ型和Ⅱ型氧空位(VO(I)和VO(Ⅱ))的缺陷复合。     

Strong Visible and Near-Infrared Cathodoluminescence in Alkali Feldspar

In this study, cathodoluminescence (CL) spectroscopy at direct current and alternating current under the sample temperature condition of 40–293 K using different modulation frequencies is presented for alkali feldspar from the Dartmoor granite (UK). These feldspars contain strain-controlled lamellar crypto- and microperthites that are cross-cut by strain-free deuteric microperthites. The CL spectra of the alkali feldspar at room and low temperature confirm that the observed emission peaked at ～460 nm could be associated with Al-O^?-Al or Ti impurity centers, yellow emission ～560 nm could be associated with the presence of the centers such as radiation-induced defect centers, and ～756 nm emission could be associated with the Fe³⁺ impurity center on T₁ and T₂ sites. The consequence of their association is to produce different luminescence properties such as intensity, peak wavelength, and band shape.     

Luminescent properties of ZnO thin films treated by pulse-modulated high-power inductively coupled plasma

The effect of hydrogen plasma irradiation on luminescence properties of ZnO thin films was studied by using a pulse-modulated inductively coupled plasma technique. H-plasma exposure distance was changed to investigate the effect of hydrogen plasma irradiation on luminescent properties. Room temperature cathodoluminescence (CL) spectrum shows that hydrogen plasma irradiation can increase the efficiency of UV emission at 3.27 eV, and the improvement is strongly dependent on H-plasma exposure distance. For low temperature CL spectra, the intensity of donor-acceptor pair (DAP) transition at 3.315 eV has been increased more rapidly after hydrogen plasma irradiation, leading DAP to be the dominant transition.     

形貌依赖的ZnO阴极射线发光性质研究

采用溶剂热法,通过调节水和乙醇混合液的比例制备了多种形貌的ZnO微米结构。利用扫描电子显微镜（SEM）对ZnO微米结构的形貌及尺寸进行了观察。采用可以实现纳米级微观区域光谱采集的阴极射线发光（CL）技术,对不同形貌的单个粒子的光谱进行精细表征,获得了位置依赖的ZnO阴极射线发光数据。实验结果表明：ZnO材料的发光性质与形貌有关,由于形貌差异导致其局部结晶质量、界面缺陷、表面电荷分布、表面晶面等方面的差异,几种因素共同作用决定其最终的发光性质。     

Luminescence with Local Distribution and Its Possible Mechanism in Zinc Oxide Micro-Crystallites

The spatial luminescence distribution hi the ZnO micro-crystallite fihns deposited on silicon substrates by CVD at room tempezature is investigated by the cathedolumineseence （CL） image. It has been observed that the CL image of the samples constitutes a certain pattern. The UV emission pattern projective to the （0001） face of ZnO grains consists of a series of lines nearby the grain boundaries . The included angles between any two adjacent lines are almost 120°. What is more, some luminescent lines form a close hexagon similar to ZnO crystalline structure. Such a local distribution propety shows that the UV emission on as-grown ZnO crystallite should be due to some local defects congregated to {1010} facets of ZnO grain rather than free exciton recombination.     

Photoluminesence of Iodine‐Doped Crystals of ZnSe

The luminescence spectra and the luminescenceexcitation spectra of ZnSe crystals grown by the Piper–Polish method have been investigated in the temperature interval 81–300 K. An intense edge emission assigned to the presence of iodine has been detected. The analysis of the longwave photoluminescence band by the Alentsev–Fok method has revealed a yellow luminescence band which is attributed to the associative emission centers involving I _Se.     

高温氧化多孔硅的电子束辐照效应

通过高温氧化处理得到的多孔硅,其阴极射线发光谱呈现明显的三峰结构。峰强随电子束辐照时间而下降。对光致发光很弱的样品,电子束辐照后光致发光明显地增强。红外透射谱及Raman谱分析表明样品基本上成为SiO_x.进一步分析指出三峰可能来源于SiO_x中的缺陷中心发光。电子束辐照在SiO_x禁带中引进了一些缺陷能级,通过这些能级使得紫外线可激发样品发光,出现光致发光增强的现象。     

Investigation of yellow luminescence intensity of N-polar unintentionally doped GaN

This paper reports that the yellow luminescence intensity of N-polar GaN Epi-layers is much lower than that of Ga-polar ones due to the inverse polarity,and reduces drastically in the N-polar unintentionally-doped GaN after etching in KOH solution.The ratio of yellow luminescence intensity to band-edge emission intensity decreases sharply with the etching time.The full width at half maximum of x-ray diffraction of(10-12) plane falls sharply after etching,and the surface morphology characterized by scanning electron microscope shows a rough surface that changes with the etching time.The mechanism for the generation of the yellow luminescence are explained in details.     

Cathodoluminescence microcharacterization of forsterite in the chondrule experimentally grown under super cooling

Cathodoluminescence (CL) of laboratory forsterite chondrules has been characterized to clarify the formation process of chondrules and related mechanism of the crystal growth in a supercooled melt. Color CL image of the experimentally grown forsterite exhibits significant blue luminescence in the main branches of the interior structure of lab-chondrule, which reflects to the anisotropy of crystallization. A new CL band centered at 450–525 nm (2.76–2.36 eV) in blue to green region might be assigned to a microdefect-related center, which is a diagnostic peak for the forsterite that was formed due to the rapid growth as high as ～10 mm/s or higher from a supercooled melt.     

Cathodoluminescence study of extended defects in hydrothermal ZnO crystals

Understanding the luminescence of ZnO is very important for some applications. In spite of the many studies carried out, there are still some points concerning the origin of some of the luminescence emissions in ZnO crystals that require additional study; in particular, the role of extended defects remains to be a matter of controversy. We present here a cathodoluminescence analysis of the defects generated by Vickers indentation in hydrothermal HTT crystals. Special emphasis was paid to the luminescence band peaking around 3.3 eV. The origin of this band is a matter of controversy, since it has been related to different causes, extended defects being one of the candidates for this emission. The CL images were acquired around crystal defects. It is observed that the 3.3 eV emission is enhanced around the crystal defects; though it is also observed, but weaker, out of the defect regions, which suggests that there exist two luminescence emissions peaking very close to 3.3 eV. The two emissions, one related to structural defects and the other to the LO phonon replica of the free excitonic band, appear very close each other and their relative intensity should determine the shape of the spectrum.     

Cathodoluminescence study of visible luminescence in hydrothermal ZnO crystals

We present a study of the visible luminescence in ZnO hydrothermal crystals. The study is carried out on oxygen polarity basal plane (000-1) plates that are sliced through several distinct growth sectors of the crystal. The plates reveal three distinct regions that display differences in the luminescence emission, especially in the visible range. These differences should be related to the variation in the distribution of impurities and native defects in the various growth sectors of hydrothermal ZnO. CL images also expose the presence of nonradiative recombination centers that are associated with point defects or complexes of point defects. CL measurements varying the acceleration voltage of the e-beam reveal that the deep levels responsible for the green luminescence, and in a minor extension those responsible for the yellow-orange luminescence are depleted near the surface. A discussion about the main hypothesis accounting for such behavior is presented. PACS 71.55.Gs; 71.55.-i; 78.55.Et; 78.60.Hk