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Understanding peculiarities in the optoelectronic characteristics of light emitting diodes based on (In,Ga)N/GaN nanowires  [PDF]
Mattia Musolino,Abbes Tahraoui,Friederich Limbach,Jonas L?hnemann,Uwe Jahn,Oliver Brandt,Lutz Geelhaar,Henning Riechert
Physics , 2014, DOI: 10.1063/1.4894241
Abstract: We investigate the effect of the p-type top contact on the optoelectronic characteristics of light emitting diodes (LEDs) based on (In,Ga)N/GaN nanowire (NW) ensembles grown by molecular beam epitaxy on Si substrates. We compare devices fabricated with either Ni/Au or indium tin oxide (ITO) top contact. The NW-LEDs with ITO exhibit a number density of NWs emitting electroluminescence about ten times higher, significantly lower turn-on voltage and series resistance, and a relative external quantum efficiency more than one order of magnitude higher than the sample with Ni/Au. These results show that limitations in the performance of such devices reported so far can be overcome by improving the p-type top-contact.
Optoelectronic Properties of GaN-Based Light-Emitting Diodes with Different Mesa Structures  [PDF]
Xueyun Song, Xianghua Zeng, Junbin Zhang, Yuzhe Jin, Xiangdong Meng
Materials Sciences and Applications (MSA) , 2012, DOI: 10.4236/msa.2012.312122
Abstract: GaN/InGaN lighting-emitting diodes with different mesa structures are studied. The current-voltage characteristics, light output power, luminous efficiency, and peak wavelength of the GaN/InGaN lighting-emitting diodes with different mesa patterns are compared. It shows that the current-voltage characteristics of the chips with more mesa areas are im- proved greatly by reducing the current crowding. With higher injection current the light output powers of GaN-based LED with more mesa areas are enhanced. And the chips with more P-electrode area have a smaller red shift and a little bit blue shift due to the reduction of the current crowding.
Crystal quality and electrical properties of p-type GaN thin film on Si(111) substrate by metal-organic chemical vapor deposition MOCVD  [PDF]
G.M. Wu,T.H. Hsieh
Journal of Achievements in Materials and Manufacturing Engineering , 2007,
Abstract: Purpose: In this paper, p-GaN samples have been grown on silicon substrates under various processing conditions. The effects of growth tenperature and thermal annealing on the crystal quality and strain were carefully investigated. The electrical properties such as hole concentration and mobility would be discussed.Design/methodology/approach: GaN-based III–V semiconductors have become promising materials for short-wavelength optoelectronic devices because of their large and direct band gap energies. In this paper, p-GaN has been grown by metal-organic chemical vapor deposition (MOCVD) at 900°C, 950°C, 1000°C, and 1050°C with low temperature LT-deposited AlN/AlGaN buffer layer.Findings: The mobility was achieved at 150 cm2/Vs and the hole concentration was 8x1017 cm-3. SIMS and XRD were used to measure and explain the relationships between hole concentration and the growth temperature. When the growth temperature was increased to 1000°C, the hole concentration was increased by ten times. According to the experimental results, the optimal growth temperature was 1000°C. After the thermal annealing process at temperature 850°C for 2 minutes, the FWHM of p-GaN was lowered to 617 arcsec. The effects of growth temperature were explained in the two temperature regions. From 900°C to 1000°C, the incorporation rate of Mg was slightly increased and the strain decreased with the growth temperature. Mg would provide holes and the lower strain would result in better crystal quality. The crystal quality and Mg concentration effects on hole concentration below 1000°C was thus beneficiary. On the other hand, when the growth temperature was further increased, the strain and FWHM increased while hole concentration decreased at 1050°C. At this high temperature, Si might become donor in GaN.Research limitations/implications: It was suggested that the hole concentration reduced at 1050°C due to the Si diffusion and the strain caused by Mg dopant. According to the experimental data, the optimal growth temperature was 1000°C. After the annealing process, the FWHM of p-GaN was lowered to 617 arcsec.Originality/value: Determination of crystal quality and electrical properties of p-type GaN thin film on Si(111) substrate by metal-organic chemical vapor deposition MOCVD.
GaN Schottky Barrier Ultraviolet Detector

Wang Jun,Zhao Degang,Liu Zongshun,Wu Mo,Jin Ruiqin,Li Na,Duan Lihong,Zhang Shuming,Zhu Jianjun,Yang Hui,

半导体学报 , 2004,
Abstract: 在蓝宝石 (0 0 0 1)衬底上采用低压金属有机物化学气相沉积 (MOCVD)方法生长GaN外延层结构 ,以此为材料制作了GaN基肖特基结构紫外探测器 .测量了该紫外探测器的暗电流曲线、C V特性曲线、光响应曲线和响应时间曲线 .该紫外探测器在 5V偏压时暗电流为 0 4 2nA ,在 10V偏压时暗电流为 38 5nA .在零偏压下 ,该紫外探测器在2 5 0nm~ 36 5nm的波长范围内有较高的响应度 ,峰值响应度在 36 3nm波长处达到 0 12A/W ,在 36 5nm波长左右有陡峭的截止边 ;当波长超过紫外探测器的截止波长 (36 5nm左右 ) ,探测器的响应度减小了三个数量级以上 .该紫外探测器的响
I-V Characteristics of Au-GaN Schottky Junction

LIN Zhao,|jun,ZHANG Tai,|ping,WU Guo,|ying,WANG Wei,YAN Gui,|zhen,SUN Dian,|zhao,ZHANG Jian,|ping,ZHANG Guo,|yi,

半导体学报 , 2000,
Abstract: Au\|GaN Schottky junction has been fabricated on n\|GaN materials by MOCVD and MBE.I\|V characteristics of the Schottky junctions have been determined at room temperature.It is shown that Schottky junction characteristics are seriously affected by the carrier concentration of GaN materials.
Stress and Grain Boundary Properties of GaN Films Prepared by Pulsed Laser Deposition Technique  [PDF]
D. Ghosh,S. Hussain,B. Ghosh,R. Bhar,A. K. Pal
ISRN Materials Science , 2014, DOI: 10.1155/2014/521701
Abstract: Polycrystalline gallium nitride films were successfully deposited on fused silica substrates by ablating a GaN target using pulsed Nd-YAG laser. Microstructural studies indicated an increase in the average crystallite size from ~8?nm to ~70?nm with the increase in substrate temperature from 300?K to 873?K during deposition. The films deposited here were nearly stoichiometric. XPS studies indicated two strong peaks located at ~1116.6?eV and ~395?eV for Ga2p3/2 and a N1s core-level peak, respectively. The films deposited at substrate temperature above 573?K are predominantly zinc blende in nature. PL spectra of the films deposited at higher temperatures were dominated by a strong peak at ~3.2?eV. FTIR spectra indicated a strong and broad absorption peak centered ~520?cm?1 with two shoulders at ~570?cm?1 and 584?cm?1. Characteristic Raman peak at ~531?cm?1 for the A1(TO) mode is observed for all the films. Grain boundary trap states varied between and ?m?2, while barrier height at the grain boundaries varied between 12.4?meV and 37.14?meV. Stress in the films decreased with the increase in substrate temperature. 1. Introduction Gallium nitride (GaN) is a promising material for applications in optoelectronic devices, such as ultraviolet-blue-green light-emitting diodes (LEDs) and laser diodes (LDs), due to its direct wide band gap and good thermal stability. It is equally suitable for high-temperature and high-power electronic applications. Depending on the growth conditions, GaN crystallizes either in the stable hexagonal (wurtzite, -phase) or metastable cubic (zinc-blende, -phase) polytypes. The prevalent deposition techniques for depositing GaN thin films are mainly metal-organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE). Recently, amorphous and polycrystalline GaN thin films deposited using magnetron sputtering technique [1–7] and laser ablation [8–10] technique have also been reported. GaN thin films with wurtzite structure were deposited by Chen et al. [5] by using reactive DC magnetron sputtering technique. The films exhibited a polycrystalline structure with a strong (002) orientation and were utilized as active channel layer to produce top-gate n-type thin-film transistors (TFTs). Highly textured polycrystalline GaN films having an average grain size of several hundred angstroms were obtained by Christie et al. [7] using an RF plasma-assisted molecular beam epitaxy system on quartz substrates. Zou et al. [6] reported the deposition of GaN films on glass substrates by the middle frequency magnetron sputtering method.
GaN Growth on LiGaO2(001) with MOCVD

YANG Wei-Qiao,GAN Fu-Xi,DENG Pei-Zhen,XU Jun,LI Shu-Zhi,ZHANG Rong,

无机材料学报 , 2003,
Abstract: LiGaO2 is the most promising substrate newly found for the epitaxy of GaN. Mirror-like GaN(0001) films were grown on LiGaO2(001) substrates by using MOCVD. The GaN films and substrates were investigated by means of AFM, XRD and X-ray double-crystal diffraction. The result shows that a preferable quality of GaN(0001) films can be grown on LiGaO2(001) substrates by using MOCVD. LiGaO2 being unstable under the conditions of MOCVD which should be operated at high temperature and in deoxidize ambience, LiGaO2 substrate cracks appear easily in the growth process, but no phase changes.
Multi-Buffer Layers Effect on Characteristic of GaN Grown by MOCVD

Lu Min,Fang Huizhi,Li Zilan,Lu Shu,Yang Hua,Zhang Bei,Zhang Guoyi,

半导体学报 , 2004,
Abstract: GaN films were grown with different multi buffer layers by MOCVD.X ray diffraction and photoluminence were applied to study the characteristic of GaN films.Compared to GaN film with conventional single low temperature buffer layer,the FWHM of (0002) XRD and PL of GaN films with different multi buffer layers were narrowed.It indicated that these multi buffer layers techniques could improve crystal quality of GaN films.
Effects of Mg Doping on Photoconductivity of GaN Films
Deheng ZHANG,Qingpu WANG,Yunyan LIU,

材料科学技术学报 , 2003,
Abstract: This paper presents the UV photoconductivity properties of GaN films doped with different Mg concentrations deposited by MOCVD. It was observed that for the undoped and weakly doped GaN films the UV photocurrent response was relatively large and the relax time was relatively short. With an increase in doped Mg content, the samples became p-type, the photocurrent response became weak and the relax time became longer.
The Stoichiometry of FeSe  [PDF]
A. J. Williams,T. M. McQueen,R. J. Cava
Physics , 2009, DOI: 10.1016/j.ssc.2009.07.011
Abstract: Tetragonal iron selenide, FeSe, the layered parent compound of the recently discovered superconducting arsenide family, has previously been shown to be non magnetic and superconducting with a critical temperature near 8 K. There has, however, been a lack of consensus as to whether selenium vacancies present due to large deviations from ideal stoichiometry are required to give rise to the superconductivity. Here we describe the results of experiments that demonstrate simply that superconducting iron selenide can only be synthesized as a pure material when near stoichiometric (i.e. FeSe). Significant selenium deficiency or excess gives rise to secondary magnetic phases, and a suppression of the superconductivity.
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