侧向外延生长GaN的结构特性

研究了在刻有图形的GaN"衬底”上用HVPE方法侧向外延生长(ELO)GaN的结构特性.在SiO2衬底上侧向外延生长GaN已经实现,并得到了平面的ELO GaN薄膜.采用扫描电子显微镜、透射电微镜和原子力显微镜技术研究了这种ELO GaN材料的结构和表面形貌.原子力显微镜图像表明:在ELO范围中的4μm2面积上不存在明显的阶状形貌.透射电子显微镜的观测表明在ELO范围内位错密度很低.在接合的界面上没观察到有空隙存在.但观测到晶格的弯曲高达3.3°,这被归因为由GaN层下的"籽层”和接合界面处的水平倾料和猝灭所产生的螺旋位错的积聚.     

Optical and Magnetic Properties of Fe-Doped GaN Diluted Magnetic Semiconductors Prepared by MOCVD Method

Fe-doped GaN thin films are grown on c-sapphires by metal organic chemical vapour deposition method （MOCVD） Crystalline quality and phase purity are characterized by x-ray diffraction and Raman scattering measurements. There are no detectable second phases formed during growth and no significant degradation in crystalline quality as Fe ions are doped. Fe-related optical transitions are observed in photoluminescence spectra. Magnetic measurements reveal that the films show room-temperature ferromagnetic behaviour. The ferromagnetism may originate from carrier-mediated Fe-doped GaN diluted magnetic semiconductors or nanoscale iron clusters and FeN compounds which we have not detected.     

在MOCVD系统中用预淀积In纳米点低温下合成生长InN

利用低压金属有机化学气相淀积(LP-MOCVD)系统,在(0001)蓝宝石衬底上采用预淀积In纳米点技术低温合成制备了立方相的InN薄膜.首先以TMIn作源在蓝宝石衬底表面预淀积了一层金属In纳米点,然后在一定条件下合成生长InN薄膜.X射线衍射谱(XRD)和X射线光电子发射谱(XPS)显示适当的预淀积In不仅能够促进InN的生长,同时还能够抑制金属In在InN薄膜中的聚集.原子力显微镜(AFM)观察表明,金属In纳米点不仅增强了成核密度,而且促进了InN岛的兼并.自由能计算表明预淀积的In优先和NH3分解得到的NH与N基反应生成InN.我们认为这种优先生成的InN为接下来InN的生长提供了成核位,从而促进了InN的生长.     

Fabrication and Characterization of GaN-Based Micro-LEDs on Silicon Substrate

GaN-based micro light emitting diodes(micro-LEDs) on silicon(Si)substrates with 40μm in diameter are developed utilizing standard photolithography and inductively coupled plasma etching techniques.From currentvoltage curves,the relatively low turn-on voltage of 2.8 V and low reverse leakage current in the order of 10~(-8) A/cm~2 indicate good electrical characteristics.As the injection current increases,the electroluminescence emission wavelength hardly shifts at around 433 nm, and the relative external quantum efficiency slightly decays,because the impact of quantum-confined Stark effect is not serious in violet-blue micro-LEDs.Since GaN-LEDs are cost effective on large-area Si and suitable for substrate transfer or vertical device structures,the fabricated micro-LEDs on Si should have promising applications in the fields of high-resolution display and optical communication.     

Dielectric Properties of GaN in THz Frequencies

The complex refractive indices and the dielectric function of GaN for frequencies ranging from 0.25 to 1.22THz are obtained using THz time-domain spectroscopy. The real part of the dielectric function first decreases from 0.25 to 0.42THz and then oscillates from 0.42 to 1.22THz, whereas the imaginary part of the dielectric function is oscillating within the whole range of frequency. The simple Drude model is extended to take into account the effect of defects on the dielectric function. The extended model is in agreement with the experimental data.     

MOCVD Growth and Characterization of Epitaxial AlxGa1-xN Films

We study the growth of AlxGa1-x N epilayers on （0001） sapphire by low-pressure MOCVD, using a lowtemperature AIN buffer. By varying the input flow rates of trimethylgallium （TMGa）, we obtain crack-free AlGaN films in the whole range of composition. A linear relationship between gas and solid Al content is observed. The structural properties of the layers （x =0- 1） are investigated by x-ray diffraction, atomic force microscopy （AFM） and scanning electron microscopy （SEM）. It is found that a two-direction growth appears along the c-axis and the （1011） directions for x ≥ 0.45. From the results of Raman spectroscopy, we suggest that the compressive stain and the lack of mobility orAl adatoms can induce the formation of （1011） grains.     

Growth of β-Ga_2O_3 Films on Sapphire by Hydride Vapor Phase Epitaxy

Two-inch Ga_2O_3 films with(ˉ201)-orientation are grown on c-sapphire at 850–1050°C by hydride vapor phase epitaxy. High-resolution x-ray diffraction shows that pure β-Ga_2O_3 with a smooth surface has a higher crystal quality, and the Raman spectra reveal a very small residual strain in β-Ga_2O_3 grown by hydride vapor phase epitaxy compared with bulk single crystal. The optical transmittance is higher than 80% in the visible and near-UV regions, and the optical bandgap energy is calculated to be 4.9 e V.     

Roles of V/III ratio and mixture degree in GaN growth: CFD and MD simulation study

To understand the mechanism of Gallium nitride (GaN) film growth is of great importance for their potential applica- tions. In this paper, we investigate the growth behavior of the GaN film by combining computational fluid dynamics (CFD) and molecular dynamics (MD) simulations. Both of the simulations show that V/III mixture degree can have important impacts on the deposition behavior, and it is found that the more uniform the mixture is, the better the growth is. Besides, by using MD simulations, we illustrate the whole process of the GaN growth. Furthermore, we also find that the V/III ratio can affect the final roughness of the GaN film. When the V/III ratio is high, the surface of final GaN film is smooth. The present study provides insights into GaN growth from the macroscopic and microscopic views, which may provide some suggestions on better experimental GaN preparation.