Investigation of strontium tantalate thin films for high-k gate dielectric applications

Strontium tantalate (STO) films were grown by liquid-delivery (LD) metalorganic chemical vapor deposition (MOCVD) using Sr[Ta(OEt)₅(OC₂H₄OMe)]₂ as precursor. The deposition of the films was investigated in dependence on process conditions, such as substrate temperature, pressure, and concentration of the precursor. The growth rate varied from 4 to 300 nm/h and the highest rates were observed at the higher process temperature, pressure, and concentration of the precursor. The films were annealed at temperatures ranging from 600 to 1000 °C. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and ellipsometry indicated that the as-deposited and the annealed films were uniform and amorphous and a thin (>2 nm) SiO₂ interlayer was found. Crystallization took place at temperatures of about 1000 °C. Annealing at moderate temperatures was found to improve the electrical characteristics despite different film thickness (effective dielectric constant up to 40, the leakage current up to 6×10⁻⁸ A/cm², and lowest midgap density value of 8×10¹⁰ eV⁻¹ cm⁻²) and did not change the uniformity of the STO films, while annealing at higher temperatures (1000 °C) created voids in the film and enhanced the SiO₂ interlayer thickness, which made the electrical properties worse. Thus, annealing temperatures of about 800 °C resulted in an optimum of the electrical properties of the STO films for gate dielectric applications.     

掺Si对MOCVD生长的GaN单晶膜的黄带发射及生长速率的影响

对ＭＯＣＶＤ生长ＧａＮ：Ｓｉ薄膜进行了研究,研究表明随ＳｉＨ４／ＴＭＧａ流量比增大,ＧａＮ：Ｓｉ单晶膜的电子浓度增大,迁移率下降,Ｘ射线双晶衍射峰半高宽增加,同时这发射强度得到了大大的提高,并报导了随ＳｉＨ４／ＴＭＧａ流量比增大,ＧａＮ：Ｓｉ的生长速率降低的现象,研究结果还表明,预反应对ＧａＮ：Ｓｉ单晶膜黄带发射影响很大,预反应的减小可以使黄带受到抑制。     

面向VCSEL的Al0.98Ga0.02As薄膜湿法氧化的研究

为了系统研究VCSEL制作中的湿法氧化过程和机理, 设计了专门的材料结构并采用MOCVD技术进行外延生长。对经过光刻和干法刻蚀形成的台面结构样品进行不同时间的湿法氧化, 由表面形貌及断面结构来确定氧化程度。研究发现, 氧化时间较短时, Al_0.98Ga_0.02As层的横向氧化深度随氧化时间呈线性变化; 随着氧化时间增加, 横向氧化深度与氧化时间呈抛物线变化, 并渐趋于饱和。此外实验中发现Al_0.98Ga_0.02As层的湿法氧化速度可比Al_0.9Ga_0.1As层高一个数量级, 且Al_0.9Ga_0.1As层的湿法氧化速度随其层厚增加而增大。最后根据修正的一维Deal-Grove氧化模型计算了受限空间内Al_0.98Ga_0.02As层横向氧化深度随氧化时间的变化关系。     

NO和N2O流量对ZnO薄膜p型导电性能的影响

采用金属有机化学气相沉积(MOCVD)方法,由NO和N2O混合气体在玻璃衬底上沉积了p型ZnO薄膜.NO和N2O流量分别为40和25 sccm时,得到最低电阻率5.52Ω·cm,同时样品的空穴浓度最高,为2.17×1018cm-3,电性能的稳定性也最好.全部样品放置四个月后仍为p型,但电阻率增大.     

高亮度AlGaInP红光发光二极管

对用于提高AlGaInP红光发光二极管(LED)出光效率的分布布拉格反射镜(DBR)和增透膜进行了分析,用金属有机物化学气相沉积(MOCVD)生长了包含DBR和增透膜的LED,在20 mA注入电流下,LED的峰值波长为623 nm,光强达到200 mcd,输出光功率为2.14 mW.与常规的LED相比,光强和输出光功率有很大的提高.     

MOCVD生长高反射率AlN/GaN分布布拉格反射镜

利用金属有机物化学气相沉积(MOCVD)方法在蓝宝石c面衬底上制备出高反射率AlN/GaN分布布拉格反射镜(DBR).利用分光光度计测量,在418 nm附近最大反射率达到99%.样品表面显微照片显示,有圆弧形缺陷和少量裂纹出现;在缺陷和裂纹以外的区域,DBR具有较为平坦的表面,其粗糙度在10μm×10μm面积上为3.3 m左右.样品的截面扫描电镜(SEM)照片显示,DBR具有良好的周期性.对反射率和表面分析的结果表明,该样品达到了制备GaN基垂直腔面发射激光器(VCSEL)的要求.     

MOCVD—SnO_2薄膜对Si太阳能电池性能的影响

用MOCVD法在α-Si太阳能电池上沉积SnO_2薄膜作为减反射层,约80nm厚的SnO_2薄膜可相对提高电池转换效率34%.     

Synthesis, characterization and thermostability of tris（2,2,6,6-tetramethyl-3,5- heptanedionato）yttrium（III）

The metal-organic chemical vapor deposition (MOCVD) technique is a promising process for high temperature superconductor YBa2Cu3O7-δ(YBCO) preparation. In this technique, the purity, evaporation characteristics and thermostability of adopted precursors will decide the quality and reproducible results of YBCO film. In the present report, tris(2,2,6,6-tetramethyl-3,5-heptanedionato)yttrium(III)(Y(TMHD)3) was synthesized by the interaction of yttrium nitrate hydrate with TMHD in methanol solution, and its structure was identified by FTIR, 1 H NMR, 13C NMR and EI-MS spectroscopy. Subsequently, the thermal property and the kinetics of decomposition were systematically investigated by non-isothermal thermogravimetric analysis methods (TGA) at different heating rates in streams of N2,and the average apparent activation energy of evaporation process was evaluated by the Ozawa, Kissinger and Friedman methods. The possible conversion function was estimated through the Coats-Redfern method to characterize the evaporation patterns and followed a phase boundary reaction mechanism by the contracting area equation with average activation energy of 88.9kJ/mol.     

High-Efficiency InGaN Red Mini-LEDs on Sapphire Toward Full-Color Nitride Displays: Effect of Strain Modulation

InGaN red light emitting diode (LED) is one of the crucial bottlenecks that must be broken through to realize high-resolution full-color mini/micro-LED displays. The efficiency of InGaN LEDs drops rapidly as the emission spectra go from blue/green to red range due to the poor quality of high-indium-content InGaN materials. Here, high-performance InGaN red LEDs on sapphire grown by metal–organic chemical vapor deposition through strain modulation are reported. A composite buffer layer is proposed to increase the surface lattice constant of GaN and hence successfully enhances the indium incorporation efficiency of the following InGaN active layers. Consequently, a high-efficiency InGaN red mini-LED chip (mesa area: 100 × 200 µm²) with a peak wavelength of 629 nm and an external quantum efficiency of 7.4% is realized. Finally, a full-color nitride mini-LED display panel with 74.1% coverage of Rec.2020 color gamut by using the InGaN red mini-LED chips is fabricated. The study signifies the great potentials of full-nitrides high-resolution full-color mini/micro-LED displays.     

Periodical Ripening for MOCVD Growth of Large 2D Transition Metal Dichalcogenide Domains

2D semiconductors, especially 2D transition metal dichalcogenides (TMDCs), have attracted ever-growing attention toward extending Moore's law beyond silicon. Metal–organic chemical vapor deposition (MOCVD) has been widely considered as a scalable technique to achieve wafer-scale TMDC films for applications. However, current MOCVD process usually suffers from small domain size with only hundreds of nanometers, in which dense grain boundary defects degrade the crystalline quality of the films. Here, a periodical varying-temperature ripening (PVTR) process is demonstrated to grow wafer-scale high crystalline TMDC films by MOCVD. It is found that the high-temperature ripening significantly reduces the nucleation density and therefore enables single-crystal domain size over 20 µm. In this process, no additives or etchants are involved, which facilitates low impurity concentration in the grown films. Atom-resolved electron microscopy imaging, variable temperature photoluminescence (PL) spectroscopy, and electrical transport results further confirm comparable crystalline quality to those observed in mechanically exfoliated TMDC films. The research provides a scalable route to produce high-quality 2D semiconducting films for applications in electronics and optoelectronics.