The surface quality of the substrate has an important effect on the quality of the growth film.The roughness,uniformity,adhesion residue and oxide layer of the substrate are the evaluation criteria of its surface performance.In this paper,an in-situ thermal treatment method to remove the natural oxides on GaSb(001)substrates for epitaxial growth of CdZnTe films by close-spaced sublimation method was reported.By controlling the temperature and time of the thermal treatment,a clean and smooth substrate state is obtained.The effect of thermal treatment on the morphology and composition of GaSb substrate was analyzed by atomic force microscopy and X-ray photoelectron spectroscopy.The crystal quality of CdZnTe epitaxial film grown on GaSb substrate after thermal treatment was evaluated by double crystal X-ray curve.In order to further study the properties and epitaxial formation mechanism of the micro-defects near the heterogeneous interface,TEM analysis of CdZnTe/GaSb cross section was also carried out.After 180 s thermal treatment at 600 ℃,the GaSb substrate can obtain a clean and relatively flat surface after most of the oxide is removed from the substrate surface,thus improving the crystallization quality of CdZnTe epitaxial film.The full width of half maximum of double crystal X-ray curve is 94",which approached the crystalline quality of bulk CdZnTe crystal ever reported.
Objective Periodically poled lithium niobate (PPLN) is an excellent nonlinear crystal for laser wavelength conversion. Conventional nonlinear crystals typically require high peak pulse power input. However, because of its periodic non -critical phase matching characteristics, PPLN has high conversion efficiency. It is extremely suitable for continuous wave (CW) laser wavelength conversion and widely used in CW laser systems. In addition, PPLN can realize full -color laser output by flexibly designing its quasi -phase matching (QPM) period, which has strong practical value. There has recently been a gradual shift from bulk PPLN to PPLN thin-film optical waveguides to improve the nonlinear frequency conversion efficiency of CW lasers. In recent years, many domestic research institutions, such as Nanjing University, East China Normal University, Shandong University, and the Chinese Academy of Sciences, have conducted in-depth detailed research on the preparation and application of PPLN thin film optical waveguide devices. Nonlinear frequency conversion devices based on PPLN waveguides have been used in various applications, such as optical communication, quantum optics, microwave optics, and spectroscopy. As applications continue to grow, new requirements are set for the volume and portability of waveguides. This study briefly introduces the basic structure and principle of a silicon -based PPLN thin film ridge waveguide, and a commercially available compact fiber -in -fiber -out PPLN waveguide package module is designed and fabricated. Methods The fabrication process of the silicon -based PPLN thin-film ridge waveguide is as follows. First, a Z -cut lithium niobate wafer (0.5 mm thick) doped with MgO is poled at high voltage. According to the FDTD software analysis results, the poled period is chosen to be 18.7 mu m to obtain phase matching of the pump wavelength near 1560 nm. After poling, a silicon dioxide buffer layer with a thickness of approximately 600 nm is deposited on one side of the PPLN wafer, subsequently, a gold layer of approximately 300 nm thickness is sputtered. Then, another 0.5 -mm thick precision polished silicon wafer is coated with a layer of gold of approximately 300 nm thickness and bonded to the PPLN wafer. This process is realized at room temperature, avoiding mechanical stress caused by the different thermal expansion coefficients of both wafers. Next, thinning and polishing are conducted to form the PPLN film. Finally, the PPLN ridge waveguide with the desired size is prepared based on a precision cutting mechanism. The waveguide direction is X direction (Fig. 4). The PPLN ridge waveguide prepared herein has a cross section of 10 p.m x 10 p.m and a length of 20 mm. A single -mode polarization -holding fiber with a core diameter of 8.5 p.m, numerical aperture (NA) of 0.125, and mode field diameter of 10.1 p.m is used for end -face direct coupling, and the packaged device is shown in Fig. 5. Results and Discussions A tunable laser source is used to tune the wavelength to 1560 nm. Subsequently it is incident into the PPLN ridge waveguide through a narrow -band erbium -doped fiber amplifier (EDFA). The light at the output of the waveguide passes through a 1560-nm high reflection and 780-nm high transmission filter and enters the optical power meter (Fig. 6). Because the refractive index of PPLN is a function of temperature, it is necessary to control the crystal temperature. Here, a temperature controller (the accuracy is 0. 01 degrees C, temperature control range is from room temperature to 200 degrees C) is used to control the temperature of the PPLN waveguide package module. As shown in Fig. 7(a), when the temperature is 24.8 degrees C, the output wavelength of the module is 780 nm (the deviation of the spectrometer used in the experiment is 0.2 nm). When the pump power Ppin (shown in Fig. 6) at the output of EDFA reaches 1.6 W, the input pump power Pp0 is calculated to be 1.2 W after deducting coupling loss between the fiber and waveguide at the input, while the coupling pump power PpL [without second harmonic generation (SHG)] at the output of the waveguide is 0.9 W. The power of SHG is 653 mW [Fig. 7(b)], the optical -optical conversion efficiency is 54.4% (Pp0 to SHG power). The normalized conversion efficiency is 20.2% center dot W-1 center dot cm-2 (PpL to SHG power). According to the input pump power Pp0, after deducting the coupling loss between the input fiber and the waveguide, the optical -optical conversion efficiency of the waveguide is 72.5%. Conclusions This study simulate and analyze the relationship between the QPM period of the PPLN ridge waveguide with a ridge height or width of 10 p.m at 25 degrees C and the corresponding ridge width or height. The QPM period of the PPLN waveguide increases with the increase of ridge height or width at the same pump wavelength and ridge height or width and finally tends to a constant, that is, the period of bulk PPLN crystal. The relationship between the QPM period and temperature of the PPLN ridge waveguide with constant ridge height and width at the same pump wavelength is analyzed. The QPM period decreases gradually with the increase in temperature, and the QPM period decreases by approximately 3 nm when the temperature rises by 1 degrees C. Here, the fabrication process of the PPLN thin-film ridge waveguide is improved. For example, the thickness of the silicon dioxide buffer layer is 600 nm. The waveguide package module with compact fiber in and out is fabricated, and its performance tested. When the temperature is 24.8 degrees C and the input power of 1560 nm pump light is 1.2 W, the maximum power of SHG is 653 mW, the optical -optical conversion efficiency is 54.4%, and the normalized conversion efficiency is 20.2% center dot W-1 center dot cm-2.
碳化硅(SiC)电子器件的性能和成本受衬底质量影响,因此生长大直径高品质SiC单晶意义重大.物理气相传输(PVT)法是一种常用的生长方法,但其主要面临热场设计与气流控制问题.本工作对电阻加热PVT法生长150 mm SiC单晶完整过程开展数值仿真研究,建立描述SiC原料热解和再结晶及其多孔结构演变、热-质输运、晶体形貌变化的数理模型,用数值模拟手段研究晶体生长、原料演变与热场变化等过程间的耦合关系.结果显示:原料区侧面高温导致气流不均匀,晶面呈"W"形,原料区底部高温得到均匀气流和微凸晶面;长晶界面通过径向温度变化调节气相组分平衡压力,使晶面生长成等温线形状;晶体生长速率与原料温度、剩余原料量呈正相关.模拟结果与已报道实验结果吻合,对优化生长SiC单晶有指导意义.
GaN基微型发光二极管(Micro-LED)作为新型显示技术有着广泛的应用前景,在近些年得到了快速的发展.但随着尺寸的降低,Micro-LED的发光效率急剧降低,主要是由于侧壁损伤的影响.本文通过光刻工艺和电感耦合等离子体(ICP)刻蚀制作了5、10、20 μm等不同尺寸的Micro-LED结构,分析了刻蚀对Micro-LED带来的台面物理损伤及杂质元素富集的影响,并采用20％浓度四甲基氢氧化铵(TMAH)修复侧壁损伤,采用阴极荧光(CL)分析钝化处理前后Micro-LED的光学特性.结果表明,随着尺寸的降低,侧壁损伤的影响越加严重,采取TMAH钝化工艺能够对侧壁进行有效的修复,提升Micro-LED的发光强度与发光均匀性.
4H-SiC单晶是典型的难加工材料,研磨加工后表面损伤的密度和深度直接影响后续抛光工序的质量和效率.采用普通铸铁盘研磨工艺会导致晶圆表面划痕多、边缘破片以及去除率不稳定等问题.本实验采用聚氨酯垫研磨工艺,减少研磨划痕,提高了研磨后的表面质量,实现了SiC衬底的精准研磨.通过改变金刚石磨料粒度、磨抛盘转速、研磨压强进行SiC衬底的研磨实验,探究最优工艺参数及各条件对研磨效果的影响规律.实验结果表明:随着研磨盘速度增大,研磨的去除率增大,其对应的粗糙度先降低后升高;增大金刚石磨料的粒径会增大研磨的去除率,但研磨后表面粗糙度也会持续增大;通过增加研磨压强,材料的去除率和表面粗糙度都将增加,但去除率增加的速率由快变慢,而粗糙度增加的速率逐渐加快.综合考虑,采用聚氨酯垫研磨时,较优研磨工艺参数为:金刚石研磨液浓度为3％,金刚石粒径为1 μm,研磨液供给速度为5 mL/min,研磨压强为47 kPa,研磨转速35 r/min.该工艺下SiC材料的去除率为0.7 μm/h,研磨后SiC衬底的表面粗糙度为24 nm.
