基于键合金丝补偿的太赫兹瓦级功率合成技术研究

针对太赫兹波段固态大功率应用需求,基于氮化镓功率放大器单片集成电路（Monolithic Microwave Integrated Circuit,MMIC）,采用功率合成技术实现了太赫兹波段瓦级功率输出。通过太赫兹波段微带/波导转换结构和键合金丝补偿技术,结合E面T型结二路合成功率分配/合成器,将两片MMIC封装成最大输出功率为160 mW的功率单元模块。在此基础上,采用八路E面合成器设计了频率覆盖180～238 GHz的十六路功率合成放大器。在漏极电压为+10 V时,带内输出功率大于300 mW,189 GHz输出功率达到了1.03 W。     

一种P-GaN栅结合混合帽层结构的HEMT器件

为了进一步提升P-GaN栅HEMT器件的阈值电压和击穿电压,提出了一种具有P-GaN栅结合混合掺杂帽层结构的氮化镓高电子迁移率晶体管(HEMT)。新器件利用混合掺杂帽层结构,调节整体极化效应,可以进一步耗尽混合帽层下方沟道区域的二维电子气,提升阈值电压。在反向阻断状态下,混合帽层可以调节栅极右侧电场分布,改善栅边电场集中现象,提高器件的击穿电压。利用Sentaurus TCAD进行仿真,对比普通P-GaN栅增强型器件,结果显示,新型结构器件击穿电压由593 V提升至733 V,增幅达24%,阈值电压由0.509 V提升至1.323 V。     

GaN功率器件应用可靠性增长研究

GaN功率器件是雷达T/R组件或发射功放组件中的核心元器件,随着器件的输出功率和功率密度越来越高,器件的长期可靠性成为瓶颈。文章对雷达脉冲工作条件下GaN功率器件的失效机理进行了分析和研究,指出高漏源过冲电压、栅源电压的稳定性以及GaN管芯的沟道温度的高低是影响GaN功率器件长期应用可靠性的主要因素,同时给出了降低漏源过冲电压、提高栅源电压稳定性以及改善GaN管芯的沟道温度的措施和方法。     

C波段全集成GaN MMIC Doherty功率放大器设计

采用0.25 μm氮化镓高电子迁移率晶体管（GaN HEMT）工艺设计了一种全集成单片微波集成电路（MMIC）多尔蒂（Doherty）功率放大器（DPA）。采用了新型的拓扑结构,去除了传统DPA中主路放大器的阻抗变换器以及两路合成后的阻抗转换器,直接在主路输出匹配网络（OMN）中实现饱和点和回退点的阻抗的转换,采取适当的阻抗,与传统电路相比,降低了阻抗转换率,拓宽了频带。此外功率分配器也采用了新颖的拓扑结构,减少了元器件的使用,并且在DPA的匹配网络中使用集总电感的电容降低版图的面积。设计了一款工作在4.6~5.4 GHz的Doherty类功放,版图后仿真结果显示,饱和输出功率为40 dBm,饱和点漏极效率DE为58.9%~61.3%,6 dB回退点的漏极效率为38.3%~45%,增益为8.4~11.3 dB,版图面积为2.4 mm×1.1 mm。     

短波长半导体激光器开发动向

对ＧａＮ系和ＺｎＳｅ系两类主要材料制备蓝绿光激光器方面的问题和发展动向作了介绍。     

Plasma assisted molecular beam epitaxy growth of GaN

The growth of GaN on sapphire by plasma assisted molecular beam epitaxy (MBE) is investigated with the object of optimizing the material quality. The V/III flux ratio as well as the growth temperature are discussed in relation to their impact on electrical, optical and structural layer properties. Samples grown under nearly stoichiometric conditions exhibit both the highest mobilities and the highest photoluminescence efficiencies. Growth temperatures above 800°C were found to result in narrow reflections in X-ray diffraction. However, the chemical decomposition of GaN at temperatures above 850°C limits the suitable temperature range for the growth under high vacuum conditions.     

Valence-band discontinuity between GaN and AIN measured by x-ray photoemission spectroscopy

The valence-band discontinuity at a wurtzite GaN/AIN (0001) heterojunction is measured by means of x-ray photoemission spectroscopy. The method first measures the core level binding energies with respect to the valence-band maximum in both GaN and A1N bulk films. The precise location of the valenceb and maximum is determined by aligning prominent features in the valenceb and spectrum with calculated densities of states. Subsequent measurements of separations between Ga and Al core levels for thin overlayers of GaN film grown on A1N and vice versa yield a valence-band discontinuity of ΔE_v = 0.8+- 0.3 eV in the standard Type I heterojunction alignment.     

Epitaxial growth of cubic gan on (111) GaAs by metalorganic chemical vapor deposition

We are reporting the first comprehensive investigation of the structural properties of cubic GaN grown on (111) GaAs substrates by low-pressure metalorganic chemical vapor deposition. The minimum full width at half maximum (FWHM) of the x-ray diffraction (XRD) peak of (111) GaN was found to be ∼12 min. The use of low temperature GaN buffers helps to reduce the FWHM of the XRD. Cross-sectional transmission electron microscopy (XTEM) revealed the presence of columnar structures in the GaN film with widths of the order of 500A. Selected area electron diffraction (SAD) patterns at the interface confirmed that cubic (111) GaN was grown in-plane with the (111) GaAs substrate. Highresolution transmission electron microscopy (HRTEM) showed that the interface characteristics of GaN on (111)A GaAs substrate were better than those of the GaN on (lll)B GaAs substrate.     

Active matrix monolithic micro‐LED full‐color micro‐display

An active matrix monolithic micro‐LED full‐color micro‐display with a pixel density of 317 ppi is demonstrated. Starting from large‐scale and low‐cost GaN‐on‐Si epilayers, monolithic 64 × 36 blue micro‐LED arrays are fabricated and further transformed to full‐color micro‐displays by applying a photo‐patternable color conversion layer. This full‐color fabrication scheme shows feasible manufacturability, suggesting a potential for volume production of micro‐LED full‐color micro‐display.     

Study of GaAs and GaN based heterostructure surfaces and interfaces using ion beams and other complementary techniques

GaAs and GaN semiconductors and their heterostructures have been of interest for a few years now, because of their promising applications. Ion beams and other complimentary techniques are used for characterization of the surface and interfaces, to understand the novel properties of these materials. In this work we have reported the use of complimentary techniques like high-resolution X-ray diffraction (HRXRD), Rutherford backscattering/channelling (RBS/C), atomic force microscopy (AFM), and transmission electron microscopy (TEM) for characterization of these materials. We have studied InGaAs/GaAs heterostructures of various thicknesses by RBS/C, HRXRD, AFM, and TEM before and after irradiation. Bulk epitaxial layers of GaN grown on sapphire with and without AlN cap layer were characterized by HRXRD and AFM while the AlGaN/GaN heterostructures were characterized by RBS/C. The results are analyzed by taking account of the information extracted from these complementary techniques.