Manipulable and Hybridized,Ultralow‐Threshold Lasing in a Plasmonic Laser Using Elliptical InGaN/GaN Nanorods

Manipulating stimulated‐emission light in nanophotonic devices on scales smaller than their emission wavelengths to meet the requirements for optoelectronic integrations is a challenging but important step. Surface plasmon polaritons (SPPs) are one of the most promising candidates for sub‐wavelength optical confinement. In this study, based on the principle of surface plasmon amplification by the stimulated emission of radiation (SPASER), III‐Nitride‐based plasmonic nanolaser with hybrid metal–oxide–semiconductor (MOS) structures is designed. Using geometrically elliptical nanostructures fabricated by nanoimprint lithography, elliptical nanolasers able to demonstrate single‐mode and multimode lasing with an optical pumping power density as low as 0.3 kW cm^?2 at room temperature and a quality Q factor of up to 123 at a wavelength of ≈490 nm are achieved. The ultralow lasing threshold is attributed to the SPP‐coupling‐induced strong electric‐field‐confinement in the elliptical MOS structures. In accordance with the theoretical and experimental results, the size and shape of the nanorod are the keys for manipulating hybridization of the plasmonic and photonic lasing modes in the SPASER. This finding provides innovative insight that will contribute to realizing a new generation of optoelectronic and information devices.     

深紫外激光对GaN薄膜的激光抛光研究

为了研究157nm深紫外激光的激光抛光加工特性,采用小光斑对GaN半导体薄膜进行了微平面扫描刻蚀.通过探讨激光工艺参量与激光抛光质量的影响关系,得到了最佳的工艺参量范围.结果表明,随着激光抛光扫描速率的增加,材料加工表面粗糙度值Ra逐渐减小,其中扫描速率在0.014mm/s～0.015mm/s处,激光抛光质量最高;而激光抛光扫描间距的减小,或者脉冲频率的增加,都将导致被加工表面粗糙度增大;当脉冲频率取8Hz时,抛光效果较好,表面粗糙度值Ra≈20nm.     

基于并行FDTD方法分析表面等离子波导的特性

设计了一种双L形表面等离子体矩形环谐振器波导,采用并行时域有限差分方法,对这种波导的传输特性随几何结构参数的依赖关系进行了分析.计算结果表明通过改变输入/输出光波导的结构参数,可以调节该波导的消光比和频率选择特性.该波导结构能够有效地抑制后向辐射干扰并且大幅度地提高其场消光比,这使得此类谐振器结构更具有功能性.     

InGaN/GaN LEDs with a Si-doped InGaN/GaN short-period superlattice tunneling contact layer

Nitride-based light-emitting diodes (LEDs) with Si-doped n⁺-In_0.23Ga_0.77N/GaN short-period superlattice (SPS) tunneling contact top layer were fabricated. It was found that although the measured specific-contact resistance is around 1 × 10⁻² Ω-cm² for samples with an SPS tunneling contact layer, the measured specific-contact resistance is around 1.5×10⁰ Ω-cm² for samples without an SPS tunneling contact layer. Furthermore, it was found that one could lower the LED-operation voltage from 3.75 V to 3.4 V by introducing the SPS structure. It was also found that the LED-operation voltage is almost independent of the CP₂Mg flow rate when we grow the underneath p-type GaN layer. The LED-output intensity was also found to be larger for samples with the SPS structure.     

Investigation of the current collapse induced in InGaN back barrier AIGaN/GaN high electron mobility transistors

Current collapses were studied, which were observed in A1GaN/GaN high electron mobility transistors （HEMTs） with and without InGaN back barrier （BB） as a result of short-term bias stress. More serious drain current collapses were observed in InGaN BB A1GaN/GaN HEMTs compared with the traditional HEMTs. The results indicate that the defects and surface states induced by the InGaN BB layer may enhance the current collapse. The surface states may be the primary mechanism of the origination of current collapse in A1GaN/GaN HEMTs for short-term direct current stress.     

p型InGaN/GaN超晶格N面GaN基LED的光电特性

随着氮(N)面GaN材料生长技术的发展,基于N面GaN衬底的高亮度发光二极管(LED)的研究具有重要的科学意义.研究了具有高发光功率的N面GaN基蓝光LED的新型结构设计,通过在N面LED的电子阻挡层和多量子阱有源层之间插入p型InGaN/GaN超晶格来提高有源层中的载流子注入效率.为了对比N面GaN基LED优异的器件性能,同时设计了具有相同结构的Ga面LED.通过对两种LED结构的电致发光特性、有源层中能带图、电场和载流子浓度分布进行比较可以发现,N面LED在输出功率和载流子注入效率上比Ga面LED有明显的提升,从而表明N面GaN基LED具有潜在的应用前景.     

Temperature-dependent electroluminescence in InGaN/GaN multiple-quantum-well light-emitting diodes

We present a comparative study on temperature dependence of electroluminescence (EL) of InGaN/GaN multiple-quantum-well (MQW) light-emitting diodes (LEDs) with identical structure but different indium contents in the active region. For the ultraviolet (UV) and blue LEDs, the EL intensity decreases dramatically with decreasing temperature after reaching a maximum at 150 K. The peak energy exhibits a large redshift in the range of 20–50 meV with a decrease of temperature from 200 K to 70 K, accompanying the appearance of longitudinal-optical (LO) phonon replicas broadening the low energy side of the EL spectra. This redshift is explained by carrier relaxation into lower energy states, leading to dominant radiative recombination at localized states. In contrast, the peak energy of the green LED exhibits a minimal temperature-induced shift, and the emission intensity increases monotonically with decreasing temperature down to 5 K. We attribute the different temperature dependences of the EL to different degrees of the localization effects in the MQW regions of the LEDs.     

Heavily doped silicon:A potential replacement of conventional plasmonic metals

The plasmonic property of heavily doped p-type silicon is studied here.Although most of the plasmonic devices use metal-insulator-metal(MIM)waveguide in order to support the propagation of surface plasmon polaritons(SPPs),metals that possess a number of challenges in loss management,polarization response,nanofabrication etc.On the other hand,heavily doped p-type silicon shows similar plasmonic properties like metals and also enables us to overcome the challenges pos-sessed by metals.For numerical simulation,heavily doped p-silicon is mathematically modeled and the theoretically obtained re-lative permittivity is compared with the experimental value.A waveguide is formed with the p-silicon-air interface instead of the metal-air interface.Formation and propagation of SPPs similar to MIM waveguides are observed.     

Electrical properties and structural optimization of GaN/InGaN/GaN tunnel junctions grown by molecular beam epitaxy

The InGaN films and GaN/InGaN/GaN tunnel junctions (TJs) were grown on GaN templates with plasma-assisted molecular beam epitaxy. As the In content increases, the quality of InGaN films grown on GaN templates decreases and the surface roughness of the samples increases. V-pits and trench defects were not found in the AFM images. p⁺⁺-GaN/InGaN/n⁺⁺-GaN TJs were investigated for various In content, InGaN thicknesses and doping concentration in the InGaN insert layer. The InGaN insert layer can promote good interband tunneling in GaN/InGaN/GaN TJ and significantly reduce operating voltage when doping is sufficiently high. The current density increases with increasing In content for the 3 nm InGaN insert layer, which is achieved by reducing the depletion zone width and the height of the potential barrier. At a forward current density of 500 A/cm², the measured voltage was 4.31 V and the differential resistance was measured to be 3.75 × 10⁻³ Ω·cm² for the device with a 3 nm p⁺⁺-In_0.35Ga_0.65N insert layer. When the thickness of the In_0.35Ga_0.65N layer is closer to the “balanced” thickness, the TJ current density is higher. If the thickness is too high or too low, the width of the depletion zone will increase and the current density will decrease. The undoped InGaN layer has a better performance than n-type doping in the TJ. Polarization-engineered tunnel junctions can enhance the functionality and performance of electronic and optoelectronic devices.     

InGaN/GaN多量子阱蓝光LED电学特性研究

对不同温度(120～363 K)下InGaN/GaN多量子阱(MQW)结构蓝光发光二极管(LED)的电学特性进行了测试与深入的研究.发现对数坐标下I-V特性曲线斜率随温度变化不大.分别用载流子扩散-复合模型和隧道复合模型对其进行计算,发现室温下其理想因子远大于2,并且随着温度的下降而升高;而隧穿能量参数随温度变化不大.这说明传统的扩散-复合载流子输运模型不再适用于InGaN/GaN MQW蓝光LED.分析指出由于晶格失配以及生长工艺的制约,外延层中具有较高的缺陷密度和界面能级密度,导致其主要输运机制为载流子的隧穿.     

InGaN背势垒AlGaN/GaN HEMT中的电流崩塌研究

Current collapses were studied,which were observed in AlGaN/GaN high electron mobility transistors(HEMTs) with and without InGaN back barrier(BB) as a result of short-term bias stress.More serious drain current collapses were observed in InGaN BB AlGaN/GaN HEMTs compared with the traditional HEMTs.The results indicate that the defects and surface states induced by the InGaN BB layer may enhance the current collapse.The surface states may be the primary mechanism of the origination of current collapse in AlGaN/GaN HEMTs for short-term direct current stress.     

LP—MOCVD生长InGaN及InGaN／GaN量子阱的研究

利用MOCVD系统在Al2O3衬底上生长InGaN材料和InGaN/GaN量子阱结构材料，研究发现InGaN材料中In组份几乎不受TMG与TMI的流量比的影响，而只与生长温度有关，生长温度由800℃降低到740℃，In组份的从0.22增加到0.45；室温InGaN光致发光光谱（PL）峰全半高宽（FWHM）为15.5nm;InGaN/GaN量子阱区InGaN的厚度2nm，但光荧光的强度与100nm厚InGaN的体材料相当。     

InGaN/GaN超晶格垒层用于InGaN发光二极管发光增强研究

设计了InGaN/GaN超晶格垒层替代p-GaN和n-GaN附近传统GaN垒层的InGaN/GaN多量子阱(MQW)发光二极管(LEDs)结构。通过数值方法模拟出两种LED结构的光功率-电压(L-V)曲线、电致发光(EL)谱、能带图、电子浓度分布和辐射复合速率。结果表明InGaN/GaN超晶格替代n-GaN附近GaN垒层的LED结构比替代p-GaN附近GaN垒层的LED显示出更高的发光强度。这种发光增强的原因是InGaN/GaN超晶格替代n-GaN附近GaN垒层可以提高电子注入效率和辐射复合速率。     

408nm InGaN/GaN LED的材料生长及器件光学特性

通过提高InGaN量子阱结构的生长温度,降低量子阱In组分的掺入效率,提高InGaN/GaN量子阱结构生长质量,缩短LED输出波长等手段,实现了紫光LED高效率输出.采用高分辨率X射线双晶衍射、扫描隧道显微镜和光致发光谱技术研究了高温生长InGaN/GaN多量子阱的结构和光学特性.封装后的300μm×300μm LED器件在20mA的注入电流下输出功率为5.2mW,输出波长为408nm.     

408nm InGaN/GaN LED的材料生长及器件光学特性

通过提高InGaN量子阱结构的生长温度,降低量子阱In组分的掺入效率,提高InGaN/GaN量子阱结构生长质量,缩短LED输出波长等手段,实现了紫光LED高效率输出.采用高分辨率X射线双晶衍射、扫描隧道显微镜和光致发光谱技术研究了高温生长InGaN/GaN多量子阱的结构和光学特性.封装后的300μm×300μm LED器件在20mA的注入电流下输出功率为5.2mW,输出波长为408nm.     

InGaN/GaN MQW p–n junction photodetectors

InGaN/GaN multiquantum well (MQW) p–n junction photodetectors with semi-transparent Ni/Au electrodes were fabricated and characterized. It was found that the fabricated InGaN/GaN MQW p–n junction photodetectors exhibit a 20 V breakdown voltage and a 3.5 V forward 20 mA turn on voltage. It was also found that the photocurrent to dark current contrast ratio is higher than 10⁵ when a 0.4 V reverse bias was applied to the InGaN/GaN MQW p–n junction photodetectors. Furthermore, it was found that the maximum responsivity was 1.28 and 1.76 A/W with a 0.1 and 3 V applied reverse bias, respectively.     

InGaN/GaN light emitting diodes with Ni/Au mesh p-contacts

In order to improve the light transmittance and output efficiency of the InGaN/GaN multi-quantum well (MQW) light emitting diodes (LEDs), we proposed a novel Ni/Au mesh p-contact. As compared with the traditional Ni/Au film p-contact, the proposed Ni/Au mesh p-contact has the less light blocking nature yet still keeps well ohmic contact. Our lab result shows that for 470 nm wavelength the Ni/Au mesh p-contact has 95% light transmittance and 11.3 mW output power at a 20 mA injection current. In contrast, at the same 470 nm wavelength, the traditional Ni/Au film p-contact has 72% light transmittance and 8.12 mW output power at a 20 mA injection current.     

GaN基450nm波长LD在阈值处的反常电学特性

精确表征了GaN基450nm 波长LD的电学 特性,表观测量的电学参量在阈值附近都出现了明显的突变。器件的(IdV/dI-I)曲线在阈值处突 然上跳。与此对应,其他电学参量在阈值处的突变也与以往观察到的窄带隙780nm 波长LD在阈值处的突变完全反向。表观特性的反常必定造成反常的结特性,利 用 ac－IV方法精确表征了器件的结特性,在阈值区各结电学参 量的突变趋势与以往报道的 窄带隙780nm波长LD也完全相反。光学实验表明,在阈值区内(约3mA)光功率增加 近1个量级。光特性的突然增加必定与电学特性的突变存在必然联系。所有这些反常的电学 特性是传统的激光器理论难以解释的,将促使LD理论的进一步发展。     

低压下激光剥离的研究

为了研究低压环境对激光剥离的影响,利用准分子激光剥离系统和真空腔对GaN/蓝宝石样品分别在低压下和常压下进行多脉冲激光照射,之后用台阶仪测量样品的分解深度,得知相比常压环境,低压下GaN分解深度在脉冲次数为10次、20次、30次时分别增加了为10.2%,19.0%,24.3%,之后结合GaN材料分解过程和脉冲激光照射GaN/蓝宝石结构过程进行理论分析得到相应低压和常压下的GaN材料的理论分解深度,得到与实验一致的趋势。证明了低压环境能提高激光剥离速率。