RCLED的制作工艺与性能研究

设计并用MOCVD在GaAs衬底上分别生长了以34对AlAs/Al0.5Ga0.5As材料为下DBR,6对(Al0.3Ga0.7)0.5In0.5P/AlInP材料为上DBR,以及有源区为3个GaInP/(Al0.5Ga0.5)0.5In0.5P量子阱的外延片。设计了以SiO2做阻挡层,并且深腐蚀过有源区的台形RCLED的工艺结构,利用光刻、腐蚀、等离子化学气相沉淀(PECVD)以及溅射等工艺,成功制备了波长为650nm的谐振腔发光二极管(RCLED),并对其性能进行了测试。通过与普通LED相比较发现,RCLED不仅具备更强的轴向光强和更高的提取效率,而且具有更窄的光谱线宽、更小的发散角、更好的发射方向性,利于与塑料光纤进行耦合。     

Mode-coupling control and new index profile of GI POF for restricted-launch condition in very-short-reach networks

This paper confirms that numerical aperture (NA) is a key factor in mode coupling [the energy transfer among propagating modes in multimode fibers (MMF)] and that providing a high NA is a viable solution to reduce mode coupling in graded-index plastic optical fibers (GI POFs). Furthermore, the authors propose a new refractive-index-profile design of GI POFs when only small mode groups are launched (restricted-launch condition), which is a combined profile with the index exponents lower and higher than optimum value for the core center and periphery, respectively. The advantage of the new index profile is investigated both experimentally and theoretically. Furthermore, it is verified that the high-bandwidth performance of GI POF with the new index profile under the restricted-launch condition is maintained even when statistical fiber bendings are added to the GI POF and when misalignment is caused at the optical coupling between the light source and the GI POF.     

纳米柱InGaN/GaN多量子阱的干法刻蚀制备技术

纳米柱GaN基多量子阱(MQW)拥有量子尺寸效应以及应变释放等特性,对于提高GaN基发光二极管(LED)的发光效率具有重要意义.采用快速热退火(RTA)形成的自组装Ni纳米颗粒作为刻蚀掩膜,利用电感耦合等离子体反应离子刻蚀(ICP-RIE)制备纳米柱InGaN/GaN MQW.通过改变RTA温度发现在800℃以上才能有效形成Ni纳米颗粒掩膜.不同的ICP和射频(RF)功率条件下制备的纳米柱MQW光致发光强度相比于相同结构的平面MQW会发生显著变化.通过优化ICP-RIE的刻蚀条件,可以获得发光强度显著提高的纳米柱MQW结构.同时,纳米柱MQW中压电极化场的减弱会形成光致发光峰位蓝移.     

MOCVD生长Al0.48Ga0.52N/Al0.54Ga0.36N多量子阱的结构和光学特性

采用金属有机物化学气相淀积(MOCVD)技术,在蓝宝石衬底上生长了Al0.48Ga0.52N/Al0.54Ga0.36N多量子阱(MQWs)结构。通过双晶X射线衍射(DCXRD)、原子力显微镜(AFM)和阴极荧光(CL)等测试技术,分别对样品的结构和光学特性进行了表征。在DCXRD图谱中,可以观察到明显的MQWs衍射卫星峰,通过拟和,MQWs结构中阱和垒的厚度分别为2.1和9.4nm,Al组分分别为0.48和0.54。在AFM表面形貌图上,可以观察到清晰的台阶流,表明MQWs获得了二维生长;与此同时,MQWs结构存在一些裂缝,主要原因为AlGaNMQWs结构和下层GaN层间存在很大的应力。CL测试表明,AlGaNMQWs结构的发光波长为295nm,处于深紫外波段,同时观察到处于蓝光、绿光波段的缺陷发光。     

Optimum index profile of the perfluorinated polymer-based GIpolymer optical fiber and its dispersion properties

The significant advantages in bandwidth and low material dispersion of perfluorinated (PF) polymer-based graded-index polymer optical fiber (GI POF) are theoretically and experimentally reported for the first time. It is confirmed that the low attenuation and low material dispersion of the PF polymer enables 1 Gb/s km and 10 Gb/s km transmission at 0.85-μm and 1.3-μm wavelengths, respectively. The PF polymer-based CI POF has very low material dispersion (0.0055 ns/nm·km at 0.85 μm), compared with those of the conventional PMMA-based POF and of multimode silica fiber (0.0084 ns/nm km at 0.85 μm). Since the PF polymer-based GI POF has low attenuation from the visible to near infrared region, not only the 0.65-μm wavelength which is in the low attenuation window of the PMMA-based GI POF, but other wavelengths such as 0.85-μm or 1.3-μm etc. can be adopted for the transmission wavelength. It is clarified in this paper that the wavelength dependence of the optimum index profile shape of the PF polymer-based GI POF is very small, compared to the optimum index profile shape of the silica-based multimode fiber. As a result, the PF polymer-based GI POF has greater tolerance in index profile variation for higher speed transmission than multimode silica fiber. The impulse response function of the PF polymer-based GI POF was accurately analyzed from the measured refractive index profile using a Wentzel, Kramers, Brillouin (WKB) numerical computation method. By considering all dispersion factors involving the profile dispersion, predicted bandwidth characteristic of the PF polymer-based GI POF agreed well with that experimentally measured     

MOCVD生长InGaAs／Alj0.2Ga0.8As应变多量子阱

用MOCVD方法生长了3种InGaAs/Al0.2Ga0.8As应变多量子阱（MQWs）样品，用于研究在气相中TMIn的含量对MQWs的发光波长和半峰宽（FWHM）以及在X射线中零级峰位的影响。研究表明，随着In组分在MQW中的增加，MQWs中应变也随之增加，这是造成FWHM增大的原因。同时也研究了应变MQWs中In组分与气相中TMIn含量的关系，为准确设计和控制MQWs的组分提供了依据。     

掺Si对AlGaInP/GaInP多量子阱发光性能的影响

研究了Si掺杂对MOCVD生长的（Al0.3Ga0.7）In0.5P/Ga0.5In0.5P多量子阱发光性能的影响．样品分为两类：一类只生长了（Al0.3Ga0.7）In0.5P/Ga0.5In0.5P多量子阱结构;另一类为完整的多量子阱LED结构．对于只生长了（Al0.3Ga0.7）In0.5P/Ga0.5In0.5P多量子阱结构的样品,掺Si没有改变量子阱发光波长,但使得量子阱发光强度略有下降,发光峰半高宽明显增大．这应是掺Si使量子阱界面质量变差导致的．而在完整LED结构的情况下,掺Si却大大提高了量子阱的发光强度．相对于未掺杂多量子阱LED结构,垒层掺Si使多量子阱的发光强度提高了13倍,阱层和垒层均掺Si使多量子阱的发光强度提高了28倍,并对这一现象进行了讨论．     

生长停顿改善MOCVD生长InGaN/GaN多量子阱的特性

利用金属有机物化学气相淀积(MOCVD)生长了InGaN/GaN多量子阱(MQWs)结构,研究了生长停顿对InGaN/GaN MQWs特性的影响.结果表明,采用生长停顿,可以改善MQWs界面质量,提高MQWs的光致发光(PL)与电致发光(EL)强度;但生长停顿的时间过长,阱的厚度会变薄,界面质量变差,不仅In组分变低,富In的发光中心减少,而且会引入杂质,致使EL强度下降.     

GaAs (110)量子阱的电子自旋弛豫

采用固态源分子束外延的方法在GaAs(110)取向衬底上生长了GaAs/AlGaAs多量子阱结构.对样品进行了低温光致发光谱和时间分辨光致发光谱的测量,结果表明激发功率和激发波长对室温下量子阱内电子的自旋弛豫时间有强烈的影响.对于常见的GaAs(100)量子阱起支配作用的D'yakonov-Perel' (DP)自旋弛豫机制,在GaAs (110)量子阱材料里被充分地抑制了.对于缺失了DP相互作用的GaAs (110)多量子阱,电子-空穴相互作用对自旋弛豫时间随激发功率变化有重要的影响.     

Structural and optical properties of AlxGa1-xN/AlyGa1-yN multiple quantum wells for deep ultraviolet emission

The AlxGa1-xN/AlyGa1-yN multiple quantum well (MQW) structure for deep ultraviolet emission has been grown on sapphire by metal organic chemical vapor deposition (MOCVD).High resolution X-ray diffraction (HRXRD), atomic force microscopy (AFM), and cath-odoluminescence (CL) are used to characterize the structural and optical properties of MQWs, respectively.Clear step flows can be observed in the AFM image indicating a two-dimensional growth model.There are many cracks on the surface of the MQW structure because of the high tensile stress.HRXRD shows multiple satellite peaks to the 2rid order.The HRXRD simulation shows that the MQW period is about 11.5 nm.The emission peak of AlxGa1-xN/AlyGa1-yN MQWs is about 295 nm in the deep ultraviolet region from the CL spectra.     

Temperature dependence of performance of InGaN/GaN MQW LEDs with different indium compositions

The temperature dependence of performance of InGaN/GaN multiple-quantum-well (MQW) light-emitting diodes (LEDs) with different indium compositions in the MQWs was investigated. With increasing In composition in the MQWs, the optical performance of the LEDs at room temperature was increased due to an increase in the localized energy states caused by In composition fluctuations in MQWs. As the temperature was increased, however, the decrease in output power for LED with a higher In composition in the MQWs was higher than that of LED with a lower In composition in the MQWs. This could be due to the increased nonradiation recombination through the high defect densities in the MQWs resulted from the increased accumulation of strain between InGaN well and GaN barrier.     

Influence of Mg Doping on the Morphological, Optical, and Structural Properties of InGaN/GaN Multiple Quantum Wells

In this report, the influence of magnesium doping on the characteristics of InGaN/GaN multiple quantum wells (MQWs) was investigated by means of atomic force microscopy (AFM), photoluminescence (PL), and X-ray diffraction (XRD). Five-period InGaN/GaN MQWs with different magnesium doping levels were grown by metalorganic chemical vapor deposition. The AFM measurements indicated that magnesium doping led to a smoother surface morphology. The V-defect density was observed to decrease with increasing magnesium doping concentration from ∼10⁹ cm⁻² (no doping) to ∼10⁶ cm⁻² (Cp₂Mg: 0.04 sccm) and further to 0 (Cp₂ Mg: 0.2 sccm). The PL measurements showed that magnesium doping resulted in stronger emission, which can be attributed to the screening of the polarization-induced band bending. XRD revealed that magnesium doping had no measurable effect on the indium composition and growth rate of the MQWs. These results suggest that magnesium doping in MQWs might improve the optical properties of GaN photonic devices.     

Effects of growth interruption on the properties of InGaN/GaN MQWs grown by MOCVD

These applications normally employ an InGaN/GaN mul- tiple quantum wells (MQWs) as the active layer. But the growth of high quality MQWs is very difficult. Firstly, the growth condition is strict due to the high volatility of InN and the low thermal pyrol…     

InGaN/GaN和InGaN/AlGaN多量子阱中应变对光致发光特性的影响

对蓝宝石衬底上的InGaN/GaN和InGaN/AlGaN多量子阱结构和经激光剥离去除衬底的InGaN/GaN和InGaN/AlGaN多量子阱结构薄膜样品,进行了光致发光谱、高分辨XRD和喇曼光谱测量.PL测量结果表明,相对于带有蓝宝石衬底的样品,InGaN/GaN多量子阱薄膜样品的PL谱峰值波长发生较小的蓝移,而InGaN/AlGaN多量子阱薄膜样品的PL谱峰值波长发生明显的红移;喇曼光谱的结果表明,激光剥离前后E2模的峰值从569.1减少到567.5cm-1.这说明激光剥离去除衬底使得外延层整体的压应力得到部分释放,但InGaN/GaN与InGaN/AlGaN多量子阱结构中阱层InGaN的应力发生了不同的变化.XRD的结果证实了这一结论.     

Design of Low-Loss Graded-Index Plastic Optical Fiber Based on Partially Fluorinated Methacrylate Polymer

As a promising candidate of optical home network, a novel Gigabit Ethernet prepared by inexpensive partially fluorinated polymer-based graded-index plastic optical fiber (GI POF) was proposed. Poly (2,2,2-trifluoroethyl methacrylate) (P3FMA) was selected as a base material for the GI POF because of its high transparency, low material dispersion, and low cost. The transmission characteristics were investigated, and it was clarified that the newly developed GI POF has low-loss (71 dB/km at 650 nm), high humidity stability, and high-bandwidth (4.86 GHz for 50-m transmission) property. Moreover, 1.25-Gbps data transmission over 50 m was demonstrated by P3FMA-based GI POF.      

MOCVD生长的CdZnTe／ZnTe多量子附的激子光学特性

用常压ＭＯＣＶＤ方法在ＧａＡｓ（１００）衬底上生长了ＣｄＺｎＴｅ／ＺｎＴｅ多量子阱。在室温下，观测到了ＣｄＺｎＴｅ／ＺｎＴｅ多量子阱的三个谱带发光。根据ＣｄＺｎＴｅ／ＺｎＴｅ多量子阱的吸收光谱和不同激发光强下的发光光谱，分别归结ＣｄＺｎＴｅ／ＺｎＴｅ多量子阱中观测到的三个发光谱带于覆盖层发光、ｎ＝１的重空穴激子发光及杂质发光。     

A Superlattice Infrared Photodetector Integrated With Multiple Quantum Wells to Improve the Performance

An infrared photodetector using the structure of a 15-period superlattice (SL) integrated with 50-period multiple quantum wells (MQWs) is investigated. The MQWs are utilized to reduce the noise current power and to add the response range. From the results of current ratio and response, the photocurrent of the SL is not reduced by the additional MQWs but the dark current is. Hence, due to the low noise gain and low dark current, the maximum detectivity (D^*) can occur at low negative bias. In addition, the photovoltaic response even appears at 80 K. It is observed that the photoelectron transport directions from the SL and the MQWs are opposite under zero bias. In comparison with the SL with a single barrier, this structure also demonstrates the higher photocurrent and lower dark current. From our experimental results, this structure is appropriate for the operation at low bias and high temperature. However, the tradeoff is the small operational voltage range     

Effect of Si doping on the photoluminescence properties of AlGaInP/GaInP multiple quantum wells

The influence of Si doping on the photoluminescence (PL) properties of (Al_0.3Ga_0.7)_0.5In_0.5P/Ga_0.5In_0.5P multiple-quantum-wells (MQWs) was studied. For the samples without p-type layers, the PL peak wavelength from (Al_0.3Ga_0.7)_0.5In_0.5P/Ga_0.5In_0.5P MQWs did not vary when Si was doped in MQWs, the PL peak intensity did not change obviously and the PL FWHM broadened. We consider that Si doping results in worse interface quality of (Al_0.3Ga_0.7)_0.5In_0.5P/Ga_0.5In_0.5P MQWs. However, for the full light-emitting diode (LED) structure samples, the PL intensity of MQWs obviously increased when Si was doped in MQWs. The PL intensity from MQWs with Si-doped barriers was about 13 times stronger than that of undoped MQWs. The PL intensity from MQWs with Si-doped barriers and wells was strong as 28 times as that of undoped MQWs. The reasons are discussed.     

GaN/AIN multiple quantum wells grown on GaN-AIN waveguide structure by metalorganic vapor-phase epitaxy

High-optical-confinement waveguide structure based on nitride semiconductors is proposed and demonstrated for the first time with metal organic vaporphase epitaxy. The waveguide structure composed of 1-μm-thick AIN cladding layer, 2-μm-thick GaN guiding layer, and 40 periods of GaN/AIN multiple quantum wells (MQWs) was grown using optimized growth conditions for each layer. For improved material quality, the two-step growth technique using low-temperature AIN and GaN nucleation layers was utilized to reduce the stress induced by lattice mismatch between each layer. The high-optical-confinement structure could therefore be grown with high quality, leading to a successful observation of inter-sub-band absorption in GaN/AIN MQWs. The inter-sub-band absorption wavelength observed in such structure is in good agreement with that of MQWs grown on GaN layer, showing that the proposed waveguide structure can be used as a standard structure for optical devices based on inter-sub-band absorption.     

High Color Rendering Index Hybrid III‐Nitride/Nanocrystals White Light‐Emitting Diodes

An excellent hybrid III‐nitride/nanocrystal nanohole light‐emitting diode (h‐LED) has been developed utilizing nonradiative resonant energy transfer (NRET) between violet/blue emitting InGaN/GaN multiple quantum wells (MQWs) and various wavelength emitting nanocrystals (NCs) as color‐conversion mediums. InGaN/GaN MQWs are fabricated into nanoholes by soft nanoimprint lithography to minimize the separation between MQWs and NCs. A significant reduction in the decay lifetime of excitons in the MQWs of the hybrid structure has been observed as a result of the NRET from the nitride emitter to NCs. The NRET efficiency of the hybrid structures is obtained from the decay curves, as high as 80%. Moreover, a modified Förster formulation has exhibited that the exciton coupling distance in the hybrid structures is less than the Förster's radius, demonstrating a strong coupling between MQWs and NCs. Finally, based on a systemic optimization for white emission indexes, a series of hybrid ternary complementary color h‐LEDs have been demonstrated with a high color rendering index, up to 82, covering the white light emission at different correlated color temperatures ranging from 2629 to 6636 K, corresponding to warm white, natural white, and cold white.