Electrical and luminescent properties and the spectra of deep centers in GaMnN/InGaN light-emitting diodes

Electrical and electroluminescent properties were studied for GaN/InGaN light-emitting diodes (LEDs) with the n-GaN layer up and with the top portion of the n layer made of undoped GaMnN to allow polarization modulation by applying an external magnetic field (so-called “spin-LEDs”). The contact annealing temperature was kept to 750°C, which is the thermal stability limit for retaining room-temperature magnetic ordering in the GaMnN layer. Measurable electroluminescence (EL) was obtained in these structures at threshold voltages of ∼15 V, with a lower EL signal compared to control LEDs without Mn. This is related to the existence of two parasitic junctions between the metal and the lower contact p-type layer and between the GaMnN and the n-GaN in the top contact layer.     

Luminescence properties of blue and green dual wavelength InGaN/GaN multi-quantum well light-emitting diode

Blue and green dual wavelength InGaN/GaN multi-quantum well (MQW) light-emitting diode (LED) has wide applications in full color display, monolithic white LED and solid state lighting, etc. Blue and green dual wavelength LEDs, which consist of InGaN strain-reduction layer, green InGaN/GaN MQW and blue InGaN/ GaN MQW, were grown by metal-organic chemical vapor deposition (MOCVD), and the luminescence properties of dual wavelength LEDs with different well arrangements were studied by photoluminescence and electrolumines-cence. The experimental results indicated that well position played an important role on the luminescence evolvement from photoluminescence to electroluminescence.     

Enhanced output power in an InGaN-GaN multiquantum-welllight-emitting diode with an InGaN current-spreading layer

InGaN-GaN multiple quantum-well (MQW) light-emitting diodes (LEDs) with InGaN current-spreading layer were grown by metal-organic vapor-phase epitaxy (MOVPE) and their characteristics were evaluated by current-voltage (I-V), as well as output power measurements. Experimental results indicate that the LEDs exhibited a higher output power and a lower operation voltage than that of conventional LEDs. The external quantum efficiency of InGaN-GaN MQW LEDs for bare chips operated at injection current of 20 mA with InGaN current spreading layer near 5%. This is two times higher than that of conventional LEDs. This could be tentatively attributed to the better current-spreading effect resulting from Si-doped In_0.18Ga_0.82N wide potential well in which electron states are not quantized     

Characteristics of Green Light-Emitting Diodes Using an InGaN:Mg/GaN:Mg Superlattice as p-Type Hole Injection and Contact Layers

Mg-doped InGaN/GaN p-type short-period superlattices (SPSLs) are developed for hole injection and contact layers of green light-emitting diodes (LEDs). V-defect-related pits, which are commonly found in an InGaN bulk layer, can be eliminated in an InGaN/GaN superlattice with thickness and average composition comparable to those of the bulk InGaN layer. Mg-doped InGaN/GaN SPSLs show significantly improved electrical properties with resistivity as low as ∼0.35 ohm-cm, which is lower than that of GaN:Mg and InGaN:Mg bulk layers grown under optimized growth conditions. Green LEDs employing Mg-doped InGaN/GaN SPSLs for hole injection and contact layers have significantly lower reverse leakage current, which is considered to be attributed to improved surface morphology. The peak electroluminescence intensity of LEDs with a SPSL is compared to that with InGaN:Mg bulk hole injection and contact layers.     

Advantage of InGaN-based light-emitting diodes with trapezoidal electron blocking layer

In this study, a trapezoidal-shaped electron blocking layer is proposed to improve efficiency droop of InGaN/GaN multiple quantum well light-emitting diodes. The energy band diagram, carrier distribution profile, electrostatic field, and electron current leakage are systematically investigated between two light-emitting diodes with different electron blocking layer structures. The simulation results show that, when traditional AlGaN electron blocking layer is replaced by trapezoidal-shaped electron blocking layer, the electron current leakage is dramatically reduced and the hole injection efficiency in markedly enhanced due to the better polarization match, the quantum-confined Stark effect is mitigated and the radiative recombination rate is increased in the active region subsequently, which are responsible for the alleviation of efficiency droop. The optical performance of light-emitting diodes with trapezoidal-shaped electron blocking layer is significantly improved when compared with its counterpart with traditional AlGaN electron blocking layer.     

表面粗化高空穴浓度InGaN:Mg性能及其发光二极管应用

利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InGaN:Mg薄膜,对不同源流量InGaN:Mg材料特件进行了研究.光学和电学特性观测表明,当外延生长温度在760℃,三甲基铟(TMIn)摩尔流量不变时,随CP2Mg和Ⅲ族源摩尔比([CP2Mg]/[Ⅲ])增加,当In摩尔成分增加,空穴浓度也线性增加;当...     

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.     

Determination of the direction of piezoelectric field in InGaN/GaN multiple quantum-well structures grown by metal-organic chemical vapor deposition

The direction of the piezoelectric field in InGaN/GaN multiple quantum-well (MQW) structures grown by metal-organic vapor deposition (MOCVD) was determined using excitation-power-density variable photoluminescence (PL). By comparing the excitation-power-density dependence of the shift of the PL peak and the change of the full-width at half-maximum (FWHM) of the peak from an InGaN/GaN MQW structure and an InGaN MQW-based light-emitting diode (LED), the piezoelectric field in the InGaN/GaN MQW structures was unambiguously determined to be pointing toward the substrate. This result helps to identify the surface polarity of the LED wafer as Ga-faced.     

Nitride-based near-ultraviolet multiple-quantum well light-emitting diodes with AlGaN barrier layers

The In_0.05Ga_0.95N/GaN, In_0.05Ga_0.95N/Al_0.1Ga_0.9N, and In_0.05Ga_0.95N/Al_0.18Ga_0.82N multiple-quantum well (MQW) light-emitting diodes (LEDs) were prepared by metal-organic chemical-vapor deposition. (MOCVD). It was found that the 20-mA electroluminescence (EL) intensity of the InGaN/Al_0.1Ga_0.9N MQW LED was two times larger than that of the InGaN/GaN MQW LED. The larger maximum-output intensity and the fact that maximum-output intensity occurred at a larger injection current suggest that Al_0.1Ga_0.9N-barrier layers can provide a better carrier confinement and effectively reduce leakage current. In contrast, the EL intensity of the InGaN/Al_0.18Ga_0.82N MQW LED was smaller because of the relaxation that occurred in the MQW active region of the sample.     

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.     

红橙光InGaN/GaN量子阱的结构与光学性质研究

采用金属有机物化学气相沉积(MOCVD)技术生长了具有高In组分InGaN阱层的InGaN/GaN多量子阱(MQW)结构,高分辨X射线衍射(HRXRD)ω-2θ扫描拟合得到阱层In含量28%。比较大的表面粗糙度表明有很大的位错密度。室温下光致荧光(PL)研究发现该量子阱发射可见的红橙光,峰位波长在610 nm附近。变温PL(15～300 K)进一步揭示量子阱在低温下有两个发光机制,对应的发射峰波长分别为538 nm和610 nm。由于In分凝和载流子的局域化导致的载流子动力改变,使得量子阱PL发光峰值随温度增加呈明显的"S"变化趋势。     

Solution-Processed and Room-Temperature Spin Light-Emitting Diode Based on Quantum Dots/Chiral Metal-Organic Framework Heterostructure

Spin optoelectronics is an indispensable key for the future development of spintronics. In conventional spin light emitting diodes (LEDs), spin-polarized carrier pairs are injected electrically into the light emitting layer and create circularly polarized light (CPL). Generally, spin-polarized carriers are accomplished using ferromagnetic contacts or applying an external magnetic field, which will produce several drawbacks, including low temperature operation, low spin-polarized carriers injection efficiency, etc. To circumvent the existing shortcomings, here, an alternative approach is proposed and achieves spin-polarized LEDs at room temperature based on quantum dots (QDs)/chiral metal-organic framework heterojunction without using ferromagnetic contacts or magnetic fields. The spin-polarized injected layer composed of self-assembled monolayer (SAM)/Chiral-MOF ([Sr(9,10-adc)(DMAc)2]n)) film, which produces spin-polarized holes with spin orientation, determining the polarization and strength of circularly polarized electroluminescence (CP-EL). The spin-QLED emits CP-EL at a rate of 12.24% efficiency, which provides an excellent alternative to generate new functionality for conventional QLEDs. The approach is anticipated to be very useful, enabling to offer a general methodology for generating not yet realized spin optoelectronic devices.     

MOVPE growth of strained InGaAs/lnAIAs MQWs for a polarization-insensitive electroabsorption modulator

Metalorganic vapor phase epitaxial growth of a strained InGaAs/lnAIAs multiquantum well (MQW) structure was carried out for optical electroabsorption modulators. A high-quality MQW layer can be grown by introducing compressive strain into InAlAs barrier layers against tensile-strained well layers. We have also demonstrated strained InGaAs/lnAIAs MQW electroabsorption modulators with polarization insensitivity by using these layers and have obtained a highquality modulator with a low driving voltage of 1.7 V and a wide 3-dB bandwidth of over 20 GHz.     

InGaN/GaN多量子阱纳米线发光二极管制备及研究

用SiO2纳米图形层作为模板在以蓝宝石为衬底的n-GaN单晶层上制备了InGaN/GaN多量子阱纳米线,并成功实现了其发光二极管器件(LED).场发射扫描电子显微镜(FESEM)的测量结果表明,InGaN/GaN多量子阱纳米线具有光滑的表面形貌和三角形的剖面结构.室温下阴极射线荧光谱(CL)的测试发现了位于461 nm...     

InGaN-AlInGaN multiquantum-well LEDs

InGaN-GaN and InGaN-AlInGaN multiquantum-well (MQW) light-emitting diodes (LEDs) were both fabricated and their optical properties were evaluated by photoluminescence (PL) as well as electroluminescence (EL). We found that the PL peak position of the InGaN-AlInGaN MQW occurs at a much lower wavelength than that of the InGaN-GaN MQW. The PL intensity of the InGaN-AlInGaN MQW was also found to be larger. The EL intensity of the InGaN-AlInGaN MQW LED was also found to be larger than that of the InGaN-GaN MQW LED under the same amount of injection current. Furthermore, it was found that EL spectrum of the InGaN-AlInGaN MQW LED is less sensitive to the injection current. These observations all suggest that we can improve the properties of nitride-based LEDs by using AlInGaN as the barrier layer     

Inserting a low-temperature n-GaN underlying layer to separate nonradiative recombination centers improves the luminescence efficiency of blue InGaN/GaN LEDs

We have investigated the effects of nonradiative recombination centers (NRCs) on the device performance of InGaN/GaN multi-quantum-well (MQW) light-emitting diodes (LEDs) inserting low-temperature n-GaN (LT-GaN) underlying layers. Inserting an LT-GaN underlying layer prior to growing the MQWs is a successful means of separating the induced nonradiative recombination centers because a growth interrupt interface exists between the n-GaN template and the InGaN QW. We found that by introducing this technique would improve the external quantum efficiency of the as-grown conventional LEDs. The electroluminescence relative intensity of a blue LED incorporating a 70-nm-thick LT-GaN was 20.6% higher (at 20 mA current injection) than that of the corresponding as-grown blue LED in the best case.     

InGaN/GaN multiple quantum well green light-emitting diodes prepared by temperature ramping

High-quality InGaN/GaN multiple-quantum well (MQW) light-emitting diode (LED) structures were prepared by a temperature-ramping method during metal-organic chemical-vapor deposition (MOCVD) growth. Two photoluminescence (PL) peaks, one originating from well-sensitive emission and one originating from an InGaN quasi-wetting layer on the GaN-barrier surface, were observed at room temperature (RT). The observation of high-order double-crystal x-ray diffraction (DCXRD) satellite peaks indicates that the interfaces between InGaN-well layers and GaN-barrier layers were not degraded as we increased the growth temperature of the GaN-barrier layers. With a 20-mA and 160-mA current injection, it was found that the output power could reach 2.2 mW and 8.9 mW, respectively. Furthermore, it was found that the reliability of the fabricated green LEDs prepared by temperature ramping was also reasonably good.     

Diffusion and tunneling currents in GaN/InGaN multiple quantum welllight-emitting diodes

We have studied the electrical characteristics and optical properties of GaN/InGaN multiple quantum well (MQW) light-emitting diodes (LEDs) grown by metalorganic chemical vapor deposition. It appears that there is an essential link between material quality and the mechanism of current transport through the wide-bandgap p-n junction. Tunneling behavior dominates throughout all injection regimes in a device with a high density of defects in the space-charge region, which act as deep-level carrier traps. However, in a high-quality LED diode, temperature-dependent diffusion-recombination current has been identified with an ideality factor of 1.6 at moderate biases. Light output has been found to follow a power law, i.e., L ∝ I^m in both devices. In the high-quality LED, nonradiative recombination centers are saturated at current densities as low as 1.4 × 10^-2 A/cm². This low saturation level indicates that the defects in GaN, especially the high density of edge dislocations, are generally optically inactive     

Stability and interface abruptness of InxGa1−xN/InyGa1−yN multiple quantum well structures grown by OMVPE

The abruptness of hetero-interfaces in InGaN multiple quantum well structures is shown to degrade when a high temperature growth follows growth of the multiple quantum well (MQW) region, as is generally required for the growth of full device structures. We have analyzed MQW samples both with and without high temperature GaN “cap” layers, using x-ray diffraction (XRD), grazing incidence x-ray reflection (GIXR), and photoluminescence. While all of these techniques indicate a degradation of the MQW structure when it is followed by growth at high temperature, GIXR is shown to be especially sensitive to changes of heterointerface abruptness. GIXR measurements indicate that the heterojunctions are less abrupt in samples that have high temperature cap layers, as compared to samples with no cap layer. Furthermore, the degree of roughening is found to increase with the duration of growth of the high temperature cap layer. The degradation of the heterointerfaces is also accompanied by a reduction in the intensity of satellite peaks in the x-ray diffraction spectrum.     

AlGaN/GaN/InGaN对称分别限制多量子阱激光器的优化设计

采用一维传递矩阵法模拟计算了AlGaN/GaN/InGaN对称分别限制多量子阱激光器(发射波长为396.6nm)的波导特性.以光限制因子、阈值电流密度和功率效率作为优化参量,获得激光器的优化结构参数为:3周期量子阱In0.02Ga0.98N/In0.15Ga0.85N(10.5nm/3.5nm)作为有源层,90nm In0.1Ga0.9N为波导层,120周期Al0.25Ga0.75N/GaN(2.5nm/2.5nm)为限制层.