AlGaN/GaN层叠结构插入层改善氮化镓基发光二极管抗静电性能研究

在GaN基发光二极管的uGaN与nGaN之间插入AlGaN/GaN层叠结构,增大了外延层的张应力,降低了外延层中的穿透位错密度,改善了外延材料的质量。对比了AlGaN/GaN层叠结构中不同Al组分对LED的抗静电能力的影响,含6.8%铝组分AlGaN/GaN层叠结构的LED人体模式抗静电能力提高到了6000V,合格率超过了95%。     

抛物线型衬底InGaN/GaN发光二极管的模拟研究

针对发射到衬底中的光子,提出了一种具有抛物线型衬底结构的InGaN/GaN发光二极管,并对平面衬底和抛物线型衬底InGaN/GaN发光二极管的光子运动轨迹、发射功率角度分布和外量子效率进行了模拟计算.结果表明:相对于平面衬底发光二极管,抛物线型衬底发光二极管可以充分利用发射到衬底中的光子,使其正向光子发射功率增加12.6倍,外量子效率提高1.22倍,同时具有发射准平行光的功能.     

抛物线型衬底InGaN/GaN发光二极管的模拟研究

针对发射到衬底中的光子,提出了一种具有抛物线型衬底结构的InGaN/GaN发光二极管,并对平面衬底和抛物线型衬底InGaN/GaN发光二极管的光子运动轨迹、发射功率角度分布和外量子效率进行了模拟计算.结果表明:相对于平面衬底发光二极管,抛物线型衬底发光二极管可以充分利用发射到衬底中的光子,使其正向光子发射功率增加12.6倍,外量子效率提高1.22倍,同时具有发射准平行光的功能.     

生长条件对InGaN/GaN多量子阱表面v型缺陷的影响

我们研究了生长温度、TMIn/TEGa和Ⅴ/Ⅲ比对 InGaN/GaN多量子阱表面v型缺陷的影响。当TMIn的流量从180sccm增加到200sccm,v型缺陷的密度也从2.7210¹⁸/cm² 增加到了5.2410¹⁸ /cm², v型缺陷的深度和宽度也随着TMIn流量的增加而增加。当生长温度从748℃增加到758℃, v型缺陷的密度分别是2.0510⁸/cm², 2.7210⁸/cm² 和 4.2310⁸/cm²,V型缺陷的密度随着生长温度的增加而增加。当NH3的流量从5000sccm增加到8000sccm, v型缺陷的密度分别为 6.3410¹⁸/cm², 2.7210¹⁸/cm², 4.1310¹⁸/cm²。我们在753℃, TMIn 流量为180sccm, NH3 流量为6600sccm时,得到了晶体质量最好的InGaN/GaN 多量子阱,表面平整,v型缺陷的密度也比较少。V型缺陷的深度从10nm到30nm,宽度从100nm到200nm,为了抑制v型缺陷对GaN基LEDs反向电流(IR)和静电放电 (ESD) 的影响,我们需要生长更厚的p-GaN来填充这些v型缺陷。     

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.     

生长温度对InGaN/GaN多量子阱LED光学特性的影响

利用低压MOCVD系统,在蓝宝石衬底上外延生长了InGaN/GaN多量子阱蓝紫光LED结构材料.研究了生长温度对有源层InGaN/GaN多量子阱的合金组分、结晶品质及其发光特性的影响.结果表明当生长温度从730℃升到800℃时,LED的光致发光波长从490nm移到380nm,室温下PL谱发光峰的半高全宽从133meV降到73meV,表明了量子阱结晶性的提高.高温生长时,PL谱中还观察到了GaN的蓝带发光峰,说明量子阱对载流子的限制作用有所减弱.研究表明,通过改变生长温度可以对LED发光波长及有源层InGaN的晶体质量实现良好的控制.     

电流拥挤效应对GaN基发光二极管可靠性的影响

文中报道了绝缘蓝宝石衬底上的GaN基发光二极管（LEDs）中,由于横向电阻的存在造成了靠近n型电极台面边缘局部区域电流拥挤,为此从焦耳热和金属电迁移两方面研究了电流拥挤效应对器件可靠性的影响,加速寿命实验结果表明：电流均匀扩展可以使可靠性得到有效改善。     

生长压力对GaN材料光学与电学性能的影响

研究了采用MOCVD技术分别在100与500Torr反应室压力下生长的非故意掺杂GaN薄膜的光学与电学性能。研究表明,低压100Torr外延生长条件可以有效地降低Ga与NH3气相反应造成GaN薄膜的碳杂质沾污,从而抑制造成光致发光中黄光峰与蓝光峰的深受主的形成,所制备的材料表现出较好的光学性能。同时,不同生长压力下的GaN薄膜表现出相异的电学性能,即在500Torr下生长的样品通常表现出更高的载流子浓度（（4.6-6.4）×1016 cm-3）与更高的迁移率（446-561cm2/（V.s））,而100Torr下生长的样品通常表现为更低的载流子浓度（1.56-3.99）×1016 cm-3与更低迁移率（22.9-202cm2/（V.s））。     

多缓冲层对MOCVD生长的GaN性能的影响

采用多低温缓冲层法和高低温联合缓冲层法在 MOCVD系统上生长 Ga N外延膜 .对薄膜进行了 X射线衍射和光致发光谱 (PL)测试 ,(0 0 0 2 ) X射线摇摆曲线和 PL 谱的半高宽与常规的单低温缓冲层法制备的薄膜相比均有不同程度的改善 .实验结果表明改进的缓冲层法能提高 MOCVD生长的氮化镓外延膜晶体质量     

多缓冲层对MOCVD生长的GaN性能的影响

采用多低温缓冲层法和高低温联合缓冲层法在MOCVD系统上生长GaN外延膜.对薄膜进行了X射线衍射和光致发光谱(PL)测试,(0002)X射线摇摆曲线和PL谱的半高宽与常规的单低温缓冲层法制备的薄膜相比均有不同程度的改善.实验结果表明改进的缓冲层法能提高MOCVD生长的氮化镓外延膜晶体质量.     

Magnetic resonance studies of GaN based light emitting diodes

We report the application of electrical detection of magnetic resonance (EDMR) and electroluminescence detection of magnetic resonance (ELDMR) to study the recombination processes in InGaN/AlGaN double heterostructure p-n junctions. These techniques are especially well suited to the problems of defects in device structures in that they are much more sensitive than conventional paramagnetic resonance and are responsive to only those defects involved in the electrooptical properties of the structure. One resonance is observed at g≈2.00 and is identified as a Zn-related acceptor trap in the InGaN layer. A second resonance with g≈1.99 is identified as a deep donor.     

Mg fluctuation in p-GaN layers and its effects on InGaN/GaN blue light-emitting diodes dependent on p-GaN growth temperature

Correlation between material properties of bulk p-GaN layers grown on undoped GaN and device performance of InGaN/GaN blue light-emitting diodes (LEDs) as a function of p-GaN growth temperature were investigated. The p-GaN layers of both structures grown by metal-organic chemical-vapor deposition were heavily doped with Mg. As the growth temperature of the bulk p-GaN layer increased up to 1,080°C, N_A-N_D increased. However, above 1,110°C, N_A-N_D sharply decreased, while the fluctuation of Mg concentration ([Mg]) increased. At this time, a peculiar surface, which originated from inversion domain boundaries (IDBs), was clearly observed in the bulk p-GaN layer. The IDBs were not found in all LEDs because the p-GaN contact layer was relatively thin. The change in photoluminescence emission from the ultraviolet band to blue band is found to be associated with the fluctuation of [Mg] and IDBs in bulk p-GaN layers. The LED operating voltage and reverse voltage improved gradually up to the p-GaN contact-layer growth temperature of 1,080°C. However, the high growth temperature of 1,110°C, which could favor the formation of IDBs in the bulk p-GaN layer, yielded poorer reverse voltage and saturated output power of the LEDs.     

带有锥状反射结构的AlGaInP键合衬底LED

本研究通过光辅助化学腐蚀技术在衬底键合AlGaInP反极性发光二极管中制备出锥状反射镜结构提升器件的光提取效率。首先利用氢氟酸与双氧水在532nm激光的辐射下载GaP:Mg层制备出锥状腐蚀结构,然后将金属反射镜蒸镀在锥状结构之上制备锥状的反射镜结构。在完成全部芯片工艺后,测试结果表明锥状反射镜结构可以显著提升光提取效率,并在光通量测量中与表面粗化集成平板反射镜LED相比较,得到了18.55%的增强。     

Molecular beam epitaxial growth of green light emitting diodes on ZnSe wafers

We have performed a preliminary investigation into the use of ZnSe bulk crystals fabricated by Sumitomo Electric Industries, Ltd. as substrates for the epitaxial1 deposition of ZnSe-based materials and light emitting devices. A low temperature (<380 °C)in- situ cleaning process has been developed for the (100) oriented ZnSe wafers involving the use of a remotely generated atomic hydrogen beam. The process produces a (1 × 1) atomically smooth ZnSe surface which is highly suitable for epitaxy. Hall-effect measurements performed on nitrogen-doped ptype ZnSe/S.I. ZnSe epilayers have revealed free-hole concentrations in the homoepitaxial material as high as 2.1 × 10¹⁷cm⁻³, so far, with room temperature and 77Khole mobility values of 20 and 100 cm²V _su−1 ^ins/su−1 , respectively. Finally, green light emitting diodes have been grown on the ZnSe wafers having Cd_0.2Zn_0.8Se/ ZnSe multiple quantum well active regions which have exhibited electroluminescence peak linewidths around 9.9 nm at room temperature.     

InGaN/GaN light emitting diodes with a p-down structure

Nitride-based p-down blue light emitting diodes (LEDs) were successfully fabricated. It was found that we could improve the crystal quality of these nitride-based p-down LEDs by inserting a codoped interlayer between the p-type cladding layer and MQW active layers. It was also found that the turn-on voltage could be reduced from 15 V to less than 5 V for the p-down LED with codoped layer and tunnel layer. The 20 mA output power was 1 mW for the p-down LED with an Mg+Si codoped interlayer and a rough p-tunnel layer.     

利用ZnO薄膜界面层改善ZnO纳米棒/p-GaN发光二极管的电致发光性能

Heterostructure light-emitting diodes(LEDs)were fabricated by growing ZnO nanorods and undoped ZnO films on p-GaN templates.The heterojunction showed a diode-like I–V characteristic and emitted electroluminescence(EL)peaks at 383 nm,402 nm,438 nm,and 507 nm under forward bias.Since the electrons from ZnO nanorods and the holes from p-GaN could be injected into ZnO films with a relatively low carrier concentration and mobility,the radiative recombination was mainly confined in the ZnO film region.As a result,the ZnO nanorods/i-ZnO/p-GaN light emitting diode exhibits a stronger ultraviolet–violet emission peak.     

基于深隔离槽刻蚀的高压发光二极管制造

在制作高压发光二极管(HV LED)时,为了将数个独立的LED 串联起来,需要将GaN进行电感耦合等离子(ICP)深隔离刻蚀。本文制作了隔离槽深度为5um,台面侧壁为79.2?的GaN基HV LED。刻蚀表面和结构侧面的形貌通过激光显微镜和扫描电子显微镜进行观察分析。在形成金属接触并退火之后,测量HV LED输入电流-正向电压曲线,分析了其电学特性。与传统LED相比,I-V曲线趋势一致;相同尺寸和发光面积下,接触电阻下降了4.6Ω,而输出功率提高了5W。结果表明,可以应用于实际生产     

Tunneling current and electroluminescence in InGaN: Zn,Si/AlGaN/GaN blue light emitting diodes

We investigate electrical and optical characteristics of Nichia NLPB-500 double-heterostructure blue light-emitting diodes (LEDs), measured over a wide temperature range from 10 to 300K. Current-voltage characteristics have complex character and suggest involvement of at least two different tunneling mechanisms. The peak energy of the optical emission follows the applied bias for voltages between 2.3–2.6 V and can be tuned in large spectral range from 2.3 up to 2.8 eV (yellow to blue). This behavior can be understood invoking the photon-assisted tunneling model which was previously successfully applied to highly doped GaAs LEDs. Even at the lowest temperatures, light emission still continues while the increase in the series resistance does not exceed a few tens of kΩ, which indicates absence of complete carrier freeze-out. On leave from P.N. Lebedev Physics Institute, Russian Academy of Sciences, Moscow, Russia On leave from High Pressure Research Center, Warsaw, Poland     

发光二极管表面结构对出光特性的影响

用传输矩阵法模拟计算了AlGaInP发光二极管(LED)不同表面结构的光学特性,用等离子体增强化学气相沉积(PECVD)或磁控溅射掺铟氧化锡(ITO)设备,在带有DBR结构的外延衬底上制备出具有不同表面层结构的LED.通过实验结果对比表明,表面生长λ/4n SiON加λ2n ITO增透膜结构复合增透膜的LED,器件光学性能提高最佳,在20 mA注入电流下,光强和光通量分别达到141.7 mcd和0.4733 lm.比同样结构的无增透膜LED轴向光强和光通量分别提高138%和91%.     

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.