InGaN/GaN多量子阱电池的垒层结构优化及其光学特性调控

InGaN基量子阱作为太阳电池器件的有源区时,垒层厚度设计以及实际生长对其光学特性的影响极为重要.采用金属有机化学气相沉积(MOVCD)技术,在蓝宝石衬底上外延生长了垒层厚度较厚的InGaN/GaN多量子阱,使用高分辨X射线衍射和变温光致发光谱研究了垒层厚度对InGaN多量子阱太阳电池结构的界面质量、量子限制效应及其光学特性的影响.较厚垒层的InGaN/GaN多量子阱的周期重复性和界面品质较好,这可能与垒层较薄时对量子阱的生长影响有关.同时,厚垒层InGaN/GaN多量子阱的光致发光光谱峰位随温度升高呈现更为明显的“S”形(红移-蓝移-红移)变化,表现出更强的局域化程度和更高的内量子效率.     

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.     

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.     

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E2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.     

预应变InGaN/GaN多量子阱发光特性调控研究

为了减弱InGaN/GaN量子阱内的压电极化场,在蓝紫光InGaN/GaN多量子阱激光器结构中采用了预应变InGaN插入层,通过变温电致发光和高分辨X射线衍射测量研究了预应变插入层对量子阱晶体质量和发光特性的影响。实验结果显示,常温下有预应变层的量子阱电致发光谱积分强度显著提高。模拟计算进一步表明,预应变层对量子阱内压电极化场有调制效果,有利于量子阱中的应力弛豫,可以有效减弱量子限制斯塔克效应,有助于提高量子阱的发光效率。     

Si衬底InGaN/GaN多量子阱LED外延材料的微结构

用透射电子显微镜(TEM)和X射线双晶衍射仪(DCXRD)对在Si(111)衬底上生长的InGaN/GaN多量子阱(MQW)LED外延材料的微结构进行了观察和分析.从TEM高分辨像观察到,在Si和AlN界面处未形成SixNy非晶层,在GaN/AlN界面附近的GaN上有堆垛层错存在,多量子阱的阱(InGaN)和垒(GaN)界面明锐、厚度均匀;TEM和DCXRD进一步分析表明MQW附近n型GaN的位错密度为10acm-2量级,其中多数为b=1/3〈112-0〉的刃位错.     

Si衬底InGaN/GaN多量子阱LED外延材料的微结构

用透射电子显微镜(TEM)和X射线双晶衍射仪(DCXRD)对在Si(111)衬底上生长的InGaN/GaN多量子阱(MQW)LED外延材料的微结构进行了观察和分析.从TEM高分辨像观察到,在Si和AlN界面处未形成SixNy非晶层,在GaN/AlN界面附近的GaN上有堆垛层错存在,多量子阱的阱(InGaN)和垒(GaN)界面明锐、厚度均匀;TEM和DCXRD进一步分析表明MQW附近n型GaN的位错密度为10acm-2量级,其中多数为b=1/3〈112-0〉的刃位错.     

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。     

阱宽和垒厚对lnGaN/GaN多量子阱结构光电特性的影响

通过求解修正的基于K·p方法的有效质量哈密顿方程并与泊松方程进行自洽,得到在极化效应影响下的不同阱宽和垒厚的InGaN/GaN多量子阱导带和价带的能带结构,并计算了不同多量子阱结构的自发辐射谱.仿真结果表明:阱宽和垒厚对InGaN/GaN多量子阱结构的光电子学特性有很大的影响.随着阱宽和垒厚的增加,InGaN/GaN多...     

实现双蓝光波长发光二极管光谱均衡辐射的研究

采用数值分析方法进行模拟分析InGaN/GaN混合多量子阱中不同活性层结构对GaN基双蓝光波长发光二极管光谱的影响。结果发现只依靠改变活性层中的In0.12Ga0.88N/GaN量子阱和In0.18Ga0.82N/GaN量子阱的数量或位置,难以有效改善电子空穴在混合多量子阱中的分布和实现双蓝光均衡辐射。但随着p-AlGaN层的移去和n-AlGaN层的引入,或在量子阱引入应力补偿层AlGaN,能有效实现双蓝光平衡辐射。     

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.     

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.     

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LED电致发光谱中双峰起源的研究

研究了MOCVD生长的具有双发射峰结构的InGaN/GaN多量子阱发光二极管(LED)的结构和发光特性.在透射电子显微镜(TEM)下可以发现量子阱的宽度不一致,电致发光谱(EL)发现了位于2.45eV的绿光发光峰和2.81eV处的蓝光发光峰.随着电流密度增加,双峰的峰位没有移动,直到注入电流密度达到2×104 mA/cm2时,绿光发光峰发生蓝移,而蓝光发光峰没有变化.单色的阴极荧光谱(CL)发现绿光发射对应的发光区包括絮状区域和发光点,而蓝光发射对应的发光区仅包含絮状区域.通过以上的结果,我们认为蓝光发射基本上源于InGaN量子阱发光,而绿光发射则起源于量子阱和量子点的发光.     

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.     

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。     

Optical and electrical characterization of (Ga,Mn)N/InGaN multiquantum well light-emitting diodes

(Ga,Mn)/N/InGaN multiquantum well (MQW) diodes were grown by molecular beam epitaxy (MBE). The current-voltage characteristics of the diodes show the presence of a parasitic junction between the (Ga,Mn)N and the n-GaN in the top contact layer due to the low conductivity of the former layer. Both the (Ga,Mn)N/InGaN diodes and control samples without Mn doping show no or very low (up to 10% at the lowest temperatures) optical (spin) polarization at zero field or 5 T, respectively. The observed polarization is shown to correspond to the intrinsic optical polarization of the InGaN MQW, due to population distribution between spin sublevels at low temperature, as separately studied by resonant optical excitation with a photon energy lower than the bandgap of both the GaN and (Ga,Mn)N. This indicates efficient losses in the studied structures of any spin polarization generated by optical spin orientation or electrical spin injection. The observed vanishing spin injection efficiency of the spin light-emitting diode (LED) is tentatively attributed to spin losses during the energy relaxation process to the ground state of the excitons giving rise to the light emission.     

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.