不同周期数的GaInAs/GaAsP多量子阱太阳能电池

为了研究不同量子阱周期数下GaInAs/GaAsP多量子阱太阳能电池性能的变化规律,利用金属有机化学气相沉积技术(MOCVD)制备了不同周期数的双结多量子阱太阳能电池样品以及无量子阱双结结构的参考样品,利用高分辨率X射线衍射仪(HXRD)和高分辨率透射电镜(TEM)测试了样品的晶体质量,同时在AM0(1×)光谱条件下测试了样品的I-V特性曲线和相应子电池的外量子效率。最终得到了高晶体质量、吸收截止波长在954 nm的Ga_(0.89)In_(0.11)As/GaAs_(0.92)P_(0.08)多量子阱结构,扩展波段的外量子效率最高达到75.18%,电池光电转换效率相对于无量子阱结构提升2.77%。通过对比测试结果发现,随着量子阱结构周期数的增加,太阳能电池在扩展波段(890~954 nm)的外量子效率不断提高,常规波段的短波响应(300~700 nm)会出现下降,长波响应(700~890 nm)会出现上升,短路电流和转换效率相应提升并趋于饱和。     

非对称ZnO/ZnMgO双量子阱内量子效率的提高

在c-plane面蓝宝石衬底上生长了ZnO/Zn0.85Mg0.15O非对称双量子阱,其内量子效率相对于对称量子阱有了显著的提高。ZnO/Zn0.85Mg0.15O的10周期对称量子阱和5周期非对称双量子阱都是利用等离子体辅助分子束外延技术制备的。ZnO/Zn0.85Mg0.15O非对称双量子阱的内量子效率提高至对称阱的1.56倍。时间分辨光谱和光致发光谱测试结果证实,在ZnO/Zn0.85Mg0.15O非对称双量子阱中存在从窄阱到宽阱的激子隧穿过程,这是内量子效率提高的主要原因。     

GaAlAs／GaAs量子阱结构的光致发光研究

阐述了用ＭＯＣＶＤ生长的ＧａＡｌＡｓ／ＧａＡｓ梯度折射率分别限制量子阱结构及其光学性质。样品经高分辨率光致发光（ＰＬ）测试显示,在１０Ｋ下对于８ｎｍ的单量子阱,通过激发产生的荧光谱半峰宽（ＦＷＨＭ）为６．２ｎｍ,同时具有较高的强度。表明量子阱结构具有陡峭的界面;另外还观察到,Ｘ（ｅ－ｈｈ）峰值位置相对于激发能级的移动。测试结果表明,样品质量符合设计要求,结果令人满意。     

掺铍GaAs量子阱的光致荧光

测量了掺铍的,阱宽约为10nm的GaAs量子阱在4.2K的光致荧光。掺杂浓度分别为1×10¹⁷和5×10¹⁸cm^-3。测量结果表明:对于无规掺杂,局域在阱中心的铍的状态密度与导带电子从n=1量子能级到阱中心中性铍的跃迁概率的乘积大于对应于介面铍的乘积。另外,实验结果也表明:当掺杂浓度升高时,由于带隙收缩的影响,阱中心铍的电离能减小。     

GaAs／AlGaAs多量子阱红外探测器研制成功

红外量子阱探测器是利用量子阱材料导带内子带间光跃迁对红外辐射的强吸收,来测量红外辐射强度的一种新型的、快速灵敏的红外探测器.其工作原理是:首先利用掺杂使量子阱中的基态上填充上具有一定浓度的二维电子,当入射光子能量■等于子带间能隙时。照射到器件接收面上的红外辐射将处于基态上的电子激发到较高激发态上,这些激发热电子在外场作用下,在匹配的外电路中形成与入射光强度成正比的电流或电压信号.该探测器的响应波段可以覆盖8—14μm的波长范围,响应速度快(皮秒量级),灵敏度较高(D*～1010cmHz1/2/W),并且可以通过改变材料的生长…     

GaAlAs／GaAs量子阱结构的实验研究

利用分子束外延生长法生长出了ＧａＡｌＡｓ／ＧａＡｓ梯度折射率分别限制单量子阱结构材料，对样品进行了光荧光谱、双晶Ｘ射线衍射和电化学电容－电压分布测量。实验结果表明，样品质量达到了设计要求，利用该材料制作的激光二极管获得了初步结果。     

外电场对直接带隙Ge量子阱中的光学性质的影响

在有效质量近似下,考虑到外电场的影响,详细研究了直接带隙Ge/GeSi量子阱中带间光跃迁吸收系数和阈值能量随量子阱阱宽,外电场强度的变化情况。结果表明：随着外电场的增强,带间光跃迁吸收强度会逐渐减弱,阈值能量减小,吸收曲线向低能方向移动,出现了红移现象。此外,当量子阱比较大时,外电场对量子阱中带间光跃迁阈值能量的影响更加明显。     

直接带隙Ge耦合双量子阱中的光吸收系数

在有效质量近似下,详细研究了直接带隙Ge/GeSi耦合双量子阱中带间光跃迁吸收系数和阈值能量随量子阱结构参数的变化情况。结果表明：随着量子阱阱宽增大,带间光跃迁吸收强度会逐渐减弱,阈值能量减小,吸收曲线向低能方向移动,出现了红移现象。增强耦合量子阱间的耦合效应使得带间光吸收强度显著提升。此外,与非对称耦合量子阱相比,耦合效应对对称耦合量子阱中光吸收系数的影响更为显著。     

直接带隙Ge耦合双量子阱中的光吸收系数

在有效质量近似下,详细研究了直接带隙Ge/Ge Si耦合双量子阱中带间光跃迁吸收系数和阈值能量随量子阱结构参数的变化情况.结果表明:随着量子阱阱宽增大,带间光跃迁吸收强度会逐渐减弱,阈值能量减小,吸收曲线向低能方向移动,出现了红移现象.增强耦合量子阱间的耦合效应使得带间光吸收强度显著提升.此外,与非对称耦合量子阱相比,耦合效应对对称耦合量子阱中光吸收系数的影响更为显著.     

三光子量子剪裁系统后置提高太阳能电池效率

稀土离子材料量子剪裁的研究能有效的提高基质发光材料的发光效率,近年来量子剪裁也不断的在太阳能电池领域取得比较重要的位置。利用稀土离子掺杂材料能有效的获得三光子量子剪裁能拓展太阳光谱的响应范围,同时在太阳能电池中产生多个电子空穴对,电子空穴对多元化有效的减少能量损失以及太阳光谱利用范围的拓宽有效提高了太阳能电池的效率。根据量子剪裁的理论设置相应的具有下转换系统太阳能电池的物理模型及等效电路图,根据太阳能电池效率计算的细致平衡原理求得其最大的极限效率。把稀土离子三光子量子剪裁应用于实际太阳能电池的应用价值进行粗略的估算,三光子量子剪裁系统后置太阳能电池时可以得到最大效率为58.58%,与Trupke双光子下转换模型相比效率有很大的提高。三光子系统后置太阳能电池理论模型的设置比较好的证明了稀土材料三光子量子剪裁对于推进太阳能电池课题的发展具有重要意义。     

Influence of thermal effect on the efficiency of a solar cell

The short-circuit current and open-circuit voltage of a solar cell based on the p-n junction are studied theoretically, taking into account the thermoemf originating due to the temperature difference between the front and back surfaces of the solar cell. It is shown that the consideration of the thermal motion of photogenerated carriers leads to the increase in the collection coefficient. Calculations show that at the irradiation intensity 5 × 10²⁰ photon/cm² s and at the temperature gradient ～ 30–40°C for silicon solar cells the open circuit voltage increases by ～ 6–7% and the short circuit current by ～40–50%.     

Intersubband absorption with difference-frequency generation in GaAs asymmetric quantum wells

An asymmetric quantum well(AQW) is designed to emit terahertz(THz) waves by using difference frequency generation(DFG) with the structure of GaAs/Al 0.2 Ga 0.8 As/Al 0.5 Ga 0.5 As.The characteristics of absorption coefficients are analysed under the parabolic and non-parabolic energy-band conditions in detail.We find that the absorption coefficients vary with the two pump optical intensities,and they reach the maxima when the pump wavelengths are given as λ p1 = 9.70 μm and λ p2 = 10.64 μm,respectively.Compared with non-parabolic conditions,the total absorption coefficient under parabolic conditions shows a blue shift,which is due to the increase in the energy difference between the ground and excited states.By adjusting the two pump optical intensities,the wave vector phase-matching condition inside the AQW is satisfied.     

Pressure effect on the electron mobility in AlAs/GaAs quantum wells

By taking the influence of optical phonon modes into account, this paper adopts the dielectric continuum phonon model and force balance equation to investigate the electronic mobility parallel to the interfaces for AlAs/GaAs semiconductor quantum wells (QWs) under hydrostatic pressure. The scattering from confined phonon modes, interface phonon modes and half-space phonon modes are analysed and the dominant scattering mechanisms in wide and narrow QWs are presented. The temperature dependence of the electronic mobility is also studied in the temperature range of optical phonon scattering being available. It is shown that the electronic mobility reduces obviously as pressure increases from 0 to 4GPa, the confined longitudinal optical (LO) phonon modes play an important role in wide QWs, whereas the interface optical phonon modes are dominant in narrow QWs, the half-space LO phonon modes hardly influence the electronic mobility expect for very narrow QWs.     

Advantages of InGaN/GaN multiple quantum well solar cells with stepped-thickness quantum wells

InGaN/GaN multiple quantum well (MQW) solar cells with stepped-thickness quantum wells (SQW) are designed and grown by metal-organic chemical vapor deposition. The stepped-thickness quantum wells structure, in which the well thickness becomes smaller and smaller along the growth direction, reveals better crystalline quality and better spectral overlap with the solar spectrum. Consequently, the short-circuit current density (Jsc) and conversion efficiency of the solar cell are enhanced by 27.12% and 56.41% compared with the conventional structure under illumination of AM1.5G (100 mW/cm2). In addition, approaches to further promote the performance of InGaN/GaN multiple quantum well solar cells are discussed and presented.     

GaAs/AlGaAs多量子阱中载流子动力学的实验研究

利用瞬态光栅激光光谱技术测量了(110)方向生长的本征GaAs/AlGaAs多量子阱的双极扩散系数.室温下,光激发的载流子浓度n_ex=3.4×10¹⁰/cm²时,测得双极扩散系数D_a=13.0 cm²/s,载流子的寿命τ_R=1.9 ns.改变光激发的载流子浓度(n_{ex关键词： 瞬态光栅 量子阱 空穴输运}     

Intersubband absorption in strained AlGaN/GaN double quantum wells

The intersubband absorption of the four-energy-level system in strained AlGaN/GaN double quantum wells is calculated by considering the polarization effect and the strain modification on material parameters (e.g., the conduction band offset, the electron effective mass and the static dielectric constant). It is found that the electron wavefunctions mainly locate at the left well and penetrate into the left barrier. The absorption spectrum exhibits multiple peaks contributed by different transitions. The position and height of absorption peaks are not very sensitive to the structural parameters (i.e., composition and thickness) of the central barrier because of the strong built-in electric field. However, the coupling between two wells can be enhanced by strain modulation.     

基于GaAs/InAs-GaAs/ZnSe量子点太阳电池结构的优化

基于GaAs/InAs-GaAs/ZnSe的P-i-N量子点太阳电池结构, 根据光学原理和扩散理论建立了光生电流密度与膜层厚度相关的数学模型, 定量分析了量子点层厚度等参数对太阳电池性能的影响,以期达到提高量子 点太阳电池转换效率的目的.理论模拟表明:在i层厚度取3000 nm时,优化后P(GaAs)型、N(ZnSe)型层 薄膜的最佳膜厚为1541 nm, 78 nm, 并在单一波长下太阳电池转换效率为20.1%;同时量子 点体积和温度对于量子点太阳电池I-V特性也会产生影响, 当量子点体积和温度逐渐增大时, 开路电压呈现减小趋势,使得转换效率降低.     

Nonlinear intersubband optical absorption in semiparabolic quantum wells

The linear and third-order nonlinear optical absorptions in semiparabolic quantum wells are studied in detail. Analytic formulas for the linear and third-order nonlinear optical absorption coefficients are obtained using the compact density matrix approach. Based on this model, numerical results are presented for typical GaAs/AlGaAs semiparabolic quantum wells. The results show that the factors of the incident optical intensity and the semiparabolic confinement frequency have great influences on the total optical absorption coefficients.     

InGaN/GaN multiple quantum well solar cells with an enhanced open-circuit voltage

In this paper,InGaN/GaN multiple quantum well solar cells (MQWSCs) with an In content of 0.15 are fabricated and studied.The short-circuit density,fill factor and open-circuit voltage (V oc) of the device are 0.7 mA/cm 2,0.40 and 2.22 V,respectively.The results exhibit a significant enhancement of V oc compared with those of InGaN-based hetero and homojunction cells.This enhancement indicates that the InGaN/GaN MQWSC offers an effective way for increasing V oc of an In-rich In x Ga 1 x N solar cell.The device exhibits an external quantum efficiency (EQE) of 36% (7%) at 388 nm (430 nm).The photovoltaic performance of the device can be improved by optimizing the structure of the InGaN/GaN multiple quantum well.     

Effect of magnetic fields on the linear and nonlinear intersubband optical absorption coefficients and refractive index changes in square and graded quantum wells

In this study, both the intersubband optical absorption coefficients and the refractive index changes as dependent on the magnetic field are calculated in square and graded quantum wells. Our results show that the position and the magnitude of the linear and total absorption coefficients and refractive index changes depend on the magnetic field strength and the shape of potential. The incident optical intensity has a great effect on the total absorption and refractive index changes.