Uniaxial strain effect on the electronic and optical properties ofwurtzite GaN-AlGaN quantum-well lasers

The valence subband structures of uniaxial-strained wurtzite (WZ) GaN-AlGaN quantum wells (QW's) are calculated using multiband effective-mass theory. The optical gain is investigated using a numerical approach in which we account for the subband structure modification and mixing due to the anisotropic strain in the QW plane. We show that the mixing of the HH and LH bases in the uniaxial-strained (0001) GaN-AlGaN QW decouples |X〉 and |Y〉 at the Γ point, giving two topmost subbands, Y1 and X1, which can be more widely separated than the HH1 and LH1 subbands in the biaxial-strained (0001) GaN-AlGaN QW. We resolve the states of the subband dispersion in terms of the |X〉, |Y〉, and |Z〉 bases, and show the compositional variation as a function of the in-plane wavevector. Under uniaxial strain, it is possible to exploit the existence of the preferred symmetry at the valence band maximum and the reduced band-edge density-of-states due to the anisotropic in-plane energy dispersion to achieve lower transparency carrier and current densities and higher differential gain in comparison with a pseudomorphic biaxial-strained QW. We show that, for a QW laser structure with the optical cavity along the x axis, uniaxial compressive strain in the y direction shows greater improvement than the uniaxial tensile strain in the x direction of the same magnitude. Thus, a suitable uniaxial strain could be used to improve the threshold performance of WZ GaN-based QW lasers     

Minimization of the linewidth enhancement factor in compressivelystrained semiconductor lasers

A comprehensive model for the optical response of a semiconductor quantum well, including valence subband mixing and many-body effects, is used to theoretically investigate means of minimizing the linewidth enhancement factor. The effects of well width and compressive strain are analyzed, and the contribution of many-body effects evaluated. Compressive strain in narrow quantum wells generally leads to reduction of the linewidth enhancement factor at gain peak. In addition, many-body effects, particularly bandgap renormalization, admit the possibility that by small detuning to below the gain peak position, a zero value is possible     

Optimization of long wavelength InGaAsP strained quantum-welllasers

A theoretical study of InGaAsP-InGaAsP multiple quantum-well lasers emitting at 1.55 μm has been carried out to investigate the variation of threshold current density and differential gain with strain, well width and well number. We show that the greatest scope for exploiting this quaternary alloy in laser structures is through the use of compressive wells with unstrained or tensile barriers. We consider structures with a fixed compressive strain of 1% but variable well width, and also with fixed well width but variable strain from 0% to 1.75%. For structures with 1% compressive wells and unstrained barriers we find that the optimum structure for lowest threshold current density with sizable differential gain consists of six 35-Å quantum wells. We find also that there is little benefit to having compressive strains greater than 1.2%. In addition we examine zero-net-strain (ZNS) structures with compressive wells and tensile barriers. We show how the conduction band offset can be significantly increased and valence band offset reduced in such structures. Our gain calculations suggest that the large modification in band offset can decrease the threshold current density compared to similar devices with unstrained barriers     

Incorporation of strain into a two-dimensional model ofquantum-well semiconductor lasers

The effect of strain quantum wells was incorporated into a 2-D semiconductor laser simulator. An anisotropic parabolic band structure was used to approximate the valence band structure obtained from a Lutinger-Kohn k.p theory to facilitate the simulation. It is shown that, with a proper choice of the anisotropic effective masses, a good approximation of the strained band structure can be obtained. This approximation allows the gain, spontaneous emission rate, and the carrier concentration to be modeled in forms usable for the 2-D laser simulator. The usefulness of the 2-D model is demonstrated with an example of a ridge-waveguide strained InGaAs-AlGaAs laser. The simulation shows that for compressive strain, the gain function is enhanced significantly, but so too are the spontaneous emission and the leakage current. The predicted effect of strain on the lasing threshold is in good agreement with experimental results     

Strain-induced modifications of the band structure ofInxGa1-xP-In0.5Al0.5Pmultiple quantum wells

The effect of strain on the band structure of In_xGa_1-xP-In_0.5Al_0.5P multiple quantum wells (MQW's) has been investigated from high-pressure and low-temperature photoluminescence measurements. The biaxial strain in the wells was varied between +0.6% compressive to -0.85% tensile strain by changing the well composition x from 0.57 to 0.37. Strain increases the valence band offsets in either tensile or compressively strained structures. Whereas relatively insensitive to tensile strain, the valence band offsets showed a strong dependence on the magnitude of the compressive strain. Good agreement is found between the measured valence band offsets and those predicted by the model solid theory, except for the largest compressively strained MQW's, for which the model calculations underestimate the measured valence band offset. Strain and the associated variations in composition also modified the separation among the well states associated with Γ_1c, L_1c , and X_1c. From these results, the bandgaps of each conduction band extrema were calculated in In_xGa_1-xP for 0.37相似文献   

Optical Gain of V—groove Zn1—xCdxSe／ZnSe Quantum Wires

The subband structures, distributions of electron and hole wave functions, state density, optical gain spectra, and transparency carrier density of the V-groove Zn 1-x Cd x Se/ZnSe quantum wires are investigated theoretically using four band effective-mass Hamiltonian, which takes into account the effects of the valence band anisotropy and the band mixing. The biaxial strain effect for quantum wires is included in the calculation. The compressive strain in the Zn 1-x Cd x Se wire region increases the energy separation between the uppermost subbands. The optical gain with xy -polarized light is enhanced, while optical gain with z -polarized light is strongly decreased. The xy -polarized optical gain spectrum has a peak at around 2.541 eV, with the transparency carrier density of 0.75×10 18 cm -3 . The calculated results also show that the strain tends to increase the quantum confinement and enhance the anisotropy of the optical transitions.     

Six-band k·p approach to the effects of doping on energydispersion in p-type strained In0.15Ga0.85As-Al0.33Ga0.67As quantum-well structures

We report an application of the six-band Luttinger-Kohn model to the subband energy dispersions in the valence band for the p-type In_0.15Ga_0.85As-Al_0.33Ga_0.67 As quantum-well (QW) structures. It was found that, in addition to the contentional biaxial compressive strain related to the lattice constant and well width of the structures, the p-type doping also caused a shift of the subband energy levels in the valence band by varying the barrier height. It was also found that the strain of the QW structures was not a constant but was sensitive to the p-type doping density, which also induced the shift of the subband energy levels. The calculated results, based on intersubband transitions of the heavy holes and taking the doping-related changes in strain and barrier height into account, were in good agreement with the experimental data, measured using Fourier transform infrared technique     

Minimization of the linewidth enhancement factor intensile-strained quantum-well lasers

Means of minimizing the linewidth enhancement factor in tensile-strained semiconductor lasers are theoretically investigated using a detailed microscopic model including many-body effects, strain, and valence subband mixing. The effects of well width and strain are analyzed and fundamental trends in the behavior of the linewidth enhancement factor are highlighted. Qualitatively different behavior of the linewidth enhancement factor is observed in tensile-strained devices, as compared to compressive and unstrained devices. In particular, the linewidth enhancement factor in highly tensile-strained devices displays reduced sensitivity to the device threshold gain. In contrast to unstrained and compressively strained structures, such devices offer improved performance at wider well widths     

P型张应变Si/SiGe量子阱红外探测器的能带设计

提出P型张应变Si/SiGe量子阱红外探测器(QWIP)结构,应用k·P方法计算应变Si/SiGe量子阱价带能带结构和应变SiGe合金空穴有效质量.结果表明量子阱中引入张应变使轻重空穴反转,基态为有效质量较小的轻空穴态,因此P型张应变Si/SiGe QWIP与n型QWIP相比具有更低的暗电流;而与P型压应变或无应变QWIP相比光吸收和载流子输运特性具有较好改善.在此基础上讨论了束缚态到准束缚态子带跃迁型张应变p-Si/SiGe QWIP的优化设计.     

P型张应变Si/SiGe量子阱红外探测器的能带设计

提出P型张应变Si/SiGe量子阱红外探测器(QWIP)结构,应用k·P方法计算应变Si/SiGe量子阱价带能带结构和应变SiGe合金空穴有效质量.结果表明量子阱中引入张应变使轻重空穴反转,基态为有效质量较小的轻空穴态,因此P型张应变Si/SiGe QWIP与n型QWIP相比具有更低的暗电流;而与P型压应变或无应变QWIP相比光吸收和载流子输运特性具有较好改善.在此基础上讨论了束缚态到准束缚态子带跃迁型张应变p-Si/SiGe QWIP的优化设计.     

GaInAs/GaAs应变量子阱能带结构的计算

讨论了GaInAs/GaAs应变量子阱结构的应变效应 ,给出了量子阱层的临界厚度随In组份的变化关系。由克龙尼克 -潘纳模型计算了GaInAs/GaAs应变量子阱的量子化能级 ,给出了cl -hhl跃迁对应的发射波长随阱宽和In组份的变化关系曲线 ,并与实验测量的GaInAs/GaAs量子阱的发射波长进行了比较 ,基本一致。与此同时 ,对GaInAs/GaAs应变量子阱向长波长方向的发展也进行了计算分析 ,最后计算研究了应变量子阱中价带子能级及态密度的色散关系     

不同形状量子阱的量子限制效应

采用差分法求解有效质量方程，考虑轻重空穴的混合效应及应变效应，对三种不同形状的量子阱的能带结构、价带态密度、跃迁矩阵元进行了比较。在阱宽相同的条件下，方阱有最大的限制能力，但抛物阱和三角阱有更平坦的态密度曲线，使得以抛物阱和三角阱为有源区的激光器和半导体激光放大器可以有较低的透明电流密度。同时价带子带的耦合强烈改变了跃迁矩阵元，这对量子阱的增益特性会产生影响。     

Enhanced optical polarization anisotropy in quantum wells under anisotropic tensile strain

Anisotropic in-plane strain in quantum wells leads to an optical polarization anisotropy that can be exploited in optoelectronic devices such as modulators. A theoretical model shows that the behavior of the polarization anisotropy with increasing strain anisotropy is radically different for quantum wells under anisotropic tensile and compressive strains of equal magnitude. This strikingly different behavior arises from the different valence-subband mixing that occurs in the cases of anisotropic tensile and compressive strain. Specifically, the mixing of the first heavy- and light-hole subbands that occurs only under anisotropic tensile strain is central to the polarization anisotropy.     

Analysis of Gain and Luminescence in Violet and Blue GaInN–GaN Quantum Wells

In this paper, gain in GaInN quantum wells with 8% and 19% indium is analyzed using a comparison of a microscopic model to experimental data. It is shown that localized valence states can explain the characteristics of the gain spectra, in particular the broadening features at the red side of the spectrum. From an analysis of experimental and simulation data, the nonradiative current component is extracted, and is shown to dominate the total current density at laser threshold operation. The increase of nonradiative current with density explains the drop in internal quantum efficiency in GaInN light-emitting diodes.     

Finite-element analysis of valence band structure and opticalproperties of quantum-wire arrays on vicinal substrates

The valence subband dispersion of quantum-wire arrays grown on vicinal substrates in GaAs-Al_xGa_1-xAs material system is calculated using a finite-element method with periodic boundary conditions. The variational functional for the Luttinger-Kohn Hamiltonian is derived using the integration by parts with proper boundary conditions. The validity of this method is confirmed by calculating subband structure of quantum wells and rectangular quantum wires. Along with the electronic band structure, a detailed study of gain in the quantum-wire arrays with rectangular and serpentine shapes is presented, including the effect of coupling between wires and polarization dependence of the momentum matrix element. Finally, these results are compared to those of quantum wells     

High-speed modulation of strain-compensated InGaAs-GaAsP-InGaP multiple-quantum-well lasers

Small signal direct modulation characteristics of InGaAs-GaAsP-InGaP multiple quantum well ridge waveguide lasers (4.5/spl times/220 /spl mu/m/sup 2/) are described. The compressive strain of four InGaAs quantum wells is compensated by the tensile strain of GaAsP barriers. The lasers have a threshold current of 8 mA and an internal differential quantum efficiency of 80%. A 3-dB bandwidth of 25 GHz is obtained at 54 mA. It is found that the strain-compensated lasers have a K factor as low as 0.15 ns, implying a maximum 3-dB bandwidth of 59 GHz.     

多量子阱的声子喇曼散射理论

<正> 近年来多量子阱的声子喇曼散射,在实验方面已有许多富有成果的工作。为了提供系统的理论基础,推动实验的进一步深入,我们系统地研究了多量子阱喇曼散射的微观理论。本文将介绍理论的部分内容,侧重说明理论基础和讨论区别于体材料最具特色的一些结果。 在微观理论中,最便于表征喇曼散射的是喇曼张量(以下具体讨论Stokes散射):     

Free carrier and many-body effects in absorption spectra ofmodulation-doped quantum wells

The temperature-dependent optical absorption and luminescence spectra of GaAs/AlGaAs and InGaAs/InAlAs n-doped modulation-doped quantum wells is discussed with emphasis on the peak seen at the edge of the absorption spectra of these samples. A many-body calculation of the electron-hole correlation enhancement is presented, which identifies this peak with the Mahan exciton-the result of the Coulomb interaction between the photoexcited hole in the valence band and the sea of electrons in the conduction band. This calculation accounts for the strong dependence of the absorption edge peak on both the temperature and carrier concentration, in good qualitative agreement with experimental data and with previously published results. The changes induced by the carriers on the subband structure through self-consistent calculations are also analyzed, and it is concluded that in these symmetric structures, the changes are small for achievable carrier densities     

Empirical formulas for design and optimization of 1.5 μmInGaAs/InGaAsP strained-quantum-well lasers

The effects of strain and number of quantum wells on optical gain, differential gain, and nonlinear gain coefficient in 1.55-μm InGaAs/InGaAsP strained-quantum-well lasers are theoretically investigated. Well-approximated empirical expressions are proposed to model these effects. Using these formulas, one can easily and accurately predict the performance of a laser diode for a given structure. Therefore, these empirical formulas are useful tools for design and optimization of strained quantum well lasers. As a general design guideline revealed from the empirical formulas, the threshold current is reduced with the compressive strain, and the modulation bandwidth is most efficiently increased with the number of wells     

GaInAs/AlGaAs应变量子阱结构的荧光特性

本文报道了4—300K温度范围内量子阱宽度分别为20、40、90和130A的GaInAs/AlGaAs应变量子阱结构的光荧光特性。我们考虑量子尺寸对载流子子能带的影响和弹性应变引起带隙的移动,计算了量子阱中本征激子发光的能量位置,计算值与实验结果基本吻合。还研究了荧光峰强度随阱宽的变化以及不同温度下荧光峰的半高宽度。