低阈值量子结构激光器的优化结构设计

针对低阈值半导体量子结构激光器（简称量子结构激光器）,包括量子阱、量子线和量子点结构,给出了一个完整简便的方法用以优化设计最低阈值条件所需要的有源区结构。以对数形式给出了量子结构激光器材料增益和注入载流子浓度的关系,并且以ＩｎＧａＡｓ（Ｐ）／ＩｎＰ量子阱激光器和ＩｎＡｓ／ＧａＡｓ自组装量子点结构激光器为例,分别计算了为得到最低阈值电流所需要的量子阱阱数和自组装量子点的面密度以及激光器的腔长。     

GaAlAs/GaAs多量子阱激光器结构设计

本文详细地讨论了多量子阱激光器材料的结构设计、量子阱结构对激射波长的影响以及波导限制层铝含量x值对光限制因子的影响.用由密度矩阵理论推导的线性光增益公式,计算了光增益.从受激阈值条件得到最佳阱数和最佳腔长.为多量子阱激光器材料结构设计提供了有效的方法.     

基于对数关系的多量子阱VCSELs阈值特性研究

采用光增益与载流子浓度的对数关系，考虑到非辐射复合的影响，从理论上推导出多量子阱垂直腔面发射半导体激光器(VCSELs)的速率方程。讨论了阈值电流密度、最佳阱数等与器件参数(腔长和端面反射率)之间的依赖关系。为改善VCSELs阈值特性和优化器件结构提供了理论依据。     

基于对数关系的多量子阱VCSELs阈值特性研究

采用光增益与载流子浓度的对数关系,考虑到非辐射复合的影响,从理论上推导出多量子阱垂直腔面发射半导体激光器(VCSELs)的速率方程。讨论了阈值电流密度、最佳阱数等与器件参数(腔长和端面反射率)之间的依赖关系。为改善VCSELs阈值特性和优化器件结构提供了理论依据。     

AlGaAs/GaAs-MQW激光器光增益谱理论和实验

本文简明地描述了由载流子带内弛豫加宽的半经典的密度矩阵理论.根据该理论计算了AlGaAs/GaAs多量子阱激光器的线性偏振光增益及量子阱宽L_x、Al_xGa_(1-x)As势垒层x值和带内弛豫时间τ_(in)对TE增益的影响.实验测量了多量子阱激光器的偏振光增益谱.理论与实验进行了比较.     

多量子阱VCSEL速率方程的数值模拟分析

采用光增益与载流子浓度的对数关系,考虑到非辐射复合的影响,从理论上推导出多量子阱垂直腔面发射半导体激光器(VCSEL) 的速率方程.讨论了阈值电流密度、最佳阱数与器件参数(腔长和端面反射率) 之间的关系,为改善VCSEL阈值特性和优化器件结构提供了理论依据.     

光抽运垂直外腔面发射激光器的增益特性数值模拟

为了深入研究光抽运垂直外腔面发射激光器的增益特性,以InGaAs/GaAs应变量子阱系统为例,建立了将带隙、带边不连续性计算和带结构计算系统结合起来的完整体系,考虑在应变影响下能带及波函数的混合效应。利用有限差分法对含6×6 Luttinger-Kohn哈密顿量的有效质量方程精确求解,得到了InGaAs/GaAs应变量子阱导带、价带的能带结构和包络函数,然后选用Lorentzian线形函数,数值模拟了量子阱的材料增益谱和自发辐射谱。最后讨论了阱宽、载流子浓度、温度等因素对量子阱材料增益的影响,为光抽运垂直外腔面发射激光器的优化设计提供了理论依据。     

量子阱DBR微腔激光器中自发发射的控制

应用腔量子电动力学和量子阱物理 ,计算了量子阱 DBR微腔激光器的自发发射谱 .发现由于 DBR微腔和量子阱分别对光子和载流子的限制 ,单方向的自发发射可以增进约三个量级 ,总的自发发射增强一个量级 .     

量子阱DBR微腔激光器中自发发射的控制

应用腔量子电动力学和量子阱物理,计算了量子阱DBR微腔激光器的自发发射谱.发现由于DBR微腔和量子阱分别对光子和载流子的限制,单方向的自发发射可以增进约三个量级,总的自发发射增强一个量级.     

多量子阱VCSELs阈值特性的分析

采用光增益与载流子浓度的对数关系,从理论上推导出量子阱垂直腔面发射半导体激光器的速率方程。比较了三维理想封闭腔与普通开腔中的特性曲线这将对于ＶＣＳＥＬｓ的理论研究和优化器件结构有所裨益。     

Wavelength chirp and dependence of carrier temperature on currentin MQW InGaAsP-InP lasers

In this paper, we derive a relation between the wavelength chirp and carrier temperature in semiconductor lasers. The coefficient relating the change in carrier temperature and chirp is expressed in terms of the temperature derivative of the optical gain, and two parameters describing the variation of refractive index produced by the variation of optical gain due to change of carrier quasi-Fermi level separation or carrier temperature. We have measured these parameters for MQW InGaAsP lasers, Using this data, we estimated the rate of the temperature increase with current above threshold in these devices, which is 0.13 K/mA     

1.3-μm InAsP modulation-doped MQW lasers

The effect of both n-type and p-type modulation doping on multiple-quantum-well (MQW) laser performances was studied using gas-source molecular beam epitaxy (MBE) with the object of the further improvement of long-wavelength strained MQW lasers. The obtained threshold current density was as low as 250 A/cm² for 1200-μm-long devices in n-type modulation-doped MQW (MD-MQW) lasers. A very low CW threshold current of 0.9 mA was obtained in 1.3-μm InAsP n-type MD-MQW lasers at room temperature, which is the lowest ever reported for long-wavelength lasers using n-type modulation doping, and the lowest value for lasers grown by all kinds of MBE in the long-wavelength region. Both a reduction of the threshold current and the carrier lifetime in n-type MD MQW lasers caused the reduction of the turn-on delay time by about 30%. The 1.3-μm InAsP strained MQW lasers using n-type modulation doping with very low power consumption and small turn-on delay time are very attractive for laser array applications in high-density parallel optical interconnection systems. On the other hand, the differential gain was confirmed to increase by a factor of 1.34 for p-type MD MQW lasers (N_A=5×10¹⁸ cm ^-3) as compared with undoped MQW lasers, and the turn-on delay time was reduced by about 20% as compared with undoped MQW lasers. These results indicate that p-type modulation doping is suitable for high-speed lasers     

Compressively strained 1.3 μm InAsP/InP and GaInAsP/InP multiplequantum well lasers for high-speed parallel data transmission systems

Turn-on delay times in the pulse response of compressively strained InAsP/InP double-quantum-well (DOW) lasers and GaInAsP/InP multiple-quantum-well (MQW) lasers emitting at 1.3 μm were investigated. DQW lasers with 200-μm cavity length and high-reflection coating achieved both a very low threshold current (1.8 mA) and a small turn-on delay time (200 ps), even under a biasless 30-mA pulse current. Compressively strained or lattice-matched GaInAsP MQW lasers and GaInAsP double-heterostructure (DH) lasers were also fabricated and compared. It was observed that the carrier lifetime was enhanced for InAsP DQW lasers and strained GaInAsP MQW lasers compared to the lattice-matched GaInAsP MQW lasers and conventional double-heterostructure lasers. To explain this increase in the carrier lifetime, the effect of the carrier transport on the carrier lifetime was studied. The additional power penalty due to the laser turn-on delay was simulated and is discussed     

SPICE simulation for analysis and design of fast 1.55 μm MQWlaser diodes

A rate equation model for static and dynamic behavior of 1.55 μm InGaAsP multiquantum-well (MQW) semiconductor lasers has been developed. A three level scheme for the rate equations has been chosen in order to model carrier transport effects. The introduction of quasi-two dimensional (quasi-2-D) gateway states between unbound and confined states has been used to calculate, for each well independently, carrier density and gain, allowing to take nonuniform injection into account. Starting from the formal identity between a rate equation and a Kirchoff current balance equation at a capacitor node, the model has been implemented on a SPICE circuit emulator, SPICE has granted an easy handling of parasitics and opens the possibility of integration with electrical components. The model's parameters have been directly derived from a complete set of measurements on real devices. Thanks to this characterization and the model accuracy, we have obtained good agreement between simulations and experimental data. The model was finally used to improve both static and dynamic properties of MQW devices. Based on this optimization, compressive strained InGaAsP-InP MQW Fabry-Perot lasers were realized, achieving low threshold current, high efficiency, and more than 10 GHz of direct modulation bandwidth     

Analysis and application of theoretical gain curves to the design of multi-quantum-well lasers

Gain/current curves for a single quantum well are calculated. The optimum well number, cavity length, threshold current, and current density of multi-quantum-well (MQW) lasers are derived in terms of this gain curve. The limiting performance of MQW lasers is found to be better than that of graded refractive index (GRIN) lasers, assuming comparable efficiencies and spontaneous emission linewidths. The optimum threshold current for an MQW laser with a 7 μm cavity and 90 percent facet reflectivity issim50 muA/μm.     

Calculating the optical properties of multidimensionalheterostructures: Application to the modeling of quaternary quantum welllasers

A method for calculating the electronic states and optical properties of multidimensional semiconductor quantum structures is described. The method is applicable to heterostructures with confinement in any number of dimensions: e.g. bulk, quantum wells, quantum wires and quantum dots. It is applied here to model bulk and multiquantum well (MQW) InGaAsP active layer quaternary lasers. The band parameters of the quaternary system required for the modeling are interpolated from the available literature. We compare bulk versus MQW performance, the effects of compressive and tensile strain, room temperature versus high temperature operation and 1.3 versus 1.55 pm wavelength operation. Our model shows that: compressive strain improves MQW laser performance. MQW lasers have higher amplification per carrier and higher differential gain than bulk lasers, however, MQW performance is far from ideal because of occupation of non-lasing minibands. This results in higher carrier densities at threshold than in bulk lasers, and may nullify the advantage of MQW lasers over bulk devices for high temperature operation     

半导体微腔激光器中的自发辐射耦合增强效应

针对半导体微腔激光器的结构特点,以及腔量子电动力学中自发辐射增强效应,采用光增益与载流子密度的对数关系,引入增益饱和项和非辐射复合项的贡献,指出即便是对于理想的封闭微腔,由于非辐射衰减速率的影响,光输出并不随泵浦线性变化。结合频谱和相图分析,给出了自发辐射耦合因子与微腔激光器的辐射阈值、开关延迟时间、驰豫振荡频率和光输出等参量关系的仿真结果,这对于微腔激光器的理论研究和优化器件结构有所裨益。     

Novel design scheme for high-speed MQW lasers with enhanceddifferential gain and reduced carrier transport effect

We present a theoretical analysis exploring the optimum design of high-speed multiple-quantum-well (MQW) lasers for 1.55-μm operation. Various combinations of well and barrier materials are examined for lattice-matched, strained-layered (SL), and strain-compensated (SC) MQW lasers with InGaAsP and InGaAlAs barriers. The gain characteristics are investigated for these MQW lasers with various barrier bandgap wavelengths and are used to evaluate the modulation characteristics based on the carrier dynamics model which includes a set of Poisson, continuity, and rate equations. The importance of band engineering aimed at simultaneously reducing the carrier transport effect and enhancing the differential gain is described. It is shown that SC-MQW lasers with InGaAlAs barriers have an advantage in reducing the density of states in the valence band by reducing the overlap integral between the heavy- and light-hole wave functions, which effect has previously been discarded as a minor correction in designing conventional InGaAsP-based MQW lasers. Furthermore, the hole transport rate across the barriers can be drastically reduced in SC-MQW lasers due to the reduced effective barrier height for the holes. Based on this novel design scheme, a 3-dB bandwidth approaching 70 GHz is expected for 20-well SC-MQW lasers with InGaAlAs barriers as a result of both the large differential gain and reduced transport effect     

Microscopic simulation of the temperature dependence of static and dynamic 1.3-/spl mu/m multi-quantum-well laser performance

The temperature dependence of the performance of 1.3-/spl mu/m Fabry-Perot (FP) multiple-quantum-well (MQW) lasers is analyzed using detailed microscopic simulations. Both static and dynamic properties are extracted and compared to measurements. Devices with different profiles of acceptor doping in the active region are studied. The simulation takes into account microscopic carrier transport, quantum mechanical calculation of the optical and electronic quantum well properties, and the solution of the optical mode. The temperature dependence of the Auger coefficients is found to be important and is represented by an activated form. Excellent agreement between measurement and simulation is achieved as a function of both temperature and doping profile for static and dynamic properties of the lasers, threshold current density, and effective differential gain. The simulations show that the static carrier density, and hence the contribution to the optical gain, varies significantly from the quantum wells on the p-side of the active layer to those on the n-side. Furthermore, the modal differential gain and the carrier density modulation also vary. Both effects are a consequence of the carrier dynamics involved in transport through the MQW active layer. Despite the complexity of the dynamic response of the MQW laser, the resonance frequency is determined by an effective differential gain, which we show can be estimated by a gain-weighted average of the local differential gain in each well.     

Effect of linear gain saturation on small-signal dynamics of MQWDFB lasers

The linear gain saturation effect is shown to be important in determining the dynamics of multiple-quantum-well (MQW) distributed-feedback (DFB) lasers. A more realistic logarithmic dependence of material gain on carrier density is assumed in a comprehensive MQW DFB laser model. It is found through simulation that because of the linear gain saturation, the interplay between modal gain and differential gain leads to an optimal κL for maximum small-signal modulation bandwidth in λ/4-shifted MQW DFB lasers