Ge–SiGe Quantum-Well Waveguide Photodetectors on Silicon for the Near-Infrared

We demonstrate near-infrared waveguide photodetectors using Ge-SiGe quantum wells epitaxially grown on a silicon substrate. The diodes exhibit a low dark current of 17.9 mA/cm² at 5-V reverse bias. The photodetectors are designed to work optimally at 1480 nm, where the external responsivity is 170 mA/W, which is mainly limited by the fiber-to-waveguide coupling loss. The 1480-nm wavelength matches the optimum wavelength for quantum-well electroabsorption modulators built on the same epitaxy, but these photodetectors also exhibit performance comparable to the demonstrated Ge-based detectors at longer wavelengths. At 1530 nm, we see open eye diagrams at 2.5-Gb/s operation and the external responsivity is as high as 66 mA/W. The technology is potentially integrable with the standard complementary metal-oxide-semiconductor process and offers an efficient solution for on-chip optical interconnects.     

An Overgrowth-Free Design for InGaAlAs Spot-Size-Converted Ridge Waveguide Lasers

A great deal of work has been done over the past several years toward the development of lasers with integrated spot-size converters, for better coupling directly to flat cleaved fiber or better alignment tolerance in lensed systems. Many of the techniques, such as butt-coupling or lateral-taper-vertical-shift, require etch-and-regrowth over the active region and as such are not applicable directly to Al-containing lasers. In this letter, we demonstrate a simple method to achieve narrow (15deg times 15deg) far fields in Al-containing devices with a moderate degradation of dc, dynamic and thermal characteristics. At room temperature, uncoated 300-mum-long devices have thresholds of about 18 mA and slope efficiencies of about 0.24 W/A, with 27% power coupled directly into flat cleaved fiber compared to ~10% for a conventional (>30deg far field) device. Comparison between calculated and measured far fields versus ridge width and number of quantum wells gives design curve information for optimizing far field performance.     

Spontaneous Radiative Efficiency and Gain Characteristics of Strained-Layer InGaAs–GaAs Quantum-Well Lasers

The optical gain spectra, unamplified spontaneous emission spectra, and spontaneous radiative efficiency are extracted from the measurement of amplified spontaneous emission (ASE) on a single pass, segmented contact 0.98-mum-emitting aluminum-free InGaAs-InGaAsP-GaAs quantum-well (QW) laser diode. These measurements provide a baseline for which to compare higher strain InGaAs QW lasers emitting near 1.2 mum. The peak gain-current relationship is extracted from gain spectra and the peak gain parameter go is found to agree within 25% of the value extracted using conventional cavity length analysis for 0.98-mum-emitting devices. The spontaneous radiative current is extracted using the fundamental connection between gain and unamplified spontaneous emission, which in turn gives an estimate of the amount of nonradiative recombination in this material system. The spontaneous radiative efficiency, the ratio of spontaneous radiative current to total current, at room temperature of 0.98-mum-emitting InGaAs QW laser material is found to be in the range of 40%-54%, which is 2.5-3.5 times larger than that of highly strained InGaAs QW laser emitting near lambda = 1.2 mum. Whereas the gain parameter, g₀ = dg/d(ln j), was measured to be 1130 and 1585 cm^-1 for the 0.98-mum- and 1.2-mum-emitting materials, respectively. From the calculated below threshold current injection efficiency of 75%-85%, we deduce that the internal radiative efficiency of the QW material is ~ 20% higher than the ratio of internal radiative current to external injected current extracted directly from ASE measurements.     

Direct Observation of Lateral Carrier Diffusion in Ridge Waveguide InGaNAs Lasers

We present results from measurements of the subthreshold lateral spontaneous emission profile in 1.3-mu m wavelength ridge waveguide InGaNAs quantum-well lasers using a scanning near-field optical microscopy technique. The measurements reveal the presence of significant lateral carrier diffusion which has a profound effect on the temperature dependence of the threshold current. This effect is frequently omitted when the characteristic temperature of the threshold current is considered.     

AlInP–AlGaInP Quantum-Well Lasers Grown by Molecular Beam Epitaxy

We have examined a possibility to use an Al $_{x}$In $_{1 - {x}}$P layer as an active region of a 650-nm semiconductor laser. Encouraging results have been obtained with compressively strained oxide-stripe AlInP–AlGaInP quantum-well lasers, which operated in continuous-wave mode at room temperature, producing an optical power of 460 and 320 mW per uncoated facet at 10 $^{circ}$C and 20 $^{circ}$C, respectively. In pulsed mode, a power level of 780 mW/facet was achieved at 2-A drive current at 5 $^{circ}$C. The results indicate that wide-bandgap AlInP affords an opportunity to develop lasers for the wavelengths $600leq lambda leq 650$ nm, which is difficult to achieve by any semiconductor heterostructure.      

On the Evolution of Carrier Distribution and Wavelength Switching in Asymmetric Multiple Quantum-Well Lasers

The evolution of the carrier distribution with current in two different asymmetric multiple quantum laser structures was studied experimentally through measurements of electroluminescence (EL). The EL was measured through the substrates of lasers and provided information about the carrier distributions. The carrier concentration was observed to increase with current both below and above threshold, presumably owing to the change of threshold conditions. The switch of the lasing wavelength from long to short wavelength was explained by inhomogeneous broadening of the gain of the wells and by incomplete clamping of the carrier concentration above threshold, as inferred from the measured EL and gain spectra. The role of thermal effects was investigated by comparing the laser performance under continuous-wave and pulsed operation     

Operational Properties of Ridge Waveguide Lasers with Laterally Tapered Waveguides for Monolithic Integration

We report on a ridge waveguide laser diode with laterally tapered waveguides fabricated in a single growing step using a double patterning method. In this structure, nearly constant output power is obtained with the change of the lower tapered waveguide width, and the facet power ratio of 1.4 to 1.5 is observed over the current range. The asymmetric facet power property is also investigated.     

High-Efficiency 808-nm InGaAlAs–AlGaAs Double-Quantum-Well Semiconductor Lasers With Asymmetric Waveguide Structures

The InGaAlAs-AlGaAs double-quantum-well semiconductor lasers grown by molecular beam epitaxy show high quantum efficiency and high power conversion efficiency at continuous-wave power output using asymmetric waveguide structures. The threshold current density and slope efficiency of the device are 180 A/cm² and 1.4 W/A, respectively. The internal loss and the internal quantum efficiency are 1.1 cm^-1 and 97%, respectively. The 75% maximum power conversion efficiency is achieved in 100-mum stripe widths 808-nm-emitting laser diodes with 1000-mum cavity length.     

Ray tracing for the optics at nano‐textured ZnO–air and ZnO–silicon interfaces

We investigate the scattering behavior of nano‐textured ZnO–Air and ZnO–Silicon interfaces for the application in thin film silicon solar cells. Contrary to the common approach, the numerical solution of the Maxwell's equations, we introduce a ray tracing approach based on geometric optics and the measured interface topography. The validity of this model is discussed by means of scanning near‐field optical microscopy (SNOM) measurements and numerical solutions of the Maxwell's equations. We show, that the ray tracing model can qualitatively describe the formation of micro lenses, which are the dominant feature of the local scattering properties of the investigated interfaces. A quantitative analysis for the ZnO–Silicon interface at λ = 488 and 780 nm shows that the ray tracing model corresponds well to the numerical solution of the Maxwell's equations, especially within the first 1.5 µm distance from the interface. Direct correlations between the locally scattered intensity and the interface topographies are found. Copyright © 2011 John Wiley & Sons, Ltd.     

氦离子注入形成980nm脊型波导激光器腔面非注入区的研究

报道了氦离子注入技术在提高 980nm半导体激光器灾变性光学损伤 (catastrophicopticaldamage,COD)阈值上的应用 .p GaAs材料经氦离子注入后可以获得高的电阻率 .在距离腔面 2 5 μm的区域内进行氦离子注入 ,由此形成腔面附近的电流非注入区 .腔面附近非注入区减少了腔面载流子的注入 ,因此减少了非辐射复合的发生 ,提高了激光器的灾变性光学损伤阈值 .应用氦离子注入形成腔面非注入区的管芯的平均最大功率达到 44 0 5mW ,没有发生COD现象 .而应用常规工艺制作的管芯的平均COD阈值功率为 40 7 5mW .同常规工艺相比 ,应用氦离子注入形成腔面非注入区技术     

氦离子注入形成980nm脊型波导激光器腔面非注入区的研究

报道了氦离子注入技术在提高980nm半导体激光器灾变性光学损伤(catastrophic optical damage,COD)阈值上的应用.p-GaAs材料经氦离子注入后可以获得高的电阻率.在距离腔面25μm的区域内进行氦离子注入,由此形成腔面附近的电流非注入区.腔面附近非注入区减少了腔面载流子的注入,因此减少了非辐射复合的发生,提高了激光器的灾变性光学损伤阈值.应用氦离子注入形成腔面非注入区的管芯的平均最大功率达到440.5mW,没有发生COD现象.而应用常规工艺制作的管芯的平均COD阈值功率为407.5mW.同常规工艺相比,应用氦离子注入形成腔面非注入区技术使管芯的最大输出功率提高了8%.     

对单模光纤具有高耦合功率的980nm量子阱脊波导激光器

我们描述了用应变单量子阱外延结构制作的２μｍ宽脊波导激光器，其发射波长为９８０ｎｍ。这种器件对单模光纤呈现出高的耦合效率，我们用工业标准的１４脚双列宜插封装，耦合出高达６０ｍＷ的功率。这种器件是泵浦掺Ｅｒ光纤放大器的理想光源。     

Rectangular and Ridge Waveguide

This paper describes the present state of the art with respect to rectangular ridge waveguide giving tables and data from standard waveguide sizes and constructional techniques for both rigid and flexible waveguide. The problems inherent in waveguide connectors are discussed along with the various methods for producing waveguide assemblies. The problems inherent with present-day waveguide standardization are also discussed. It is essential that a series of standard waveguide for high pressure operation and for extremely broadband operation (ridgeguide) be standardized. The latest RETMA miniature standard flanges are shown along with present-day thinking on a series of pressurized contact flanges.     

红外量子阱激光器的大信号调制特性研究

本文研究了工作波长为980nm的InGaAs/AsGaAs大功率红外量子阱F-P腔激光器在接近1A的大电流调制下的特性.在大信号调制下,通过数值求解,对大功率半导体激光器的参数进行了比较.随着调制深度m的增加,激光峰值不断变窄和变尖锐,而且调制频率不断减小.还比较了脉冲和正弦调制信号的输出波形,二者的波形在同频率下相似.输出光功率由于大信号瞬态响应而发生波形变形,产生啁啾效应.调制脉冲电流越大,啁啾越大,大小在nm数量级.     

Dynamics and Temperature-Dependence of 1.3-μm GaInNAs Double Quantum-Well Lasers

We have measured the small-signal modulation response of 1.3-mum ridge waveguide GaInNAs double quantum-well lasers over a wide range of temperatures (25 degC-110 degC) and analyzed the temperature dependence of the modulation bandwidth and the various bandwidth limiting effects. The lasers have low threshold currents and high differential efficiencies with small temperature dependencies. A short-cavity (350 mum) laser has a modulation bandwidth as high as 17 GHz at room temperature, reducing to 4 GHz at 110 degC, while a laser with a longer cavity (580 mum) maintains a bandwidth of 8.6 GHz at 110 degC. We find that at all ambient temperatures the maximum bandwidth is limited by thermal effects as the temperature increases with current due to self-heating. The reduction and subsequent saturation of the resonance frequency with increasing current is due to a reduction of the differential gain and an increase of the threshold current with increasing temperature. We find large values for the differential gain and the gain compression factor. The differential gain decreases linearly with temperature while there is only a weak temperature dependence of the gain compression. At the highest temperature we also find evidence for transport effects that increase the damping rate and reduce the intrinsic bandwidth     

电极分离的980nm锥形激光器的研制

对脊形波导区和锥形区电极分离的980nm锥形激光器(简称电极分离的980nm锥形激光器)改变脊形波导区所加电流,测试激光器的P-I特性和光束质量因子,与脊形波导区和锥形区共用电极的980nm锥形激光器(简称电极共用的980nm锥形激光器)的测量参数进行对比.发现电极分离的980nm锥形激光器的P-I特性曲线比较光滑,没有明显的扭折.随着脊形波导区的电流逐渐超过150mA以后,器件的最大输出功率逐渐达到4.28W,与电极共用的980nm锥形激光器相同并趋于饱和,光束质量因子从3.79降到2.45(输出功率为1W).     

980nm脊型波导激光器腔面非注入区的研究

报导了质子注入技术在提高980nm半导体激光器可靠性上的应用。P-GaAs材料经过质子注入后获得高的电阻率。在距离腔面25μm的区域内进行质子注入，由此形成腔面附近的电流非注入区。腔面附近非注入区减少了腔面载流子的注入，因此减少了非辐射复合的发生，提高了激光器的灾变性光学损伤(COD)阈值。应用质子注入形成腔面非注入区的管芯的平均COD阈值功率达到268mW，而应用常规工艺的管芯的平均COD阈值功率为178mW。同常规工艺相比，应用质子注入形成腔面非注入区技术使管芯的COD阈值功率提高了50％。     

Transient Thermal Analysis of Ridge Waveguide InAsP／InGaAsP MQW Lasers Operating in Pulse Driving Conditions

The transient thermal characteristics of the ridge waveguide InAsP/lnGaAsP MQW lasers, especially in various pulse driving conditions, have been simulated by using FEM. The temperature at the active core of the laser versus the time has been calculated as well as pulse width dependence of the apparent thermal resistance. The results show that the thermal characteristics of the lasers are related to both the thermal conductivity and the specific heat of the materials.     

电极分离的980nm锥形激光器的研制

对脊形波导区和锥形区电极分离的980nm锥形激光器(简称电极分离的980nm锥形激光器)改变脊形波导区所加电流,测试激光器的P-I特性和光束质量因子,与脊形波导区和锥形区共用电极的980nm锥形激光器(简称电极共用的980nm锥形激光器)的测量参数进行对比.发现电极分离的980nm锥形激光器的P-I特性曲线比较光滑,没有明显的扭折.随着脊形波导区的电流逐渐超过150mA以后,器件的最大输出功率逐渐达到4.28W,与电极共用的980nm锥形激光器相同并趋于饱和,光束质量因子从3.79降到2.45(输出功率为1W).