Optically pumped intersubband lasers based on quantum wells

A far infrared (FIR) laser based on intersubband transitions in quantum wells is proposed where a pumping laser is used to create population inversion in the structure. The goal is to develop a structure which operates essentially as a 4-level laser, to minimize bottlenecking of the lower laser state. Multiple quantum wells can be used in the active laser of these structures to enhance the laser gain and the minimum required reflectivity in the cavity structure. The possibility of using both conduction and valence band quantum-well structures are investigated. Our study shows that, due to high intersubband scattering rates in the valence band structure, the creation of population inversion is more difficult and requires a high pumping power density while in the conduction band structure, population inversion can be achieved by a moderate pumping power density. The maximum population inversion in the conduction band structure is estimated to be 2.1×10¹¹ cm², which requires a pumping power density 2 kW cm^-2 for a single quantum well. The threshold power as well as the minimum required reflectivity of the cavity structure for the conduction band scheme are estimated for different well numbers     

Carrier capture competition between two different quantum wells in dual-wavelength semiconductor lasers

Based on a three-level model, we have numerically shown that a semiconductor gain medium with a structure consisting of two different quantum wells may lead to dual-wavelength laser operation if the balance of carrier capture competition between the two wells can be reached. The major controlling parameters for the operation are the ratio of the carrier quantum capture times of the two wells and the absorption constant of the short-wavelength photons by the long-wavelength quantum well. It is shown that there exists a large parameter space for dual-wavelength operation.     

低阈值电流、高量子效率脊形波导激光器

研制了低阈值电流、高量子效率670nm压缩应变单量子阱GaInP/AIGalnP脊形波导激光器。测量解理成的激光器条,腔长为300μm时,阈值电流为12．8mA,双面外部量子效率之和达到94．6％。     

Design of double and triple quantum wells for InGaAs-AlAsSbintersubband unipolar semiconductor lasers

InGaAs-AlAsSb double and triple quantum well (QW) structures were designed in an effort to shorten the wavelength to less than 2 μm for possible application to intersubband unipolar lasers. Wavelengths corresponding to the intersubband separation, the minimum and maximum operating electric field, optical-phonon-limited nonradiative scattering time, and escape time from the QW were simulated. It was found that suitable nonradiative transition times can be obtained by properly designing the coupling layer thickness for both kinds of QW's. The minimum wavelength is 1.5 μm and an operating electric field is above 130 kV/cm for wavelengths <2 μm in the double QW. On the other hand, the minimum operating electric field is less than 10 kV/cm and the minimum wavelength is about 1.7 μm for the triple QW. The triple QW is suitable for an electric-field induced wavelength tunable laser     

All-optical modulation for semiconductor lasers by using threeenergy levels in n-doped quantum wells

An all-optical modulation method for semiconductor lasers using three energy levels in n-doped quantum wells is demonstrated. The modulation principle is based on the third-order interaction between interband-and intersubband-resonant light in the quantum-well structure. The modulation is demonstrated by a real-time single-shot experiment using a semiconductor laser for the interband-resonant light and a CO ₂ laser for the intersubband-resonant light. The dependences of the modulation depth on the intersubband-resonant light polarization and on the interband-resonant light wavelength indicate that the modulation is achieved by this principle. It is pointed out that the thermal effect appears when the power of the intersubband-resonant light becomes strong     

Internal efficiency of semiconductor lasers with a quantum-confined active region

We discuss in detail a new mechanism of nonlinearity of the light-current characteristic (LCC) in heterostructure lasers with reduced-dimensionality active regions, such as quantum wells (QWs), quantum wires (QWRs), and quantum dots (QDs). It arises from: 1) noninstantaneous carrier capture into the quantum-confined active region and 2) nonlinear (in the carrier density) recombination rate outside the active region. Because of 1), the carrier density outside the active region rises with injection current, even above threshold, and because of 2), the useful fraction of current (that ends up as output light) decreases. We derive a universal closed-form expression for the internal differential quantum efficiency /spl eta//sub int/ that holds true for QD, QWR, and QW lasers. This expression directly relates the power and threshold characteristics. The key parameter, controlling /spl eta//sub int/ and limiting both the output power and the LCC linearity, is the ratio of the threshold values of the recombination current outside the active region to the carrier capture current into the active region. Analysis of the LCC shape is shown to provide a method for revealing the dominant recombination channel outside the active region. A critical dependence of the power characteristics on the laser structure parameters is revealed. While the new mechanism and our formal expressions describing it are universal, we illustrate it by detailed exemplary calculations specific to QD lasers. These calculations suggest a clear path for improvement of their power characteristics. In properly optimized QD lasers, the LCC is linear and the internal quantum efficiency is close to unity up to very high injection-current densities (15 kA/cm/sup 2/). Output powers in excess of 10 W at /spl eta//sub int/ higher than 95% are shown to be attainable in broad-area devices. Our results indicate that QD lasers may possess an advantage for high-power applications.     

Buried heterostructure quantum cascade lasers with a large optical cavity waveguide

We report the fabrication and characterization of buried heterostructure quantum cascade (BH-QC) lasers formed by selective lateral regrowth of InP on the laser ridge by metal organic chemical vapor deposition (MOCVD). A fivefold improvement in maximum average power (up to 10 mW) and a twofold improvement in maximum operation duty cycle (up to 17%) are measured at 273 K and are attributed to lower lateral waveguide losses and a better heat dissipation.     

Simulation of semiconductor quantum well lasers

A new quantum well laser simulator that accounts for details of carrier transport, distribution of two-dimensional (2-D) carriers within the quantum well, optical gain spectra, and photon rate equations, is presented. The resulting set of complicated equations is solved using “slack variables”-a new algorithm that is both efficient and stable. Results are compared with experiments to verify the simulator     

Advances in self-assembled semiconductor quantum dot lasers

In the past 20 years the semiconductor laser has become a key device in optical electronics because of its pure output spectrum and high quantum efficiency. As the capabilities of laser diodes have grown, so has the range of applications contemplated for them. A great success in semiconductor lasers has been brought by the ability to artificially structure new materials on an atomic scale by using advanced crystal growth methods such as MBE and MOVPE. The laser performance successes gained using quantum wells in optoelectronic devices can be extended by adopting quantum wire and quantum dot structures. There have been several reports of successful lasing action in semiconductor dot structures within the past few years. In this article I will briefly review the recent progress in the development of quantum dot lasers.     

Wide-range tunable semiconductor lasers using asymmetric dualquantum wells

Using asymmetric dual quantum wells for the laser material, the semiconductor lasers are broadly tunable. In a grating coupled ring cavity, the semiconductor laser is continuously tunable from 766 to 856 nm using a 400-μm semiconductor laser amplifier in the cavity. This letter also demonstrates that the grating coupled ring cavity could well eliminate the amplified stimulated emission noise and about 40-dB amplified spontaneous emission (ASE) suppression ratio is obtained over the entire tuning range     

非对称异质波导半导体激光器结构

提出了一种非对称异质波导半导体激光器外延结构,即通过优化选择材料体系和结构厚度,对器件外延层的P侧限制结构和N侧限制结构分别设计,从而降低器件的电压损耗,使其满足高输出功率以及高的电光转换效率的要求.从载流子的输运和限制等微观机制出发,对器件的主要输出特性进行了理论分析和数值模拟,并以此为根据设计和制作了一种1060 nm In Ga As/Ga As单量子阱非对称异质波导结构半导体激光器,并对器件的主要输出特性进行了测试.实验结果表明,非对称异质结构是降低器件的电压降、增大限制结构对注入载流子的限制,提高半导体激光器电光转换效率的有效措施.     

A dual-color injection laser based on intra- and inter-band carriertransitions in semiconductor quantum wells or quantum dots

A new type of semiconductor injection laser capable of simultaneously generating radiation in the mid-infrared (MIR) (λ~10 μm) and near-infrared (NIR) (λ~0.9 μm) spectral regions is proposed. The MIR emission is a result of intersubband (intraband) electron transitions within a three-level conduction band in a quantum well or a quantum dot. The NIR emission, on the other hand, is due to conventional interband recombination of injected electrons and holes into the conduction and valence bands, respectively. The conditions for population inversion in the intersubband emission process are determined by an appropriately engineered energy structure for a three-level system in the conduction band of a quantum well or dot structure: for the quantum-well-based system, the structure has an asymmetric funnel shape to provide long electron-phonon lifetime at the third (top) energy level. Under high carrier injection, NIR interband emission depopulates the conduction ground level of the quantum well, thereby stabilizing the electron concentration at this level-a necessary condition fur the operation of the MIR laser. This paper discusses the calculation of the population inversion conditions, the requisite gain, and threshold current for MIR laser operation. We also present a preliminary design of the laser structure with a composite waveguide that accommodates both mid- and NIR stimulated emission     

Low-threshold 1.3-µm injection lasers based on single InGaAsN quantum wells

Semiconductors - The design of the active region in InGaAsN quantum well (QW) injection lasers is investigated. Long-wavelength (1.27–1.3 mm), low-threshold (&;lt;400 A/cm2), and...     

共腔双区激光器的外量子效率

推导了共腔双区激光器的外量子效率,计算了GaAs-Al_(0.3)Ga_(0.7)As DH共腔双区激光器的外量子效率与注入电流的关系.测量了GaAs一Al_(0.3)Ga_(0.7)As DH共腔双区波导激光器的外量子效率,实验结果和理论分析基本一致.     

High-power long-wavelength room-temperature MOVPE-grown quantum cascade lasers with air-semiconductor waveguide

Quantum cascade lasers grown by metal organic vapour phase epitaxy (MOVPE) with high peak output power of 1.3 W at 300 K emitting a wavelength of 9.8 mum are reported. The devices are processed in wide ridge waveguide structures with an air-semiconductor interface to confine the laser optical mode. This design increases the optical overlap factor and reduces waveguide losses.     

Dependence of linewidth enhancement factor ? on waveguide structure in semiconductor lasers

In semiconductor lasers, the ratio ? of the real part to the imaginary part of the change in refractive index due to the change in carrier density determines the magnitude of dynamic and static line broadenings. The letter reports that the effective value of ? depends on the structure of the waveguide, where both index and gain mechanisms induce transverse-mode guiding.     

Intervalley scattering in GaAs/AlGaAs quantum wells and quantum cascade lasers

The results of simulations of Γ−X scattering in GaAs/AlGaAs quantum wells are presented, discussing the importance of the mole fraction, doping density, and lattice and electron temperatures in determining the scattering rates. A systematic study of Γ−X scattering in GaAs/Al_xGa_1−xAs heterostructures, using a single quantum well to determine the importance of well width, molar concentration x, lattice temperature, and doping density, has been performed. After this we consider a double quantum well to determine the role of intervalley scattering in the transport through single-layer heterostructures, i.e. Γ−X−Γ scattering compared with Γ−Γ scattering. Finally, we estimate the relative importance of intervalley scattering in a GaAs-based quantum-cascade laser device and compare it with other relevant scattering mechanisms important to describe carrier dynamics in the structure. Our simulations suggest that Γ−X scattering can be significant at room temperature but falls off rapidly at lower temperatures.     

Study of waveguide coupling efficiency in hybrid silicon lasers

This paper presents a new method to increase the waveguide coupling efficiency in hybrid silicon lasers.We find that the propagation constant of the InGaAsP emitting layer can be equal to that of the Si resonant layer through improving the design size of the InP waveguide.The coupling power achieves 42% of the total power in the hybrid lasers when the thickness of the bonding layer is 100 nm.Our result is very close to 50% of the total power reported by Intel when the thickness of the thin bonding layer is less than 5 nm.Therefore,our invariable coupling power technique is simpler than Intel's.     

Coupling efficiency in grating tuned carbon dioxide waveguide lasers

The coupling efficiency in typical CO₂ waveguide lasers when the feedback element is a diffraction grating is investigated theoretically. A scalar diffraction integral approach is adopted, and the laser is assumed to operate on its lowest loss waveguide mode.