Surface plasmon modulated nano-aperture vertical-cavity surface-emitting laser

We have fabricated surface plasmon modulated nano-aperture vertical-cavity surface-emitting lasers (VCSELs) from common 850 nm VCSELs using focus ion beam etching with Ga+ ion source. The far-field output power is about 0.3 mW at a driving current of 15 mA with a sub-wavelength aperture surrounded by concentric periodic grooves. The enhancement of transmission intensity can be explained by diffraction and enhanced fields associated with surface plasmon. This structure also exhibits beaming properties.

Modulation response analysis of 1.3 mu m quantum dot vertical-cavity surface-emitting lasers

Some important parameters, such as gain, 3 dB bandwidth and threshold current of 1.3 mu m quantum dot vertical-cavity surface-emitting laser (QD VCSEL) are theoretically investigated. Some methods are developed to improve the VCSEL's modulation response. Significant improvement are prediced for p-type modulation doping. In connection with the threshold characteristic, we found that a structure with short cavity, multilayer quantum dots stack, p-type modulation doping and double intracavity contact on an un-doped DBR is much better suited to high speed quantum dot VCSELs. The parasitic effects of the VCSEL are,analyzed and the influence of packaging of the VCSEL on its modulation responds is analyzed.

Transport phenomena in radial flow MOCVD reactor with three concentric vertical inlets

Transport phenomena in radial flow metalorganic chemical vapor deposition (MOCVD) reactor with three concentric vertical inlets are studied by two-dimensional numerical modeling. By varying the parameters such as gas pressure, flow rates combination of multi-inlets, geometric shapes and sizes of reactor and flow distributor, temperatures of susceptor and ceiling, and susceptor rotation, the corresponding velocity, temperature, and concentration fields inside the reactor are obtained; the onset and change of flow recirculation cells under influences of those parameters are determined. It is found that recirculation cells, originated from flow separation near the bend of reactor inlets, are affected mainly by the reactor height and shape, the operating pressure, the flow rates combination of multi-inlets, and the mean temperature between susceptor and ceiling. By increasing the flow rate of mid-inlet and the mean temperature, decreasing the pressure, maintaining the reactor height below certain criteria, and trimming the bends of reactor wall and flow distributor to streamlined shape, the recirculation cells can be minimized so that smooth and rectilinear flow prevails in the susceptor region, which corresponds to smooth and rectilinear isotherms and larger reactant concentration near the susceptor. For the optimized reactor shape, the reactor size can be enlarged to diameter D = 40 cm and height H = 2 cm without flow recirculation. The susceptor rotation over a few hundred rpm around the reactor central axis will induce the recirculation cell near the exit and deflect the streamlines near the susceptor, which is not the case for vertical reactors. (c) 2006 Elsevier B.V. All rights reserved.

Electronic structure of coupled vertically stacked self-assembled InAs quantum disks in a vertical electric field

In the framework of the effective-mass and adiabatic approximations, by setting the effective-mass of electron in the quantum disks (QDs) different from that in the potential barrier material, we make some improvements in the calculation of the electronic energy levels of vertically stacked self-assembled InAs QD. Comparing with the results when an empirical value was adopted as the effective-mass of electron of the system, we can see that the higher levels become heightened. Furthermore, the Stark shifts of the system of different methods are compared. The Stark shifts of holes are also studied. The vertical electric field changes the splitting between the symmetric level and the antisymmetric one for the same angular momentum. (C) 2003 Elsevier Ltd. All rights reserved.

Transport properties through quantum dot in a vertical electric field

The transport properties through a quantum dot are calculated using the recursion method. The results show that the electric fields can move the conductive peaks along the high- and low-energies. The electric field changes the intensity of conductance slightly. Our theoretical results should be useful for researching and making low-dimensional semiconductor optoelectronic devices. (C) 2002 Elsevier Science B.V. All rights reserved.

Origin of the vertical-anticorrelation arrays of InAs/InAlAs nanowires with a fixed layer-ordering orientation

InAs/In0.52Al0.48As nanowire multilayer arrays were grown on (001) InP substrate by molecular-beam epitaxy. The structural property of the arrays was investigated by transmission electron microscopy. The results clearly showed the formation of InAs nanowires, evolution of InAs/InAlAs interface, and composition and thickness modulations in the InAlAs spacer layer. A fixed spatial ordering of InAs/InAlAs nanowires was revealed for all the samples. Regardless of the change in InAlAs spacer thickness of different samples, (i) the nanowires of one InAs layer are positioned above the nanowire spacing in the previous InAs layer and (ii) the layer-ordering orientation angle of nanowires is fixed. The results were explained from the viewpoint of the growth kinetics. The effect of InAlAs spacers is suggested to play an important role on the spatial ordering of the nanowire arrays. (C) 2002 American Institute of Physics.

Electrolyte electroreflectance spectroscopy studies on the interfacial behavior of the near-surface In0.15Ga0.85As/GaAs quantum well electrode vertical bar non-aqueous electrolyte

Electrolyte electroreflectance spectra of the near-surface strained-layer In0.15Ga0.85As/GaAs double single-quantum-well electrode have been studied at different biases in non-aqueous solutions of ferrocene and acetylferrocene. The optical transitions, the Franz-Keldysh oscillations (FKOs) and the quantum confined Stark effects (QCSE) of In0.15Ga0.85As/GaAs quantum well electrodes are analyzed. Electric field strengths at the In0.15Ga0.85As/GaAs interface are calculated in both solutions by a fast Fourier transform analysis of FKOs. A dip is exhibited in the electric field strength versus bias (from 0 to 1.2 V) curve in ferrocene solution. A model concerning the interfacial tunneling transfer of electrons is used to explain the behavior of the electric field. (C) 2001 Elsevier Science B.V. All rights reserved.

Investigation on anisotropy of vertical-cavity surface-emitting lasers

We have studied the spontaneous emission of polarized excitons in the GaInP/AlGaInP vertical-cavity surface-emitting lasers from 50 K to room temperature. It is observed that the spontaneous emission peak enters and leaves the resonant regime. At the resonant regime, the emission intensities of the perpendicularly and horizontally polarized excitons are enhanced and their proportions are different from that in nonresonant regime. These experimental results are explained by the dressed exciton theory of the semiconductor microcavity device. Based on this theory, the intensity enhancement and the polarization dependence are understood as cooperative emission and the microcavity anisotropy. (C) 2000 American Institute of Physics. [S0021-8979(00)05315-9].

Photoelectrochemical behavior of a novel composite In0.15Ga0.85As/GaAs vertical bar GaAs/Al0.3Ga0.7As multiple quantum well electrode

A novel composite InxGa1-xAs/GaAs/GaAs/AlxGa1-xAs multiple quantum well material with different well widths was studied as a new kind of photoelectrode in a photoelectrochemical cell. The photocurrent spectrum and photocurrent-electrode potential curve were measured in ferrocene nonaqueous solution. Pronounced quantization effects and strong exciton absorption were observed in the photocurrent spectrum. The effects of surface states and interfacial states on the photocurrent-electrode potential curve are discussed. (C) 2000 Elsevier Science S.A. All rights reserved.

Influence of lateral propagating modes on laser output characteristics in selectively oxidized vertical cavity surface-emitting lasers with double oxide layers

The influence of lateral propagating modes on the threshold current and the spontaneous emission factor in selectively oxidized vertical cavity surface-emitting lasers (VCSELs) is investigated based on the mode behaviors of lateral propagating modes and the rate equation model. The numerical results show that the lateral propagating modes may be trapped in the aperture region for the selectively oxidized VCSEL with two oxide layers, one above and one below the active region. The output characteristics of VCSELs can be affected due to the reabsorption of the quasitrapped lateral propagating modes. A lower threshold current can be expected for a VCSEL with double oxide layers than that with a single oxide layer. The numerical results of rate equations also show that a larger spontaneous emission factor can be obtained by fitting the output-input curves for the VCSEL with double oxide layers. (C) 1999 American Institute of Physics. [S0021-8979(99)07919-0].

Stability improvement of selective oxidation during the fabrication of InGaAs/GaAs vertical cavity surface emitting laser

The effects of the carrier gas flow and water temperature on the oxidation rate for different reaction temperatures were investigated. The optimum conditions for stable oxidation were obtained. Two mechanisms of the oxidation process are revealed. One is the flow-controlling process, which is unstable. The other is the temperature-controlling process, which is stable. The stable region decreases for higher reaction temperatures. The simulation results for the stable oxidation region are also given. With optimum oxidation conditions, the stability and precision of the oxidation can be dramatically improved.

Effect of reflectivity at the interface of oxide layer on transverse mode control in oxide confined vertical-cavity surface-emitting lasers

The transverse mode control in oxide confined vertical-cavity surface-emitting lasers is discussed by modeling the dielectric aperture as a uniform waveguide and an extra reflectivity at the oxide layer. The phase of the extra reflectivity and the refractive index step can be adjusted to change the mode threshold gain. We calculate the lateral refractive index step from the mode wavelength difference between aperture and perimeter modes, and compare it with that obtained from the weighted average index. The mode reflectivity in terms of the lateral optical confinement factor at the oxide layer is considered in calculating the threshold gain for transverse modes. The numerical results show that higher transverse modes can be suppressed by adjusting the position of a thin AlAs-oxide layer inside a three-quarter-wave layer in the distributed Bragg reflector. (C) 1998 American Institute of Physics. [S0021-8979(98)04007-9].

Theoretical investigation on quantum well lasers with extremely low vertical beam divergence and low threshold current

A specially designed quantum well laser for achieving extremely low vertical beam divergence was reported and theoretically investigated. The laser structure was characterized by two low index layers inserted between the waveguide layers and the cladding layers. The additional layers were intended to achieve wide optical spread in the cladding layers and strong confinement in the active region. This enabled significant reduction of beam divergence with no sacrifice in threshold current density. The numerical results showed that lasers with extremely low vertical beam divergence from 20 degrees down to 11 degrees and threshold current density of less than 131 A/cm(2) can be easily achieved by optimization of the structure parameters. Influences of individual key structure parameters on beam divergence and threshold current density are analyzed. Attention is also paid to the minimum cladding layer thicknesses needed to maintain low threshold current densities and low internal loss. The near and far field patterns are given and discussed. (C) 1998 American Institute of Physics.

Vertical PIN ultraviolet photodetectors based on 4H-SiC homoepilayers

Vertical PIN ultraviolet photodetectors based on 4H-SiC homoepilayers are presented. The growth of the 4H-SiC homoepilayers was carried out in a LPCVD system. The size of the active area of the photodetector was 300 x 300 mu m(2). The dark and illuminated I-V characteristics were measured at reverse biases from 0 V to 30 V at room temperature. The illuminated current was at least two orders of magnitude higher than the dark current at a bias of below 12 V. The photoresponse was measured from 200 nm to 400 nm at different reverse biases and the peak values of the photo response were located at 3 10 nm. The calculated spectral detectivity D* was shown to be higher than 10(13) cmHz(1/2)/W from 260 to 360 nm with a peak value of 5.9 x 10(13) cmHz(1/2) /W at 310 nm. The peak value of the photoresponse was hundreds of times higher than the response at 400 nm, which showed the device had good visible blind performance. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Investigation of vertical radiation loss for whispering-gallery modes in 3-D microresonators by FDTD simulation

The vertical radiation loss of three-dimensional (3-D) microresonators is investigated by 3-D finite-difference time-domain (FDTD) simulation. The simulation shows that the vertical radiation causes an important loss in the microresonators with weak waveguiding, and result in decrease of the quality factors (Q-factors) of whispering-gallery (WG) modes. Through the simulation, we find that TM-like modes have much weaker vertical radiation loss than TE-like modes. High Q-factor TM-like modes are observed in the 3-D microresonators with weak vertical waveguiding, but the Q-factors of TE-like modes decrease greatly.