A new method to reduce the dark current of GaN based Schottky barrier ultraviolet photodetector

A new method to reduce the dark current of GaN based Schottky barrier ultraviolet photodetector is proposed. In comparision with conventional i-CaN/n(+)-GaN structure, an additional thin p-GaN cap layer is introduced on the i-GaN(n(-)-GaN) in the new structure. The simulation results showed that the additional layer makes the dark current to decrease in the photodetector due to the increase of the Schottky barrier height. The effects of thickness and carrier concentration of p-GaN layer on the dark current of the photodetector were also studied. It is suggested that the dark current of the new structure device could be better reduced by employing p-GaN with higher carrier concentration as the cap layer.

Preliminary design of a tensile-strained p-type Si/SiGe quantum well infrared photodetector

Considering tensile-strained p-type Si/Si1-yGey quantum wells grown on a relaxed Si1-xGex ( 0 0 1) virtual substrate ( y < x), the hole subband structure and the effective masses of the first bound hole state in the quantum wells are calculated by using the 6 x 6 k center dot p method. Designs for tensile-strained p-type quantum well infrared photodetectors ( QWIPs) based on the bound-to-quasi-bound transitions are discussed, which are expected to retain the ability of coupling normally incident infrared radiation without any grating couplers, have lower dark current than n-type QWIPs and also have a larger absorption coefficient and better transport characteristics than normal unstrained or compressive-strained p-type QWIPs.

Highly anisotropic and electric field tunable Zeeman splittings in Mn-doped CdS nanowires

The electronic structure, Zeeman splitting, and g factor of Mn-doped CdS nanowires are studied using the k center dot p method and the mean field model. It is found that the Zeeman splittings of the hole ground states can be highly anisotropic, and so can their g factors. The hole ground states vary a lot with the radius. For thin wire, g(z) (g factor when B is along the z direction or the wire direction) is a little smaller than g(x). For thick wire, g(z) is mcuh larger than g(x) at small magnetic field, and the anisotropic factor g(z)/g(x) decreases as B increases. A small transverse electric field can change the Zeeman splitting dramatically, so tune the g(x) from nearly 0 to 70, in thick wire. The anisotropic factor decreases rapidly as the electric field increases. On the other hand, the Zeeman splittings of the electron ground states are always isotropic.

Polarization dependence of absorption in strongly vertically coupled InAs/GaAs quantum dots for two-color far-infrared photodetector

Strongly vertically coupled InAs/GaAs quantum dots (QDs) with modulation doping are investigated, and polarization dependence of two-color absorptions was observed. Analysis of photoluminescence (PL) and absorption spectra shows that s-polarized absorptions at. 10.0 and 13.4 mu m, stem from the first excited state E-1 and the second excited state E-2 in the QDs to the bound state E-InGaAs in the InGaAs spacer, respectively, whereas p-polarized absorptions at 10.0 and 8.2 mu m stem from the first excited state E-1 and the ground E-g in the QDs to the bound state E-InGaAs in the InGaAs spacer, respectively. These measurements illustrate that transitions from excited states are more sensitive to normal incidence, which are very important in designing QD infrared detector. (C) 2007 Elsevier B.V. All rights reserved.

Hole-mediated electric field tunable high Curie temperature in Mn-doped wurtzite ZnO nanowires

The hole-mediated Curie temperature in Mn-doped wurtzite ZnO nanowires is investigated using the k center dot p method and mean field model. The Curie temperature T-C as a function of the hole density has many peaks for small Mn concentration (x(eff)) due to the density of states of one-dimensional quantum wires. The peaks of T-C are merged by the carriers' thermal distribution when x(eff) is large. High Curie temperature T-C > 400 K is found in (Zn,Mn)O nanowires. A transverse electric field changes the Curie temperature a lot. (Zn,Mn)O nanowires can be tuned from ferromagnetic to paramagnetic by a transverse electric field at room temperature. (c) 2007 American Institute of Physics.

DISCRETELY TUNABLE FIBER RING LASER USING FBG TUNABLE FILTER AND MACH-ZEHNDER INTERFEROMETER

A discretely tunable Er-doped fiber-ring laser using a fiber Mach-Zehnder interferometer (MZI) and a tunable fiber Bragg grating (FBG) is proposed. In this scheme, the combination of MZI and FBG acts as a discrete wavelength selector. Analysis of its transmission function shows that discrete wavelength tuning can be realized, and experiments demonstrate 64 single-mode outputs with a mode spacing of 181.7 pm, and the output power is quite stable in the whole tuning range. (C) 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51 2595-2598, 2009; Published online in Wiley InterScience (www. interscience.wiley.com). DOI 10.1002/mop.24690

A ridge width varied two-section index-coupled DFB self-pulsation laser with a wide continuously tunable frequency range

A 1.55 mu m InGaAsP-InP index-coupled two-section DFB self-pulsation laser (SPL) with a varied ridge width has been fabricated. A record wide self-pulsation tuning range above 450 GHz has been achieved for this index-coupled DFB SPL. Furthermore, frequency locking to an optically injected modulated signal is successfully demonstrated.

Zero biased Ge-on-Si photodetector with a bandwidth of 4.72 GHz at 1550 nm

High quality Ge was epitaxially grown on Si using ultrahigh vacuum/chemical vapor deposition (UHV/CVD). This paper demonstrates efficient germanium-on-silicon p-i-n photodetectors with 0.8 mu m Ge, with responsivities as high as 0.38 and 0.21 A/W at 1.31 and 1.55 mu m, respectively. The dark current density is 0.37 mA/cm(2) and 29.4 mA/cm(2) at 0 V and a reverse bias of 0.5 V. The detector with a diameter of 30 mu m, a 3 dB-bandwidth of 4.72 GHz at an incident wavelength of 1550 nm and zero external bias has been measured. At a reverse bias of 3 V, the bandwidth is 6.28 GHz.

Electric-tunable magneto resistance effect in a two-dimensional electron gas modulated by hybrid magnetic-electric barrier nanostructure

The electric-tunable spin-independent magneto resistance effect has been theoretically investigated in ballistic regime within a two-dimensional electron gas modulated by magnetic-electric barrier nanostructure. By including the omitted stray field in previous investigations oil analogous structures, it is demonstrated based on this improved approximation that the magnetoresistance ratio for the considered structure can be efficiently enhanced by a proper electric barrier up to the maximum value depending on the specific magnetic suppression. Besides, it is also shown the introduction of positive electrostatic modulation can effectively overcome the degradation of magnetoresistance ratio for asymmetric configuration and enhance the visibility of periodic pattern induced by the size effect, while for an opposite modulation the system magnetoresistance ratio concerned may change its sign. (C) 2009 Elsevier B.V. All rights reserved.

High responsivity resonant-cavity-enhanced InGaAs/GaAs quantum-dot photodetector for wavelength of similar to 1 mu m at room temperature

The characteristics of a resonant cavity-enhanced InGaAs/GaAs quantum-dot n-i-n photodiode with only a bottom distributed Bragg reflector used as the cavity mirror, are reported. To suppress the dark current, an AlAs layer is inserted into the device structure as the blocking layer. It turns out that the structure still possesses the resonant coupling nature, and makes Rabi splitting discernible in the photoluminescence spectra. The measured responsivity spectrum of the photocurrent shows a peak at lambda = 1030 nm, and increases rapidly as the bias voltage increases. A peak responsivity of 0.75 A/W, or equivalently an external quantum efficiency of 90.3%, is obtained at V-bias = -1.4 V.

1 x 4 Ge-on-SOI PIN Photodetector Array for Parallel Optical Interconnects

High-quality Ge film was epitaxially grown on silicon on insulator using the ultrahigh vacuum chemical vapor deposition. In this paper, we demonstrated that the efficient 1 4 germanium-on-silicon p-i-n photodetector arrays with 1.0 mu m Ge film had a responsivity as high as 0.65 A/W at 1.31 mu m and 0.32 A/W at 1.55 mu m, respectively. The dark current density was about 0.75 mA/cm(2) at 0 V and 13.9 mA/cm(2) at 1.0 V reverse bias. The detectors with a diameter of 25 mu m were measured at 1550 nm incident light under 0 V bias, and the result showed that the 3-dB bandwidth is 2.48 GHz. At a reverse bias of 3 V, the bandwidth is about 13.3 GHz. The four devices showed a good consistency.

Tunable edge-emitting microlaser on photonic crystal slab

A tunable edge-emitting microlaser is realised by a chirped line-defect photonic crystal waveguide. A tunable range of 57 nm is obtained experimentally.

All-optical continuously tunable delay with a high linear-chirp-rate fiber Bragg grating based on four-wave mixing in a highly-nonlinear photonic crystal fiber

A scheme for hi-fi all-optical continuously tunable delay is proposed. The signal wavelength is converted to a desired idler wavelength and converted back after being delayed by a high linear-chirp-rate (HLCR) fiber Bragg grating (FBG) based on four-wave mixing (FWM) in a highly-nonlinear photonic crystal fiber (HN-PCF). In our experiment, 400 ps (more than 8 full width of half maximum, FWHM) tunable delay is achieved for a 10 GHz clock pulse with relative pulse width broaden ratio (RPWBR) of 2.08%. The power penalty is only 0.3 dB at 10(-9) BER for a 10 Gb/s 2(31)-1 pseudo random bit sequence (PRBS) data. (c) 2009 Elsevier B.V. All rights reserved.

A new p-n structure ultraviolet photodetector with p(-)-GaN active region

A new ultraviolet photodetector of employing p menus type GaN (p(-)-GaN) as the active layer is proposed. It is easy to obtain the p(-)-GaN layer with low carrier concentration. As a result, the depletion region can be increased and the quantum efficiency can be improved. The influence of some structure parameters on the performance of the new device is investigated. Through the simulation calculation, it is found that the quantum efficiency increases with the decrease of the barrier height between the metal electrode and the p(-)-GaN layer, and it is also found that the quantum efficiency can be improved by reducing the thickness of the p(-)-GaN layer. To fabricate the new photodetector with high performance, we should employ thin p(-)-GaN layer as the active layer and reduce the Schottky barrier height.

A Si-based tunable narrow-band flat-top filter with multiple-step-type Fabry-Perot cavity structure

In the optical network, the quick and accurate alignment with wavelength is an important issue during the channel detection. At this point, a filter having flat-top response characteristic is an effective solution. Based on multiple-step-type Fabry-Perot cavity structure, a novel all-Si-based thermooptical tunable flat-top filter with narrow-band has been fabricated, using our patent silicon-on-reflector bonding technology. The device demonstrated a 1-dB flat-top width of 1 nm, 3-dB band of 3 nm, free spectra range of 8 nm, and the tuning range of 4.6 nm was obtained under the applied voltage of 4 V.