Influence of growth parameters of frequency-radio plasma nitrogen source on extending emission wavelengths from 1.31 mu m to 1.55 mu m GaInNAs/GaAs quantum wells grown by molecular-beam epitaxy

High (42.5%) indium content GaInNAs/GaAs quantum wells with room temperature emission wavelength from 1.3 mu m to 1.5 mu m range were successfully grown by Radio Frequency Plasma Nitrogen source assisted Molecular Beam Epitaxy. The growth parameters of plasma power and N-2 How rate were optimized systematically to improve the material quality. Photoluminescence and transmission electron microscopy measurements showed that the optical and crystal quality of the 1.54 mu m GaInNAs/GaAs QWs was kept as comparable as that in 1.31 mu m.

Post-growth and in situ annealing on GaInNAs(Sb) and their application in 1.55 mu m lasers

Rapid thermal annealing (RTA) has been demonstrated as an important way to improve the crystal quality of GaInNAs(Sb)/GaAs quantum wells. However little investigation has been made into their application in laser growth, especially at a wavelength of 1.55 mu m. When a GaAs-based laser is grown, AlGaAs is usually used for cladding layers. The growth of the p-cladding layer usually takes 30-45 min at a growth temperature higher than that of the GaInNAs(Sb) active region, which affects the material quality. To investigate this effect, various post-growth annealing processes were performed to simulate this process. Great enhancement of the PL intensity was obtained by a two-step process which consisted of annealing first at 700 degrees C for 60 s and then at 600 degrees C for 45 min. We transferred this post-growth annealing to in situ annealing. Finally, a GaInNAsSb laser was grown with a 700 degrees C in situ annealing process. Continuous operation at room temperature of a GaAs-based dilute nitride laser with a wavelength beyond 1.55 mu m was realized for the first time.

A 1.5 mu m n-type InGaAsP/InGaAsP modulation-doped multiple quantum well DFB laser by MOCVD

1.5 mu m n-type InGaAsP/InGaAsP modulation-doped multiple quantum well (MD-MQW) DFB lasers have been fabricated successfully by low pressure metal organic chemical vapour deposition (LP-MOCVD) technology. The experimental results indicate that n-type MD-MQWs can effectively reduce the threshold Current compared with conventional multiple quantum well DFB lasers. Theoretical analysis indicates that such an effect is due to the much smaller absorption loss and lower Auger recombination, compared with that in an undoped MQW structure. Moreover, the introduction of n-type dopant of suitable levels of concentration in the barrier layers enhances the dynamic characteristics of DFB lasers, due to a coupling between the adjacent quantum well layers and tunnelling-assisted injection, which can reduce the relatively long capture time and increase the effective differential gain 1/X dG/dn .

Enhancement of 1.53 mu m photoluminescence from spin-coated Er-Si-O (Er2SiO5) crystalline films by nitrogen plasma treatment

Er-Si-O (Er2SiO5) crystalline films are fabricated by the spin-coating and subsequent annealing process. The fraction of erbium is estimated to be 21.5 at% based on Rutherford backscattering measurement. X-ray diffraction pattern indicates that the Er-Si-O films are similar to Er2SiO5 compound in the crystal structure. The fine structure of room-temperature photoluminescence of Er3+-related transitions suggests that Er has a local environment similar to the Er-O-6 octahedron. Our preliminary results show that the intensity of 1.53 mu m emission is enhanced by a factor of seven after nitrogen plasma treatment by NH3 gas with subsequent post-annealing. The full-width at half-maximum of 1.53 pm emission peak increases from 7.5 to 12.9 nm compared with that of the untreated one. Nitrogen plasma treatment is assumed to tailor Er3+ local environment, increasing the oscillator strength of transitions and thus the excitation/emission cross-section. (c) 2005 Elsevier B.V. All rights reserved.

1.55-mu m Ridge DFB laser and electroabsorption modulator integrated with buried-ridge-stripe dual-waveguide spot-size converter output

A 1.55-mu m ridge distributed feedback laser and electroabsorption modulator monolithically integrated with a buried-ridge-stripe dual-waveguide spot-size converter (SSC) at the output port for low-loss coupling to a cleaved single-mode optical fiber was fabricated by means of selective area growth, quantum-well intermixing, and dual-core technologies. These devices exhibit threshold current of 28 mA, 3-dB modulation bandwidth of 12.0 GHz, modulator extinction ratios of 25.0-dB dc. The output beam divergence angles of the SSC in the horizontal and vertical directions are as small as 8.0 degrees x 12.6 degrees, respectively, resulting in 3.2-dB coupling loss with a cleaved single-mode optical fiber.

Fabrication of Ge nano-dot heterojunction phototransistors for improved light detection at 1.55 mu m

Heterojunction phototransistors (HPTs) with several Ge/Si nano-dot layers as the absorption region are fabricated to obtain improved light detectivity at 1.55 mu m. The HPT detectors are of n-p-n type with ten layers of Ge(8ML)/Si(45nm) incorporated in the base-collector junction and are grown by an ultrahigh-vacuum chemical-vapor deposition system. The detectors are operated with normal incidence. Because of the good quality of the grown material and fabrication process, the dark current is only 0.71pA/mu m(2) under 5 V bias and the break-down voltage is over 20 V. Compared to the positive-intrinsic-negative (PIN) reference detector with the same absorption layer, the responsivity is improved over 17 times for normal incidence at 1.55 mu m.

Growth and characterization of 0.8-mu m gate length AlGaN/GaN HEMTs on sapphire substrates

AlGaN/GaN high electron mobility transistor (HEMT) structures were grown on 2 inch sapphire substrates by MOCVD, and 0.8-mu m gate length devices were fabricated and measured. It is shown by resistance mapping that the HEMT structures have an average sheet resistance of approximately 380 Omega/sq with a uniformity of more than 96%. The 1-mm gate width devices using the materials yielded a pulsed drain current of 784 mA/mm at V-gs=0.5 V and V-ds=7 V with an extrinsic transconductance of 200 mS/mm. A 20-GHz unity current gain cutoff frequency (f(T)) and a 28-GHz maximum oscillation frequency (f(max)) were obtained. The device with a 0.6-mm gate width yielded a total output power of 2.0 W/mm (power density of 3.33 W/mm) with 41% power added efficiency (PAE) at 4 GHz.

High performance of 1.55 mu m DFB integrated with vertically tapered self-aligned spot-size converter

A new type of self-aligned spotsize converter (SSC) integrated 1.55 mum DFB lasers had been proposed in this article. The upper optical confinement layer and the butt-coupled tapered thickness waveguide were regrown simultaneously, which not only offered the separate optimization of the active region and the integrated SSC, but also reduced the difficulty of the butt-joint selective regrowth. The vertical and horizontal far field angles were 9degrees and 12degrees respectively, the 1- dB misalignment tolerance were both 3.6 and 3.4 mum. The directed coupling efficiency to tapered single mode fiber was 48%.

Surface morphology and optical property of 1.3 mu m In0.5Ga0.5As/GaAs self-organized quantum dots grown by MBE

Surface morphology and optical properties of 1.3 mum self-organized InGaAs/GaAs quantum dots structure grown by molecular beam epitaxy have been investigated by atomic force microscopy and photoluminescence measurements. It has been shown that the surface morphology evolution and emission wavelengths of InGaAs/GaAs QDs can be controlled effectively via cycled monolayer deposition methods due to the reduction of the surface strain. Our results provide important information for optimizing the epitaxial parameters for obtaining 1.3 mum long wavelength emission quantum dots structures. (C) 2002 Elsevier Science B.V. All rights reserved.

A method to obtain ground state electroluminescence from 1.3 mu m emitting InAs/GaAs quantum dots grown by molecular beam epitaxy

1.3 mum emitting InAs/GaAs quantum dots (QDs) have been grown by molecular beam epitaxy and QD light emitting diodes (LEDs) have been fabricated. In the electroluminescence spectra of QD LEDs, two clear peaks corresponding to the ground state emission and the excited state emission are observed. It was found that the ground state emission could be achieved by increasing the number of QDs contained in the active region because of the state filling effect. This work demonstrates a way to control and tune the emitting wavelength of QD LEDs and lasers.

Dependence of optical properties on the structure of multi-layer self-organized InAs quantum dots emitting near 1.3 mu m

Self-organized InAs quantum dots (QDs) have been fabricated by molecular beam epitaxy and characterized by photoluminescence (PL). For both single- and multi-layer QDs, PL intensity of the first excited state is larger than that of the ground state at 15 K. Conversely, at room temperature (RT), PL intensity of the first excited state is smaller than that of the ground state. This result is explained by the phonon bottleneck effect. To the ground state, the PL intensities of the multi-layer QDs are larger than that of the single-layer QDs at 15 K, while the intensities are smaller than that of the single-layer QDs at RT. This is due to the defects in the multi-layer QD samples acting as the nonradiative recombination centers. The inter-diffusion of Ga and In atoms in the growth process of multi-layer QDs results in the PL blueshift of the ground state and broadening of the full-width at half-maximum (FWHM), which can be avoided by decreasing the spacers' growth temperature. At the spacers' growth temperature of 520degreesC, we have prepared the 5-layer QDs which emit near 1.3 mum with a FWHM of 31.7 meV at RT, and 27.9 meV at 77 K. (C) 2002 Published by Elsevier Science B.V.

Angular dependent characteristics of a 1.3-mu m GaInNAs/GaAs quantum-well resonant cavity enhanced photodetect

Characteristics of a 1.3-mum GaInNAs RCE PD with respect to the incident light angle were analyzed both in theoretical simulation and experiments. The results show the influence can be neglected when the light incidence angle is less than 3degrees. This is a requirement for the PD to be applied in WDM networks. (C) 2002 Wiley Periodicals, Inc.

SiGe/Si resonant-cavity-enhanced photodetectors for 1.3 mu m operation fabricated using wafer bonding techniques

A SiGe/Si multiple-quantum-well resonant-cavity-enhanced (RCE) photodetector for 1.3 mum operation was fabricated using bonding reflector process. A full width at half maximum (FWHM) of 6 nm and a quantum efficiency of 4.2% at 1314 nm were obtained. Compared to our previously reported SiGe RCE photodetectors fabricated on separation-by-implanted-oxygen wafer, the mirrors in the device can be more easily fabricated and the device can be further optimized. The FWHM is expected to be less than 1 nm and the detector is fit for density wavelength division multiplexing applications. (C) 2002 American Institute of Physics.

GaInNAs/GaAs multiple-quantum well resonant-cavity-enhanced photodetectors at 1.3 mu m

A GaInNAs/GaAs multiple quantum well (MQW) resonant-cavity enhanced photodetector (RCF-PD) operated at a wavelength of 1.3 mum with the full width at half maximum of 4nm has been demonstrated. The GaInNAs RCE - PD was grown by molecular beam epitaxy using a homemade ion-removed dc plasma cell as a nitrogen source. GaInNAs/GaAs MQW shows a strong exciton peak at room temperature, which is very beneficial for applications in long-wavelength absorption devices. For a 100 mum diameter RCE-PD, the dark current is 20 and 32 pA at biases of 0 and 6 V, respectively, and the breakdown voltage is - 18 V. The measured 3 dB bandwidth is 308 MHz, which is limited by the resistance of p-type distributed Bragg reflector mirror. The tunable wavelength in a range of 18 nm with the angle of incident light was observed.

A narrow photoluminescence linewidth of 19.2 meV at 1.35 mu m from In0.5Ga0.5As/GaAs quantum island structure grown by molecular beam epitaxy

A self-organized In0.5Ga0.5As/GaAs quantum island structure emitting at 1.35 mum at room temperature has been successfully fabricated by molecular beam epitaxy via cycled (InAs)(1)/GaAs)(1)monolayer deposition method. The photoluminescence measurement shows that a very narrow linewidth of 19.2 meV at 300 K has been reached for the first time, indicating effective suppression of inhomogeneous broadening of optical emission from the In0.5Ga0.5As island structure due to indium segregation reduction by introducing an AlAs layer and the strain reduction by inserting an In0.2Ga0.8As layer overgrown on the top of islands. The mound-like morphology of the islands elongated along the [1 (1) over bar0] azimuth are observed by the atomic force microscopy measurement, which reveals the fact that strain in the islands is partially relaxed along the [1 (1) over bar0] direction. Our results present important information for the fabrication of 1.3 mum wavelength quantum dot devices.