Unselective regrowth buried heterostructure long-wavelength superluminescent diode realized with MOVPE

A novel unselective regrowth buried heterostructure (BH) long-wavelength superluminescent diode (SLD), which has a grade-strained bulk InGaAs active region, was developed by metalorganic vapor-phase epitaxy (MOVPE). The 3 dB emission spectrum bandwidth of the SLD is about 65 nm with the range from 1596 to 1661 nm at 90 mA and front 1585 to 1650 nm at 150 mA. An output power of 3.5 mW is obtained at 200 mA injection current under CW operation at room temperature. (c) 2006 Elsevier B.V. All rights reserved.

Unselective regrowth of 1.5-mu m InGaAsP multiple-quantum-well distributed-feedback buried heterostructure lasers

Unselective regrowth for fabricating 1.5-mu m InGaAsP multiple-quantum well (MQW) distributed-feedback (DFB) buried heterostructure (BH) lasers is developed. The experimental results exhibit superior characteristics, such as a low threshold of 8.5 mA, high slope efficiency of 0.55 mW/mA, circular-like far-field patterns, the narrow line-width of 2.5 MHz, etc. The high performance of the devices effectively proves the feasibility of the new method to fabricate buried heterostructure lasers. (c) 2006 Society of Photo-Optical Instrumentation Engineers.

Diode-pumped passively Q-switched Yb : YAG microchip laser with a GaAs as saturable absorber

A passively Q-switched Yb: YAG microchip laser has been constructed by using a doped GaAs as the saturable absorber as well as the output coupler. At 13.5 W of pump power the device produces high-quality 3.4 muJ 52 ns pulses at 1030nm with a pulse repetition rate of 7.8kHz in a TEM00-mode.

Structural and photoluminescent properties of ternary Zn1-xCdxO crystal films grown on Si(111) substrates

The ternary Zn1-xCdxO (0less than or equal toxless than or equal to0.6) alloying films with highly c-axis orientation have been deposited on Si(111) substrates by direct current reactive magnetron sputtering method. X-ray diffraction measurement indicates that the wurtzite-type structure of ZnO can be stabilized up to nominal Cd content x similar to 0.6 without cubic CdO phase separation. The lattice parameter c of Zn1-xCdxO increases almost linearly from 5.229 Angstrom (x = 0) to 5.247 Angstrom (x = 0.6), indicating that Cd substitution takes place on the Zn lattice sites. The photoluminescence spectra of the Zn1-xCdxO thin films measured at 12 K display a substantial red shift (similar to0.3 eV) in the near-band-edges (NBEs) emission of ZnO: from 3.39 eV of ZnO to 3.00 eV of Zn0.4Cd0.6O. The direct modulation of band gap caused by Zn/Cd substitution is responsible for the red shift effect in NBE emission of ZnO. (C) 2003 Elsevier Science B.V. All rights reserved.

Structural and optical characterization of Zn1-xCdxO thin films deposited by dc reactive magnetron sputtering

Zn1-xCdxO crystal thin films with different compositions were prepared on silicon and sapphire substrates by the dc reactive magnetron sputtering technique. X-ray diffraction measurements show that the Zn1-xCdxO films are of completely (002)-preferred orientation for x less than or equal to 0.6. For x = 0.8, the Elm is a mixture of ZnO hexagonal wurtzite crystals and CdO cubic crystals. For pure CdO, it is highly (200) preferential-oriented. Photoluminescence spectrum measurement shows that the Zn1-xCdxO (x = 0.2) thin film has a redshift of 0.14 eV from that of ZnO reported previously.

Characterization of deep levels in Pt-GaN Schottky diodes deposited on intermediate-temperature buffer layers

Gallium nitride (GaN)-based Schottky junctions were fabricated by RF-plasma-assisted molecular beam epitaxy (MBE). The GaN epitaxial layers were deposited on novel double buffer layers that consist of a conventional low-temperature buffer layer (LTBL) grown at 500 degreesC and an intermediate-temperature buffer layer (ITBL) deposited at 690 degreesC. Low-frequency excess noise and deep level transient Fourier spectroscopy (DLTFS) were measured from the devices. The results demonstrate a significant reduction in the density of deep levels in the devices fabricated with the GaN films grown with an ITBL. Compared to the control sample, which was grown with just a conventional LTBL, a three-order-of-magnitude reduction in the deep levels 0.4 eV below the conduction band minimum (Ec) is observed in the bulk of the thin films using DLTFS measurements.

Study of GaN thin films grown on intermediate-temperature buffer layers by molecular beam epitaxy

A detailed characterisation study of GaN thin films grown by rf-plasma molecular beam epitaxy on intermediate-temperature buffer layers (ITBL) was carried out with Hall, photoluminescence (PL) and deep-level transient Fourier spectroscopy (DLTFS) techniques. The unique feature of our GaN thin films is that the GaN epitaxial layers are grown on top of a double layer that consists of an ITBL, which is grown at 690 degreesC, and a conventional low-temperature buffer layer deposited at 500 degreesC. It is observed that the electron mobility increases steadily with the thickness of the ITBL, which peaks at 377 cm(2)V(-1)S(-1) for an ITBL thickness of 800 nm. The PL also demonstrated systematic improvements with the thickness of the ITBL. The DLTFS results suggest a three-order-of-magnitude reduction in the deep level at E-c-0.40 eV in the device fabricated with the GaN films grown on an ITBL thickness of 1.25 mum in comparison with the control device without an ITBL. Our analyses indicate that the utilization of an ITBL in addition to the conventional low-temperature buffer layer leads to the relaxation of residual strain within the material, resulting in an improvement in the optoelectronic properties of the films. (C) 2002 Elsevier Science BN. All rights reserved.

Self-aligned current aperture in native oxidized AlInAs buried heterostructure InGaAsP/InP distributed feedback laser

A InGaAsP/InP self-aligned, native oxidized buried heterostructure (BH) distributed feedback (DFB) laser is proposed. It is as easy to process as the ridge waveguide DFB laser and has superior performance. The current aperture can be easily controlled without selective regrowth. The laser exhibits a low threshold of 5.0 mA with 36 dB side mode suppression ratio at the emission wavelength of 1.562 mu m. It emits in a single lobe with full width at half maximum angles of 33.6 degrees and 42.6 degrees for the lateral and vertical fields, respectively. Its beam is more circular than that of the as-grown BH laser because the lower refractive index of oxide compared to the as-grown layer and results in a larger lateral optical confinement. Its characteristic temperature (T-0) is 50 K at room temperature but increases in value at the higher temperature range. (C) 2000 American Institute of Physics. [S0003-6951(00)00812-3].

Cyclotron resonance mass of magnetopolaron in a polar crystal slab at finite temperatures

Using the Green function method, we have studied the cyclotron resonance of an electron interacting with bulk longitudinal optical(BO) phonons as well as surface optical(SO) phonons in a polar crystal slab at finite temperatures. It is found that the temperature dependence of magnetopolaron depends strongly on the strength of the magnetic field. The numerical results show that the cyclotron resonance mass of polaron in a slab is an increasing or decreasing function of temperature when the magnetic field is lower or higher than the resonant magnetic field region, respectively. The magnetic field and slab width dependence of cyclotron resonance mass are also studied in this paper. (C) 1999 Elsevier Science B.V. All rights reserved.

A novel 1.3-mu m high T-0 AlGaInAs/InP strained-compensated multi-quantum well complex-coupled distributed feedback laser diode

A 1.3-mu m AlGaInAs/InP buried heterostructure (BH) stripe distributed feedback laser with a novel AlInAs/InP complex-coupled grating grown by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) is proposed and demonstrated. A high characteristic temperature (T-0 = 90K between 20-80 degrees C) and temperature-insensitive slope efficiency (0.25 dB drop from 20 to 80 degrees C) in 1.3 mu m AlGaInAs/InP DFB lasers was obtained by introducing AI(Ga)InAs graded-index separate-confinement heterostructure (GRINSCH) layers and a strained-compensated (SC) multi-quantum well (MQW).

Hard magnetic properties of Sm3Fe26.7VxN4 and Sm3Fe26.7VxCy

Sm3Fe26.7V2.3N4 nitrides and Sm3Fe26.7V2.3Cy carbides have been synthesized by gas-solid phase reaction. Their hard magnetic properties have been investigated by means of additional ball-milling at room temperature. The saturation magnetization of Sm3Fe26.7V2.3N4 almost decreases linearly with increasing ball-milling time t, but that of Sm3Fe26.7V2.3Cy has no obvious change when the ball-milling time increases from t = 1 to 28 h. As a preliminary result, the maximum remanence B-r of 0.94 and 0.88 T, the coercivity mu(0i)H(C) of 0.75 and 0.25 T, and the maximum energy product (BH) of 108.5 and 39.1 kJ/m(3) for their resin-bonded permanent magnets are achieved, respectively, by ball-milling at 293 K. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

Native-oxidized InAlAs blocking layer buried heterostructure InGaAsP-InP MQW laser for high-temperature operation

A novel idea of InAlAs native oxide utilized to replace the p-n-p-n thyristor blocking layer and improve the high-temperature performance of buried heterostructure InGaAsP-InP laser is first proposed and demonstrated. A characteristic temperature (T-0) of 50 K is achieved from an InA1As native oxide buried heterostructure (NOBH) InGaAsP-InP multiquantum-well laser with 1.5-mu m-wide diode leakage passage path. The threshold current and slope efficiency of NOBH laser changes from 5.6 mA, 0.23 mW/mA to 28 mA, 0.11 mW/mA with the operating temperature changing from 20 degrees C to 100 degrees C. It is comparable to conventional p-n reverse biased junction BH laser with minimized diode leakage current, and is much better than the buried ridge strip with proton implanted laterally confinement laser.

Thermomagnetic behavior and first order magnetization processes of Sm3Fe29-xTx and Sm3Fe29-xTxN4 (T = V and Cr)

A systematic investigation of structure and intrinsic magnetic properties of the compounds Sm3Fe29-xTx (T = V and Cr) and their nitrides has been performed. Nitrogenation resulted in remarkable improvements in the saturation magnetization and anisotropy fields at 4.2 K and room temperature. First order magnetization processes are observed at around 5.7 T for Sm3Fe26.7V2.3 and around 2.8 T for Sm3Fe24.0Cr5.0 and Sm3Fe24.0Cr5.0N4, respectively. The spin reorientation of the easy magnetization direction of Sm3Fe26.7V2.3 is observed at around 230 K. As a preliminary result, the maximum remanence B-r of 0.94 T, the coercivity mu(0)H(C) of 0.75 T, and the maximum energy product (BH) of 108.5 kJ/m(3) for the nitride magnet Sm3Fe26.7V2.3N4 are achieved by ball-milling at 293 K.

Narrow stripe selective growth of InGaAlAs waveguides used for buried heterostructure lasers - art. no. 63210I

The narrow stripe selective growth of the InGaAlAs bulk waveguides and InGaAlAs MQW waveguides was first investigated. Flat and clear interfaces were obtained for the selectively grown InGaAlAs waveguides under optimized growth conditions. These selectively grown InGaAlAs waveguides were covered by specific InP layers, which can keep the waveguides from being oxidized during the fabrication of devices. PL peak wavelength shifts of 70 nm for the InGaAlAs bulk waveguides and 73 nm for the InGaAlAs MQW waveguides were obtained with a small mask stripe width varying from 0 to 40 gm, and were interpreted in considering both the migration effect from the masked region (MMR) and the lateral vapor diffusion effect (LVD). The quality of the selectively grown InGaAlAs MQW waveguides was confirmed by the PL peak intensity and the PL FWHM. Using the narrow stripe selectively grown InGaAlAs MQW waveguides, then the buried heterostructure (BH) lasers were fabricated by a developed unselective regrowth method, instead of conventional selective regrowth. The InGaAlAs MQW BH lasers exhibit good performance characteristics, with a high internal differential quantum efficiency of about 85% and an internal loss of 6.7 cm(-1).

PASSIVATION OF COPPER BY LITHIUM IN P-TYPE GAAS

We report the passivation of two deep copper-related acceptor levels in Cu-diffused p-type GaAs by the group-I element lithium. The deep-level-transient-spectroscopy (DLTS) signals of the well-known Cu-related levels with apparent activation energies 0.15 eV and 0.40 eV disappear in Cu-diffused samples when they are diffused with Li, but can be reactivated by annealing. Photoluminescence measurements show a corresponding disappearance and reappearance of the copper-related luminescence at 1.36 eV. Also we observe with DLT'S an energy level at E(V) + 0.32 eV in the Cu-Li-diff-used samples. The level is neither present in the Cu-diffused samples before Li diffusion nor in Cu-Li-diffused samples after annealing. As the level is not observed in starting materials or solely Li-diffused samples we suggest that it is related to a Cu-Li complex.