Influence of Mg content on molecular-beam-epitaxy-grown ZnMgS ultraviolet photodetectors

Zn1-xMgxS-based Schottky barrier ultraviolet (UV) photodetectors were fabricated using the molecular-beam-epitaxy (MBE) technique. The influence of Mg content on MBE-grown Zn1-xMgxS-based UV photodetectors has been investigated in details with a variety of experimental techniques, including photoresponse (PR), capacitance-voltage, deep level transient Fourier spectroscopy (DLTFS) and photoluminescence (PL). The room-temperature PR results show that the abrupt long-wavelength cutoffs covering 325, 305 295. and 270 nm with Mg contents of 16%, 44%, 57%, and 75% in the Zn1-xMgxS active layers, respectively, were achieved. But the responsivity and the external quantum efficiency exhibited a slight decrease with the Mg content increasing. In good agreement with the PR results, both of the integrated intensity of the PL spectra obtained from Zn1-xMgxS thin films with different Mg compositions (x = 31% and 52%, respectively) and the DLTFS spectra obtained from Zn1-xMgxS-based (x = 5% and 45%, respectively) UV photodetector samples clearly revealed a significant concentration increase of the non-radiative deep traps with increasing Mg containing in the ZnMgS active layers. Our experimental results also indicate that the MBE-grown ZnMgS-based photodetectors can offer the promising characteristics for the detection of short-wavelength UV radiation. (C) 2004 Elsevier B.V. All rights reserved.

Mn implanted GaAs by low energy ion beam deposition

High dose Mn was implanted into semi-insulating GaAs substrate to fabricate embedded ferromagnetic Mn-Ga binary particles by mass-analyzed dual ion beam deposit system at room temperature. The properties of as-implanted and annealed samples were measured with X-ray diffraction, high-resolution X-ray diffraction to characterize the structural changes. New phase formed after high temperature annealing. Sample surface image was observed with atomic force microscopy. All the samples showed ferromagnetic behaviour at room temperature. There were some differences between the hysteresis loops of as-implanted and annealed samples as well as the cluster size of the latter was much larger than that of the former through the surface morphology. (C) 2004 Elsevier B.V. All rights reserved.

FexSi grown with mass-analyzed low-energy dual ion beam deposition

Heavily iron-implanted silicon was prepared by mass-analyzed low-energy dual ion beam deposition technique. Auger electron spectroscopy depth profiles indicate that iron ions are shallowly implanted into the single-crystal silicon substrate and formed 35 nm thick FexSi films. X-ray diffraction measurements show that as-implanted sample is amorphous and the structure of crystal is partially restored after as-implanted sample was annealed at 400degreesC. There are no new phases formed. Carrier concentration depth profile of annealed sample was measured by Electrochemical C-V method and indicated that FexSi film shows n-type conductivity while silicon substrate is p-type. The p-n junction is formed between FexSi film and silicon substrate showing rectifying effect. (C) 2003 Elsevier B.V. All rights reserved.

Fabrication of GdSi2 film by low-energy ion-beam implantation

Single-phase gadolinium disilicide was fabricated by a low-energy ion-beam implantation technique. Auger electron spectroscopy and X-ray photoelectron spectroscopy were used to determine the composition and chemical states of the film. The structure of the sample was analyzed by X-ray diffraction and the surface morphology was investigated by scan electron microscopy. Based on the measurements, only orthorhombic GdSi2 phase was found in the sample and the surface morphology was pitting. After annealing at 350degreesC for 30 min at Ar atmosphere, the full-width at half-maximum of GdSi2 became narrower. It indicates that the GdSi2 is crystallized better after annealing. (C) 2003 Elsevier B.V. All rights reserved.

(Ga, Gd, As) film growth on GaAs substrate by low-energy ion-beam deposit

(Ga, Gd, As) film was fabricated by the mass-analyzed dual ion-beam epitaxy system with the energy of 1000 eV at room temperature. There was no new peak found except GaAs substrate peaks (0 0 2) and (0 0 4) by X-ray diffraction. Rocking curves were measured for symmetric (0 0 4) reflections to further yield the lattice mismatch information by employing double-crystal X-ray diffraction. The element distributions vary so much due to the ion dose difference from AES depth profiles. The sample surface morphology indicates oxidizing layer roughness is also relative to the Gd ion dose, which leads to islandlike feature appearing on the high-dose sample. One sample shows ferromagnetic behavior at room temperature. (C) 2003 Elsevier B.V. All rights reserved.

GaAs-based room-temperature continuous-wave 1.59 mu m GaInNAsSb single-quantum-well laser diode grown by molecular-beam epitaxy

Starting from the growth of high-quality 1.3 mu m GaInNAs/GaAs quantum well (QW), the QW emission wavelength has been extended up to 1.55 mu m by a combination of lowering growth rate, using GaNAs barriers and incorporating some amount of Sb. The photoluminescence properties of 1.5 mu m range GaInNAsSb/GaNAs QWs are quite comparable to the 1.3 mu m QWs, revealing positive effect of Sb on improving the optical quality of the QWs. A 1.59 mu m lasing of a GaInNAsSb/GaNAs single-QW laser diode is obtained under continuous current injection at room temperature. The threshold current density is 2.6 kA/cm(2) with as-cleaved facet mirrors. (c) 2005 American Institute of Physics.

High structural and optical quality 1.3 mu m GaInNAs/GaAs quantum wells with higher indium content grown by molecular-beam expitaxy

High structural and optical quality 1.3 mu m GaInNAs/GaAs quantum well (QW) samples with higher (42.5%) indium content were successfully grown by molecular-beam epitaxy. The cross-sectional transmission electron microscopy measurements reveal that there are no structural defects in such high indium content QWs. The room-temperature photoluminescence peak intensity of the GaIn0.425NAs/GaAs (6 nm/20 nm) 3QW is higher than, and the full width at half maximum is comparable to, that of In0.425GaAs/GaAs 3QW, indicating improved optical quality caused by strain compensation effect of introducing N to the high indium content InGaAs epilayer. (C) 2005 American Institute of Physics.

High-quality GaNAs/GaAs quantum wells with light emission up to 1.44 mu m grown by molecular-beam epitaxy

High-quality GaNAs/GaAs quantum wells with high substitutional N concentrations, grown by molecular-beam epitaxy, are demonstrated using a reduced growth rate in a range of 0.125-1 mu m/h. No phase separation is observed and the GaNAs well thickness is limited by the critical thickness. Strong room-temperature photoluminescence with a record long wavelength of 1.44 mu m is obtained from an 18-nm-thick GaN0.06As0.94/GaAs quantum well. (C) 2005 American Institute of Physics.

Self-organized superlattices along the [001] growth direction in In0.52Al0.48As layers grown on nominally (001) InP substrates by molecular beam epitaxy

Horizontal self-organized superlattice structures consisting of alternating In-rich and Al-rich layers formed naturally during solid-source molecular beam epitaxy (MBE) growth of In0.52Al0.48As on exactly (001) InP substrates, with In and At fluxes unchanged. The growth temperatures were changed from 490 to 510 degrees C, the most commonly used growth temperature for In0.52Al0.48As alloy. No self-organized superlattices (SLs) were observed at the growth temperature 490 degrees C, and self-organized SLs were observed in InAlAs layers at growth temperatures ranging from 498 to 510 degrees C. The results show that the period of the SLs is very highly regular, with the value of similar to 6 nm, and the composition of In or Al varies approximately sinusoidally along the [001] growth direction. The theoretical simulation results confirm that the In composition modulation amplitude is less than 0.02 relative the In composition of the In0.52Al0.48As lattice matched with the InP substrate. The influence of InAs self-organized quantum wires on the spontaneously formed InxAl1-xAs/InyAl1-yAs SLs was also studied and the formation of self-organized InxAl1-xAs/InyAl1-yAs SLs was attributed to the strain-mediated surface segregation process during MBE growth of In0.52Al0.48As alloy. (C) 2005 Published by Elsevier Ltd.

Formation of GaAs/AlGaAs and InGaAs/GaAs nanorings by droplet molecular-beam epitaxy

GaAs/AlGaAs lattice-matched nanorings are formed on GaAs (100) substrates by droplet epitaxy. The crucial step in the formation of nanorings is annealing Ga droplets under As flux for proper time. The observed morphologic evolution of Ga droplets during annealing does not support the hypothesis that As atoms preferentially react with Ga around the periphery of the droplets, but somehow relates to a dewetting process similar to that of unstable films. Photoluminescene (PL) test results confirm the quantum-confinement effect of these GaAs nanorings. Using similar methods, we have fabricated InGaAs/GaAs lattice-mismatched rings. (c) 2005 American Institute of Physics.

Gal(1-x)Mn(1-x)Sb grown on GaSb with mass-analyzed low-energy dual ion beam deposition

The Ga1-xMnxSb samples were fabricated by the implantation of Mn ions into GaSb (1 0 0) substrate with mass-analyzed low-energy dual ion beam deposition system, and post-annealing. Auger electron spectroscopy depth profile of the Ga1-xMnxSb samples showed that the Mn ions were successfully implanted into GaSb substrate. Clear double-crystal X-ray diffraction patterns of the Ga1-xMnxSb samples indicate that the Ga1-xMnxSb epilayers have the zinc-blende structure without detectable second phase. Magnetic hysteresis-loop of the Ga1-xMnxSb epilayers were obtained at room temperature (293 K) with alternating gradient magnetometry. (c) 2005 Elsevier B.V. All rights reserved.

Photoluminescence study of (GaAs1-xSbx/InyGa1-yAs)/GaAs bilayer quantum well grown by molecular beam epitaxy

Photoluminescence study of (GaAs1-xSbx/InyGa1-yAs)/GaAs bilayer quantum wells (BQWs) grown by molecular beam epitaxy (MBE) were carried out. Temperature and excitation power dependent photoluminescence (PL) study indicated that the band alignment of the BQWs is type - II. The origin of the double-peak luminescence was discussed. Under optimized growth conditions, the PL emission wavelength from the BQWs has been extend up to 1.31 mu m with a single peak at room temperature.

Electron beam and laser testing on the novel stripixel detectors

The novel Si stripixel detector, developed at BNL (Brookhaven National Laboratory), has been applied in the development of a prototype Si strip detector system for the PHENIX Upgrade at RHIC. The Si stripixel detector can generate X-Y two-dimensional (2D) position sensitivity with single-sided processing and readout. Test stripixel detectors with pitches of 85 and 560 mu m have been subjected to the electron beam test in a SEM set-up, and to the laser beam test in a lab test fixture with an X-Y-Z table for laser scanning. Test results have shown that the X and Y strips are well isolated from each other, and 2D position sensitivity has been well demonstrated in the novel stripixel detectors. (c) 2005 Elsevier B.V. All rights reserved.

Molecular beam epitaxy growth and photoluminescence study of room temperature 1.31 mu m (InyGa1-yAs/GaAs1-x Sb-x)/ GaAs bilayer quantum wells

Molecular beam epitaxy (MBE) growth of (InyGa1-yAs/GaAs1-xSbx)/GaAs bilayer quantum well (BQW) structures has been investigated. It is evidenced by photo luminescence (PL) that a strong blue shift of the PL peak energy of 47 meV with increasing PL excitation power from 0.63 to 20 mW was observed, indicating type II band alignment of the BQW. The emission wavelength at room temperature from (InyGa1-yAs/GaAs1-xSbx)/GaAs BQW is longer (above 1.2 μ m) than that from InGaAs/GaAs and GaAsSb/GaAs SQW structures (1.1 μ m range), while the emission efficiency from the BQW structures is comparable to that of the SQW. Through optimizing growth conditions, we have obtained room temperature 1.31 μ m wavelength emission from the (InyGa1-yAs/GaAs1-xSbx)/GaAs BQW. Our results have proved experimentally that the GaAs-based bilayer (InyGa1-yAs/GaAs1-xSbx)/GaAs quantum well is a useful structure for the fabrication of near-infrared wavelength optoelectronic devices. © 2005 Elsevier B.V. All rights reserved.

Room temperature 1.25 mu m emission from high indium content InxGa1-xAs/GaAs quantum wells grown by molecular beam epitaxy

Long-wavelength high indium content InxGa1-xAs/GaAs single/multi quantum wells (QWs) structures have been successfully grown by molecular beam epitaxy. It is evidenced by X-ray measurements that the critical thickness of the well width of InxGa1-xAs/GaAs QWs with an indium content x of 47.5% can be raised up to 7nm without strain relation. 1.25μ m photoluminescence (PL) emission is obtained from the QWs with narrower full-width at half maximum (FWHM) less than 30meV. Our results are important basements which are useful for further fabricating GaAs-based long-wavelength devices. © 2005 Elsevier B.V. All rights reserved.