Double Crystal X-ray Diffraction Research Articles

Strain-compensated GaInNAs structures for 1.3-μm lasers

GaAs-based dilute nitride lasers are potential light sources for future optical fiber communication systems at the wavelength of 1.3 /spl mu/m. In this paper we discuss the results of studies of optimization of the growth conditions and active regions of the GaAs-based lasers. To this end, a series of samples were grown using the molecular beam epitaxy technique. The active regions consisted of quantum wells, strain-compensating layers, and strain-mediating layers. They were characterized by photoluminescence and double crystal X-ray diffraction methods. The optical properties were very much affected by a choice of growth conditions, details of the quantum wells, and postgrowth thermal treatment. Preliminary results on diode-pumped vertical-cavity surface emitting lasers, which launch light power of 3.5 mW coupled into a single-mode fiber, are also presented.

The influence of InGaP barrier layer on the characteristics of 1.3 μm strain-compensated multiquantum-well InAsP/InP/InGaP laser diodes

In this article, we report the influence of InGaP barrier layer on the performance of 1.3 μm InAsP/InP/InGaP strain-compensated multiquantum-well (SCMQW) laser diodes (LDs) grown by metalorganic chemical vapor deposition. Sharp satellite peaks with narrow width in double-crystal X-ray diffraction measurements and abrupt interface in secondary ion mass spectrometry analyses are observed, indicating that a good epitaxial-layer quality can be obtained through the use of strain-compensation coupled by InGaP barrier layers. By increasing InGaP barrier thickness to above 6 nm, a redshift of the photoluminescence peak is observed in the (1 0 0)-oriented strained layers. It is probably attributed to redistribution across the samples of the huge built-in electric field induced by the piezoelectric effect. The threshold current of InAsP/InP/InGaP SCMQW ridge-waveguide LDs decreases from 78.8 to 33.8 mA through the employ of tensile-strained InGaP barrier layer and the lasing wavelength is 1.307 μm under 44 mA. In addition, the experimental data of broad-area LDs for the InAsP/InP strained multiquantum-well and InAsP/InP/InGaP SCMQW structures are compared in detail.

Strain relaxation of InP film directly grown on GaAs patterned compliant substrate

In order to overcome the large lattice mismatch in the heteroepitaxy, a new patterned compliant substrate method has been introduced, which has overcome the disadvantages of previously published methods. InP film of thickness 800 nm was directly grown on this substrate. Scanning electron microscopy (SEM) has shown that good surface morphology has been obtained. In addition, Photoluminescence (PL) and double crystal X-ray diffraction (DCXRD) study have shown that the residual strain has been reduced, and that the structure quality has been improved.

X-ray diffraction topography investigation of the core in Bi12SiO20 crystals

The core in a large Bi12SiO20 crystal as well as the regions free of optical inhomogenities was examined by X-ray double-crystal diffraction topography. It was established that the observed defects in the central core are two-dimensional. The absorption of some impurities as well as the composition changes observed in this area by other authors, should be considered as a consequence of the formation of these defects.

Gd xSi grown with mass-analyzed low energy dual ion beam epitaxy technique

Semiconducting gadolinium silicide Gd x Si samples were prepared by mass-analyzed low-energy dual ion beam epitaxy technique. Auger electron spectroscopy depth profiles indicate that the gadolinium ions are implanted into the single-crystal silicon substrate and formed 20 nm thick Gd x Si film. X-ray double-crystal diffraction measurement shows that there is no new phase formed. The XPS spectra show that one type of silicon peaks whose binding energy is between that of silicide and silicon dioxide, and the gadolinium peak of binding energy is between that of metal Gd and Gd 2O 3. All of these results indicate that an amorphous semiconductor is formed.

Characterization of rapid-thermal-annealed InAs/In0.15Ga0.85As dots-in-well heterostructure using double crystal x-ray diffraction and photoluminescence

The effect of rapid thermal annealing on a 10-layer InAs/In0.15Ga0.85As dots-in-a-well (DWELL) heterostructure was studied using double crystal x-ray diffraction (DCXRD) and photoluminescence (PL). From the x-ray rocking curves obtained for symmetric (004) and asymmetric (224) scans, the change in the in-plane and out-of-plane lattice constant and average composition in the DWELL structure were calculated. Thermally induced strain relaxation, which leads to an enhanced In/Ga interdiffusion preferentially along the growth direction, is believed to be the main mechanism for the changes in the structural and optical properties of the sample. Excellent correlation was observed between the PL and the DCXRD measurements.

Molecular-beam epitaxy growth and properties of BexZn1−xTe alloys for optoelectronic devices

We report the molecular-beam epitaxy growth and characterization of BexZn1−xTe epitaxial layers on (100) InP substrates. BexZn1−xTe layers with x varying from 0 to 0.58 were grown. Good control of the composition is achieved by adjusting either the Be or the Zn cell temperatures. The layers exhibit high-crystalline quality, as established by double crystal x-ray diffraction and etch pit density measurements. Narrow x-ray rocking curves with a linewidth of 72 arcsec and etch pit density of 5×105 cm−2 are obtained for the BexZn1−xTe layers closely lattice matched to the InP substrate. BexZn1−xTe layers under tensile strain, which have higher BeTe content, exhibit slower degradation of the crystalline quality as a function of lattice mismatch than layers under compressive strain. The lattice-hardening properties of BeTe are proposed to be the reason for this behavior.

Investigation on the origin of crystallographic tilt in lateral epitaxial overgrown GaN using selective etching

The crystallographic tilt of the lateral epitaxial overgrown (LEO) GaN on sapphire substrate with SiN x mask is investigated by double crystal X-ray diffraction. Two wing peaks beside the GaN 0002 peak can be observed for the as-grown LEO GaN. During the selective etching of SiN x mask, each wing peak splits into two peaks, one of which disappears as the mask is removed, while the other remains unchanged. This indicates that the crystallographic tilt of the overgrown region is caused not only by the plastic deformation resulted from the bending of threading dislocations, but by the non-uniformity elastic deformation related with the GaN/SiN x interfacial forces. The widths of these two peaks are also studied in this paper.

Planar Hall Effect of GaMnAs Grown via low Temperature Molecular Beam Epitaxy

Planar Hall effect of ferromagnetic GaMnAs thin films was investigated for the first time. The films were grown in an optimized growth condition via molecular beam epitaxy at low temperatures. For the optimization of the growth conditions, we used reflection high-energy electron diffraction, electrical conductivity, double crystal x-ray diffraction, and superconducting quantum interference device measurements techniques. We observed that the difference between the longitudinal resistance and the transverse resistance matches the planar Hall resistance. The ratio of the planar Hall resistance at saturation magnetic field to that at zero reached above 500%.

Characteristics of δ-doped InP heterostructures using In0.34Al0.66As0.85Sb0.15 Schottky layer

Single and coupled δ-doped InP channel heterostructure field-effect transistors using high barrier height (>0.73 eV) and wide energy band gap (∼1.8 eV) In0.34Al0.66As0.85Sb0.15 Schottky layer have been successfully grown by low-pressure metalorganic chemical vapor deposition. Comprehensive material characterizations have been conducted and investigated for various growth specifications, including the Hall measurement, secondary ion mass spectrometry, double crystal x-ray diffraction technique, and photoluminescence measurement. Excellent gate-source breakdown characteristics (>40 V), low leakage current (111 μA/mm), improved gate voltage swing, improved carrier mobility, good saturation and pinch-off properties, and low output conductance (0.5 mS/mm) have been achieved by using the high barrier height In0.34Al0.66As0.85Sb0.15 Schottky layer and InP channels. The proposed structure provides good potential for high-power circuit applications.

InGaN-GaN multiquantum-well blue and green light-emitting diodes

InGaN-GaN multiquantum-well (MQW) blue and green light-emitting diodes (LEDs) were prepared by organometallic vapor phase epitaxy, and the properties of these LEDs were evaluated by photoluminescence (PL), double crystal X-ray diffraction, and electroluminescence (EL) measurements. It was found that there were only small shifts observed in PL and EL peak positions of the blue MQW LEDs when the number of quantum well (QW) increased. However, significant shifts in PL and EL peak positions were observed in green MQW LEDs when the number of QW increased. It was also found that there was a large blue shift in EL peak position under high current injection in blue MQW LEDs. However, the blue shift in green MQW LEDs was negligibly small when the injection current was large. These observations could all be attributed to the rapid relaxation in green MQW LEDs since the In composition ratio in the InGaN well was high for the green MQW LEDs. The forward voltage V/sub f/ of green MQW LEDs was also found to be larger than that of blue MQW LEDs due to the same reason.

Lateral Epitaxial Overgrowth of InAs on (100) GaAs Substrates

ABSTRACTThe microstructure of epitaxial InAs thin films grown by MOCVD on mask-patterned “LEO” (lateral epitaxial overgrowth) GaAs and on unpatterned GaAs substrates was studied using double-crystal x-ray diffraction, scanning electron microscopy and cross-sectional transmission electron microscopy. This paper describes the improvement in crystal quality (factor of 20 reduction in x-ray rocking curve width), the order of magnitude reduction in dislocation density, and the rearrangement of the remaining extended defects that were observed in the LEO material when compared to the film grown on the unpatterned wafer.

Metalorganic Vapor-Phase Epitaxy of ZnTe and CdZnTe on GaAs

ZnTe and Cd1 – y Zn y Te epilayers were grown on GaAs(111)B and GaAs(100) substrates by metalorganic chemical vapor deposition. The structural perfection and surface morphology of the layers were investigated by double-crystal x-ray diffraction and scanning electron microscopy. The effect of deposition conditions on the growth rate, zinc content (y), surface morphology, and structural perfection of the epilayers was studied. The results suggest that the optimal structures for depositing HgCdTe(111)B and HgCdTe(100) are CdTe(111)B/GaAs(111)B and CdTe(100)/ZnTe(100)/GaAs(100), respectively.

Content analyses in GaMnAs by double-crystal X-ray diffrac-tion

A model for analyzing point defects in compound crystals was improved. Based on this modified model, a method for measuring Mn content in GaMnAs was established. A technique for eliminating the zero-drift-error was also established in the experiments of X-ray diffraction. With these methods, the Mn content in GaMnAs single crystals fabricated by the ion-beam epitaxy system was analyzed.

LiNbO/sub 3/ optical waveguides formed in a new proton source

Proton-exchanged planar waveguides have been fabricated on Z-cut and X-cut lithium niobate crystals by using a new proton source formed by a mixture of benzoic and adipic acids. Waveguide index profiles and optical characteristics have been obtained at different values of the adipic-benzoic acid concentration ratio. The samples have been structurally characterized by Raman and infrared (IR) absorption spectroscopy and double-crystal X-ray diffraction. Good quality samples have been fabricated by using 30 mol% ratio dilution, showing very low scattering levels (<0.1 dB/cm), relatively high electrooptic coefficient (r/sub 33/=0.88 pm/V), and low relative percentage of interstitial protons (26%). The main factor limiting the waveguide optical properties is the substitutional-interstitial proton ratio, which can be easily controlled to produce good quality waveguides. A demonstration of the repeatability of the exchange process in the acid mixture is also provided.

Growth and characterization of carbon-doped low-temperature GaAs

We present the results of double crystal X-ray diffraction and infrared absorption measurements on C-doped low-temperature GaAs (LT-GaAs:C) layers grown by solid source molecular beam epitaxy at different growth temperatures T G and C concentrations. Strain compensation is achieved at T G=220°C with a C concentration of 2.5×10 19 cm −3. The density of As Ga antisite point defects and the incorporation of C is studied by IRA. At T G=250°C and high C concentrations, we observe a drastic decrease in the intensity of the local vibrational mode of substitutionally incorporated C As. Simultaneously, new local vibrational modes appear whose intensity increases by a further lowering of T G. This result, which is neither observed at low C concentrations nor in the heavily doped GaAs:C grown at conventional T G, is ascribed to the formation of CC complexes in heavily doped LT-GaAs:C.

Optical properties of as-grown and annealed InAs(N)/InGaAsP strained multiple quantum wells

Optical and structural properties of as-grown and annealed InAs(N)/InGaAsP strained multiple quantum-well (MQW) structures grown by gas source molecular-beam epitaxy are investigated by photoluminescence (PL), double crystal x-ray diffraction, and photoconductivity spectroscopies. Properties of the as-grown and annealed MQW’s are studied and those of the InAs/InGaAsP MQW (C821) and the InAsN/InGaAsP MQW with the lowest nitrogen contents N=1.1% in the well (C822) are compared. For the C821 InAs/InGaAsP MQW with a very large total strain, a low energy shoulder, possibly induced by defects or impurities, can be seen in the low temperature PL spectrum, and a large density of nonradiative recombination centers is found. For nitrogen-containing MQW’s, the PL full width at half maximum and PL peak evolutions with increasing annealing temperature are influenced by the alloy inhomogeneities. The initial redshift of the PL peak after rapid thermal annealing means that the luminescence is dominated by As-rich regions in these as-grown samples. Exciton localization induced by alloy disorders is also found in high-nitrogen-content samples. By comparing the experimental results of C821 and C822, adding a little nitrogen to reduce the rather large total strain in the structure is beneficial to structural and optical quality improvement.

Influences of Initial Nitridation Process on the Optical and Structural Characterization of GaN Layer Grown on Sapphire (0001) by Metalorganic Chemical Vapor Deposition

In this paper, we investigate the influences of the initial nitridation of sapphire substrates on the optical and structural characterizations in GaN films. Two GaN samples with and without 3 min nitridation process were investigated by photoluminescence (PL) spectroscopy in the temperature range of 12-300 K and double-crystal X-ray diffraction (XRD). In the 12 K PL spectra of the GaN sample without nitridation, four dominant peaks at 3.476, 3.409, 3.362 and 3.308 eV were observed, which were assigned to donor bound exciton, excitons bound to stacking faults and extended structural defects. In the sample with nitridation, three peaks at 3.453, 3.365, and 3.308 eV were observed at 12 K, no peak related to stacking faults. XRD results at different reflections showed that there are more stacking faults in the samples without nitridation.

Influences of Initial Nitridation Process on the Optical and Structural Characterization of GaN Layer Grown on Sapphire (0001) by Metalorganic Chemical Vapor Deposition

In this paper, we investigate the influences of the initial nitridation of sapphire substrates on the optical and structural characterizations in GaN films. Two GaN samples with and without 3 min nitridation process were investigated by photoluminescence (PL) spectroscopy in the temperature range of 12–300 K and double-crystal X-ray diffraction (XRD). In the 12 K PL spectra of the GaN sample without nitridation, four dominant peaks at 3.476, 3.409, 3.362 and 3.308 eV were observed, which were assigned to donor bound exciton, excitons bound to stacking faults and extended structural defects. In the sample with nitridation, three peaks at 3.453, 3.365, and 3.308 eV were observed at 12 K, no peak related to stacking faults. XRD results at different reflections showed that there are more stacking faults in the samples without nitridation.

Defect interaction by dual MeV ion implantation in silicon

In this study we conducted experiments to reveal the interactions between different types of ion-induced defects upon annealing in MeV (phosphorous + carbon) implanted silicon. We intentionally tried to overlap the interstitial-rich zone induced by P implantation with the vacancy-rich zone induced by C implantation. Double crystal X-ray diffraction (DCXRD) rocking curve analyses for the samples annealed at 550 °C indicated that a positive strain built up at ∼2.3 μm by a single 3 MeV P + implantation was effectively reduced by ∼50% using dual implantation ( 3 MeV P ++3 MeV C + ). However, the amount of strain relaxation in the C implanted layer does not decrease upon annealing.