Double Crystal X-ray Diffraction Measurements Research Articles

A Comparison of Defects Between InAs Single Crystals Grown by LEC and VGF Methods

InAs single crystals grown by the liquid-encapsulated Czochralski (LEC) method and vertical gradient freezing (VGF) are studied by low-temperature photoluminescence spectroscopy, infrared transmission and reflectance spectroscopy, double-crystal x-ray diffraction and Hall effect measurement, respectively. A properly controlled etching solution is used to reveal beautiful square dislocation etch pits in the crystals. In addition to extremely low dislocation density, the concentration of native defects in the VGF-InAs single crystals is much lower than that in LEC-InAs, giving VGF-InAs better electrical and optical properties. The nature of the defects in InAs single crystals is discussed by considering the variation in stoichiometry and environment during the crystal growth processes.

The Effect of Buffer Types on the In0.82Ga0.18As Epitaxial Layer Grown on an InP (100) Substrate.

In0.82Ga0.18As epitaxial layers were grown on InP (100) substrates at 530 °C by a low-pressure metalorganic chemical vapor deposition (LP-MOCVD) technique. The effects of different buffer structures, such as a single buffer layer, compositionally graded buffer layers, and superlattice buffer layers, on the crystalline quality and property were investigated. Double-crystal X-ray diffraction (DC-XRD) measurement, Raman scattering spectrum, and Hall measurements were used to evaluate the crystalline quality and electrical property. Scanning electron microscope (SEM), atomic force microscope (AFM), and transmission electron microscope (TEM) were used to characterize the surface morphology and microstructure, respectively. Compared with the In0.82Ga0.18As epitaxial layer directly grown on an InP substrate, the quality of the sample is not obviously improved by using a single In0.82Ga0.18As buffer layer. By introducing the graded InxGa1−xAs buffer layers, it was found that the dislocation density in the epitaxial layer significantly decreased and the surface quality improved remarkably. In addition, the number of dislocations in the epitaxial layer greatly decreased under the combined action of multi-potential wells and potential barriers by the introduction of a In0.82Ga0.18As/In0.82Al0.18As superlattice buffer. However, the surface subsequently roughened, which may be explained by surface undulation.

Influences of ultrathin amorphous buffer layers on GaAs/Si grown by metal–organic chemical vapor deposition

In this work, a technique for the growth of GaAs epilayers on Si, combining an ultrathin amorphous Si buffer layer and a three-step growth method, has been developed to achieve high crystalline quality for monolithic integration. The influences of the combined technique for the crystalline quality of GaAs on Si are researched in this article. The crystalline quality of GaAs epilayer on Si with the combined technique is investigated by scanning electron microscopy, double crystal X-ray diffraction (DCXRD), photoluminescence, and transmission electron microscopy measurements. By means of this technique, a 1.8-µm-thick high-quality GaAs/Si epilayer was grown by metal–organic chemical vapor deposition. The full-width at half-maximum of the DCXRD rocking curve in the (400) reflection obtained from the GaAs/Si epilayers is about 163 arcsec. Compared with only using three-step growth method, the current technique reduces etch pit density from 3 × 106 cm−2 to 1.5 × 105 cm−2. The results demonstrate that the combined technique is an effective approach for reducing dislocation density in GaAs epilayers on Si.

Defect analysis of the LED structure deposited on the sapphire substrate

Transmission electron microscope (TEM) and double-crystal X-ray diffraction (DCXRD) measurements have been performed to investigate dislocations of the whole structure of the LED layers deposited on both the conventional (unpatterned sapphire substrate, UPSS) and patterned sapphire substrates (PSS). TEM results show that there exists a dislocation-accumulated region near the substrate/GaN interface, where the dislocation density is much higher with the UPPS than that with the PSS. It indicates that the pattern on the substrate surface is able to block the formation and propagation of dislocations. Further analysis discloses that slope of the pattern is found to suppress the deposition of GaN, and thus to provide more spaces for the epitaxially lateral overgrowth (ELO) of high temperature GaN, which significantly reduces the number of the initial islands, and minimizes dislocation formation due to the island coalescence. V-defect incorporating the threading dislocation is detected in the InGaN/GaN multi-quantum wells (MQWs), and its propagation mechanism is determined as the decrease of the surface energy due to the incorporation of indium. In addition, temperature dependence of dislocation formation is further investigated. The results show that dislocation with the screw component decreases monotonously as temperature goes up. However, edge dislocation firstly drops, and then increases by temperature due to the enhanced thermal mismatch stress. It implies that an optimized range of the growth temperature can be obtained to improve quality of the LED layers.

Impurity Free Vacancy Disordering (IFVD) of InGaAs/AlGaAs Quantum Well Laser Structures

Impurity free vacancy disordering (IFVD) has been used to investigate the atomic interdiffusion of InGaAs/InGaAs quantum well laser structures using double-crystal X-ray diffraction (DCXRD) and photoluminescence measurements. X-ray measurements showed that some part of the carbon was electrically activated after annealing without a dielectric capping layer, but not after annealing with a TiO2 capping layer. For a SiO2 capping layer, the tensile peak was still observed after annealing which is comparable to the samples annealed without capping layer. Photoluminescence results showed that a large energy shift was observed when the samples were coated with SiO2. A negligible photoluminescence shift was observed after annealing when the samples coated with TiO2.

Postgrowth Annealing of CdTe Layers Grown on Si Substrates by Metalorganic Vapor-Phase Epitaxy

Annealing conditions of CdTe layers grown on Si substrates by metalorganic vapor-phase epitaxy were studied. Typically, 3-μm-thick n-type (211) CdTe layers were annealed for 60 s in flowing hydrogen at atmospheric pressure by covering their surfaces with bulk CdTe wafers. At annealing temperatures above 700°C, improvement of crystal quality was confirmed from full-width at half-maximum values of double-crystal rocking-curve measurements and x-ray diffraction measurements. Photoluminescence measurements revealed no deterioration of electrical properties in the annealed n-CdTe layers. Furthermore, annealing at 900°C improved the performance of radiation detectors with structure of p-like CdTe/n-CdTe/n+-Si substrate.

1×1 mm2대면적 녹색 LED의 전기 광학적 특성 분석

본 논문은 InGaN/GaN 다중양자우물 구조를 가지는 녹색 발광다이오드의 활성층 내 인듐(In) 조성비와 piezoelectric field에 대한 전계 흡수 현상을 연구하였다. 활성층 내 결정학적 성질과 In 조성비는 double crystal X-ray diffraction 측정으로 분석하였으며, 1×1 ㎟ 대면적 칩을 제작하여 발광특성을 조사하였다. 또한, 활성층 내 piezoelectric field는 electro-reflectance spectroscopy로부터 측정한 compensation voltage를 이용해 계산하였고, 인가전압에 따른 photocurrent의 변화를 측정함으로써 녹색 발광 소자의 전기 광학적 특성을 분석하였다.

Epitaxial growth of Ge0.975Sn0.025alloy films on Si(001) substrates by molecular beam epitaxy

Ge0.975Sn0.025 alloy films have been grown on Si(001) substrates by molecular beam epitaxy with high-quality Ge films as buffer layers.The alloys have high crystalline quality without Sn surface segregation, determined by double crystal X-ray diffraction and Rutherford backscattering spectra measurement. In addition, the Ge0.975Sn0.025 alloy has rather good thermal stability at 500 ℃, which makes it possible to be used in Si-based optoelectronic devices.

Influence of thermal annealing duration of buffer layer on the crystalline quality of In 0.82Ga 0.18As grown on InP substrate by LP-MOCVD

In 0.82Ga 0.18As epilayers were grown on InP substrates using a two-step growth technique by LP-MOCVD. A homogeneous low-temperature (450 °C) In 0.82Ga 0.18As buffer layer was introduced to improve the crystalline quality of epilayers. The influence of low-temperature buffer layer deposition condition, such as thermal annealing duration, on the crystalline quality of the In 0.82Ga 0.18As epilayer was investigated. Double-crystal X-ray diffraction measurement, Hall measurement, and Raman scattering spectrum were used to evaluate the In 0.82Ga 0.18As epilayers. Atomic force microscope was used to study the surface morphology. It is found that the In 0.82Ga 0.18As epilayer, with buffer layer thermal annealing for 5 min, exhibits the best crystalline quality. The change of the surface morphology of the buffer layer after thermal annealing treatment was suggested to explain the phenomenon.

Epitaxial Heusler alloy Co2FeSi films on Si(1 1 1) substrates grown by molecular beam epitaxy

The influence of growth temperature on the structural and magnetic properties of Heusler alloy Co2FeSi films grown on Si(1 1 1) substrates has been studied. Reflection high energy electron diffraction, double crystal x-ray diffraction (DCXRD) and transmission electron microscopy (TEM) measurements revealed that Co2FeSi layers were epitaxially grown on Si(1 1 1) substrates in an optimized growth temperature range 150 °C < TG < 200 °C. From DCXRD measurements and TEM, it was shown that in the optimized temperature range the Co2FeSi/Si(1 1 1) films crystallize in the B2 + L21 structures. All layers are ferromagnetic and well-ordered films on Si(1 1 1) show high magnetic moments with an average value of (1140 ± 250) emu cm−3, which is in good agreement with the value of bulk Co2FeSi at 300 K. The magnetic anisotropy is correlated with the structural properties of the layers.

Ultra-shallow Junction Formation Using Plasma Doping and ExcimerLaser Annealing for Nano-technology CMOS Applications

A plasma-doping (PLAD) process utilizing a PH3 plasma is presented to fabricate a n /p ultrashallow junction at room temperature. When PLAD is completed, an excimer laser annealing (ELA) process is performed using an ArF (193 nm) excimer laser with pre-annealing. In our case, the preannealing is conducted for 5 min at 500 ◦C in a thermal furnace. The energy density of the excimer laser used for the ELA process ranged from 400 to 500 mJ/cm. Transmission electron microscope (TEM) and double-crystal X-ray diffraction (DXRD) measurements were employed to investigate defects on the plasma-doped samples. Some point defects were found in the DXRD analysis while TEM images reveal no crystalline defects. The result of a secondary ion mass spectrometry (SIMS) analysis on the formed shallow n/p junction revealed that the junction depth was thinner than 40 nm. We found that the drive-in process of phosphorous occurred only when the energy density of the laser was larger than 460 mJ/cm, and an increased laser energy density resulted in a decreased sheet resistance. With an energy density of 460 mJ/cm, a junction depth of 30 nm and a sheet resistance of 151.6 Ω/ were obtained. The leakage current for the fabricated n/p junction was indirectly investigated by measuring the I-V characteristics of the diode fabricated using PLAD, followed by the ELA processes.

Ultra-Shallow Junction Formation by Plasma doping and Excimer Laser Annealing

Plasma doping (PLAD) process using PH3 plasma is presented to fabricate n+/p ultra shallow junction at room temperature. Directly after the PLAD, a pre-annealing has been conducted for 5 min at 500 {degree sign}C in thermal furnace. ArF excimer laser annealing (ELA) process was then followed with an increment of 20 mJ/cm2 in the laser energy ranging from 400 to 500 mJ/cm2. When the laser energy density was larger than 460 mJ/cm2, a reduced sheet resistance was observed. In order to examine the crystalline defects generated during PLAD, the transmission electron microscopy (TEM) and double crystal X-ray diffraction (DXRD) measurements have been made. With optimized PLAD and ELA conditions, junction depth of 30 nm and sheet resistance of 151.6 Ω/□ could be obtained.

Investigation of the effect of growth interruption on the formation of InAs/GaAs quantum dot superlattice near the InAs critical thickness

Two kinds of superlattices (i) with and (ii) without growth interrupt (GI) after deposition of 1.77 monolayers (ML) of InAs on GaAs (001) were grown by solid-source molecular beam epitaxy (MBE) and assessed by transmission electron microscopy (TEM) techniques, double crystal X-ray diffraction (DCXRD) and photoluminescence (PL) measurements in order to gain an understanding of the structural and compositional properties. In case (i) formation of coherent dislocation free self-organized quantum dots (SOQDs) with 2.8–3.2nm height and 13–16nm lateral size was observed, whereas in case (ii) no quantum dots had formed. In order to better understand the implication of growth interruption for the formation mechanism, highly localised assessment of the composition of the QD was carried out via atomic resolution Z-contrast imaging and electron energy loss spectroscopy (EELS).

Characterization of radiation damage annealing of recoil-implanted GaP

The recovery of crystallinity as a function of annealing temperature in GaP recoil-implanted with 111In has been monitored on an atomic scale using the perturbed angular correlation (PAC) technique. This technique is based on hyperfine interaction of the electric quadrupole moment of probe nuclei with the electric field gradient (EFG) of the host lattice. The 111In/Cd probe nuclei were recoil-implanted at room temperature with an energy of up to 8 MeV following heavy-ion nuclear fusion evaporation reactions. Measurements were performed at room temperature for as-implanted and furnace annealed samples. Isochronal annealing in ambient nitrogen up to 950 °C showed a progressive reduction of disorder around the probe nuclei as indicated by a continual decrease in the width of the EFG distribution. These measurements suggest that recoil implantation did not result in drastic damage to the sample, and that annealing at 800 °C for 30 min is sufficient to produce an optimum recovery of crystallinity. Also, complementary double crystal X-ray diffraction measurements were in qualitative agreement with the results derived from PAC.

Improvement in the characteristics of GaN-based light-emitting diodes by inserting AlGaN-GaN short-period superlattices in GaN underlayers

We report the influence of short-period superlattice (SPSL)-inserted structures in the underlying undoped GaN on the characteristics of GaN-based light-emitting diodes (LEDs). The measurements of current-voltage (I-V) curves indicate that GaN-based LEDs having pseudomorphic Al/sub 0.3/Ga/sub 0.7/N(2 nm)-GaN(2 nm) SPSL-inserted structures exhibit improvements in device characteristics with the best LED being inserted with two sets of five-pair Al/sub 0.3/Ga/sub 0.7/N(2 nm)-GaN(2 nm) SPSL structure. Based upon the results of etch pit counts, double-crystal X-ray diffraction measurements and transmission electron microscopic observations of the GaN-based LEDs, it was found that the Al/sub 0.3/Ga/sub 0.7/N(2 nm)-GaN(2 nm) SPSL-inserted structures tended to serve as threading dislocation filters in the LEDs so that the improved I-V characteristics were achieved.

The effect of a-GaAs/a-Si double buffer layers on GaAs-on-Si as determined by transmission electron microscopy

A high-quality GaAs epilayer was successfully grown on a Si substrate using a-GaAs/a-Si double buffers, which were crystallized by thermal cyclic annealing. Double crystal x-ray diffraction measurements showed that the full width at half maximum of the rocking curve for the GaAs epilayer was only 102 arcs. The effect of a-GaAs/a-Si double buffers was examined in detail by transmission electron microscopy. Transmission electron microscopy characterizations revealed obvious bending behaviour of dislocations in the a-GaAs/a-Si buffered epilayer. Most threading dislocations and planar defects were confined within the crystallized double buffers. The dislocation density was reduced to 2.6 × 106 cm−2 at a thickness of 1.0 µm in the first epitaxial layer and was further improved to under 1.3 × 106 cm−2 in the second epitaxial layer. Transmission electron microscopy observation and analysis revealed a defect reduction mechanism.

Optical and structural properties of InGaAs/InP double quantum wells grown by molecular beam epitaxy with polycrystalline GaAs and GaP decomposition sources

We report successful growth of high-quality InGaAs/InP double quantum wells (DQWs) with safer and more cost-effective decomposition source molecular beam epitaxy (MBE). The transmission electron microscopy (TEM) images and double crystal X-ray diffraction (TCXD) measurement reveal the formation of abrupt interfaces between InGaAs and InP layers. In the case of optical quality, the line width of 12 K-photoluminescence of the DQWs is 8.2 meV, which is comparable to that of single quantum well grown by MBE with PH 3 cracker and more complex instrument (∼4 meV).

Optimization of active region for 1.3-µm GalnAsP compressive-strain multiple-quantum-well ridge waveguide laser diodes

We report on the optimization of Ga0.27In0.73As0.67P0.33/Ga0.11In0.89As0.24P0.76 compressive-strain multiple-quantum-well (CS-MQW) grown by low-pressure metalorganic chemical vapor deposition for 1.3-µm ridge-waveguide laser diodes (LDs). The structural and optical properties are characterized by doublecrystal x-ray diffraction and photoluminescence (PL) measurements, respectively. The optimum thicknesses of the well, barrier, and waveguide layer of the active region are 4 nm, 10 nm, and 100 nm, respectively. The GaInAsP/GaInAsP CS-MQW as-cleaved LDs with the optimum active region, a 3.5-µm-width ridge, and a 900-µm-cavity length exhibit the threshold current density of 1.09 kA/cm2, a differential quantum efficiency of 30%, a characteristic temperature of 60 K, a maximum operating temperature up to 75°C, and a redshift rate of 0.30 nm/°C.

Formation mechanism of ferromagnetism in Si 1− xMn x diluted magnetic semiconductors

Si 1− x Mn x diluted magnetic semiconductor (DMS) bulks were formed by using an implantation and annealing method. Energy dispersive X-ray fluorescence, transmission electron microscopy (TEM), and double-crystal rocking X-ray diffraction (DCRXD) measurements showed that the grown materials were Si 1− x Mn x crystalline bulks. Hall effect measurements showed that annealed Si 1− x Mn x bulks were p-type semiconductors. The magnetization curve as a function of the magnetic field clearly showed that the ferromagnetism in the annealed Si 1− x Mn x bulks originated from the interaction between interstitial and substitutional Mn + ions, which was confirmed by the DCRXD measurements. The magnetization curve as a function of the temperature showed that the ferromagnetic transition temperature was approximately 75 K. The present results can help to improve understanding of the formation mechanism of ferromagnetism in Si 1−xMn x DMS bulks.

Mobility and Charge Density Tuning in Double-Doped Enhancement-Mode Pseudomorphic High-Electron-Mobility Transistors Grown by Metalorganic Chemical Vapor Deposition

We present mobility and charge density tuning for metalorganic chemical vapor deposition (MOCVD)-grown double-doped enhancement-mode (E-mode) pseudomorphic high-electron-mobility transistors (PHEMTs) by varying the supplier layer doping level and spacer layer thickness. From the resolvable Pendellosung oscillation in double-crystal X-ray diffraction measurements and a pronounced two-dimensional electron-gas peak in capacitance–voltage (C–V) analyses, good epitaxial wafers are obtained by MOCVD. The 1-µm-gate-length E-mode PHEMT device exhibits a good pinch-off characteristic with a threshold voltage of 0.025 V and a maximum transconductance of 203 mS/mm. The dependences of the pinch-off characteristic in C–V measurement on sheet carrier concentration and spacer layer thickness for E-mode PHEMT application is also described in detail.