X-ray Diffraction Rocking Curve Research Articles

Epitaxial AlN film with improved quality on Si (111) substrates realized by boron pretreatment via MOCVD

This study investigated the growth of AlN epitaxial films on 2-in. Si(111) via metal-organic chemical vapor deposition. By introducing triethylboron (TEB) during trimethylaluminum pretreatment, a nearly crack free AlN epilayer with a thickness of 500 nm was acquired. The x-ray diffraction rocking curves of AlN (002) and (102) exhibited full width at half maximum values of 0.22° and 0.36°, respectively. Atomic force microscopy image analysis showed that after the introduction of TEB, larger grains appeared on the surface of Si(111) substrate, promoting the 3D growth pattern of the subsequent AlN buffer layer. Laytec reflection curves depicted the morphological transition from 3D to 2D growth mode during AlN deposition. At the same time, the curvature value was significantly reduced by 20 km−1, and the Raman spectrum peak of E2(high) shifted from 648.7 to 652.5 cm−1, indicating that the surface tensile stress was greatly reduced, effectively suppressing the crack problem of AlN on Si(111).

Unraveling evolution of microstructural domains in the heteroepitaxy of β -Ga2O3 on sapphire

Addressing microstructural domain disorders within epitaxial β-Ga2O3 is critical for phase engineering and property improvement, whereas the associated evolution of β-Ga2O3 heteroepitaxial domains remains largely unexplored. In this Letter, we conducted a quantitative investigation of microstructural domains in (−201)-oriented epitaxial β-Ga2O3 films grown on (0001) sapphire using halide vapor-phase epitaxy technique with a β-(Al0.57Ga0.43)2O3 buffer layer. The distinct split of x-ray diffraction rocking curves for (−201) β-Ga2O3 grown below 950 °C was observed, indicative of domain tilt disorders. As quantitatively assessed by transmission electron microscopy, the domain tilt angle significantly decreases from 2.33° to 0.90° along the [132] zone axis and from 2.3° to 0.56° along the [010] zone axis, respectively, as the growth temperature is elevated from 850 to 1100 °C. The reduction in tilt disorders is accompanied by the decrease in in-plane domain twist. It indicates that the elimination of small-angle domain boundaries is energetically favorable at high growth temperature above 1000 °C. The quantitative investigation on the evolution of domain disorders in β-Ga2O3 shed light on the pathway to improve epitaxial quality for cutting-edge power electronic and optoelectronic device applications.

Molecular dynamics simulations and experimental studies on low-temperature growth of GaN

Growth mechanisms of (0001) wurtzite GaN films at low temperature are investigated by molecular dynamics simulations and experiments. The crystallization properties of GaN films deteriorate dramatically at low temperature due to the limited energy available for atomic surface migration and incorporation into the perfect lattice sites. In our simulation, growth interruption stage is periodically introduced and the as-deposited GaN films are treated with energy-carrying argon ions at this stage. The surface atoms located at the weak binding sites can acquire energy from the argon ions for secondary migration and incorporation into the perfect lattice sites. As a result, the crystallization properties of GaN films are significantly improved. GaN films are experimentally grown on sputtered AlN/sapphire substrates at 600 °C via inductively coupled plasma metal organic chemical vapor deposition along with periodic argon plasma treatment. The as-deposited film acquires energy from the plasma, leading to significant improvement of the crystalline properties. The surface morphology of the GaN film demonstrates a noticeable smoothing effect, with an evident increase in grain size from submicron to micron level. Additionally, GaN film with the optimized surface morphology exhibits high c-axis and in-plane orientations, and the full width half maximums of (002) and (102) x-ray diffraction rocking curves are 0.25° and 0.32°, respectively. These results provide effective guidance for the growth of GaN films at low temperature.

Theoretical and Experimental Study of High‐Electromechanical‐Coupling Surface Acoustic Wave Resonators Based on A‐Plane (112¯0)$\left(\right. 11 \overset{\cdot}{2} 0 \left.\right)$ Al0.56Sc0.44N Films

Herein, a high‐quality Al0.56Sc0.44N piezoelectric thin‐film‐based surface acoustic wave (SAW) resonator is developed. The Al0.56Sc0.44N is deposited on r‐plane Al2O3 substrate by reactive magnetron sputtering. X‐ray diffraction (XRD) spectroscopy shows that the grown Al0.56Sc0.44N films are single‐phased and a‐plane oriented. The full width at half maximum of the XRD rocking curve is only 0.4°, which is smaller than most of the reported values. The effects of normalized thickness of the piezoelectric layer, electrode materials, and thickness on acoustic properties of the SAW resonators are investigated through the 3D finite‐element method equipped with the hierarchical cascading technique. A monotonically decreasing resonant frequency can be obtained with the mass loading of both the electrode metals. For the devices with a Pt electrode, it is observed that the electromechanical coupling coefficient () exhibits a nonlinear characteristic of first increasing and then decreasing with the increase of electrode thickness. SAW resonators with a nonpolar a‐plane Al0.56Sc0.44N thin films are fabricated, showing an exceptionally high of 4.6%. This result demonstrates a significant potential of AlScN films with the a‐plane orientation in radio frequency application.

Characterization of single-crystal phenothiazine synthesized using the vertical Bridgman method

Abstract A bulk organic single crystal of phenothiazine measuring 65 mm in length and 10 mm in width was grown using the single zone vertical Bridgman technique (VBT), which was visible to the naked eye. Powder X-ray diffraction, also known as XRD, was used in order to perform crystal structural verification on the manufactured crystal. The Fourier transform infrared spectroscopy (FT-IR) approach was used in order to ascertain the crystals’ respective vibrational frequencies. In order to evaluate the single crystal’s crystalline perfection and optical quality, high-resolution X-ray diffraction rocking curve measurement (HRXRD) and UV transmittance spectrum analysis were used. So as to investigate the nonlinear optical (NLO) activity of the generated single crystals, a Q-switched and pulsed Nd: YAG laser was used in the research. This led to the discovery of the SHG efficiency. The single crystal’s mechanical strength was evaluated using Vicker’s microhardness measurement, which provided an approximation of the true value. Furthermore, the single crystal was examined and reported for its optical birefringence, photoluminescence, and refractive index.

Enhancing the quality of homoepitaxial (−201) β-Ga2O3 thin film by MOCVD with in situ pulsed indium

This article innovatively uses pulsed metal-organic chemical vapor deposition technology to optimize the quality of β-Ga2O3 thin films on (−201) β-Ga2O3 homo-substrate using indium pulse-assisted technology. The results demonstrate that the pulsed indium-assisted method, when compared with the traditional indium-assisted method, effectively suppresses the desorption of Ga2O, enhances the flatness of the β-Ga2O3 film, and reduces the surface roughness from 34.8 to 0.98 nm. The optimized single crystalline β-Ga2O3 film was grown with pulsed-indium, and the full width at half maximum of x-ray diffraction rocking curve was 30.42 arc sec, smaller than that of the continuous indium β-Ga2O3 (56.1 arc sec). In combination with the x-ray photoelectron spectroscopy O1s split-peak fitting analysis, the relative content of oxygen vacancies in the film was significantly reduced by pulsed indium-assisted method. The Hall mobility of films assisted by pulsed-indium is approximately 14 times higher than that of films assisted by traditional indium. The pulsed indium technology provides an idea for homoepitaxial growth of high-quality β-Ga2O3 films.

High conductivity of n-type β-Ga2O3(010) thin films achieved through Si doping by mist chemical vapor deposition

Currently, β-Ga2O3 has attracted significant attention as a wide bandgap semiconductor, and numerous growth techniques are being explored to control its carrier concentration for various applications. In this study, we investigated the homoepitaxial growth of Si-doped β-Ga2O3 thin films on a Fe-doped β-Ga2O3 substrate using the mist chemical vapor deposition (CVD) technique developed in our group to obtain highly conductive thin films. Using mist CVD, we obtained highly crystalline Si-doped β-Ga2O3 thin films with a full-width at half-maximum of ∼40 arc sec for the (020) peak in the x-ray diffraction rocking curve. Atomic force microscopy studies indicated considerably smooth surfaces of the films with a small root mean square roughness (less than 0.5 nm). Furthermore, we controlled the carrier concentration in the range of 3.85 × 1018 to 2.58 × 1020 cm−3 by varying the Si concentration in the precursor solution. The film exhibits the highest conductivity of 2368 S/cm (mobility = 57.2 cm2/V s at the carrier concentration of 2.58 × 1020 cm−3). This study is expected to promote the application of β-Ga2O3 in devices.

Interface-Tension-Assisted Temperature-Gradient Crystallization of High-Quality MAPbBr3 Perovskite Single Crystals with Low Defect Densities.

Comprehensive understanding and precise manipulation of the crystallization process for organic-inorganic hybrid perovskite materials are crucial for advancing perovskite single-crystal optoelectronic technology. In this study, we theoretically and experimentally investigated the influence of interface tension on the synthesis of perovskite single crystals. On the basis of the understanding of the nucleation and growth mechanisms, we developed a polydimethylsiloxane-assisted temperature-gradient growth technique to prepare high-quality MAPbBr3 single crystals. Using this technique, we harvested some high-quality MAPbBr3 single crystals, with the narrowest reported full width at half-maximum (0.00806°) of X-ray diffraction rocking curve, the longest carrier lifetime of 1002 ns, and an ultralow trap-state density of 4.25 × 109 cm-3. Furthermore, the X-ray detector fabricated using our MAPbBr3 single crystal exhibited a high sensitivity of 7275 μC Gy1- cm2 and a low minimum detection limit of 0.67 μGy s-1. This paper presents a novel method to control the crystallization and growth processes of high-quality perovskite single crystals.

Evolutionary growth strategy of GaN on (1 1 1) diamond modulated by nano-patterned buffer engineering

GaN-on-diamond wafers are investigated to overcome the heat accumulation issues in GaN-based electronic devices. Until now, growing the high-quality GaN film on the diamond for device manufacture is still a great challenge. In this study, a new strategy of high-quality GaN on (111) diamond was proposed for the realization of high-performance GaN-on-diamond devices. The nano-patterned buffer engineering was utilized to greatly improved the GaN film on (111) diamond. The Al0.78Ga0.22N nano-patterned buffer reformed the morphology, ensuring that c orientation is the primary growth direction. The subsequent overgrowth of Al0.47Ga0.53N broadened the nano pillars and introduced stacking faults, improving the coalescence process and dislocations blockage. In addition, the coalescence process of the Al0.26Ga0.74N layer bent the treading dislocations, inducing the dislocations to annihilate. As a result, we could obtain remarkably high-quality GaN films on (111) diamond. The high-resolution X-ray diffraction rocking curve showed a full width at half maximum (FWHM) value of 770/986 arcsec at (002)/(102), which is the narrowest result reported. To the best of our knowledge, the RC FWHM at (102) of epitaxial GaN on diamond is reported firstly. Overall, this study provided a new strategy for obtaining high-quality GaN films on (111) diamonds for high-performance GaN-on-diamond devices.

The solution of wetting issues in GaN epitaxy on (111) SCD with magnetron sputtered AlN

Single crystal diamond (SCD) is an ideal heatsink for GaN-based devices. However, wetting issue of buffer on SCD hinders the GaN quality, limiting the full utilization of SCD's heat-dissipation ability. In this paper, the first-principles calculation revealed the high adsorption energy of Al and N adatoms on the surface of (111) SCD. The high energy of adatoms lead to a poor nucleation of AlN on (111) SCD, which caused inferior buffer layer. We propose a solution by pre-depositing AlN on (111) SCD via the ex-magnetron sputtering, which greatly enhances the quality of buffer layer and GaN film. Three different thicknesses of sputtered AlN (25 nm, 50 nm, and 100 nm were studied, and all showed improvement in GaN quality. The enhanced quality had been confirmed by the detailed characterization. GaN on (111) SCD with sputtered AlN presents narrower rocking curves of X-ray Diffraction (XRD). Additionally, GaN on 50 nm sputtered AlN/(111) SCD demonstrated superior quality, achieving a full width at half maximum of XRD for 1878/1945″ at 002/102.

Mid-wave infrared photoluminescence from low-temperature-grown PbSe epitaxial films on GaAs after rapid thermal annealing

We investigate the beneficial effects of rapid thermal annealing on structure and photoluminescence of PbSe thin films on GaAs (001) grown below 150 °C, with a goal of low temperature integration for infrared optoelectronics. Thin films of PbSe deposited on GaAs by molecular beam epitaxy are epitaxial at these reduced growth temperatures, yet the films are highly defective with a mosaic grain structure with low angle and dendritic boundaries following coalescence. Remarkably, we find that rapid thermal annealing for as short as 180 s at temperatures between 300 and 425 °C in nitrogen ambient leads to extensive re-crystallization and transformation of these grain boundaries. The annealing at the same time dramatically improves the band edge luminescence at 3.7 μm from previously undetectable levels to nearly half as intense as our best conventionally grown PbSe films at 300 °C. We show using an analysis of laser pump-power dependent photoluminescence measurements that this dramatic improvement in the photoluminescence intensity is due to a reduction in the trap-assisted recombination. However, we find it much less correlated with improved structural parameters determined by x-ray diffraction rocking curves, thereby pointing to the importance of eliminating point defects over extended defects. Overall, the success of rapid thermal annealing in improving the luminescent properties of low growth temperature PbSe is a step toward the integration of PbSe infrared optoelectronics in low thermal budget, back end of line compatible fabrication processes.

Investigation of Doping Processes to Achieve Highly Doped Czochralski Germanium Ingots

Highly doped germanium (HD-Ge) is a promising material for mid-infrared detectors, bio-sensors, and other devices. Bulk crystals with a doping concentration higher than 1018 cm−3 would be desirable for such device fabrication technologies. Hence, an effective method needs to be developed to dope germanium (Ge) ingots in the Czochralski (Cz) growth process. In this study, a total of 5 ingots were grown by the Cz technique: two undoped Ge ingots as a reference and three doped ingots with 1018, 1019 , and 1020 atoms/cm3 respectively. To obtain a uniform p-type doping concentration along the crystal, co-doping of boron-gallium (B-Ga) via the Ge feed material was also attempted. Both B and Ga are p-type dopants, but with a large difference in their segregation behavior (contrary segregation profile) in Ge, and hence it is expected that the incorporation of dopants in the crystal would be uniform along the crystal length. The distribution of the dopants followed the Scheil-predicted profile. The etch pit density maps of the grown crystals showed an average dislocation density in the order of 105 cm−2. No increase in the overall etch pit count was observed with increasing dopant concentration in the crystal. The grown highly doped Ge crystals have a good structural quality as confirmed by x-ray diffraction rocking curve measurements.

Secondary electron emission of B-doped/undoped double-layer heteroepitaxial single crystal diamond film

A B-doped/undoped double-layer single crystal diamond structure was proposed to enhance secondary electron emission (SEE), and the double-layer single crystal diamond film was heteroepitaxially grown on MgO substrate by microwave plasma chemical vapor deposition. The crystal quality, surface morphology and conductivity of the film were studied. It is found that the film has high crystal quality, the full width at half maximum of X-ray diffraction rocking curve is 0.14°, and the surface roughness is small. For these reasons, the B-doped/undoped double-layer single crystal diamond film has better SEE performance than the B-doped/undoped double-layer polycrystalline diamond film. At the incident electron energy of 2 keV, the SEE yield of B-doped/undoped double-layer single crystal diamond reached 22.4. The physical model calculation results indicate that at a low B doping concentration, less sp2 carbon and smaller surface roughness are beneficial to improve the SEE yield.

Homoepitaxial growth of Ge doped β-gallium oxide thin films by mist chemical vapor deposition

This study demonstrated homoepitaxial growth of Ge-doped β-Ga2O3 thin films on β-Ga2O3 substrates via mist chemical vapor deposition (CVD) using GeI4, a water-soluble Ge precursor. The carrier concentration of the Ge-doped β-Ga2O3 thin films was controlled by varying the Ge precursor concentration in the solution. A mobility of 66 cm2 V−1 s−1 was obtained at a carrier density of 3.4 × 1018 cm−3 using oxygen carrier gas. X-ray diffraction (XRD) scans 2θ-ω revealed that homoepitaxial Ge-doped β-Ga2O3 thin films were grown on β-Ga2O3 without phase separation. However, the XRD rocking curves revealed that the mist CVD- grown Ge-doped β-Ga2O3 was degraded compared to the substrate as the Ge concentration increased. The surface morphologies of the Ge-doped β-Ga2O3 exhibited atomically flat surfaces with a root mean square roughness of less than 1 nm. These results indicate that the Ge-doped β-Ga2O3 thin films prepared by mist chemical vapor deposition are promising for device applications.

High quality GaN films on miscut (1 1 1) diamond substrates through non-c orientation suppression

The GaN films are grown on 4° miscut to (110) and (100) orientation (111) diamond substrates by metal organic chemical vapor deposition respectively. The ordinary (111) diamond substrate is used as reference. The morphology and crystal quality of the three GaN films are characterized by atomic force microscope, scanning electron microscope, Raman spectra, photoluminescence, and X-ray diffraction (XRD). The GaN epilayer on miscut to (110) orientation (111) diamond presents a superior quality with smooth surface, clear A1(LO) peak of Raman shift and XRD rocking curve with full width half maximum of 1357 arcsec, which is a remarkable result reported. Through the analysis, we found that when GaN grows on miscut to (110) orientation (111) diamond substrates, non-c orientation grain would be greatly suppressed so that c orientation buffers easier to grow laterally and merge into thin films. The non-c orientation suppression process greatly improves the quality of GaN film on (111) diamond.

Influence of the temperature on growth by ammonia source molecular beam epitaxy of wurtzite phase ScAlN alloy on GaN

Due to its large piezoelectric and spontaneous polarization coefficients combined with the possibility of being grown lattice-matched with GaN, wide bandgap ScAlN is becoming a promising material in III-nitride semiconductor technology. In this work, and for the first time, ScAlN growth has been performed by molecular beam epitaxy with ammonia source as nitrogen precursor. High electron mobility transistor heterostructures with a 26 nm thick Sc0.15Al0.85N barrier have been grown on GaN-on-sapphire substrates. The effect of growth temperature, ranging between 620 and 800 °C, was carefully investigated. A smooth surface morphology with a mean roughness below 0.5 nm is obtained whatever the temperature while for 670 °C the (0002) and (101̄3) x-ray diffraction rocking curves show minimum full-width at half-maximum of 620 and 720 arc sec, respectively. Furthermore, two-dimensional electron gases with a high density of 3-3.5 × 1013/cm2 were evidenced in the heterostructures grown below 720 °C.

Epitaxial growth of β-Ga2O3 thin films on SrTiO3 (1 1 1) and (1 0 0) substrates by chemical vapor deposition

Due to good lattice matching and bipolar doping behavior, wide bandgap SrTiO3 (STO) is a promising substrate for the heteroepitaxial growth of β-Ga2O3 to construct heterojunctions for (opto-)electronic device applications. However, the investigation of the growth of β-Ga2O3 film on the STO (111) substrate is still lacking. In this work, for the first time, the β-Ga2O3 (2¯ 01) thin films were epitaxially grown on the supercell matched STO (111) substrates by low pressure chemical vapor deposition. The effects of the source and growth temperatures on the surface roughness and crystalline quality of the β-Ga2O3 films were systemically investigated. By controlling the supply of Ga source, the heteroepitaxial β-Ga2O3 film grown under the optimized conditions exhibits a narrow X-ray diffraction rocking curve of 0.75° and a low root-mean-square roughness of 1.10 nm. Furthermore, the epitaxial growth of β-Ga2O3 films on the STO (100) substrate was also investigated. The heteroepitaxy of β-Ga2O3 films on STO lays the foundation for future device applications of β-Ga2O3-based heterojunctions.

Heterogeneous integration of lithium tantalate thin film on quartz for high performance surface acoustic wave resonator

Surface acoustic wave (SAW) resonator based on the piezo film on a foreign substrate is promising to enhance the performance of radio frequency filters. In this work, the 4 inch wafer-scale lithium tantalate thin film on quartz (LTOQ) heterogenous substrate was fabricated by ion-cut process. The cut angle of quartz was optimized to achieve high-quality factor (Q) based on finite element analysis. The average film thickness and the film nonuniformity for the whole wafer are 602 nm and ±2.2%, respectively. The lithium tantalate film exhibits single-crystalline quality where the full width at half-maximum of high-resolution X-ray diffraction rocking curve is 47.4 arcsec. The shear horizonal surface acoustic wave resonator based on the LTOQ structure exhibits a maximum Bode-Q exceeding 3000 and the electromechanical coupling coefficient of 10.26%. The temperature coefficient of frequency at resonant frequency and anti-resonant frequency are −25.21 ppm °C−1 and −35.22 ppm °C−1, respectively.

Pt/ZnGa₂O₄ Schottky Barrier Diodes Fabricated by Using Single Crystal n-ZnGa₂O₄ (111) Substrates

In this letter, we fabricated Schottky barrier diodes (SBDs) using n-type zinc gallium oxide (n-ZnGa2O4) single-crystal substrates, which were grown from the melt by the vertical gradient freeze (VGF) method. X-ray diffraction rocking curve and Laue diffraction results indicate the good crystal quality. The electrical properties of SBDs fabricated on substrates with two doping concentrations are systematically investigated. Heavily-doped (HD) SBDs exhibit lower differential specific on-resistance (~1.13 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}\Omega \cdot $ </tex-math></inline-formula> cm2) and lower turn-on voltage (~0.16 V) while the lightly-doped (LD) SBDs exhibit better ideality factor (1.17), rectification characteristics (on/off ratio ~1011) and lower reverse leakage. In addition, we separately tested the electrical properties of the two devices at different temperatures (298 K-473 K). The results of varying temperature show that LD-SBDs have better temperature stability in smaller variation of ideality factor and barrier height with temperature. Based on these experimental results, this work demonstrates the great promise of ZnGa2O4 materials to fabricate high-performance power devices.

Effect of oxygen on the crystallinity and defect state of AlxGa1−xN epilayers

The effect of oxygen incorporation on the crystal quality and defect states in AlxGa1−xN epilayers (x = 0.4, 0.6, 0.8) grown by hydride vapor phase epitaxy with and without oxygen gas flow were studied. On the basis of the full width at half-maximum value of the (102) X-ray diffraction rocking curve, the crystal quality of AlxGa1−xN with oxygen was better than that of AlxGa1−xN without oxygen as the Al/Ga ratio increased. In Al0.6Ga0.4N epilayers with and without oxygen, two deep traps of H1ʹ and H2ʹ were measured by deep level transient spectroscopy. All traps were hole-like traps with activation energies of 1.28 eV (H1ʹ) and 0.61 eV (H2ʹ), which are the same as traps H1 and H2 measured in Al0.4Ga0.6N. Al0.8Ga0.2N with oxygen had only the D1 trap, as observed by thermally stimulated current, while the sample without oxygen has two traps of D1 (0.80 eV) and D2 (0.64 eV). The trap densities in AlxGa1−xN epilayers decreased with oxygen as the Al mole fraction increased in AlxGa1−xN. Therefore, the oxygen atoms can improve the crystal quality and suppress the defect states in AlxGa1−xN epilayers.