Radio-frequency Plasma-excited Molecular Beam Epitaxy Research Articles

Control of Metal‐Rich Growth for GaN/AlN Superlattice Fabrication on Face‐to‐Face‐Annealed Sputter‐Deposited AlN Templates

GaN/AlN superlattices consisting of few‐monolayer GaN wells have attracted considerable attention for use in deep‐ultraviolet (DUV) light‐emitting devices. To avoid the formation of droplets and AlGaN interface layers, precise growth control is essential for fabricating superlattices with flat and abrupt interfaces. Herein, GaN/AlN superlattice structures are grown on face‐to‐face‐annealed sputter‐deposited AlN (FFA Sp‐AlN) template substrates using radio‐frequency plasma‐excited molecular beam epitaxy (RF‐MBE) utilizing in situ reflection high‐energy electron diffraction (RHEED) monitoring. Both AlN and GaN are grown under metal‐rich conditions, and subsequently, the droplets are eliminated by droplet elimination by radical beam irradiation (DERI) method for AlN and by growth interruption for GaN. Furthermore, the dependence of AlN thickness on the properties of superlattices is investigated. The AlN thickness changes linearly with the supply time of the Al metal; thus, the AlN thickness is easily controllable. A total of 20‐period GaN/AlN superlattices with flat and abrupt interfaces is fabricated, as confirmed using atomic force microscopy and X‐ray diffraction. Cathodoluminescence with a peak wavelength of 230–260 nm at room temperature is obtained from the fabricated superlattices. Moreover, the emission wavelength shifts with an increase in AlN thickness.

Direct growth of GaN film on ScAlMgO4 substrate by radio-frequency plasma-excited molecular beam epitaxy

ScAlMgO4 (SAM) has attracted attention as a substrate for nitride semiconductor crystal growth owing to its small a-axis lattice mismatch with GaN and InGaN. In this study, we investigated GaN growth on a SAM substrate via radio-frequency plasma-excited molecular beam epitaxy. By optimizing the growth conditions, GaN with the following epitaxial orientation relations (0001)GaN//(0001)SAM and [11–20]GaN//[11–20]SAM was successfully grown directly on the SAM substrate. The atomically flat and abrupt interface of GaN directly grown on the SAM substrate was observed via high-resolution transmission electron microscopy, and uniform GaN growth on a two-inch SAM substrate was also demonstrated.

Repeatability and Mechanisms of Threading Dislocation Reduction in InN Film Grown with In Situ Surface Modification by Radical Beam Irradiation

The objective of this study was to investigate the repeatability of in situ surface modification by radical beam irradiation to reduce threading dislocation density in InN film. The growth of InN template and N radical irradiation processes were repeated twice in situ in the radio-frequency plasma-excited molecular beam epitaxy chamber before the regrowth of InN film on the N radical irradiated template. Transmission electron microscopy was applied to study dislocation behaviors of the InN film grown. In this letter, we show cross-sectional-view transmission electron microscopy evidence of the threading dislocation reduction from ~2.8×1010 cm-2 in the first irradiated InN layer to ~2.0×1010 cm-2 in the second irradiated InN layer, and to ~1.3×1010 cm-2 in the top regrown InN layer. The mechanisms of threading dislocation reduction were also studied.

Reduction of Threading Dislocation Density in InN Film Grown with in situ Surface Modification by Radio-frequency Plasma-excited Molecular Beam Epitaxy

ABSTRACTThe objective of this study was to investigate the relationship between the thickness of N radical irradiated InN template with crystallographic quality and electrical properties of InN film grown with the previously proposed method, in situ surface modification by radical beam irradiation. In this study, three InN samples were grown with this method on different thickness of irradiated templates. The crystallographic quality of InN films was analyzed by X-ray diffraction and the electrical properties were studied by Hall effect measurement. InN grown on 100 nm thick irradiated template shows lower full-width at half-maximum of X-ray rocking curves and lower carrier concentration compared to InN grown on 200 nm and 450 nm thick irradiated templates. Transmission electron microscopy revealed that threading dislocation density in the InN film decreased by an order of magnitude to ∼4.6×109cm-2. These results suggest that this method is possible for reduction of threading dislocation density in InN and the thickness of irradiated template should be minimized for higher crystallographic quality and electrical properties of the entire InN film.

Radio-frequency plasma-excited molecular beam epitaxy growth of GaN on graphene/Si(100) substrates

Strong c-axis-oriented hexagonal (0001) GaN was grown on graphene/Si(100) substrates by radio-frequency plasma-excited molecular beam epitaxy. The hexagonal symmetry of graphene transferred onto the Si(100) surface enabled the growth of a highly c-axis-oriented GaN film. The GaN showed a full width at half maximum of 11.3 arcmin for a (0002) rocking curve measured by X-ray diffraction. Strong luminescence at 3.4 eV was also observed by cathodoluminescence with a luminescence at 3.2 eV, which originated from a cubic-phase inclusion. A microstructural study using transmission electron microscopy also confirmed the growth of hexagonal (0001) GaN on a graphene/Si(100) substrate.

Epitaxial Growth of AlInGaN Quaternary Alloys by RF-MBE

AlInGaN quaternary alloys were successfully grown on sapphire substrate by radio-frequency plasma-excited molecular beam epitaxy (RF-MBE). AlInGaN quaternary alloys with different compositions were acquired by changing the Al cell's temperature. The streaky RHEED patterns were observed during AlInGaN quaternary alloys growth. Scanning Electron Microscope (SEM), Rutherford back-scattering spectrometry (RBS), X-Ray diffraction (XRD) and Cathodoluminescence (CL) were used to characterize the structural and optical properties of the AlInGaN alloys. The experimental results show that the AlInGaN quaternary alloys grow on the GaN buffer in the layer-by-layer growth mode. When the Al cell's temperature is 920 degrees C, the Al/In ratio in the AlInGaN quaternary alloys is about 4.7, and the AlInGaN can acquire better crystal and optical quality. The X-ray and CL full-width at half-maximum (FWHM) of the AlInGaN are 5arcmin and 25nm, respectively.

Novel InN growth method under In‐rich condition on GaN/Al2O3 (0001) templates

AbstractA novel technique is proposed for the growth of an InN film on a GaN/Al2O3 (0001) template by radio‐frequency plasma‐excited molecular beam epitaxy (RF‐MBE). The method involves 1) InN growth under an In‐rich condition and 2) additional nitrogen radical irradiation after the InN growth under an In‐rich condition. Excess In that appeared on the InN surface in the InN growth under an In‐rich condition is transformed to InN by the additional nitrogen radical irradiation. The effective V/III ratio is easily controlled by monitoring the intensity in a reflection high‐energy electron diffraction (RHEED) pattern. The growth of the InN film by repeating the InN growth under an In‐rich condition and the additional nitrogen radical irradiation is also demonstrated. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The growth of high-Al-content InAlGaN quaternary alloys by RF-MBE

High-Al-content InxAlyGa1−x−yN (x = 1–10%, y = 34–45%) quaternary alloys were grown on sapphire by radio-frequency plasma-excited molecular beam epitaxy. Rutherford back-scattering spectrometry, high resolution x-ray diffraction and cathodoluminescence were used to characterize the InAlGaN alloys. The experimental results show that InAlGaN with an appropriate Al/In ratio (near 4.7, which is a lattice-match to the GaN under-layer) has better crystal and optical quality than the InAlGaN alloys whose Al/In ratios are far from 4.7. Some cracks and V-defects occur in high-Al/In-ratio InAlGaN alloys. In the CL image, the cracks and V-defect regions are the emission-enhanced regions.

Growth and characterization of InN on sapphire substrate by RF-MBE

Indium nitride (InN) films were grown on sapphire substrates by radio-frequency plasma-excited molecular beam epitaxy (RF-MBE). Atomic force microscopy (AFM), reflection high-energy electron diffraction (RHEED), double-crystal X-ray diffraction (DCXRD) and photoluminescence (PL) spectroscopy were used to characterize the InN films. The results show that the InN films have good crystallinity, with full-width at half-maximum (FWHM) of InN (0 0 0 2) DCXRD peak being 14 arcmin. At room temperature, a strong PL peak at 0.79 eV was observed. At 1.9 eV or so, no peak was observed. In addition, it is found that the InN films grown with low-temperature (LT) InN buffer layer are of better quality than those without LT-InN buffer layer.

Single Crystalline InN Films Grown on Si Substrates By Using A Brief Substrate Nitridation Process

ABSTRACTInN films were grown on Si (111) substrates by radio-frequency plasma-excited molecular beam epitaxy. InN films highly oriented to the c-axis were obtained by optimizing growth conditions in the direct growth on Si. Growth of single crystalline InN films was realized on Si substrates with substrate nitridation for 3 min. On the other hands, when the substrate nitridation was lasted over 30 min, obtained InN films were polycrystalline due to the amorphous SiNx layer formed on a substrate surface. We also studied the local atomic structure in the single crystalline InN film using extended X-ray absorption fine structure measurements.

Electricaland Optical Properties of InN/Si Heterostructure

ABSTRACTSingle crystalline InN films were grown on Si substrates by radio-frequency plasma-excited molecular beam epitaxy. Electrical property of InN/Si heterojunction was investigated. We obtained rectifying characteristics in n-InN/p-Si heterostructure for the first time. Forward I-V characteristics were affected by both the buffer layer deposition and the nitridation process. Strong photoluminescence peaks for both single crystalline and polycrystalline InN films grown on the Si substrates were observed at around 0.8 eV, which were smaller than the previous reported PL emission peak of around 1.9 eV.

Growth of high-quality InN using low-temperature intermediate layers by RF-MBE

InN with a film thickness of 600 nm was grown on a (0 0 0 1) sapphire substrate using low-temperature-grown intermediate layers by radio frequency plasma-excited molecular beam epitaxy (RF-MBE). From SEM observation, it was found that InN films with uniform surface morphology were grown. The electron mobility at room temperature obtained in this study was 830 cm 2 /V s and the corresponding carrier density was 1.0×10 19 cm −3. To our knowledge, this electron mobility is the highest value ever reported for single-crystal InN films.

Effect of sapphire substrate nitridation on determining rotation domain in GaN growth

GaN films were grown at various V/III ratios on sapphire (0 0 0 1) substrates with and without nitridation process by radio-frequency plasma-excited molecular beam epitaxy. Based on the results of X-ray diffraction pole-figure and φ scan measurements, the GaN film grown without nitridation process has a tendency to form the metastable in-plane rotation domain by ∼11° from the substrate, in addition to the main domain rotated by 30° from the substrate. In suppressing the formation of the metastable in-plane rotation domain, it is found to be very effective to perform the nitridation process. In addition, even in GaN films grown without nitridation process, decrease in V/III ratio enables us to suppress the formation of the metastable domain. The rotation domains are considered to have the epitaxial relationship of [1 2 3 ̄ 0] GaN ∥[1 1 2 ̄ 0] sapphire and [ 1 ̄ 2 ̄ 3 0] GaN ∥[1 1 2 ̄ 0] sapphire .