Radical Beam Irradiation 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.

Nitrogen Radical Beam Irradiation on InN Film for Surface Modification

Nitrogen Radical Beam Irradiation on InN Film for Surface Modification

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.

Effect of different buffer layers on the quality of InGaN layers grown on Si

This work studies the effect of four different types of buffer layers on the structural and optical properties of InGaN layers grown on Si(111) substrates and their correlation with electrical characteristics. The vertical electrical conduction of n-InGaN/buffer-layer/p-Si heterostructures, with In composition near 46%, which theoretically produces an alignment of the bands, is analyzed. Droplet elimination by radical-beam irradiation was successfully applied to grow high quality InGaN films on Si substrates for the first time. Among several buffer choices, an AlN buffer layer with a thickness above 24 nm improves the structural and optical quality of the InGaN epilayer while keeping a top to bottom ohmic behavior. These results will allow fabricating double-junction InGaN/Si solar cells without the need of tunnel junctions between the two sub-cells, therefore simplifying the device design.

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.

Threading dislocation reduction in InN grown with in situ surface modification by radical beam irradiation

In this study, the applicability of in situ surface modification by radical beam irradiation method to reduce threading dislocation density in InN was investigated. The dislocation behavior, crystallographic quality, electrical properties, and photoluminescence properties of InN grown with this method were studied. Transmission electron microscopy observation revealed that dislocation density in the InN layer reduced by a factor of 3 in certain regions and showed good agreement with the results from photoluminescence spectroscopy. If this technology is established, high-quality InN with low threading dislocation density can be achieved with a very simple and repeatable growth process.

Influence of MBE growth modes and conditions on spontaneous formation of metallic In nanoparticles and electrical properties of InN matrix

Influence of the molecular beam epitaxy (MBE) growth conditions on the electrical properties of the InN epilayers in terms of minimization of the effect of spontaneously formed In nanoparticles was studied. A three-step growth sequence was used, including direct MBE growth of an InN nucleation layer, migration enhanced epitaxy (MEE) of an InN buffer layer, and In-rich MBE growth of the main InN layer, utilizing the droplet elimination by radical-beam irradiation (DERI) technique. The three-step growth regime was found to lead to decreasing the relative amount of In nanoparticles to 4.8% and 3.8% in In-rich and near-stoichiometric conditions, respectively, whereas the transport properties are better for the In-rich growth. Further reduction of the metallic indium inclusions in the InN films, while keeping simultaneously satisfactory transport parameters, is hardly possible due to fundamental processes of InN thermal decomposition and formation of the nitrogen vacancy conglomerates in the InN matrix. The In inclusions are shown to dominate the electrical conductivity of the InN films even at their minimum amount.

Influence of defects and indium distribution on emission properties of thick In-rich InGaN layers grown by the DERI technique

We report on the spatial variation of optical properties in thick, In-rich InGaN layers, grown by a novel droplet elimination by radical beam irradiation (DERI) technique. The increase of layer thickness causes layer relaxation and results in double-peaked photoluminescence spectra. Spatially resolved measurements show that the defects in the strained sub-layer are distributed inhomogeneously. An increase in the layer thickness results in faster nonradiative recombination due to increasing density of nonradiative recombination centers, as evidenced by time-resolved free carrier absorption, and facilitates larger indium incorporation in the upper part of the layer.

Growth of thick InGaN films with entire alloy composition using droplet elimination by radical-beam irradiation

Droplet elimination by radical-beam irradiation (DERI), which is suitable for the growth of InN and periodic InN/InGaN structures, was developed for the growth of thick InGaN films by radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE). In this method, Ga-to-nitrogen radical (N) beam flux ratio was fixed in the entire growth process, and In beam supply was modulated under the condition in which excess In of more than 2–3 monolayer wetting layers always existed on the surface, that is, no precise control of In beam flux during growth was needed. Thick and uniform InGaN films were successfully grown by the developed method. In addition, InGaN films with an entire alloy composition could be simply grown by controlling Ga-to-N beam flux ratio.

Application of Droplet Elimination Process by Radical-Beam Irradiation to InGaN Growth and Fabrication of InN/InGaN Periodic Structure

A growth method, named droplet elimination by radical-beam irradiation (DERI), consisting of a metal-rich growth process (MRGP) and a droplet elimination process (DEP), was developed for the growth of InGaN ternary alloys. In the MRGP using the growth of InGaN under a metal-rich condition [N*/(In+Ga)<1], Ga was preferentially incorporated into the growing InGaN and In was forced out to the surface. This In was transformed to epitaxial InN on top of the InGaN underlayer in the DEP using a subsequent nitrogen radical-beam irradiation. By repeating the MRGP and DEP, an InN/InGaN periodic structure was successfully fabricated.

Application of Droplet Elimination Process by Radical-Beam Irradiation to InGaN Growth and Fabrication of InN/InGaN Periodic Structure

Application of Droplet Elimination Process by Radical-Beam Irradiation to InGaN Growth and Fabrication of InN/InGaN Periodic Structure

New MBE growth method for high quality InN and related alloys using in situ monitoring technology

AbstractA new radio‐frequency plasma‐assisted molecular beam epitaxy (RF‐MBE) method, named droplet elimination by radical beam irradiation (DERI), is utilized for the growth of InN. This method is composed of two series of growth processes: (1) InN growth under an In‐rich condition and (2) consecutive nitrogen radical beam irradiation. This method is simple, enabling the reproducible growth of a high‐quality thick InN film with a flat surface. This method is also effective for monitoring a nitrogen radical beam that is responsible for InN growth. This new growth method is also applied to InGaN growth. The results indicate a preferable Ga capturing process on an InGaN growing surface, particularly when the samples are grown under a metal‐rich condition.

Effect of the surface treatment on the room-temperature bonding of Al to Si and SiO2

Bonding of polycrystalline Al to Si(1 0 0) and SiO2 (fused silica) was carried out at room temperature by means of surface-activated bonding method. In the present work, different means of surface activation such as irradiation of an argon fast atom beam (FAB) and a hydrogen radical beam (RB) were used. Influence of the exposure to a vacuum atmosphere of the activated surfaces by fast atom irradiation on the bonding behaviour was investigated. The strength of the Al–Si joints sputter cleaned by FAB before bonding reaches as much as 32 MPa. When the activated surfaces were exposed to 30 L (where L is the abbreviation for langmuir (1.33×10-4 Pa s)) in the residual gases (mainly vapour), the strength of the Al–Si joint decreased to 20 MPa and approached that of the Al–SiO2 joint. This indicates that the fracture strength of the joint of Al and Si with an intermediate layer of OH groups and oxide is close to that of Al and Si oxide. The adhesion between Al and Si deteriorated strongly because of hydrogen termination on the Si surface which had been irradiated by the hydrogen RB. On the contrary, bonding of Si with native oxides to Al was successful with the hydrogen RB irradiation.

Reduction of p-ZnSe/p-GaAs non-ohmic barrier by inserting a GaN buffer layer

Nitrogen (N) radical irradiated GaAs was investigated by Auger analysis and reflection high-energy electron diffraction. N radical beam irradiation on GaAs causes an exchange of As atoms for N atoms, consequently forming a GaN layer onto the GaAs surface without a Ga source. No degradation of the ZnSe layers was observed when they were grown on GaAs substrates with GaN buffer layers. The current-voltage and capacitance-voltage characteristics of p-ZnSe/p-GaAs heterodiodes are examined. The necessary voltage for hole injection across the p-ZnSe/p-GaAs heterojunction is reduced to about half when a thin GaN buffer layer is inserted into the junction.

Chemical beam epitaxy selectively-regrown n +-GaAs layer on metalorganic chemical vapor deposition grown GaInP/GaInAs/GaAs pseudomorphic high electron mobility transistor structure

We used selective chemical beam epitaxy (CBE) to fabricate low-resistance contacts on Ga 0.5In 0.5P/GaInAs/GaAs pseudomorphic high electron mobility transistor (HEMT) structures. Surfaces prepared by hydrogen radical beam irradiation exhibited better electrical and morphological properties than those cleaned by an HCl/H 2 gas mixture. After preparing the surface, an n +-GaAs layer was selectively grown at the drain and source areas. A pseudomorphic HEMT, with a 0.3 μm gate length, had a contact resistance of 0.5 Ω mm, an extrinsic transconductance of 400 mS/mm and a cutoff frequency of 55 GHz.