Ammonia-source Molecular Beam Epitaxy Research Articles

Erratum: “Influence of the temperature on growth by ammonia source molecular beam epitaxy of wurtzite phase ScAlN alloy on GaN” [APL Mater. 11, 031105 (2023)

Erratum: “Influence of the temperature on growth by ammonia source molecular beam epitaxy of wurtzite phase ScAlN alloy on GaN” [APL Mater. 11, 031105 (2023)

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.

Buried defects induced by plasma assisted molecular beam epitaxy of AlN and GaN on Silicon

The present work is dedicated to the study of peculiar defects observed in GaN/AlN structures grown on Silicon substrate using the plasma assisted Molecular Beam Epitaxy under metal-rich conditions. Optical microscopy shows that these defects have undefined shape when AlN is grown on Silicon. On the contrary such defects are not observed with AlN films grown under nitrogen-rich plasma assisted or ammonia source Molecular Beam Epitaxy, but triangular shape defects appear in case of GaN regrowth on the latter. As scanning electron microscopy is not able to evidence these defects but only protuberances connected with them, we deduce that they are located in the Silicon substrate. Complementary analysis with atomic force microscopy and energy dispersive X-ray analysis lead us to propose a scenario involving the etching of the Silicon substrate with Ga or Al diffusing through weak points in the nucleation layer.

Development of technological building blocks for the monolithic integration of ammonia-MBE-grown GaN-HEMTs with silicon CMOS

In this paper, we investigate a technological route for the monolithic integration of GaN high-electron-mobility transistors (HEMTs) on silicon complementary metal oxide semiconductor (CMOS) circuits. The CMOS-first approach developed in this work relies on the ammonia-source molecular beam epitaxy (ammonia-MBE) technique which operates at noticeably lower temperatures than the metalorganic chemical vapor deposition (MOCVD) technique. The presence of CMOS devices on the wafer is a challenge that has been addressed by reducing the maximum growth temperature of (Al,Ga)N materials from 920 to 830–850 °C without any degradation of the GaN crystal quality nor the HEMT device behavior. In addition, we developed a dielectric stack able to withstand the large stress arising from the growth process and to mitigate the related cracking and delamination issues. Capacitance–voltage measurements have shown that the HEMT epitaxial structures provide a capacitance plateau with a sharp pinch-off behavior, attesting the absence of any significant interface traps nor residual donor contamination due to the presence of a dielectric mask on the silicon substrate. Preliminary results show that thin buffer HEMT devices with normal electrical behaviors can be locally grown at low temperature.

GaN nanowires with pentagon shape cross-section by ammonia-source molecular beam epitaxy

Ammonia-based molecular beam epitaxy (NH3-MBE) was used to grow catalyst-assisted GaN nanowires on (11¯02) r-plane sapphire substrates. Dislocation free [112¯0] oriented nanowires are formed with pentagon shape cross-section, instead of the usual triangular shape facet configuration. Specifically, the cross-section is the result of the additional two nonpolar {101¯0} side facets, which appear due to a decrease in relative growth rate of the {101¯0} facets to the {101¯1} and {101¯1} facets under the growth regime in NH3-MBE. Compared to GaN nanowires grown by Ni-catalyzed metal–organic chemical vapor deposition, the NH3-MBE grown GaN nanowires show more than an order of magnitude increase in band-edge to yellow luminescence intensity ratio, as measured by cathodoluminescence, indicating improved microstructural and optical properties.

Growth of Ga- and N-polar GaN layers on O face ZnO substrates by molecular beam epitaxy

Gallium nitride (GaN) epitaxial layers have been grown on O face (0001¯) zinc oxide (ZnO) substrates by ammonia source molecular beam epitaxy. By adjusting the growth temperature and the III/V ratio during the nucleation stage, GaN layers with Ga (0001) or N (0001¯) polarities have been obtained. We show that low growth temperatures (<550°C) and Ga-rich conditions lead to Ga-polar layers, whereas higher growth temperatures (>600°C) and N-rich conditions lead to N-polar layers. Furthermore, the formation of a zinc gallate (ZnGa2O4) interfacial layer between GaN and ZnO has been evidenced, which is responsible for the growth of Ga-polar GaN layers. The structural and optical properties of Ga- and N-polar GaN layers have been characterized and Ga-polar GaN layers exhibit higher crystal quality.

Optical polarization properties of m-plane AlxGa_1-xN epitaxial films grown on m-plane freestanding GaN substrates toward nonpolar ultraviolet LEDs

Light polarization characteristics of the near-band-edge optical transitions in m-plane AlxGa1-xN epilayers suffering from anisotropic stresses are quantitatively explained. The epilayers were grown on an m-plane freestanding GaN substrate by both ammonia-source molecular beam epitaxy and metalorganic vapor phase epitaxy methods. The light polarization direction altered from E [symbol see text]c to E//c at the AlN mole fraction, x, between 0.25 and 0.32, where E is the electric field component of the light and [symbol see text] and // represent perpendicular and parallel, respectively. To give a quantitative explanation for the result, energies and oscillator strengths of the exciton transitions involving three separate valence bands are calculated as functions of strains using the Bir-Pikus Hamiltonian. The calculation predicts that the lowest energy transition (E1) is polarized to the m-axis normal to the surface (X3) for 0< x ≤ 1, meaning that E1 emission is principally undetectable from the surface normal for any in-plane tensile strained AlxGa1-xN. The polarization direction of observable surface emission is predicted to alter from c-axis normal (X1) to c-axis parallel (X2) for the middle energy transition (E2) and X2 to X1 for the highest energy transition (E3) between x = 0.25 and 0.32. The experimental results are consistently reproduced by the calculation.

Suppression of concentration quenching of Er-related luminescence in Er-doped GaN

Erbium-doped GaN with different doping concentrations were grown by ammonia-source molecular beam epitaxy. The intra-4f-shell transitions related green luminescence were observed by both photoluminescence (PL) and cathodoluminescence (CL) measurements. It was found that concentration quenching of Er-related luminescence was observed in PL measurements while not in CL measurements. The different excitation and relaxation processes are suggested as the cause of the concentration quenching characteristics between PL and CL. The strong Er-related CL intensity in highly doped GaN demonstrates that high energy excitation is a promising approach to suppress the concentration quenching in Er-doped GaN.

Light polarization characteristics of m-plane AlxGa1−xN films suffering from in-plane anisotropic tensile stresses

Polarization characteristics of the near-band-edge optical transitions in m-plane AlxGa1−xN epilayers suffering from anisotropic stresses were quantified. The epilayers were grown by both ammonia-source molecular beam epitaxy and metalorganic vapor phase epitaxy methods on an m-plane freestanding GaN substrate. The light polarization direction altered from E⊥c to E∥c at the AlN molar fraction, x, between 0.25 and 0.32, where E is the electric field component of the light and ⊥ and ∥ represent perpendicular and parallel, respectively. To give a quantitative explanation for the result, energies and oscillator strengths of the exciton transitions involving three separate valence bands were calculated as functions of strains using the Bir–Pikus Hamiltonian. The calculation predicted that the lowest energy transition (E1) is polarized to the m-axis normal to the surface (X3) for 0&amp;lt;x≤1, meaning that E1 emission is principally undetectable from the surface normal for any in-plane tensile strained AlxGa1−xN. The polarization direction of observable surface emission was predicted to alter from c-axis normal (X1) to c-axis parallel (X2) for the middle energy transition (E2) and X2 to X1 for the highest energy transition (E3) between x=0.25 and 0.32. The experimental results were consistently reproduced by the calculation.

GaN grown on (1 1 1) single crystal diamond substrate by molecular beam epitaxy

GaN epilayers are grown on (1 1 1) oriented single crystal diamond substrate by ammonia-source molecular beam epitaxy. Each step of the growth is monitored in situ by reflection high energy electron diffraction. It is found that a two-dimensional epitaxial wurtzite GaN film is obtained. The surface morphology is smooth: the rms roughness is as low as 1.3 nm for 2×2 μm 2 scan. Photoluminescence measurements reveal pretty good optical properties. The GaN band edge is centred at 3.469 eV with a linewidth of 5 meV. These results demonstrate that GaN heteroepitaxially grown on diamond opens new rooms for high power electronic applications.

AlGaN/GaN high electron mobility transistor grown by molecular beam epitaxy on Si(110): comparisons with Si(111) and Si(001)

AbstractIn this paper, we report on the growth of AlGaN/GaN based heterostructure on Si(110) substrates by ammonia source molecular beam epitaxy. The structural, optical and electrical properties of such heterostructure are assessed and compared with the ones obtained on Si(111) and Si(001). The quality of the structure on Si(110) is quite similar to the one obtained on Si(111) and better than the one obtained on Si(001). A two‐dimensional electron gas is formed at the Al0.3Ga0.7N/GaN interface with a sheet carrier density of 9.6×1012 cm–2 and a mobility of 1980 cm2/V.s. at room temperature. Preliminary results concerning high electron mobility transistor static characteristics are presented. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

The critical role of growth temperature on the structural and electrical properties of AlGaN/GaN high electron mobility transistor heterostructures grown on Si(111)

This work is dedicated to the study of the growth by ammonia source molecular beam epitaxy of AlxGa1−xN/GaN high electron mobility transistors on (111) oriented silicon substrates. The effect of growth conditions on the structural and electrical properties of the heterostructures was investigated. It is shown that even a slight variation in the growth temperature of the thick GaN buffer on AlN/GaN stress mitigating layers has a drastic influence on these properties via a counterintuitive effect on the dislocation density. Both in situ curvature measurements and ex situ transmission electron microscopy and x-ray diffraction experiments indicate that the relaxation rate of the lattice mismatch stress increases with the growth temperature but finally results in a higher dislocations density. Furthermore, a general trend appears between the final wafer curvature at room temperature and the threading dislocation density. Finally, the influence of the dislocation density on the GaN buffer insulating properties and the two-dimensional electron gas transport properties at the AlxGa1−xN/GaN interface is discussed.

Anomalous Hall Effect in Gd-implanted Wurtzite AlxGa1-xN High Electron Mobility Transistor Structures

AbstractAlxGa1-xN/GaN high electron mobility transistor (HEMT) structures grown by ammonia-source molecular beam epitaxy (MBE) are focused-ion-beam implanted with 300 keV Gd-ions at room temperature. The two-dimensional electron gas (2DEG) of these HEMT structures is located 27 nm underneath the sample surface. At 4.2 K, current-voltage characteristics across implanted rectangles show that the structures remain conducting up to a Gd-dose of 1×1012cm-2. Anomalous Hall effect (AHE) is observed at T = 4.2 K for structures implanted with Gd, whose dose is 3×1011cm-2. Measurements of AHE in the wide temperature range from 2.4 K to 300 K show that the magnetic ordering temperature of these structures is around 100 K. Therefore, these Gd-implanted HEMT structures containing the still conducting 2DEG, which is now embedded in a ferromagnetic semiconductor, open the possibility to polarize the electron spins.

Growth and optical properties of AlN homoepitaxial layers grown by ammonia-source molecular beam epitaxy

We have performed the homoepitaxial growth of high-crystalline quality Aluminium nitride (AlN) epilayers by the ammonia-gas source (GS) molecular-beam epitaxy method using the hydride vapor-phase epitaxy (HVPE) grown AlN thin layers as substrates. Surface morphologies and step-bunching structures of the homoepitaxially grown AlN epilayers were evaluated using in situ reflection high-energy electron diffraction (RHEED) patterns and scanning probe microscopy. It is noted that the step height of several monolayers was achieved on the surface of homoepitaxial layers. The homoepitaxial AlN thin films had the same or improved crystalline quality compared with the HVPE-grown AlN layers from X-ray rocking curve measurements, and its optical properties were investigated using cathodoluminescence measurements. Excitonic emission, which originates from the A free-exciton transition, was clearly observed in the present high-quality homoepitaxial AlN epilayers.

Layer quality and 2DEG behavior in AlGaN/GaN HEMTs grown by Molecular Beam Epitaxy

In this work AlGaN/GaN high electron mobility transistors have been grown by ammonia source molecular beam epitaxy on Silicon (111), Silicon Carbide and GaN templates on Sapphire. Both the structural and the electrical properties of these layers have been studied in order to determine the impact of substrate choice and buffer layer on active layer quality. Furthermore, an intercalated AlN layer grown on a GaN template is shown to enhance the insulating properties of the buffer. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Structural and electrical properties of AlGaN/GaN HEMTs grown by MBE on SiC, Si(1 1 1) and GaN templates

In this work, AlGaN/GaN high electron mobility transistors have been grown by ammonia source molecular beam epitaxy (MBE) on silicon (1 1 1), silicon carbide and GaN templates on sapphire. The structural and electrical properties of these layers have been studied in order to determine the impact of substrate choice and buffer layer on active layer quality. Furthermore, an intercalated AlN layer grown on a GaN template is shown to enhance the insulating properties of the buffer.

Magnetic and optical properties of GaMnN grown by ammonia-source molecular-beam epitaxy

Abstract Diluted magnetic semiconductor GaMnN layers were grown on sapphire substrates by ammonia-source molecular-beam epitaxy. Phase-separation in a sample with large Mn content was confirmed by X-ray diffraction and Raman scattering measurements. Two distinct regions were observed in the magnetization versus temperature curves for both phase-separated and non-phase-separated samples. The samples exhibited ferromagnetic characteristics at high temperatures and paramagnetic characteristics at low temperatures, while the phase-separated sample showed the strongest ferromagnetic character. It is considered that the non-phase-separated GaMnN is primarily paramagnetic and that the phase-separated GaMnN is dominated by the ferromagnetism of Mn-based compounds at above 50 K. Strong photoluminescence emission peaking at 3.35 eV was observed in the non-phase-separated samples, attributable to band-to-band-like transition in GaMnN. The results will enable us to fabricate novel devices with magnetic and light-emitting functions.

Growth and Characterization of Er‐Doped GaN

Single crystalline Er-doped GaN was grown by ammonia source molecular beam epitaxy, and luminescence properties, structural properties were studied. It was found that the intensity of the luminescence in green spectral region from Er-doped GaN is two orders of magnitude stronger than that of Tb-doped GaN, which shows luminescence in green spectral region as well, and that the coordination symmetry of N around Er in GaN was lower than that of Tb. The lower coordination symmetry may be one of the reasons for the improved luminescence of Er-doped GaN.

Ammonia Source MBE Growth of Polycrystalline GaN p–n Junction

We study the ammonia source molecular beam epitaxy growth of polycrystalline GaN on quartz glass substrates, and fabricate p-n diodes. Using an ammonia source, the grain size of polycrystalline GaN becomes larger than that of the ECR source growth and PL intensity is much stronger. Undoped polycrystalline GaN shows high resistivty. The n-type and p-type polycrystalline GaN layers are obtained by Si and Mg dopants, respectively. Carrier concentrations obtained are 2.2 × 10 -17 to 8.8 x 10 -17 cm -3 for n-type layers and 7.1 x 10 -17 cm -3 for p-type layers. We fabricate polycrystalline GaN p-n junction and confirm the rectifying characteristics.

Ammonia Source MBE Growth of Polycrystalline GaN p-n Junction

We study the ammonia source molecular beam epitaxy growth of polycrystalline GaN on quartz glass substrates, and fabricate p-n diodes. Using an ammonia source, the grain size of polycrystalline GaN becomes larger than that of the ECR source growth and PL intensity is much stronger. Undoped polycrystalline GaN shows high resistivty. The n-type and p-type polycrystalline GaN layers are obtained by Si and Mg dopants, respectively. Carrier concentrations obtained are 2.2 × 10 -17 to 8.8 x 10 -17 cm -3 for n-type layers and 7.1 x 10 -17 cm -3 for p-type layers. We fabricate polycrystalline GaN p-n junction and confirm the rectifying characteristics.