Growth Temperature Of Buffer Layer Research Articles

Two-step growth of β-Ga2O3 on c-plane sapphire using MOCVD for solar-blind photodetector

In this work, a two-step metal organic chemical vapor deposition (MOCVD) method was applied for growing β-Ga2O3 film on c-plane sapphire. Optimized buffer layer growth temperature (T B) was found at 700 °C and the β-Ga2O3 film with full width at half maximum (FWHM) of 0.66° was achieved. A metal−semiconductor−metal (MSM) solar-blind photodetector (PD) was fabricated based on the β-Ga2O3 film. Ultrahigh responsivity of 1422 A/W @ 254 nm and photo-to-dark current ratio (PDCR) of 106 at 10 V bias were obtained. The detectivity of 2.5 × 1015 Jones proved that the photodetector has outstanding performance in detecting weak signals. Moreover, the photodetector exhibited superior wavelength selectivity with rejection ratio (R 250 nm/R 400 nm) of 105. These results indicate that the two-step method is a promising approach for preparation of high-quality β-Ga2O3 films for high-performance solar-blind photodetectors.

Improving crystal quality of β-phase MgGaO thin films by using low-temperature homo-buffer layer

Ultra-wide bandgap (UWBG) semiconductors are promising for many applications, such as power electronics and deep-ultraviolet photonics. In this research, UWBG β-phase magnesium gallium oxide (MgGaO) thin films with a bandgap of 5.1 eV were grown using low-temperature homo-buffer layers in a plasma-assisted molecular beam epitaxy system. The role of the growth temperature and thickness of low-temperature buffer layer on the quality of the active layer was studied using x-ray diffraction and transmission electron microscopy and by analyzing the properties of metal–semiconductor–metal photodetector devices based on these films. It is found that lower buffer growth temperature at 300 °C leads to higher crystal quality of active layer. For the same low buffer growth temperature, different crystal quality in the active layer is attained with different buffer layer thickness. A buffer layer thickness at 40 nm has the best active layer quality with the highest photo current under 265 nm illumination and long decay time as a result of reduced recombination of photo-generated carriers through fewer defects in the active layer.

Effect of buffer layer and substrate growth temperature on the microstructural evolution of hexagonal boron nitride thin films

Hexagonal boron nitride (hBN) thin films have excellent optical, electrical, and corrosion resistance properties that can enable a wide range of applications. The current study explores pulsed laser deposition technique for synthesizing hBN thin films. The microstructure, mechanical, and wetting properties of hBN thin films were analyzed as a function of substrate growth temperature (25 °C, 300 °C, 500 °C, and 800 °C) and buffer layer addition (Cu or Ti). The microstructure of hBN thin films was found to be influenced by the deposition temperature. This study revealed that the layered growth (for samples deposited at 25 °C) and layer plus island growth (for samples deposited at ≥300 °C) to be the primary growth modes of the thin films regardless of the buffer layer. The roughness of hBN thin films with the Cu buffer layer, in general, increased with the increase in deposition temperature, whereas no significant differences in roughness were observed for films deposited on Si and Ti buffer layer. Grazing Incidence X-ray diffraction results showed the presence of hexagonal close packed crystal structure for all the deposited thin films. These results were corroborated with Raman spectroscopy. The hBN thin films exhibited the hardness and modulus values of ~10–14 GPa and ~120–180 GPa, respectively. No considerable differences in mechanical properties were observed for hBN thin films deposited at various temperatures except for the films deposited with the Cu buffer layer, which showed lower mechanical properties. The wettability of hBN thin films was analyzed using contact angle measurements. The wettability was found to be directly influenced by the surface roughness of hBN thin films. Characterization of hBN thin films indicates that the deposition temperature and buffer layer addition had an influence on the growth and microstructural evolution of hBN thin films.

Molecular beam epitaxy growth and characterization of AlGaN epilayers in nitrogen-rich condition on Si substrate

In this work, we investigate the molecular beam epitaxy growth and characterization of aluminum gallium nitride (AlGaN) epilayers in nitrogen (N)-rich condition on silicon using an aluminum nitride (AlN) buffer layer on a nanowire template. It is found that the growth condition of the AlN buffer layer plays an important role on the surface morphology of the AlGaN epilayers. Under the optimized growth temperature of the AlN buffer layer, a relatively smooth AlGaN epilayer can be formed, with a root-mean-square roughness of around 1.8 nm, comparable to the typical III-nitride thin films grown in N-rich conditions by molecular beam epitaxy. The epilayer is further confirmed to be N-polar from both the reflection high-energy electron diffraction 3 × 3 reconstruction and potassium hydroxide etching experiments.

Effect of nitrogen gas flow and growth temperature on extension of GaN layer on Si* *Project supported by the National Key Research and Development Program of China (Grant No. 2017YFB0402900) and the National Natural Sciences Foundation of China (Grant No. 62074144).

The effect of nitrogen flow and growth temperature on extension of GaN on Si substrate has been studied. By increasing the nitrogen flow whose outlet is located in the center of the MOCVD (metal–organic chemical vapor deposition) gas/particle screening flange and by increasing the growth temperature of HT-AlN and AlGaN buffer layers near the primary flat of the wafer, the GaN layer has extended more adequately on Si substrate. In the meantime, the surface morphology has been greatly improved. Both the AlN and GaN crystal quality uniformity has been improved. X-ray diffraction results showed that the GaN (0002) XRD FWHMs (full width at half maximum) decreased from 579 arcsec∼ 1655 arcsec to around 420 arcsec.

Direct Heteroepitaxy and Selective Area Growth of GaP and GaAs on Si by Hydride Vapor Phase Epitaxy

Direct heteroepitaxy and selective area growth (SAG) of GaP and GaAs on Si(100) and Si(111) are implemented by low‐pressure hydride vapor phase epitaxy (LP‐HVPE), which are facilitated by buffer layers grown at 410–490 °C with reactive gas mixing directly above Si substrates. High‐density islands observed on GaP buffer layers on Si result in rough morphology and defect formation in the subsequent GaP layers grown at 715 °C. The impact of growth temperature of GaAs buffer layers on the crystal quality of GaAs/Si is studied. A decreased nucleation temperature significantly improves the morphology and crystalline quality of the overall GaAs growth on Si. It is observed that Si(111) substrates are favorable for both GaP and GaAs growths in comparison with Si(100). In SAGs of GaP/Si and GaAs/Si, the high selectivity innate to HVPE is maintained in the used unconventional growth regime. The spatially resolved photoluminescence mapping reveals the material quality of GaAs/Si is enhanced by defect filtering by SAG. The outcomes of this work will pave the way of III–V/Si integration realized by cost‐effective HVPE for photonic device applications.

Optimization of the growth of GaN epitaxial layers in an indigenously developed MOVPE system

Growth of GaN epitaxial layers is optimized in an indigenously developed nitride metal organic vapour phase epitaxy (MOVPE) system. The motivation of present work is to develop a simple MOVPE reactor which is though affordable but can deliver GaN epilayers of desired quality. The design and fabrication methodology of nitride MOVPE system is briefly discussed. MOVPE growth of GaN epilayers is carried out through a two-step growth process where influence of the growth parameters of low temperature buffer layer on the crystalline properties of high temperature GaN epilayer is discussed in detail. Optimum values of the growth temperature, annealing duration and thickness of GaN buffer layer are achieved. High resolution X-ray diffraction measurements (HRXRD) confirmed that the crystalline quality of GaN epitaxial layers is reasonable. A good surface morphology of the optimized sample is strongly corroborated by the results obtained from photoluminescence (PL) and HRXRD techniques. Usefulness of a systematic Williamson-Hall analysis in the optimization of growth of GaN epitaxial layers is demonstrated where a high value of lateral coherence length of GaN buffer layer is found to be a key parameter. Such an optimization process leads to the good crystalline quality of GaN epitaxial layers with low dislocation density. It is found that the high temperature GaN epilayers grown on the optimized GaN buffer layer are compressively stressed which is also revealed by the PL measurements.

Effect of V/III ratio on the surface morphologies of N-polar GaN films grown on offcut sapphire substrates

We investigated the influence of the V/III ratio on the surface morphologies of N-polar GaN epilayers during the stage of high-temperature (HT) GaN growth. The epilayers were grown on 4°-offcut sapphire substrates by metal-organic vapor phase epitaxy. We observed prominent undulations on the GaN surface when a low V/III ratio was used, and ridged hillocks on the GaN surface when a high V/III ratio was used. With the V/III ratio increased from 128 to 2237, the density of ridged hillocks increased but the surface roughness was significantly reduced from 13.8 nm to 1.7 nm in 25 × 25 μm2 AFM images. The results differ from the existing reports in which a smoother N-polar GaN surface morphology was usually obtained with a lower V/III ratio. Non-uniform island formation in the initial growth of HT-GaN and enhanced step-bunching effect under a low V/III ratio were blamed for the large surface roughness of the N-polar GaN film. The increasing density of ridged hillocks on the N-polar surface grown under a high V/III ratio was attributed to the reduced diffusion rate of Ga adatoms due to excessive N. Completely hillock-free smooth N-polar GaN surfaces were achieved by further increasing the growth temperature of the GaN buffer layer.

Influence of surface nitridation and an AlN buffer layer on the growth of GaN nanostructures on a flexible Ti metal foil using laser molecular beam epitaxy

GaN nanorods (NRs) and hollow nanocolumns (HNCs) were grown on flexible Ti foils using laser-assisted molecular beam epitaxy at a growth temperature of 700 °C. The shape, size and density of the GaN nanostructures were tuned by surface nitridation and AlN buffer layer growth temperature on a Ti foil. Sparse (∼ 5.5 × 108 cm−2) GaN NRs were obtained on the bare surface whereas dense (∼3.47 × 109 cm−2) GaN NRs were grown on the nitridated Ti foil. The shape of the GaN changed from NRs to HNCs by introducing an AlN buffer layer on nitridated Ti foil. Raman spectroscopy showed the grown GaN nanostructures have a wurtzite crystal structure. Room-temperature photoluminescence spectroscopy measurements show that the GaN nanostructures possess an intensive near band edge emission at ∼3.42 eV with a negligible defect-related peak. The growth of tunable GaN nanostructures on flexible metal foils is attractive for flexible optoelectronics and sensor devices.

Structural Properties of Lattice-Matched InGaPN on GaAs (001)

Structural properties of lattice-matched InGaPN on GaAs (001) have comprehensively investigated by high resolution X-ray diffraction (HRXRD), Raman spectroscopy, and atomic force microscopy (AFM). The InGaPN layers were grown by metal organics vapor phase epitaxy (MOVPE). To obtain the lattice-matched InGaPN on GaAs, flow rates of trimethylindium (TMIn), trimethylgallium (TMGa) were kept, respectively, at 14.7 and 8.6 /umol/min. On the other hand, the N content optimized by varying the flow rate of dimethyhydrazine (DMHy, N precursor) was controlled at 300 /umol/min. With a combination of HRXRD and Raman scattering measurements, the In and N contents are estimated to be 55.8 and 0.9 at%, respectively. The lattice-mismatch lower than 0.47%, which corresponds to the lattice-matching condition, was confirmed for all the layers. The rapid thermal annealing (RTA) process was performed to improvement the crystalline quality of InGaPN layers. The annealing temperature was fixed at 650∘C, which is an optimum growth temperature of a GaAs buffer layer. The annealing time was varied in a range of 30 to 180 s to verify a composition uniformity. With increasing the annealing time up to 120 s, the In and N contents were slightly increased. The AFM-root mean square (RMS) roughness of the InGaPN surface was observed to be reduced. For higher annealing times, the N content was dramatically reduced, whereas the In content was still remained. Moreover, the RMS roughness was observed to be increased. RTA at 650∘C for 120 s demonstrated a significant improvement of structural properties of the lattice-matched InGaPN layers on GaAs (001).

Effects of Buffer Layer Growth Temperature on Micro-Structures in the Cubic GaN Films Grown on GaAs (001) Substrates by MOVPE

c-GaN films on GaAs (001) substrates were investigated using TEM to verify effects of buffer layer growth temperature on micro-structures. Growth temperature of the GaN buffer layer was varied in a range of 550 to 600°C and GaN film was grown at high temperature (∼900°C). For GaN buffer layer at 550°C, the plan-view TEM micrographs of c-GaN films show high density of stacking faults (SFs) and dislocations. At the GaN/GaAs interface, the electron diffraction (ED) pattern demonstrated different type of single diffraction spots which include the high intensity of streaking. This results indicated that the high density of SFs become dense into hexagonal phase single crystal. For 575°C GaN buffer layer, the wide SFs are observed that these broad lines are not expanding to the GaN surface and the dislocations are less found than the other temperature. Moreover, cross-sectional TEM micrographs and the ED pattern at interface show pyramid like structure and less intensity of the steak lines, respectively. There are no diffraction spots related to hexagonal structure. For 600°C GaN buffer layer, there are the steaking of diffraction spots which represent hexagonal phase inclusions at interface. V-shape voids defects are penetrating in the GaAs surface which were caused the thermal decomposition of As. Our results indicated that, the high quality of GaN film with cubic phase purity grown on GaAs (001) are achieved from the optimum growth temperature GaN buffer layer of 575°C.

Effect of a ZnO buffer layer on structural and electrical properties of ZnO:Al,P thin films grown by RF magnetron sputtering

Abstract Structural and electrical properties of ZnO:Al 0.01 P 0.04 thin films were investigated with respect to the growth temperature of the ZnO buffer layers deposited by RF magnetron sputtering. The ZnO buffer layers on c -plane sapphires showed three different types of in-plane orientation relationships between ZnO and Al 2 O 3 at different growth temperatures: ZnO[10 1 0] // Al 2 O 3 [10 1 0] at 200 °C, a mixture of ZnO[10 1 0] // Al 2 O 3 [10 1 0] and ZnO[10 1 0] // Al 2 O 3 [11 2 0] at 300 °C, and ZnO[10 1 0] // Al 2 O 3 [11 2 0] at 600 °C. The in-plane orientation of the ZnO:Al 0.01 P 0.04 thin film followed the orientation of the ZnO buffer layer regardless of its growth temperature. The ZnO:Al 0.01 P 0.04 film grown on a ZnO buffer layer deposited at 600 °C had a carrier concentration of 1.18 × 10 16 cm −3 , mobility of 7.16 × 10° cm 2 /(V s), and resistivity of 7.36 × 10 1 Ω cm, indicating p -type characteristics.

Nitrogen-Polar (000 1 ¯ ) GaN Grown on c-Plane Sapphire with a High-Temperature AlN Buffer.

We demonstrate growing nitrogen-polar (N-polar) GaN epilayer on c-plane sapphire using a thin AlN buffer layer by metalorganic chemical vapor deposition. We have studied the influence of the AlN buffer layer on the polarity, crystalline quality, and surface morphology of the GaN epilayer and found that the growth temperature of the AlN buffer layer played a critical role in the growth of the GaN epilayer. The low growth temperature of the AlN buffer results in gallium-polar GaN. Even a nitridation process has been conducted. High growth temperature for an AlN buffer layer is required to achieve pure N-polarity, high crystalline quality, and smooth surface morphology for a GaN epilayer.

Investigation of GaSb/GaAs Quantum Dots Formation on Ge (001) Substrate and Effect of Anti-Phase Domains

ABSTRACTThe effects of GaAs anti-phase domains (APDs) on the growth of GaSb quantum dots (QDs) are investigated by molecular beam epitaxial growth of GaAs on Ge (001) substrate. Ge is a group-IV element and GaAs is a polar III-V compound semiconductor. Due to polar/non polar interface, GaAs APDs are formed. Initial formation of APD relates to a non-uniform growth of high index GaAs surfaces. However, due to high sticking coefficient of Sb atoms at low substrate growth temperature, GaSb QDs can be formed on the whole surface of the sample without any effects from APD boundary. The buffer layer growth temperature is one of the key roles to control the APDs formation. Therefore we tried to adjust the optimum conditions such as buffer layer thickness and growth temperature to get nearly flat sample surface with large APDs for high QDs density (∼ 8×109 dots/cm2). Low-temperature photoluminescence is conducted and GaSb QDs peak is observed at the energy range of 1.0 eV-1.3 eV.

Growth of High-Quality GaAs on Ge by Controlling the Thickness and Growth Temperature of Buffer Layer

High-quality GaAs thin films grown on miscut Ge substrates are crucial for GaAs-based devices on silicon. We investigate the effect of different thicknesses and temperatures of GaAs buffer layers on the crystal quality and surface morphology of GaAs on Ge by metal-organic chemical vapor deposition. Through high resolution x-ray diffraction measurements, it is demonstrated that the full width at half maximum for the GaAs epilayer (Ge substrate) peak could achieve 19.3 (11.0) arcsec. The value of etch pit density could be 4×104 cm−2. At the same time, GaAs surfaces with no pyramid-shaped pits are obtained when the buffer layer growth temperature is lower than 360°C, due to effective inhibition of initial nucleation at terraces of the Ge surface. In addition, it is shown that large island formation at the initial stage of epitaxial growth is a significant factor for the final rough surface and that this initial stage should be carefully controlled when a device quality GaAs surface is desired.

Optical properties of the nonpolar a-plane MgZnO films grown on a-GaN/r-sapphire templates by pulsed laser deposition

Nonpolar (112¯0)a-plane MgZnO films were grown on different a-GaN/r-sapphire templates by pulsed laser deposition (PLD), where the growth temperature of GaN buffer layers varied from 700 °C to 1000 °C. High-quality a-plane MgZnO epitaxial film was deposited on the optimized 1000 °C a-GaN/r-sapphire template. Temperature-dependent PL measurements of a-plane MgZnO films reveal an S-type temperature dependence of the excitonic recombination energy. It is resulted that the excitons are localized in alloy-induced potential fluctuations at low temperature and the room-temperature quantum efficiency is calculated to be 9.2%. An involvement of band-tail states in the radiative recombination was considered, and a quantitative description of the blue temperature-induced shift was obtained assuming a Gaussian shape of the band tail.

Carbon-Related Deep-Level Defects and Turn-On Recovery Characteristics in AlGaN/GaN Hetero-Structures

ABSTRACTWe have investigated on a relation between C-related deep-level defects and turn-on recovery characteristics in bulk regions of AlGaN/GaN hetero-structures containing various C concentrations, employing their Schottky barrier diodes. With decreasing the growth temperature of the GaN buffer layer, three specific deep-level defects located at ∼2.07, ∼2.75, and ∼3.23 eV below the conduction band were significantly enhanced probably due to the C impurity incorporation into the GaN buffer layer. Among them, the ∼2.75 and ∼3.23 eV levels are considered to be strongly responsible for the two-dimensional electron gas (2DEG) carrier trapping in the bulk regions of the hetero-structures, from their turn-on current recovery characteristics under various optical illuminations.

Towards controllable growth of self-assembled SiGe single and double quantum dot nanostructures

Fabrication of semiconductor single and double quantum dot (QD) nanostructures is of utmost importance due to their promising applications in the study of advanced cavity quantum electrodynamics, quantum optics and solid-state spin qubits. We present results about the controllable growth of self-assembled single and double SiGe QD arrays with an ultra-low areal density of 1 × 10(7) cm(-2) on nanohole-patterned Si substrates via molecular beam epitaxy. The two dots in a double QD (DQD) aligned along the elongation direction of the nanoholes and show unsymmetrical features in both size and composition due to the asymmetric nanohole profiles after Si buffer layer growth. The interdot spacing between the two dots in a DQD could well be adjusted by changing the elongation ratio of nanoholes. Moreover, whether a single or a double QD formed in a given nanohole was found to be determined by the growth temperature of the Si buffer layer, the reason of which is given by the calculation of the surface chemical potential around the nanoholes after the buffer layer growth.

Reduction of Dislocation Density in HVPE-Grown GaN Epilayers by Using In Situ-Etched Porous Templates

In this paper, a method was demonstrated to reduce the dislocation density of GaN film grown by hydride vapor phase epitaxy (HVPE) on an in situ selective hydrogen-etched GaN/sapphire template. The dislocations regions were etched by hydrogen to form cavities. The porous structure was formed on the GaN template grown by metal organic chemical vapor deposition after in situ hydrogen etching. The etching condition was optimized by modulating the etching temperature, pressure, and etching time. Two-step buffer layer growth and high temperature GaN film deposition were carried on the porous template. The growth parameters were optimized to keep the porous structure unfilled. The dislocations originally located in etched cavities could not propagate to the next layer grown by HVPE. Therefore, the dislocation density could be significantly reduced. High crystal quality of GaN is obtained with a low dislocation density. The full width at half-maximum FWHM of (002) is 35 arcs, and the FWHM of (102) is 48 arcs.

Structure and magnetic properties of γ′-Fe4N films grown on MgO-buffered Si (001)

Abstract γ′-Fe4N thin films were grown on MgO-buffered Si (1 0 0) by pulsed laser deposition technique. Different crystallographic orientations and in-plane magnetic anisotropies were achieved by varying the growth temperature of the MgO buffer layer. When the MgO buffer layer was grown at room temperature, the γ′-Fe4N film shows isotropic in-plane magnetic properties without obvious texture; while in-plane magnetic anisotropy was recorded for the γ′-Fe4N films deposited on a 600 °C-grown-MgO buffer due to the formation of a (1 0 0)-oriented biaxial texture. Such a difference in in-plane magnetic anisotropy is attributed to the epitaxial growth of γ′-Fe4N film on an MgO buffer with relaxed strain when the MgO layer was grown at a high temperature of 600 °C.