Low-pressure Metalorganic Chemical Vapor Deposition Research Articles

Electrical properties of unintentionally doped β-Ga2O3 (010) thin films grown by a low-pressure hot-wall metalorganic chemical vapor deposition

We investigated the electrical properties of unintentionally doped (UID) Ga2O3 (010) layers grown by low-pressure hot-wall metalorganic chemical vapor depositions from device characteristics of Schottky barrier diodes (SBDs) fabricated on them. Highly resistive properties of the UID Ga2O3 layers were confirmed from current–voltage characteristics. The specific on-resistance of the SBD with the most resistive UID Ga2O3 layer was 2.2 × 107 Ωcm2. Capacitance–voltage characteristics revealed that most of the SBDs had complete depletion of the UID layers at thermal equilibrium, indicating that their residual effective donor densities were less than 3.0 × 1013 cm−3.

Scalable growth of atomically thin MoS2 layers in a conventional MOCVD system using molybdenum dichloride dioxide as the molybdenum source

To bring atomically thin transition metal dichalcogenides (TMDs) to practical application, a highly reproducible process to grow them over a large scale is indispensable. Here, we develop a carbon-free reproducible route for the scalable growth of high-quality monolayer MoS2 by selecting molybdenum dichloride dioxide (MoO2Cl2) as the Mo source and integrating the precursor with a standard low-pressure cold-wall metalorganic chemical vapor deposition (MOCVD) system. Specifically, combined with H2S as the sulfur source and using catalytic Dragontrail glass (DT-glass) as the main substrate, we investigate the effect of MoO2Cl2 flux, temperature, and deposition time on the growth, confirming MoO2Cl2 with reasonably high vapor pressure is well compatible with the MOCVD system that enables precise control of sources for uniform nucleation and growth of MoS2 over a large area. We successfully demonstrate the growth of carbon-free MoS2 monolayers on DT-glass with decent crystalline, optical, and electrical properties. Additionally, the initial attempts also manifest that the proposed strategy could be generalized for growing ultrathin MoS2 on other technologically important substrates, such as SiO2/Si and quartz, exhibiting superior optical quality and wafer-scale uniformity. This work provides a new avenue for the large-scale production of high-quality MoS2 monolayers and facilitates their use in practical applications.

High‐Performance Thin‐Film VCSELs Integrated with a Copper‐Plated Heatsink

AbstractHigh‐performance continuous‐wave (CW) vertical‐cavity surface‐emitting lasers (VCSELs) rely on efficient thermal management for which top‐emitting 930 nm thin‐film VCSELs are integrated with a copper‐plated heatsink by using a double‐transfer technique, exhibiting the low‐power consumption, high‐power, and temperature‐stable VCSEL operation. In this study, the top‐emitting 930 nm thin‐film VCSEL structures, including the highly n‐doped GaAs ohmic and lattice‐matched InGaP etch‐stop layers, are epitaxially grown via a low‐pressure metalorganic chemical vapor deposition (LP‐MOCVD) system. The electrical and optical properties of the substrate‐removal thin‐film VCSELs are investigated under CW operation, compared to those of the bulk‐type VCSELs onto the n‐GaAs substrates. The differential series resistance (85.92 Ω) of the thin‐film VCSEL is 9.16% lower than 94.59 Ω of the bulk‐type VCSEL onto the n‐GaAs substrates. The thermal resistance (607 K W−1) of the thin‐film VCSEL is 46.33% lower than 1131 K W−1of the bulk‐type VCSEL, by which the maximum peak power (11.70 mW) of the thin‐film VCSEL at 24 mA is 12.07% higher than 10.44 mW of the bulk‐type VCSEL at 22.40 mA under room temperature (25 °C).

Carbon and silicon background impurity control in undoped GaN layers grown with trimethylgallium and triethylgallium via metalorganic chemical vapor deposition

The unintentional impurity incorporation in GaN epitaxial layers impacts the electrical conductivity and optical properties of the films grown by metalorganic chemical vapor deposition (MOCVD). It is critical to control impurity-related states for device structure development. The aim of this work is to contribute to the understanding of the reasons for the presence of certain background impurities. In this paper, the unintentional impurity incorporation of carbon, hydrogen, oxygen, and silicon in undoped (u-) GaN films grown by low-pressure MOCVD were studied. Background impurity concentrations were evaluated by secondary ion mass spectroscopy (SIMS) to optimize growth parameters including V/III ratio, growth temperature (Tg), growth pressure (Pg), and gallium (Ga) precursors of trimethylgallium (TMG) or triethylgallium (TEG). Unintentional [C] and [Si] incorporations are found to be highly dependent on the growth parameters. For the same growth conditions, u-GaN films grown with a TEG precursor exhibited a lower background concentration of C compared to that of GaN grown with TMG. However, the lowest background [C] achieved was grown with TMG using optimized conditions and exhibited [C] < 4 × 1015 cm−3 which was at the detection limit of the SIMS measurement. These results were measured for a u-GaN layer grown with TMG at 200 Torr, 1030 °C, and a V/III of 3700. The lowest background [Si] of 4 × 1015 cm−3 was achieved by growing with TMG at 200 Torr, 1000 °C, and V/III of 650.

Effect of different substrates on material properties of cubic GaN thin films grown by LP-MOCVD method

The III-nitride cubic phase are promising materials in photovoltaics and other optoelectronic devices due to their favorable material properties. This research work presents the growth of cubic gallium nitride (c-GaN) thin films on two different substrate gallium phosphide (GaP) and gallium arsenide (GaAs) substrates using the low-pressure metal–organic chemical vapor deposition (LP-MOCVD) technique. The growth conditions are modified for each substrate to obtain c-GaN epitaxial films with good crystalline quality. Stress values for c-GaN epitaxial layers 0.62 GPa and 1.24 GPa were calculated using X-ray diffraction measurements for c-GaN grown on GaP and GaAs substrates, respectively. The stress state calculated by XRD proved that in both cases, c-GaN on GaP and on GaAs substrates, they was compressed layers. Raman measurements showed two peaks for c-GaN at 555 cm−1 (TO) and 745 cm−1 (LO) modes for c-GaN grown on GaP. For GaAs, only observed 555 cm−1 (TO) mode. It obtained the formation of c-GaN epitaxial films on both substrates. The surface morphology and the quality of the films depend on the type of substrates, compact layers with better crystalline quality are observed in the samples grown in GaP than GaAs substrate. Band gap (Eg) of GaN was obtained with approximate values of 380 nm for c-GaN of both substrates, which is where the Eg of c-GaN is found.

Sodium β-Diketonate Glyme Adducts as Precursors for Fluoride Phases: Synthesis, Characterization and Functional Validation.

Very few sodium complexes are available as precursors for the syntheses of sodium-based nanostructured materials. Herein, the diglyme, triglyme, and tetraglyme (CH3O(CH2CH2O)nCH3, n = 2–4) adducts of sodium hexafluoroacetylacetonate were synthesized in a single-step reaction and characterized by IR spectroscopy, 1H, and 13C NMR. Single-crystal X-ray diffraction studies provide evidence of the formation of the ionic oligomeric structure [Na4(hfa)6]2−•2[Na(diglyme2]+ when the diglyme is coordinated, while a mononuclear seven-coordinated complex Na(hfa)•tetraglyme is formed with the tetraglyme. Reaction with the monoglyme (CH3OCH2CH2OCH3) does not occur, and the unadducted polymeric structure [Na(hfa)]n forms, while the triglyme gives rise to a liquid adduct, Na(hfa)•triglyme•H2O. Thermal analysis data reveal great potentialities for their applications as precursors in metalorganic chemical vapor deposition (MOCVD) and sol-gel processes. As a proof-of-concept, the Na(hfa)•tetraglyme adduct was successfully applied to both the low-pressure MOCVD and the sol-gel/spin-coating synthesis of NaF films.

Top-emitting 940-nm thin-film VCSELs transferred onto aluminum heatsinks

Thin-film vertical cavity surface emitting lasers (VCSELs) mounted onto heatsinks open up the way toward low-power consumption and high-power operation, enabling them to be widely used for energy saving high-speed optical data communication and three-dimensional sensor applications. There are two conventional VCSEL polarity structures: p-on-n and n-on-p polarity. The former is more preferably used owing to the reduced series resistance of n-type bottom distributed Bragg reflection (DBR) as well as the lower defect densities of n-type GaAs substrates. In this study, the p-on-n structures of thin-film VCSELs, including an etch stop layer and a highly n-doped GaAs ohmic layer, were epitaxially grown in upright order by using low-pressure metalorganic chemical vapor deposition (LP-MOCVD). The p-on-n structures of thin-film VCSELs were transferred onto an aluminum heatsink via a double-transfer technique, allowing the top-emitting thin-film VCSELs to keep the p-on-n polarity with the removal of the GaAs substrate. The threshold current (Ith) and voltage (Vth) of the fabricated top-emitting thin-film VCSELs were 1 mA and 2.8 V, respectively. The optical power was 7.7 mW at a rollover point of 16.1 mA.

Ge Solar Cells with Micro-Rod Arrays: Structural and Optical Properties.

Ge single-junction solar cell structures are grown on micro-patterned Ge substrates using lowpressure metalorganic chemical vapor deposition. 300 nm high micro-rod arrays are formed on the p-Ge substrates using photolithography and dry etching techniques. The micro-rod arrays are designed with rod diameter varying from 5 to 15 μm and arranged in a hexagonal geometry with rod spacing varying from 2 to 12 μm. Ge p-n junction structures are fabricated by phosphorus atomic diffusion process on the micro-patterned Ge substrates. 100 nm thick InGaP window and 300 nm thick GaAs cap layers are grown to reduce the surface recombination and the ohmic contact resistivity, respectively. Our results indicate that the micro-rod structures improve the performance of the Ge solar cells. An improvement of 16.1% in the photocurrent of the Ge micro-rod solar cell is observed compared to that of a reference Ge solar cell with planar surface. The improvement in the short circuit current density can be attributed to the light trapping effect, enlarged p-n junction area, and enhanced carrier collection efficiency. As a result, the conversion efficiency of the Ge solar cell with micro-rod arrays (5 μm diameter, 2 μm spacing, and 300 nm height) is improved from 3.84 to 4.78% under 1 sun AM 1.5G conditions.

AlGaN/AlN/SiC Metal-Oxide-Semiconductor Heterostructure Field-Effect Transistors with Al2O3 Gate-Oxide and Step-Graded AlGaN Channel

Al0.75Ga0.25N/n-AlxGa1-xN/Al0.75Ga0.25N/AlN metal-oxide-semiconductor heterostructure field-effect transistors (MOS-HFETs), grown on a SiC substrate, with step-graded Si-doped (n = 3 × 1018 cm-3) widegap AlxGa1-xN channel and Al2O3 gate-dielectric are investigated. Increased Al-compositions with x = 0.25, 0.5, and 0.75 towards the buffer were devised in the composite widegap channel. The high-k Al2O3 dielectric/passivation layer was grown by using a non-vacuum ultrasonic spray pyrolysis deposition (USPD) method. Experimental comparisons were made with respect to a conventional Schottky-gate HFET.The epitaxial structure of the studied Al2O3-dielectric Al0.75Ga0.25N/n-AlxGa1-xN/Al0.75Ga0.25N/AlN MOS-HFET (sample A) and Schottky-gate HFET (sample B). Both devices have the identical epitaxial structure grown on a SiC substrate by using a low-pressure metal-organic chemical vapor deposition (LP-MOCVD) system. The layer structure includes an undoped AlN buffer, a 20-nm undoped Al0.75Ga0.25N barrier, a 150-nm step-graded Si-doped (n = 3 × 1018 cm-3) AlxGa1-xN channel (x = 0.25, 0.5, and 0.75), and a 20-nm undoped Al0.75Ga0.25N barrier. Standard photolithography and lift-off techniques were used for device processing. For sample B, mesa etching was performed with respect to a 100-nm thick Ni barrier by using an inductively coupled-plasma reactive ion etcher (ICP-RIE). Flow rates were tuned and set at 10 sccm and 20 sccm for the mixed etching gases of BCl3 and Cl2, respectively. The 20-nm undoped Al0.75Ga0.25N barrier was etched away before deposition of source/drain electrodes. Ti (10 nm)/Al (50 nm)/Ni (10 nm)/Au (50 nm) were evaporated. The source/drain ohmic contacts were formed by annealing the sample for 25 seconds at 900°C by using a rapid thermal annealing (RTA) system (ULVAC MILA-5000). Then, 30-nm thick Al2O3 layer was deposited on the Al0.75Ga0.25N barrier by using the USPD technique. Finally, gate electrode of Ni (100 nm)/Au (50 nm) was evaporated after gate photolithography. As for sample A, the gate electrode was formed directly on the surface of Al0.75Ga0.25N barrier without oxide deposition.Improved device performance of the present MOS-HFET design have been obtained, including maximum drain-source current density (IDS, max ) of 130.1 A/mm at VGS = 10 V and VDS = 20 V, IDS at VGS = 0 V (IDSS0 ) of 83.1 mA/mm, on/off-current ratio (Ion /Ioff ) of 1.4 × 107, maximum extrinsic transconductance (gm, max ) of 11.8 mS/mm, two-terminal off-state gate-drain breakdown voltage (BVGD ) of -404 V, and three-terminal on-state drain-source breakdown voltage (BVDS ) of 364 V at 300 K. The present MOS-HFET design has also shown high spectral responsivity (SR) of 737 A/W under 250-nm deep-UV radiation at 300 K.

Volatile trinuclear heterometallic beta-diketonates: Structure and thermal properties related to the chemical vapor deposition of composite thin films

A series of new trinuclear molecular complexes [PbL12{Co(hfa)2}2] (1), [PbL12{Ni(hfa)2}2] (2), [PbL22{Co(hfa)2}2] (3), [PbL22{Ni(hfa)2}2] (4), [PbL32{Co(hfa)2}2] (5), [PbL32{Ni(hfa)2}2] (6), where L = methoxy-substituted β-diketonate RCOCHCOC(CH3)2OCH3, L1: R = CH3, L2: R = CF3, L3: R = C(CH3)3; hfa = hexafluoroacetylacetonate, were synthesized. Crystal structures were determined by single crystal X-ray analysis. Volatility and thermal stability of the obtained compounds were studied by thermal gravimetric analysis, vacuum sublimation and by mass transfer in helium flow. It was established that all the obtained heterometallic complexes are volatile and can be sublimed in vacuum without dissociation into monometallic complexes. Compounds 3–6 were examined as SSP (single source precursors) in conventional low pressure MOCVD (Metalorganic Chemical Vapor Deposition) of inorganic films on Si(100) substrates. Influence of precursor composition on their structure and thermal properties as well as on the composition of the deposited inorganic films are discussed.

Improved Performance of Ge Solar Cell Using Graphene Quantum Dots.

We investigated the effect of graphene quantum dots (GQDs) on performance of single-junction Ge solar cell grown on (100) substrate by low pressure metalorganic chemical vapor deposition (LP-MOCVD). Isobutylgermane (IBuGe) is used as a Ge precursor for the Ge solar cell growth. By employing GQDs, the power conversion efficiency of the Ge solar cell is improved up to 3.90% (Voc of 0.22 V, Jsc of 28.52 mA/cm², and FF of 63.83%) through effective photon management as compared to bare Ge solar cells of 3.24% under AM 1.5G illumination.

Effects of Thermal Annealing on Optical Properties of Be-Implanted GaN Thin Films by Spectroscopic Ellipsometry

Wide bandgap III-V compounds are the key materials for the fabrication of short-wavelength optical devices and have important applications in optical displays, optical storage devices and optical communication systems. Herein, the variable-angle spectroscopic ellipsometry (SE) measurements are performed to investigate the thickness and optical properties of beryllium-implanted gallium nitride thin films that have been deposited on (0001) sapphire substrates by using low-pressure metalorganic chemical vapor deposition (LPMOCVD). The film layer details are described by using Parametric Semiconductor oscillators and Gaussian oscillators in the wavelength range of 200–1600 nm. The thickness, refractive indices and extinction coefficients of the Be-implanted films are determined at room temperature. Analysis of the absorption coefficient shows that the optical absorption edge of Be-implanted films changes from 3.328 eV to 3.083 eV in the temperature range of 300–850 K. With the variable temperature, Eg is demonstrated to follow the formula of Varshni. A dual-beam ultraviolet–visible spectrophotometer (UV–VIS) is used to study the crystal quality of samples, indicating that the quality of rapid thermal annealing (RTA) sample is better than that unannealed sample. By transport of ions in matter (TRIM) simulation and SE fitting the depths of Be implanted gallium nitride (GaN) films are estimated and in good agreement. The surface and cross-section morphologies are characterized by atomic force microscopy (AFM) and scanning electron microscope (SEM), respectively. The surface morphologies and thickness measurements of the samples show that RTA can improve crystal quality, while increasing the thickness of the surface roughness layer due to partial surface decomposition in the process of thermal annealing.

AlGaN-based UV-C distributed Bragg reflector with a λ-cavity designed for an external cavity structure electron-beam-pumped VCSEL

The external cavity structure electron-beam-pumped (EB-pumped) vertical cavity surface emitting laser (VCSEL) has an important demand for the distributed Bragg reflector (DBR) with an emission window at the working wavelength called λ-cavity. Herein, AlGaN-based UV-C band DBRs with λ-cavities around 280 nm are designed and investigated in detail, which have almost no been reported so far. The DBRs based on alternate stacked Al0.47Ga0.53N/AlN bilayers are in-situ grown by low-pressure metal-organic chemical vapor deposition (LP-MOCVD). Through a comprehensive protocol of structure optimization by theoretical simulation, epitaxial growth and in-depth characterization and analysis, a high-performance UV-C band DBR with a λ-cavity around 280 nm is successfully fabricated. The DBR presents a reflectivity as high as 81.3% at the λ-cavity, a maximum reflectivity of 89.8% at 282 nm and a stopband with a full-width at half-maximum (FWHM) of 24.7 nm, laying a foundation for developing the external cavity structure EB-pumped AlGaN-based UV-C VCSELs emerging as a promising alternative to the electrically pumped AlGaN-based UV-C lasers.

Long time aging effect on Be-implanted GaN epitaxial layer

Be-implanted GaN thin films grown by low-pressure Metalorganic Chemical Vapor Deposition (LP-MOCVD), the postimplantation rapid thermal annealing (RTA) samples and the postimplantation RTA samples after 18 years’ room temperature (RT) aging were investigated by Resonant Raman scattering (RRS). It was observed that the Resonant Raman scattering intensity is most enhanced in the 4th order A1 (LO) mode in the after aging sample rather than both the 4th and 5th order A1(LO) mode at different temperatures in the postimplantation RTA sample, which is attributed to a different prominent laser excited emission involved in the RRS processes in the sample before and after aging. A jump step of the intensities of RRS modes was observed at 170 K. Based on the temperature dependent and power dependent RRS spectra, we estimate quantitatively the properties of the optical emission participated in RRS processes below and above this temperature, with the assumption that the intensity of the RRS modes is linearly proportional to the intensity of the optical emission involved in it. We obtained the activation energy of 65 meV and 85 meV for two emissions, respectively, and confirmed both emissions are not band edge related emission with power density dependent RRS spectra. We proposed the dominant optical emission changed from band edge emission to dopant related emission after aging. This study provides an evidence of evolution of optical properties and microstructures in postimplantation RTA GaN epilayers over long time RT aging, which could be a benefit to studying reliability control of devices based on this material.

Quantifying competitive grain overgrowth in polycrystalline ZnO thin films

The grain size evolution of polycrystalline thin films, which form by competitive grain overgrowth as commonly interpreted using the van der Drift model, is understood to follow a power-law scaling of the average grain size d with film thickness h, i.e. d ∝ hα. While simulations have identified a growth exponent α = 0.4 for three-dimensional growth, previous experimental studies did not confirm this value, instead finding α values in the range of ∼0.5–0.7. Here we study competitive grain overgrowth using a system of ZnO thin films grown by low-pressure metal–organic chemical vapor deposition. We present quantitative data on the evolution of grain size and orientation across the thickness of thin films, obtained by automated crystal orientation mapping of “double-wedge” transmission electron microscopy samples. The data from a-textured ZnO films, grown under three different conditions, are compared against van der Drift model predictions of self-similarity of the grain size distribution and the power-law scaling. The results are further interpreted by comparing to simulations of faceted polycrystalline film growth, which we adapt to the ZnO system by including idiomorphic growth shapes with a six-fold symmetry and random or biased nuclei orientations. As well as showing the predicted self-similarity of grain size distributions during growth, for the first time our experimental data confirm a power-law growth exponent of α = 0.4, as also predicted by the simulations using randomly oriented nuclei. Nevertheless, interpretation of this result is contingent on the absence of factors such as textured nucleation and renucleation during film growth. Indeed, only one film, grown at a higher ratio of H2O/DEZ precursor gases, displaying random initial nucleation, and minimal grain renucleation during growth, shows a proper conformance to the model nature and predictions.

Quantifying Competitive Grain Overgrowth in Polycrystalline ZnO Thin Films

The grain size evolution of polycrystalline thin films, which form by competitive grain overgrowth as commonly interpreted using the van der Drift model, is understood to follow a power-law scaling of the average grain size d with film thickness h, i.e. d ∝ hα. While simulations have identified a growth exponent α = 0.4 for three-dimensional growth, previous experimental studies did not confirm this value, instead finding α values in the range of ~0.5-0.7. Here we study competitive grain overgrowth using a system of ZnO thin films grown by low-pressure metal-organic chemical vapor deposition. We present quantitative grain data on the evolution of grain size and orientation across the thickness of thin films, obtained by automated crystal orientation mapping of double-wedge transmission electron microscopy samples. The data from a-textured ZnO films, grown under three different conditions, are compared against van der Drift model predictions of self-similarity of the grain size distribution and the power-law scaling. The results are further interpreted by comparing to simulations of facetted polycrystalline film growth, which we adapt to the ZnO system by including idiomorphic growth shapes with a six-fold symmetry and random or biased nuclei orientations. As well as showing the predicted self-similarity of grain size distributions during growth, for the first time our experimental data confirm a power-law growth exponent of α = 0.4, as also predicted by the simulations using randomly oriented nuclei. Nevertheless, interpretation of this result is contingent on the absence of factors such as textured nucleation and renucleation during film growth. Indeed, only one film, grown at a higher ratio of H2O/DEZ precursor gases, displaying random initial nucleation, and minimal grain renucleation during growth, shows a proper conformance to the model nature and predictions.

The Effect of Buffer Types on the In0.82Ga0.18As Epitaxial Layer Grown on an InP (100) Substrate.

In0.82Ga0.18As epitaxial layers were grown on InP (100) substrates at 530 °C by a low-pressure metalorganic chemical vapor deposition (LP-MOCVD) technique. The effects of different buffer structures, such as a single buffer layer, compositionally graded buffer layers, and superlattice buffer layers, on the crystalline quality and property were investigated. Double-crystal X-ray diffraction (DC-XRD) measurement, Raman scattering spectrum, and Hall measurements were used to evaluate the crystalline quality and electrical property. Scanning electron microscope (SEM), atomic force microscope (AFM), and transmission electron microscope (TEM) were used to characterize the surface morphology and microstructure, respectively. Compared with the In0.82Ga0.18As epitaxial layer directly grown on an InP substrate, the quality of the sample is not obviously improved by using a single In0.82Ga0.18As buffer layer. By introducing the graded InxGa1−xAs buffer layers, it was found that the dislocation density in the epitaxial layer significantly decreased and the surface quality improved remarkably. In addition, the number of dislocations in the epitaxial layer greatly decreased under the combined action of multi-potential wells and potential barriers by the introduction of a In0.82Ga0.18As/In0.82Al0.18As superlattice buffer. However, the surface subsequently roughened, which may be explained by surface undulation.

Free standing c-GaN films grown by low-pressure metalorganic chemical vapor deposition on GaP (100) substrates

Gallium nitride (GaN) films were synthesized by low pressure metalorganic chemical vapor deposition on GaP (100) substrates. Samples were grown using three-step growth method, which includes a) a nitridation process of the GaP surface, b) the growth of a GaN buffer layer and c) the growth of the high-temperature epilayer. X-ray diffraction, Raman spectroscopy and FESEM and HRTEM were used to study the changes in the surface, which suggests that the cubic phase nucleation takes place during nitridation process and remained at the top surface, which results in preferential growth of c-GaN.

Effects of In0.82Ga0.18As/InP Double Buffers Design on the Microstructure of the In0.82G0.18As/InP Heterostructure

In order to reduce the dislocation density and improve the performance of high indium content In0.82Ga0.18As films, the design of double buffer layers has been introduced into the In0.82Ga0.18As/InP heterostructure. Compared with other buffer layer structures, we introduce an InP thin layer, which is the same as the substrate, into the In0.82Ga0.18As/InP heterostructure. The epitaxial layers and buffer layers were grown by the low-pressure metalorganic chemical vapor deposition (LP-MOCVD) method. In this study, the surface morphology and microstructures of the heterostructure were investigated by SEM, AFM, XRD and TEM. The residual strains of the In0.82Ga0.18As epitaxial layer in different samples were studied by Raman spectroscopy. The residual strain of the In0.82Ga0.18As epitaxial layer was decreased by designing double buffer layers which included an InP layer; as a result, dislocations in the epitaxial layer were effectively suppressed since the dislocation density was notably reduced. Moreover, the performance of In0.82Ga0.18As films was investigated using the Hall test, and the results are in line with our expectations. By comparing different buffer layer structures, we explained the mechanism of dislocation density reduction by using double buffer layers, which included a thin InP layer.

High-quality Ga-rich AlGaN grown on trapezoidal patterned GaN template using super-short period AlN/GaN superlattices for rapid coalescence

High quality crack-free Ga-rich Al26.1Ga73.9N film was grown on trapezoidal patterned GaN template (TPGT) by low-pressure metalorganic chemical vapor deposition. The super-short period AlN/GaN superlattices structure was used to grow AlGaN material instead of the direct growth method. We obtained large lateral to vertical growth rate ratio larger than 4.79. The growth rate of GaN layer was proved to be the decisive factor of the lateral to vertical growth rate ratio. Moreover, for AlGaN growth, we found that that the TPGT is more beneficial to suppression of crack and relaxation of biaxial tensile strain than planar GaN template. The obtained results demonstrate that, comparing with AlGaN grown on planar GaN template, the threading dislocation density in AlGaN grown on TPGT was reduced from 2×109cm−2 to 2×108cm−2.