Selective Area Growth and Characterization of GaN Nanorods Fabricated by Adjusting the Hydrogen Flow Rate and Growth Temperature with Metal Organic Chemical Vapor Deposition

CaN nanorods are successfully fabricated by adjusting the flow rate ratio of hydrogen （H2）/nitrogen （N2） and growth temperature of the selective area growth （SAG） method with metal organic chemical vapor deposition （MOCVD）. The SAG template is obtained by nanospherical-lens photolithography. It is found that increasing the flow rate of 1-12 will change the CaN crystal shape from pyramid to vertical rod, while increasing the growth temperature will reduce the diameters of GaN rods to nanometer scale. Finally the CaN nanorods with smooth lateral surface and relatively good quality are obtained under the condition that the H2：N2 ratio is 1：1 and the growth temperature is 1030℃. The good crystal quality and orientation of GaN nanorods are confirmed by high resolution transmission electron microscopy. The cathodoluminescence spectrum suggests that the crystal and optical quality is also improved with increasing the temperature.

Low-leakage-current AlGaN/GaN HEMTs on Si substrates with partially Mg-doped GaN buffer layer by metal organic chemical vapor deposition

High-performance low-leakage-current A1GaN/GaN high electron mobility transistors （HEMTs） on silicon （111） sub- strates grown by metal organic chemical vapor deposition （MOCVD） with a novel partially Magnesium （Mg）-doped GaN buffer scheme have been fabricated successfully. The growth and DC results were compared between Mg-doped GaN buffer layer and a unintentionally onμe. A 1μ m gate-length transistor with Mg-doped buffer layer exhibited an OFF-state drain leakage current of 8.3 × 10-8 A/mm, to our best knowledge, which is the lowest value reported for MOCVD-grown A1GaN/GaN HEMTs on Si featuring the same dimension and structure. The RF characteristics of 0.25-μ m gate length T-shaped gate HEMTs were also investigated.

In-situ wafer bowing measurements of GaN grown on Si(111) substrate by reflectivity mapping in metal organic chemical vapor deposition system

In this work, the wafer bowing during growth can be in-situ measured by a reflectivity mapping method in the 3×2 Thomas Swan close coupled showerhead metal organic chemical vapor deposition（MOCVD） system. The reflectivity mapping method is usually used to measure the film thickness and growth rate. The wafer bowing caused by stresses（tensile and compressive） during the epitaxial growth leads to a temperature variation at different positions on the wafer, and the lower growth temperature leads to a faster growth rate and vice versa. Therefore, the wafer bowing can be measured by analyzing the discrepancy of growth rates at different positions on the wafer. Furthermore, the wafer bowings were confirmed by the ex-situ wafer bowing measurement. High-resistivity and low-resistivity Si substrates were used for epitaxial growth. In comparison with low-resistivity Si substrate, Ga N grown on high-resistivity substrate shows a larger wafer bowing caused by the highly compressive stress introduced by compositionally graded Al Ga N buffer layer. This transition of wafer bowing can be clearly in-situ measured by using the reflectivity mapping method.

GaInP/GaInAs/GaInNAs/Ge Four-Junction Solar Cell Grown by Metal Organic Chemical Vapor Deposition with High Efficiency

We directly grow a lattice matched GalnP/GalnAs/GalnNAs/Ge （1.88 eVil .42 eVil .05 eV/0.67eV） four-junction （4J） solar cell on a Ge substrate by the metal organic chemical vapor deposition technology. To solve the current limit of the GalnNAs sub cell, we design three kinds of anti-reflection coatings and adjust the base region thickness of the GalnNAs sub cell. Developed by a series of experiments, the external quantum efficiency of the GalnNAs sub cell exceeds 80%, and its current density reaches 11.24 mA/cm2. Therefore the current limit of the 4J solar cell is significantly improved. Moreover, we discuss the difference of test results between 4J and GalnP/GalnAs/Ge solar cells under the 1 sun AMO spectrum.

Improved Semipolar(11(2|-)2) GaN Quality Grown on m-Plane Sapphire Substrates by Metal Organic Chemical Vapor Deposition Using Self-Organized SiN_x Interlayer

The effect of a self-organized SiNs interlayer on the defect density of （1122） semipolar GaN grown on 7n-plane sapphire is studied by transmission electron microscopy, atomic force microscopy and high resolution x-ray diffrac- tion. The SiNx interlayer reduces the c-type dislocation density from 2.5 ×10^10 cm^-2 to 5 ×10^8 cm 2. The SiNx interlayer produces regions that are free from basal plane stacking faults （BSFs） and dislocations. The overall BSF density is reduced from 2.1×10^5 cm-1 to 1.3×10^4 cm^-1. The large dislocations and BSF reduction in semipolar （1122） GaN with the SiNx, interlayer result from two primary mechanisms. The first mechanism is the direct dislocation blocking by the SiNx interlayer, and the second mechanism is associated with the unique structure character of （1122） semipolar GaN.

Fabrication of InAlGaN/GaN High Electron Mobility Transistors on Sapphire Substrates by Pulsed Metal Organic Chemical Vapor Deposition

Nearly lattice-matched InAIGaN/GaN heterostructure is grown on sapphire substrates by pulsed metal organic chemical vapor deposition and excellent high electron mobility transistors are fabricated on this heterostructure. The electron mobility is 1668.08cm2/V.s together with a high two-dimensional-electron-gas density of 1.43 × 10^13 cm-2 for the InAlCaN/CaN heterostructure of 2Onto InAlCaN quaternary barrier. High electron mobility transistors with gate dimensions of 1 × 50 μm2 and 4μm source-drain distance exhibit the maximum drain current of 763.91 mA/mm, the maximum extrinsic transconductance of 163.13 mS/mm, and current gain and maximum oscillation cutoff frequencies of 11 GHz and 21 GHz, respectively.

Growth and characterization of AlN epilayers using pulsed metal organic chemical vapor deposition

We report the growth of Al N epilayers on c-plane sapphire substrates by pulsed metal organic chemical vapor deposition（MOCVD）. The sources of trimethylaluminium（TMAl） and ammonia were pulse introduced into the reactor to avoid the occurrence of the parasitic reaction. Through adjusting the duty cycle ratio of TMAl to ammonia from 0.8 to 3.0, the growth rate of Al N epilayers could be controlled in the range of 0.24 m/h to 0.93 m/h. The high-resolution x-ray diffraction（HRXRD） measurement showed that the full width at half maximum（FWHM） of the（0002） and（10-12） reflections for a sample would be 194 arcsec and 421 arcsec, respectively. The step-flow growth mode was observed in the sample with the atomic level flat surface steps, in which a root-mean-square（RMS） roughness was lower to 0.2 nm as tested by atomic force microscope（AFM）. The growth process of Al N epilayers was discussed in terms of crystalline quality, surface morphology,and residual stress.

Superior material qualities and transport properties of InGaN channel heterostructure grown by pulsed metal organic chemical vapor deposition

Pulsed metal organic chemical vapor deposition is introduced into the growth of InGaN channel heterostructure for improving material qualities and transport properties. High-resolution transmission electron microscopy imaging shows the phase separation free InGaN channel with smooth and abrupt interface. A very high two-dimensional electron gas density of approximately 1.85 x 10^13 cm-2 is obtained due to the superior carrier confinement. In addition, the Hall mobility reaches 967 cruZ/V-s, owing to the suppression of interface roughness scattering. Furthermore, temperature-dependent Hall measurement results show that InGaN channel heterostructure possesses a steady two-dimensional electron gas density over the tested temperature range, and has superior transport properties at elevated temperatures compared with the traditional GaN channel heterostructure. The gratifying results imply that InGaN channel heterostructure grown by pulsed metal organic chemical vapor deposition is a promising candidate for microwave power devices.

The multiscale simulation of metal organic chemical vapor deposition growth dynamics of GaInP thin film

As a Group III–V compound, GaInP is a high-efficiency luminous material. Metal organic chemical vapor deposition (MOCVD) technology is a very efficient way to uniformly grow multi-chip, multilayer and large-area thin film. By combining the computational fluid dynamics (CFD) and the kinetic Monte Carlo (KMC) methods with virtual reality (VR) technology, this paper presents a multiscale simulation of fluid dynamics, thermodynamics, and molecular dynamics to study the growth process of GaInP thin film in a vertical MOCVD reactor. The results of visualization truly and intuitively not only display the distributional properties of the gas’ thermal and flow fields in a MOCVD reactor but also display the process of GaInP thin film growth in a MOCVD reactor. The simulation thus provides us with a fundamental guideline for optimizing GaInP MOCVD growth.

Growth of N-polar GaN on vicinal sapphire substrate by metal organic chemical vapor deposition

The growth and properties of N-polar Ga N layers by metal organic chemical vapor deposition（MOCVD） were reported. It is found that N-polar Ga N grown on normal sapphire substrate shows hexagonal hillock surface morphology. With the misorientation angles increasing from 0.5° to 2.0° toward the a-plane of the sapphire substrate, the number of the hillock becomes less and less and finally the surface becomes flat one on the sapphire substrate with the misorientation angle of 2°. It is also found that the crystalline quality and the strain in the Ga N are greatly influenced by the misorientation angle.

High-crystalline GaSb epitaxial films grown on GaAs(001) substrates by low-pressure metal–organic chemical vapor deposition

Orthogonal experiments of Ga Sb films growth on Ga As（001） substrates have been designed and performed by using a low-pressure metal–organic chemical vapor deposition（LP-MOCVD） system. The crystallinities and microstructures of the produced films were comparatively analyzed to achieve the optimum growth parameters. It was demonstrated that the optimized Ga Sb thin film has a narrow full width at half maximum（358 arc sec） of the（004） ω-rocking curve, and a smooth surface with a low root-mean-square roughness of about 6 nm, which is typical in the case of the heteroepitaxial single-crystal films. In addition, we studied the effects of layer thickness of Ga Sb thin film on the density of dislocations by Raman spectra. It is believed that our research can provide valuable information for the fabrication of high-crystalline Ga Sb films and can promote the integration probability of mid-infrared devices fabricated on mainstream performance electronic devices.

Quantum cascade lasers grown by MOCVD

Sharing the advantages of high optical power,high efficiency and design flexibility in a compact size,quantum cascade lasers(QCLs)are excellent mid-to-far infrared laser sources for gas sensing,infrared spectroscopic,medical diagnosis,and defense applications.Metalorganic chemical vapor deposition(MOCVD)is an important technology for growing high quality semiconductor materials,and has achieved great success in the semiconductor industry due to its advantages of high efficiency,short maintenance cycles,and high stability and repeatability.The utilization of MOCVD for the growth of QCL materials holds a significant meaning for promoting the large batch production and industrial application of QCL devices.This review summarizes the recent progress of QCLs grown by MOCVD.Material quality and the structure design together determine the device performance.Research progress on the performance improvement of MOCVD-grown QCLs based on the optimization of material quality and active region structure are mainly reviewed.

Low-resistance ohmic contacts on InAlN/GaN heterostructures with MOCVD-regrown n+-InGaN and mask-free regrowth process

This paper studied the low-resistance ohmic contacts on InAlN/GaN with metal–organic chemical vapor deposition(MOCVD)regrowth technique.The 150-nm regrown n-InGaN exhibits a low sheet resistance of 31Ω/□,resulting in an extremely low contact resistance of 0.102Ω·mm between n^(+)-InGaN and InAlN/GaN channels.Mask-free regrowth process was also used to significantly improve the sheet resistance of InAlN/GaN with MOCVD regrown ohmic contacts.Then,the diffusion mechanism between n^(+)-InGaN and InAlN during regrowth process was investigated with electrical and structural characterizations,which could benefit the further process optimization.

Characterization of Zn-doped GaN grown by metal–organic vapor phase epitaxy

The point defects and photoluminescence(PL)spectra of gallium nitride(GaN)epilayers with Mg,Zn,and unintentional doping were investigated in this study.The concentration of point defects(Ga vacancy and its related complexes)in the Zn-doped GaN is consistent with that in the Mg-doped GaN,but lower than that in undoped GaN.It is suggested that Zn(Mg)atoms occupy Ga sites and suppress the formation of Ga vacancies.Comparing the blue luminescence(BL)band intensity of GaN:Zn with that of GaN:Mg,a factor of 10 strong PL intensity demonstrates that a moderate incorporation of Zn to GaN is likely to improve the structural quality of GaN.Detailed studies on 2.93 eV BL band for GaN:Zn reveal that the Zn related BL band behaves as a donor-acceptor pairs character.For the acceptor level,isolated Zn_(Ga)with the activation energy of 0.386 eV above the valence band is obtained from temperature-dependent PL measurements,whereas the deep donor defect responsible for the 2.93 eV band is deduced to be 164 meV below the conduction band.An O_(N)-H complex model is suggested to explain the deep donor origin.

Quasi-homoepitaxial GaN-based blue light emitting diode on thick GaN template

The high power GaN-based blue light emitting diode （LED） on an 80%tm-thick GaN template is proposed and even realized by several technical methods like metal organic chemical vapor deposition （MOCVD）, hydride vapor-phase epi- taxial （HVPE）, and laser lift-off （LLO）. Its advantages are demonstrated from material quality and chip processing. It is investigated by high resolution X-ray diffraction （XRD）, high resolution transmission electron microscope （HRTEM）, Rutherford back-scattering （RBS）, photoluminescence, current-voltage and light output-current measurements. The width of （0002） reflection in XRD rocking curve, which reaches 173＂ for the thick GaN template LED, is less than that for the conventional one, which reaches 258＂. The HRTEM images show that the multiple quantum wells （MQWs） in 80%tm- thick GaN template LED have a generally higher crystal quality. The light output at 350 mA from the thick GaN template LED is doubled compared to traditional LEDs and the forward bias is also substantially reduced. The high performance of 80-~m-thick GaN template LED depends on the high crystal quality. However, although the intensity of MQWs emission in PL spectra is doubled, both the wavelength and the width of the emission from thick GaN template LED are increased. This is due to the strain relaxation on the surface of 80%tin-thick GaN template, which changes the strain in InGaN QWs and leads to InGaN phase separation.

Advantages of InGaN/GaN multiple quantum well solar cells with stepped-thickness quantum wells

InGaN/GaN multiple quantum well （MQW） solar cells with stepped-thickness quantum wells （SQW） are designed and grown by metal-organic chemical vapor deposition. The stepped-thickness quantum wells structure, in which the well thickness becomes smaller and smaller along the growth direction, reveals better crystalline quality and better spectral overlap with the solar spectrum. Consequently, the short-circuit current density （Jsc） and conversion efficiency of the solar cell are enhanced by 27.12% and 56.41% compared with the conventional structure under illumination of AM1.5G （100 mW/cm2）. In addition, approaches to further promote the performance of InGaN/GaN multiple quantum well solar cells are discussed and presented.

ALD growth of ultra-thin Co layers on the topological insulator Sb2Te3

Taking the full advantage of the conformal growth characterizing atomic layer deposition(ALD),the possibility to grow Co thin films,with thickness from several tens down to few nanometers on top of a granular topological insulator(TI)Sb2Tes film,exhibiting a quite high surface roughness(2-5 nm),was demonstrated.To study the Co growth on the Sb2Tes substrate,we performed simultaneous Co depositions also on sputtered Pt substrates for comparison.We conducted a thorough chemical-structural characterization of the Co/Sb2Tes and Co/Pt heterostructures,confirming for both cases,not only an excellent conformality,but also the structural continuity of the Co layers.X-ray diffraction(XRD)and high-resolution transmission electron microscope(HRTEM)analyses evidenced that Co on Sb2Te3 grows preferentially oriented along the[0oe]direction,following the underlying rhombohedric substrate.Differently,Co crystallizes in a cubic phase oriented along the[111]direction when deposited on Pt.This work shows that,in case of deposition of crystalline materials,the ALD surface selectivity and conformality can be extended to the definition of local epitaxy,where in-plane ordering of the crystal structure and mosaicity of the developed crystallized grains are dictated by the underlying substrate.Moreover,a highly sharp and chemically-pure Co/Sb2Tes interface was evidenced,which is promising for the application of this growth process for spintronics.

Nonpolar Al_(x)Ga_(1−x)N/Al_(y)Ga_(1−y)N multiple quantum wells on GaN nanowire for UV emission

Nonpolar m-plane AlGaN offers the advantage of polarization-free multiple quantum wells(MQWs)for ultraviolet(UV)emission and can be achieved on the sidewalls of selective area grown GaN nanowires.We reveal that the growth of AlGaN on GaN nanowires by metal organic chemical vapor deposition(MOCVD)is driven by vapor-phase diffusion,and consequently puts a limit on the pitch of nanowire array due to shadowing effect.An insight into the difficulty of achieving metal-polar AlGaN nanowire by selective area growth(SAG)in MOCVD is also provided and can be attributed to the strong tendency to form pyramidal structure due to a very small growth rate of{1011}semipolar planes compared to(0001)c-plane.The nonpolar m-plane sidewalls of GaN nanowires obtained via SAG provides an excellent platform for growth of nonpolar AlGaN MQWs.UV emission from mplane Al_(x)Ga_(1−x)N/Al_(y)Ga_(1−y)N MQWs grown on sidewalls of dislocation-free GaN nanowire is demonstrated in the wavelength range of 318–343 nm.

Influence of substrate temperature on in situ-textured ZnO thin films grown by MOCVD

The influence of substrate temperature on microstructure, electrical and optical properties of in situ- textured zinc oxide （ZnO） films fabricated by metal organic chemical vapor deposition （MOVCD） had been investigated. Results indicated that the substrate tempera- ture played a very important role on preparation of ZnO thin film. With the raising of temperature, firstly ZnO crystals were perpendicular to the substrate, then they were grown inclining toward the substrate, finally ZnO crystals grown in layers but not regular. Consequently, ZnO film surface morphology changed from smooth to a pyramid structure and then disappeared little by little. Moreover, it was also found in this study that ZnO film was characterized with high crystallinity, low resistivity （2.17 x 10 2） and high transmittance （〉 80%）. These results suggested that ZnO thin film is suitable for front electrode of silicon thin film solar cell.

Low threading dislocation density in GaN films grown on patterned sapphire substrates

The growth process of three-dimensional growth mode（3D） switching to two-dimensional growth mode （2D） is investigated when GaN films are grown on cone-shaped patterned sapphire substrates by metal-organic chemical vapor deposition.The growth condition of the 3D-2D growth process is optimized to reduce the threading dislocation density（TDD）.It is found that the condition of the 3D layer is critical.The 3D layer keeps growing under the conditions of lowⅤ/Ⅲratio,low temperature,and high pressure until its thickness is comparable to the height of the cone-shaped patterns.Then the 3D layer surrounds the cone-shaped patterns and has inclined side facets and a top（0001） plane.In the following 2D-growth process,inclined side facets coalesce quickly and the interaction of TDs with the side facets causes the TDs to bend over.As a result,the TDD of GaN films can decrease to 1×10~8 cm^（-2）,giving full-width at half maximum values of 211 and 219 arcsec for（002） and（102） omega scans, respectively.