The growth and properties of mixed group V nitrides

Bearing in mind the problems of finding a lattice-matched substrate for the growth of binary group III nitride films and the detrimental effect of the large activation energy associated with acceptors in GaN, we propose the study of the alloy system AlGaAsN. We predict that it may be possible to obtain a direct gap alloy, with a band gap as wide as 2.8eV, which is lattice-matched to silicon substrates. The paper reports our attempts to grow GaAsN alloy films by molecular beam epitaxy on either GaAs or GaP substrates, using a radio frequency plasma source to supply active nitrogen. Auger electron spectra demonstrate that it is possible to incorporate several tens of percent of nitrogen into GaAs films, though x-ray diffraction measurements show that such films contain mixed binary phases rather than true alloys. An interesting observation concerns the fact that it is possible to control the crystal structure of GaN films by the application of an As flux during growth. In films grown at 620°C a high As flux tends to increase the proportion of cubic GaN while also resulting in the incorporation of GaAs. Films grown at 700°C show no evidence for GaAs incorporation; at this temperature, it is possible to grow either purely cubic or purely hexagonal GaN depending on the presence or absence of the As beam.     

Effects of Substrate Pretreatment Conditions on Quality of GaN Epilayer

The pure cubic GaN(c-GaN) has been grown on (001) GaAs substrates by ECR-PAMOCVD technique at low temperature using TMGa and high pure N2 as Ga and N sources,respectively.The effects of substrate pretreatment conditions on quality of cubic GaN epilayer are investigated by the measurements of TEM and XRD.It is found that hydrogen plasma cleaning,nitridation and buffer layer growth are very important for quality of cubic GaN epilayer.     

立方GaAs（100）衬底上制备单相六方GaN薄膜

立方GaAs（100）衬底上制备的GaN薄膜多为立方结构且立方相为亚稳相,采用水平常压MOCVD方法在立方GaAs（100）衬底上制备出了GaN薄膜．XRD测试表明,薄膜具有单一的相．结合对工艺条件的分析,认为薄膜具有六方结构．最后,通过Raman光谱测试,证实在立方GaAs衬底上制备出了单相六方GaN薄膜．还对立方GaAs衬底上制备出六方GaN薄膜的原因进行了讨论．     

X-ray photoelectron spectroscopy of gallium nitride films grown by radical-beam gettering epitaxy

Thin GaN films were grown on GaAs(111) substrates by radical-beam gettering epitaxy. The structural quality of the films was studied by high-resolution x-ray diffraction. The chemical composition of the GaAs surface and GaN film was studied by x-ray photoelectron spectroscopy. It is shown that Ga-N and As-N bonds are formed on the GaAs surface at initial growth stages at low temperatures. The state of the film-substrate interface was studied. It was found that prolonged annealing of GaN films in nitrogen radicals shifts the composition to nitrogen excess.     

Characterization of GaNxAs1-x Alloy Grown on GaAs by Molecular Beam Epitaxy

Ga Nx As1 - x,the combination of small amount of nitrogen and Ga As,has beenexperimentally observed with the band gaps several hundreds me V lower than that ofGa As[1～ 4] .The alloy has attracted considerable attention in the applicat...     

Cubic Phase GaN on Nano‐grooved Si (100) via Maskless Selective Area Epitaxy

A method of forming cubic phase (zinc blende) GaN (referred as c‐GaN) on a CMOS‐compatible on‐axis Si (100) substrate is reported. Conventional GaN materials are hexagonal phase (wurtzite) (referred as h‐GaN) and possess very high polarization fields (～MV/cm) along the common growth direction of <0001>. Such large polarization fields lead to undesired shifts (e.g., wavelength and current) in the performance of photonic and vertical transport electronic devices. The cubic phase of GaN materials is polarization‐free along the common growth direction of <001>, however, this phase is thermodynamically unstable, requiring low‐temperature deposition conditions and unconventional substrates (e.g., GaAs). Here, novel nano‐groove patterning and maskless selective area epitaxy processes are employed to integrate thermodynamically stable, stress‐free, and low‐defectivity c‐GaN on CMOS‐compatible on‐axis Si. These results suggest that epitaxial growth conditions and nano‐groove pattern parameters are critical to obtain such high quality c‐GaN. InGaN/GaN multi‐quantum‐well structures grown on c‐GaN/Si (100) show strong room temperature luminescence in the visible spectrum, promising visible emitter applications for this technology.     

Effect of In Situ Thermal Cycle Annealing on GaN Film Properties Grown on (001) and (111) GaAs, and Sapphire Substrates

The effect of in-situ thermal cycle annealing (TCA) has been investigated for GaN growth on GaAs(lOO), GaAs(111) and sapphire substrates. X-ray diffractometry (XRD) and surface morphology studies were performed for this purpose. Enhanced cubic phase characteristics were observed by employing annealingfor GaN layers grown on (001) GaAs. The thickness of the layer subject to annealing is critical in determining the phase of the subsequently grown layer. Thin initial layers appear to permit maintenance of the cubic phase characteristics shown by the substrate, while hexagonal phase characteristics are manifested for thick initial layers. Higher temperature of annealing of thick pre-annealed layers results in changes from mixed cubic/hexagonal phase to pure hexagonal phase. Growth on GaAs(111) substrates showed single cubic phase characteristics and similar enhancement of crystal quality by using TCA as for layers on GaAs(OOl). Micro-cracks were found to be present after TCA on GaAs(lll) substrates. Thermal cycling also appears to be beneficial for layers grown on sapphire substrates.     

Epitaxial growth of cubic gan on (111) GaAs by metalorganic chemical vapor deposition

We are reporting the first comprehensive investigation of the structural properties of cubic GaN grown on (111) GaAs substrates by low-pressure metalorganic chemical vapor deposition. The minimum full width at half maximum (FWHM) of the x-ray diffraction (XRD) peak of (111) GaN was found to be ∼12 min. The use of low temperature GaN buffers helps to reduce the FWHM of the XRD. Cross-sectional transmission electron microscopy (XTEM) revealed the presence of columnar structures in the GaN film with widths of the order of 500A. Selected area electron diffraction (SAD) patterns at the interface confirmed that cubic (111) GaN was grown in-plane with the (111) GaAs substrate. Highresolution transmission electron microscopy (HRTEM) showed that the interface characteristics of GaN on (111)A GaAs substrate were better than those of the GaN on (lll)B GaAs substrate.     

The influence of nitrogen ion energy on the quality of GaN films grown with molecular beam epitaxy

Since the growth of GaN using molecular beam epitaxy (MBE) occurs under metastable growth conditions, activated nitrogen is required to drive the forward synthesis reaction. In the process of exciting the nitrogen using a plasma or ion-beam source, species with large kinetic energies are generated. Impingement on the growth surface by these species can result in subsurface damage to the growing film, as well as an enhancement of the reverse decomposition reaction rate. In this study, we investigate the effect of the kinetic energy of the impinging nitrogen ions during growth on the resulting optical and structural properties of GaN films. Strong band-edge photoluminescence and cathodoluminescence are found when a kinetic energy of ∼10 eV are used, while luminescence is not detectable when the kinetic energies exceeds 18 eV. Also, we find that the use of conductive SiC substrates results in more homogeneous luminescence than the use of insulating sapphire substrates. This is attributed to sample surface charging in the case of sapphire substrates and subsequent variation in the incident ion flux and kinetic energy across the growth surface. This study clearly shows that the quality of GaN films grown by MBE are presently limited by damage from the impingement of high energy species on the growth surface.     

Growth of zinc- blende GaN on GaAs (100) substrates at high temperature using low-pressure MOVPE with a Low V/lll molar ratio

Zinc-blende GaN films were grown on GaAs (100) substrates by low-pressure metalorganic vapor phase epitaxy using trimethylgallium or triethylgallium and NH₃. Films grown at lower temperatures contained considerable amounts of carbon, but the carbon concentration was reduced in high temperature growth. When the film was grown at 950°C using triethylgallium and NH₃, its carbon concentration was on the order of 10¹⁷ cm⁻³. The crystalline and optical quality of zinc-blende GaN crystal also improved with high-temperature growth at a low V/III ratio using a thin buffer layer. The films exhibited only one sharp photoluminescence peak at 3.20 eV with a full width at half maximum as low as 70 meV at room temperature.     

Near band-edge optical properties of cubic GaN with and without carbon doping

We report the results of studying the optical properties of cubic GaN thin films with photoluminescence and photoluminescence excitation spectroscopies. The films are deposited by plasma-assisted molecular beam epitaxy on GaAs (001) substrates, with and without intentional doping with carbon atoms (p-type doping). The evolution of the optical spectra of the C-doped samples is consistent with a picture in which carbon enters into N-vacancies at low concentrations, producing a marked improvement in the crystalline properties of the material. At higher concentrations it begins to form complexes, possibly due to interstitial occupation. The temperature dependence on the absorption edge of the doped material is also measured and is analyzed with standard theoretical models.     

Nanometer-scale studies of nitride/arsenide heterostructures produced by nitrogen plasma exposure of GaAs

We have investigated the nanometer-scale structure and electronic properties of nitride/arsenide superlattices produced by nitridation of a molecular beam epitaxially grown GaAs surface. Using cross-sectional scanning tunneling microscopy and spectroscopy, we find that the nitrided layers are not continuous films, but consist of groups of atomic-scale defects and larger clusters. We identify the defects and clusters as N_As and GaN with dilute As concentration, respectively. Thus, the nitrided regions consist of alloys from both sides of the miscibility gap predicted for the GaAsN system. In addition, spectroscopy on the clusters reveals an upward shift of the band edges and band gap narrowing, with significant change in the conduction band structure. We estimate the contribution of strain to band gap narrowing in terms of an elasticity calculation for a coherently strained spherical GaN cluster embedded in GaAs.     

α-Al2O3上生长GaN过程中氮化的研究

在自行设计研制的电子回旋共振等离子体增强金属有机物化学气相沉积(ECR?蛳EMOCVD)装置上生长氮化镓(GaN)薄膜，以氮等离子体为氮源，三乙基镓（TEG）为镓源，蓝宝石（α?蛳Al2O3）为衬底。通过反射高能电子衍射、原子力显微镜、射线衍射实验数据分析，研究了ECR等离子体所产生的活性氢源和氮源对蓝宝石（α?蛳Al2O3）衬底的氮化作用, 结果表明：在ECR等离子体中，不掺入氢气，温度较低时可以明显提高α?蛳Al2O3衬底的氮化效果，获得平整的氮化层，且生长的氮化镓缓冲层质量是最好的。     

Refractive indices of wurtzite and zincblende GaN

Refractive index measurements on both wurtzite and zincblende GaN films grown by plasma-enhanced molecular beam epitaxy are reported. For birefringent uniaxial wurtzite GaN samples the index of refraction was measured along the crystalline axis. In this direction the index is 2.78 at 3.4 eV. For cubic GaN films grown on GaAs substrates, the refractive index is 2.91 at 3.2 eV. Estimation of the confinement factor for optimised waveguides based a combination of III-V nitrides indicates very favourable values for laser operation.<>     

利用高频Plasma CVD在蓝宝石衬底上生长 立方GaN缓冲层及其光学性质

研究了采用高频PlasmaCVD技术在较低温度下(300—400℃)生长以GaN为基的Ⅲ-Ⅴ族氮化物的可行性,在蓝宝石衬底上生长了GaN缓冲层.热处理后的光致发光谱和X光衍射表明,生长的GaN缓冲层为立方相,带边峰位于3.15eV.在作者实验的范围内,最优化的TMGa流量为0.08sccm(TMAm=10sccm时),XPS分析结果表明此时的Ga/N比为1.03.这是第一次在高Ⅴ/Ⅲ比下得到立方GaN.相同条件下石英玻璃衬底上得到的立方GaN薄膜,黄光峰很弱,晶体质量较好.     

Direct Low‐Temperature Integration of Nanocrystalline Diamond with GaN Substrates for Improved Thermal Management of High‐Power Electronics

A novel approach for the direct synthetic diamond–GaN integration via deposition of the high‐quality nanocrystalline diamond films directly on GaN substrates at temperatures as low as 450–500 °C is reported. The low deposition temperature allows one to avoid degradation of the GaN quality, which is essential for electronic applications The specially tuned growth conditions resulted in the large crystalline diamond grain size of 100–200 nm without coarsening. Using the transient “hot disk” measurements it is demonstrated that the effective thermal conductivity of the resulting diamond/GaN composite wafers is higher than that of the original GaN substrates at elevated temperatures. The thermal crossover point is reached at ≈95–125 °C depending on the thickness of the deposited films. The developed deposition technique and obtained thermal characterization data can lead to a new method of thermal management of the high power GaN electronic and optoelectronic devices.     

Initial stages of GaN/GaAs (100) growth by metalorganic chemical vapor deposition

We have investigated the growth of GaN buffers by metalorganic chemical vapor deposition (MOCVD) on GaAs (100) substrates. Atomic force microscope (AFM) and reflection high-energy electron diffraction (RHEED) were employed to study the dependence of the nucleation on the growth temperature, growth rate, annealing effect, and growth time. A two-step growth sequence must be used to optimize and control the nucleation and the subsequent growth independently. The size and distribution of islands and the thickness of buffer layers have a crucial role on the quality of GaN layers. Based on the experimental results, a model was given to interpret the formation of hexagonal-phase GaN in the cubic-phase GaN layers. Using an optimum buffer layer, the strong near-band emission of cubic GaN with full-width at half maximum (FWHM) value as small as 5.6 nm was observed at room temperature. The background carrier concentration was estimated to be in the range of 10¹³ ∼ 10¹⁴ cm⁻³.     

MOCVD growth of cubic GaN on 3C-SiC deposited on Si (100) substrates

The growth of cubic GaN on 3C-SiC/Si(100) by metal-organic chemical vapor deposition (MOCVD) under various growth temperatures, thicknesses of 3C-SiC, and V/III ratios was studied. The fractions of cubic and hexagonal phases in the films were estimated from the integrated x-ray diffraction intensities of the cubic (002) and hexagonal (1011) planes. A smooth SiC layer, a high growth temperature, and a moderate V/III ratio are three key factors for the nucleation of the cubic phase and its subsequent growth. Hexagonal GaN with its c-axis perpendicular to the substrate preferentially grows at the low temperature of 750°C. The inclusion of the cubic phase increases with increasing growth temperature. The optimum growth conditions for dominant cubic GaN formation were a growth temperature of 950°C, a 1.5 μm thick SiC layer, and a V/III ratio of 1500. With these growth conditions, a cubic GaN layer with the cubic component of 91% was obtained.     

溅射后退火反应法制备GaN薄膜的结构与发光性质

报道了用溅射后退火反应法在 Ga As (110 )衬底上制备 Ga N薄膜 .XRD、XPS、TEM测量结果表明该方法制备的 Ga N是沿 c轴方向生长的六角纤锌矿结构的多晶薄膜 .PL测量结果发现了位于 36 8nm处的室温光致发光峰.     

Features of molecular beam epitaxy of the GaN (0001) and GaN (000$$ \bar 1 $$) layers with the use of different methods of activation of nitrogen

The results of comparative studies of the growth kinetics of the GaN layers of different polarity during ammonia molecular beam epitaxy and plasma-assisted molecular beam epitaxy (PA MBE) of nitrogen with the use of sapphire substrates and GaN(000\(\bar 1\))/c-Al₂O₃ templates grown by gas-phase epitaxy from metalorganic compounds are presented. The possibility is shown of obtaining the GaN layers with an atomically smooth surface during molecular beam epitaxy with plasma activation of nitrogen. For this purpose, it is suggested to carry out the growth in conditions enriched with metal near the mode of formation of the Ga drops at a temperature close to the decomposition temperature of GaN (TS ≈ 760°C). The conclusion is made that an increase in the growth temperature positively affects the structural, optical, and electrical properties of the GaN (000\(\bar 1\)) layers. A high quality of the GaN (0001) films grown by the PA MBE method at a low temperature of ～700°C on the GaN/c-Al₂O₃ templates is shown.