Criteria for versatile GaN MOVPE tool: high growth rate GaN by atmosphericpressure growth

Growth rate has a direct impact on the productivity of nitride LED production. Atmospheric pressure growth of GaN with a growth rate as high as 10 μm/h and also Al_0.1Ga_0.9N growth of 1 μm/h by using 4 inch by 11 production scale MOVPE are described. XRD of (002) and (102) direction was 200 arcsec and 250 arcsec, respectively. Impact of the growth rate on productivity is discussed.     

Criteria for versatile GaN MOVPE tool:high growth rate GaN by atmospheric pressure growth

Growth rate has a direct impact on the productivity of nitride LED production.Atmospheric pressure growth of GaN with a growth rate as high as 10μm/h and also Al_0.1Ga_0.9N growth of 1μm/h by using 4 inch by 11 production scale MOVPE are described.XRD of（002） and（102） direction was 200 arcsec and 250 arcsec, respectively.Impact of the growth rate on productivity is discussed.     

初始层生长条件和Mg活性剂对MOVPE方法生长GaN薄膜质量的影响

The initial growth conditions of a 100 nm thick GaN layer and Mg-surfactant on the quality of the GaN epilayer grown on a 6H-SiC substrate by metal-organic vapor phase epitaxy have been investigated in this research. Experimental results have shown that a high Ⅴ/Ⅲ ratio and the initially low growth rate of the GaN layer are favorable for two-dimension growth and surface morphology of GaN and the formation of a smoother growth surface. Mg-surfactant occurring during GaN growth can reduce the dislocations density of the GaN epilayer but increase the surface RMS, which are attributed to the change of growth mode.     

Thickness variations during MOVPE growth on patterned substrates

Experiments have been carried out to investigate thickness variations between epitaxial layers grown on ridges or channels and the surrounding planar surface. Results show a remarkable variation in growth velocity, even for relatively wide channels and ridges. Using these findings, a novel laser/waveguide coupling technique, which uses a single epitaxial growth step, is proposed.     

Catalyst-free growth of GaN nanowires

We have grown GaN and AlGaN nanowires on Si (111) substrates with gassource molecular beam epitaxy (MBE). No metal catalysts were used. The nanowires displayed a number of interesting materials properties, including room-temperature luminescence intensity greater than that of free-standing HVPE-grown GaN, relaxed lattice parameters, and the tendency of nanowires dispersed in solvents to align in response to electric fields. The wires were well separated, 50–250 nm in diameter, and grew to lengths ranging from 2 μm to 7 μm. Transmission electron microscopy indicated that the wires were free of defects, unlike the surrounding matrix layer.     

Investigation of three-step epilayer growth approach of GaN films to minimize compensation

The heteroepitaxial growth of gallium nitride (GaN) films using three distinct growth steps is investigated in terms of improving the electrical properties of the layer. The first step involves the deposition of a fixed quality aluminum nitride (AlN) layer on an a-plane sapphire substrate. The second step is aimed at maximizing the GaN grain size initially grown on the AlN. The third step is aimed at optimizing the surface morphology of the GaN layer. The means of transitioning the growth between steps is investigated and an optimum transition method is reported. Growth parameters investigated include pressure, trimethylgallium molar flow rate, and ratio of group V to group III precursor molar flows. Carrier statistics show a lower level of compensation in films grown at a slower growth rate in the second step and a moderate rate in the third step.     

Selective area growth of GaN using gas source molecular beam epitaxy

Ammonia cracking efficiencies on various surfaces were examined. The following is an ordering of surfaces according to their ammonia cracking efficiencies: GaN (highest), Si₃N₄, SiO₂ (lowest). Selective area growth of GaN was performed over SiO₂ masks deposited on GaN previously grown on sapphire substrates using ammonia-based molecular beam epitaxy. GaN growth on patterned SiO₂/GaN is very selective at a growth temperature of 800°C. Good quality growth occurs in the window region with no deposits on the mask surface when growth is performed at 800°C, whereas some deposits on the SiO₂ masks accumulate when growth is performed at 700°C. The ratio of lateral growth rate to vertical growth rate is ≤1.     

Quasi-Thermodynamic Model of MOVPE of InAIN

A quasi-thermodynamic model of MOVPE growth of InxAl1-xN alloy with TMAl,TMIn and ammonia as sources has been proposed. In this improved model,the effect of low decomposition rate of ammonia has been considered and the number of moles is used to express the mass conservation constraints of element N,H,Al and In. It is assumed that the alloy is synthesized by the reactions between ammonia and group Ⅲ elements. The results show that it is more difficult to grow the InxAl1-xN alloy,especially for the InxAl1-xN lattice matched the GaN. In order to enhance the incorporation of indium into InA1N,we should use the lower growth temperature,optimized input Ⅴ/Ⅲ ratio and high nitrogen fraction in the carrier gas. In addition,the decomposed fraction of ammonia should be reduced. Indium droplets would be deposited if the growth conditions have not been selected properly.     

Quasi-Thermodynamic Model of MOVPE of InAlN

Group - nitrides are very importantmaterials,which are applied to the fabrication ofgreen,blue and ultraviolet light emitting diodes(L EDs) and laser diodes(L Ds) [1 ] .Inx Al1 - xN alloy is a kind of promising material for Ga N- based...     

A Quasi-Thermodynamic Model of MOVPE of InGaN

A quasi-thermodynamic model of MOVPE growth of InxGa1-xN alloys has been proposed with TMGa, TMIn and ammonia as source materials. In this improved model, the effect of low decomposition rate of ammonia is considered and the number of moles is used to express the mass conservation constraints on element N, H, In and Ga. It is assumed that the alloy was synthesized by the reactions between ammonia and group Ⅲ elements. The equilibrium partial pressures over the InxGa1-xN have been calculated. For the InxCa1-xalloys the relationship between the input vapor and the deposited solid composition has been calculated and the results compared with the literature data. The good agreement on the compositions from calculation and the experiment shows that our improved model is suitable for applying to the In xGa1- xNalloys grown by MOVPE. It is difficult for InxGa1-xN alloy to grow, especially for high-indium alloys, because InxGa1-xN is an immiscible alloy and InN has a very high In vapor pressure. It is also shown that gallium has strong tendency of preferential incorporation into the InxGa1-xN alloy. In order to enhance the incorporation of indium into the InGaN, we should use the lower growth-temperature ,lower reactor pressure, higher input V/Ⅲ ratio and higher nitrogen fraction in the carrier gas, in addition, the decomposed fraction of ammonia should also be reduced. Indium droplets would be deoosed if the growing conditions were not selected properly.     

A Quasi-Thermodynamic Model of MOVPE of InGaN

ＧｒｏｕｐⅢ－ｎｉｔｒｉｄｅｓａｒｅｖｅｒｙｉｍｐｏｒｔａｎｔｍａｔｅｒｉａｌｓ,ｗｈｉｃｈａｒｅｓｕｉｔａｂｌｅｆｏｒｔｈｅｆａｂｒｉｃａｔｉｏｎｏｆｇｒｅｅｎ,ｂｌｕｅｏｒｕｌｔｒａｖｉｏｌｅｔｌｉｇｈｔｅｍｉｔｔｉｎ...     

InAIGaAs selective MOVPE growth with bandgap energy shift

We studied the bandgap energy shift by varying the SiO₂ mask width in selective MOVPE growth of InAIGaAs with almost no polycrystals on the masks. We found that the photoluminescence (PL) peak shifts toward the longer wavelength with wider mask width and narrower mesa width, where the In content is enhanced, and observed a maximum PL peak wavelength shift of 170 nm.     

Metal-organic vapor phase epitaxy growth and characterization of AlN/GaN heterostructures

Low-pressure, metal-organic vapor-phase epitaxy (MOVPE) was used to grow AlN/GaN metal-insulator-semiconductor (MIS) heterostructures with AlN thickness between 3 nm and 30 nm. The Hall mobility was found to decrease with increasing AlN thickness, with optimal mobility measured at 5-nm AlN. By decreasing the ammonia flow during AlN growth (lower V/III ratio), surface and interface quality were greatly improved with a corresponding improvement in electrical properties. For the optimal V/III ratio, room-temperature (RT) mobility and sheet charge were 891 cm²/Vs and 2.15×10¹³ cm⁻², respectively. The best RT mobility, for both optimal V/III and thickness, was 1015 cm²/Vs with a sheet charge of 1.1×10¹³ cm⁻².     

The photoassisted MOVPE growth of ZnSSe using tertiary-butylmercaptan

We have conducted a study of the compositional control of epitaxial ZnS_ySe_1-y grown by photoassisted metal organic vapor phase epitaxy (MOVPE) (250 torr, 340°C, UV=14 mW/cm²) on GaAs (100) substrates. We have achieved lattice matched ZnSSe films on GaAs substrates using photoassisted growth using dimethylzinc (DMZn), dimethylselenide (DMSe), and tertiary-butylmercaptan (t-BuSH) as precursors. In addition, we have obtained sulfur compositions (y), ranging from 0.023 to unity (ZnS). The growth rate of the ZnS was 1 μm/h, which was previously unattainable by our group using diethylsulfur. The closely lattice matched sample (y=0.07 as determined by high resolution x-ray diffraction) showed a near band edge peak intensity (NBE) to deep level emission intensity (DLE) ratio of 77 to 1, as determined by room temperature photoluminescence measurements. We have examined the sulfur incorporation as a function of source mole fractions, UV intensity, and growth temperature and found that optimized growth conditions (optimized for range of compositions possible, and NBE/DLE ratio) are X_DMZn=1.5 × 10⁻⁴, X_DMSe=3×10⁻⁴, UV=14 mW/cm², growth temperature=340°C. X_DMZn and X_DMSe are the mole fractions of DMZn and DMSe, respectively. We have found the growth rate to be 1 μm/h for y=0.023 to 0.24 for these optimized conditions. It was found that to achieve sulfur compositions of less than 0.9, the t-BuSH mole fractions had to be kept low. Higher UV intensities increased the incorporation of selenium, while also lowering the material quality (NBE/DLE ratios). We have shown that the optical material qualities of ZnSSe films grown with t-BuSH are much better than ZnSSe films grown with DES.     

In-situ monitoring of surface stoichiometry and growth kinetics study of GaN (0001) in MOVPE by spectroscopic ellipsometry

GaN surface stoichiometry and growth kinetics in MOVPE were studied by in-situ spectroscopic ellipsometry. The effect of MOVPE conditions on both the surface stoichiometry and growth kinetics was investigated. The surface stoichiometry, such as N-rich, Ga-rich and Ga-excess surfaces, was monitored, and was drastically changed by the variation of the NH₃ partial pressure. When the TMG supply was interrupted during the growth, the layer-by-layer decomposition/revaporation was observed in H₂/NH₃ ambient. The decomposition rate was measured as a function of the NH₃ flow rate at the conventional epilayer growth temperatures (1050–1140 C). The decomposition rate was decreased with the increase in the N coverage on the GaN surface. it was found that the surface stoichiometry is a very important parameter for the control of the MOVPE growth kinetics.     

GaN/GaAs(001)外延薄膜的湿法腐蚀特性

对在GaAs (001) 衬底上用金属有机物气相外延(MOVPE)方法生长的GaN薄膜的湿法腐蚀特性进行了研究.所用腐蚀液包括HCl、H3PO4、KOH水溶液以及熔融KOH,腐蚀温度为90～300℃.实验发现不同的腐蚀液在样品表面腐蚀出不同形状的腐蚀坑.KOH溶液腐蚀出长方形的坑,长边平行于(111)A面,表明沿相互垂直的〈110〉晶向的腐蚀特性不同.用不同晶面相对反应性的差别定性解释了腐蚀的这种非对称性.此外,还发现KOH水溶液更有可能用于显示立方相GaN外延层中的层错.     

MOVPE growth of InPSb/InAs heterostructures for mid-infrared emitters

We investigated the growth of InPSb on GaSb or InAs by low pressure (20 mbar) metalorganic vapor phase epitaxy (MOVPE). Trimethylindium, triethylantimony, and phosphine were used as starting materials. High resolution x-ray diffraction, photoluminescence at 10K, Hall measurements at 300 and 77K as well as scanning electron microscopy and scanning tunneling electron microscopy investigations were carried out to verify the layer properties. Lattice-matched InPSb layers on InAs substrate grown at 520°C show mirror-like surfaces and sharp x-ray peaks. N-type doping of InP_0.69Sb_0.31 was carried out with H₂S and p-type doping was achieved with DEZn. Maximum electron concentrations of 2×10¹⁹ cm⁻³ and hole concentrations exceeding 10¹⁸ cm⁻³ were obtained after annealing in N₂ ambient. The thermal stability of InPSb was studied during annealing experiments carried out at 500°C up to 30 min. The compositional integrity of the lattice proves to be stable and the InAs/InPSb interface can be improved. Multiple quantum well structures, pn-junction diodes and the two-dimensional electron gas at the InPSb/InAs/InPSb quantum wells were investigated to demonstrate the properties of the material.     

GaN/GaAs(001)外延薄膜的湿法腐蚀特性

对在GaAs (001) 衬底上用金属有机物气相外延(MOVPE)方法生长的GaN薄膜的湿法腐蚀特性进行了研究.所用腐蚀液包括HCl、H3PO4、KOH水溶液以及熔融KOH,腐蚀温度为90～300℃.实验发现不同的腐蚀液在样品表面腐蚀出不同形状的腐蚀坑.KOH溶液腐蚀出长方形的坑,长边平行于(111)A面,表明沿相互垂直的〈110〉晶向的腐蚀特性不同.用不同晶面相对反应性的差别定性解释了腐蚀的这种非对称性.此外,还发现KOH水溶液更有可能用于显示立方相GaN外延层中的层错.     

Effect of MOVPE growth interruptions on the gallium arsenide interior interface morphology

We have studied MOVPE-grown interior GaAs/AlAs interfaces using highly selective etching combined with atomic force microscopy. We observe substantial restructuring for samples grown on both (100) exact and vicinal substrates. Interface structures differ significantly from sample surfaces after cool-down. On (100) exact substrates, the macroscopic monolayer island and terrace structure smoothes during growth interruptions over the whole 2 min period of time studied. A new, mesoscopic scale of roughness is detected for the first time. This structure does not depend on growth interruption time but does change its typical size at different growth temperatures. On vicinal substrates, we observe and quantify step bunching during growth interruption. The growing surface itself is smooth, in sharp contrast to the corresponding macrostepped GaAs sample surface obtained after cooling down.     

Synthesis of GaN nanowires and nanorods via self-growth mode control

The synthesis of hexagonal wurzite one-dimensional (1D) GaN nanostructures on c-Al₂O₃ substrates was investigated using a thermal chemical vapor deposition (CVD) process. The diameter of the GaN nanostructures was controlled by varying the growth time using a mixture of GaN powder and Ga metal with the ammonia gas reaction. The morphologies of the GaN nanowires and nanorods were confirmed by field emission scanning electron microscopy. The micro-Raman spectroscopy and X-ray scattering measurements indicated that the GaN nanostructures had a hexagonal wurzite structure without any oxide phases. We investigated the difference in the structural properties between the GaN nanowires and nanorods. Deep-level emission bands were not observed in cathodoluminescence measurements from either the GaN nanowires or nanorods, indicating the incorporation of low-level impurities into our 1D GaN nanostructures.