Guangxu Ju

In situ X-ray investigation of changing barrier growth temperatures on InGaN single quantum wells in metal-organic vapor phase epitaxy

The effects of GaN quantum barriers with changing growth temperatures on the interfacial characteristics of GaN/InGaN single quantum well (SQW) grown on GaN templates by metalorganic vapour phase epitaxy were in situ investigated by X-ray crystal truncation rod (CTR) scattering and X-ray reflectivity measurements at growth temperature using a laboratory level X-ray diffractometer. Comparing the curve-fitting results of X-ray CTR scattering spectra obtained at growth temperature with that at room temperature, the In x Ga1- x N with indium composition less than 0.11 was stabile of the indium distribution at the interface during the whole growth processes. By using several monolayers thickness GaN capping layer to protect the InGaN well layer within temperature-ramping process, the interfacial structure of the GaN/InGaN SQW was drastically improved on the basis of the curve-fitting results of X-ray CTR scattering spectra, and the narrow full width at half-maximum and strong luminous intensity were observed in room temperature photoluminescence spectra.

X-ray characterization of GaN and related materials at growth temperatures–system design and measurements

To investigate the phenomena that occur at the growth temperatures, an MOVPE (metalorganic vapor phase epitaxy) growth system was installed in the X-ray diffractometer of the laboratory level. The present MOVPE system is capable of growing GaN and related materials that are advanced in the device applications but very little is known, especially experimentally, what is going on at the growth front and in the environment. Since MOVPE growth is conducted at an atmospheric pressure or at a low pressure, very limited tools can be used to probe the growing surface. It is demonstrated that the X-ray diffraction, X-ray CTR (crystal truncation rod) scattering, and X-ray reflectivity can be used even at 1000 o C that is a normal growth temperature for GaN and related materials.

In situ X-ray reflectivity of indium supplied on GaN templates by metal organic vapor phase epitaxy

The indium supplied on c-plane GaN templates using Metal organic vapor phase epitaxy was studied by in situ X-ray reflectivity (XRR) at 800 °C. The presence of liquid indium layers on the GaN (0001) surface was demonstrated using data-fitting of XRR measurements, ex situ atomic force microscope, auger electron spectroscopy, and cross-sectional scanning electron microscope. These measurements demonstrated that a liquid indium layer coexisted with indium droplets on top of the GaN (0001) surface at 800 °C. The liquid indium film thicknesses increased with increasing TMIn supply time and did not change during cooling from 800 °C to room temperature.

In situ X-ray Reflectivity Measurements on Annealed InxGa1-xN Epilayer Grown by Metalorganic Vapor Phase Epitaxy

The thermal decomposition of c-plane GaN/sapphire templates was studied in a metalorganic vapor phase epitaxy (MOVPE) system installed in a laboratory-level X-ray diffractometer by using in situ X-ray reflectivity (XRR). GaN remained thermally stable in pure N2 up to 900 °C, while a significant decomposition occurred at 950 °C. Then, thin InxGa1-xN epilayers were grown on the annealed templates at 830 °C. In situ XRR measurements were conducted before and after InGaN growth. By theoretical and experimental analyses of the XRR spectra, the sample structure change upon thermal annealing was clarified. Photoluminecescence (PL) and atomic force microscopy (AFM) results demonstrated that thermal annealing affected the optical properties and microstructures of InGaN films. The PL peaks from InGaN slightly blue-shifted with thermal annealing.

Role of threading dislocations in strain relaxation during GaInN growth monitored by real-time X-ray reflectivity

Ga1−xInxN epilayers (x = 0.09 or 0.14) grown on c-plane GaN layers with different densities of threading dislocations have been investigated by real-time x-ray reflectivity during metal-organic vapor phase epitaxial growth. We found that the density of pre-existing threading dislocations in GaN plays an important role in the strain relaxation of Ga1−xInxN. Critical thicknesses were obtained and compared with theoretical predictions using the mechanical equilibrium model and the energy balance model. The critical thickness of GaInN varies inversely with dislocation density in the GaN sublayer. When the threading dislocation density in the sublayer was reduced by three orders of magnitude, the photoluminescence intensity of the Ga0.86In0.14N epilayer was improved by a factor of ten.