L Wan

Microstructure of GaN films grown on Si(111) substrates by metalorganic chemical vapor deposition

We report the transmission electron microscopy (TEM) study of the microstructure of wurtzitic GaN films grown on Si(I I I) substrates with AlN buffer layers by metalorganic chemical vapor deposition (MOCVD) method. An amorphous layer was formed at the interface between Si and AlN when thick GaN film was grown. We propose the amorphous layer was induced by the large stress at the interface when thick GaN was grown. The In0.1Ga0.9N/GaN multiple quantum well (MQW) reduced the dislocation density by obstructing the mixed and screw dislocations from passing through the MQW. But no evident reduction of the edge dislocations by the MQW was observed. It was found that dislocations located at the boundaries of grains slightly in-plane misoriented have screw component. Inversion domain is also observed

MBE growth and Raman studies of cubic and hexagonal GaN films on (001)-oriented GaAs substrates

Using different nucleation layers, we have grown cubic and hexagonal GaN epilayers on (001)-oriented GaAs substrates by radio-frequency plasma-assisted molecular beam epitaxy. First- and second-order Raman spectra are taken from these epilayers in back-scattering configurations at room temperature. For the first-order Raman spectra, transverse-optical (TO) phonons and longitudinal-optical (LO) phonons of cubic GaN are found to be at 533 and 739 cm(-1), as well as the E-2 and A(1)(LO) frequency of hexagonal GaN are found to be at 568 and 733 cm(-1), and the polarized spectra are in good agreement with Raman selection rules for cubic and hexagonal GaN, respectively. These results confirm the single crystalline nature of the samples. As for the second-order Raman spectra, the bands show a continuum, at about twice the energy of the LO phonon of cubic GaN and A(1)(LO) phonon of hexagonal GaN, which are nearly 10 times weaker than the first-order scattering. Two-phonon spectra are dominated by contributions due to longitudinal optical phonons

MBE growth and X-ray study of high-quality cubic-GaN on GaAs(0 0 1)

Abstract High-quality cubic GaN epilayer on GaAs(0xa00xa01) was grown by molecular beam epitaxy equipped with radio frequency nitrogen source. The optimized growth condition is to grow two monolayers thick initial GaN at 600°C under As atmosphere. X-ray diffraction rocking curve shows that the full-width at half-maximum of cubic GaN(0xa00xa02) diffraction peak is 10xa0arcmin. The X-ray reciprocal space mapping is used to identify the secondary hexagonal phase and estimate their relative content.

Controllable cubic and hexagonal GaN growth on GaAs(001) substrates by molecular beam epitaxy

Abstract Two kinds of GaN samples were grown on GaAs(0xa00xa01) substrates. One is grown on nitridized GaAs surface, the other is grown on nitridized AlAs buffer GaAs substrate. X-ray diffraction and photoluminescence measurements find that the GaN sample directly grown on GaAs substrate is pure cubic phase and those grown on AlAs buffer is pure hexagonal phase. The present study shows that the phase of GaN samples grown on GaAs substrates can be controlled using different buffer layers.

Influence of AlN buffer on phase structure of GaN on GaAs (001) grown by radio-frequency molecular beam epitaxy

The influence of an AlN buffer layer on the phase structure of GaN is studied. Cubic GaN grown on a GaN buffer layer present on a GaAs (001) substrate, and secondary hexagonal GaN in the sample is grown according to GaN[0001]∥GaAs[111]B; when an AlN buffer layer is introduced, the single hexagonal GaN crystal is obtained with the growth direction of GaN[0001]∥GaAs[001]. X-ray diffraction and photoluminescence measurements are used to analyze the phase structure and orientation of the two epilayers. Atomic force microscopy is used to analyze the surface characteristics and it is revealed that the morphologies of the two samples differ. The results reveal different nucleation mechanisms of GaN on the GaN buffer layer and AlN buffer layer.

Transmission electron microscopy study of hexagonal GaN film grown on GaAs (001) substrate by using AlAs nucleation layer

Abstract Hexagonal gallium nitride (h-GaN) films have been grown on AlAs nucleation layer by using radio frequency (RF) plasma source-assisted molecular beam epitaxy on GaAs (0xa00xa01) substrate. Transmission electron microscopy (TEM) techniques are used to characterize such h-GaN epilayers. TEM results show that (0xa00xa00xa01) atom planes of h-GaN are parallel to (0xa00xa01) atom planes of the GaAs substrate. Defects, such as stacking faults and dislocations, have also been observed.

Photoluminescence study of Si doping cubic GaN grown on (001) GaAs substrates by molecular beam epitaxy

The photoluminescence (PL) properties of Si-doped cubic GaN with different carrier concentrations were investigated at room temperature. The epilayers were grown on GaAs (0 0 1) by radio-frequency molecular beam epitaxy. It was found that when the carrier concentration is increased fi om 5 x 10(15) to 2 x 10(18) cm(-3), the PL peak shifted towards low energy, from 3.246 to 3.227 eV, and the PL linewidth increased from 77.1 to 121 meV. The PL peak shift is explained by the bandgap narrowing effect due to the high doping concentration. The PL linewidth includes two parts: one is doping concentration independent, which is caused by the imperfection of samples and phonon scattering; the other is doping concentration dependent. We assign the second part to the broadening by the microscopic fluctuation of the doping concentration. The experimental measurements are in good agreement with the model

Nucleation of hexagonal AlN in nitridized AlAs buffer on (001) GaAs substrate

Abstract Hexagonal GaN film has been grown on (0xa00xa01) GaAs substrate with nitridized AlAs buffer layer. The (0xa00xa00xa01) plane of the hexagonal GaN(h-GaN) is parallel to the (0xa00xa01) plane of the GaAs substrate. The nitridized AlAs/GaAs(0xa00xa01) material was analyzed by high-resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM). The HRTEM observations show that hexagonal AlN(h-AlN) can nucleate on the AlAs surface after nitridation with its (0xa00xa00xa01) plane parallel to the (0xa00xa01) plane of the AlAs. Some cubic AlN(c-AlN) micro grains were also observed. The close-packed atom planes of the c-AlN grains are parallel to the (0xa00xa01) planes of the AlAs. The AFM result shows that the surface morphology of the nitridized AlAs is rough with high-density dots. Such AlN layer can be taken as a prelayer for growing h-GaN on the (0xa00xa01) GaAs substrate.

Epitaxial growth and characterization of GaN films on (001) GaAs substrates by radio-frequency molecular beam epitaxy

The intermediate nucleation layer effects on the crystal structure of GaN epitaxial layers grown on GaAs (0 0 1) substrates by solid-sourer molecular beam epitaxy using RF-N-2 plasma as a nitrogen source were investigated. The crystal structure of GaN grown on (0 0 1) GaAs substrates was critically influenced by the nucleation layer, that is, mainly cubic GaN was grown directly on the GaAs substrate with the epitaxial relationship of GaN (0 0 1)//GaAs(0 0 1) and GaN[1 1 0]//GaAs[1 1 0], while hexagonal GaN was frown on a very thin AlAs intermediate layer with the epitaxial relationship of GaN(0 0 0 1)//GaAs(0 0 1) and GaN[1 1 (2) over bar 0]//GaAs[1 1 0]. X-ray diffraction and transmission-electron-microscope are used to analyze the crystal structure of the two kinds of epilayers

Growth and properties of hexagonal GaN on GaAs(001) substrate by RF-molecular beam epitaxy using an AlAs nucleation layer

Abstract Hexagonal gallium nitride (h-GaN) films of about 400xa0nm are grown by using radio frequency (RF) plasma source assisted molecular beam epitaxy on (0xa00xa01)-oriented GaAs substrate. Before the growth of GaN epilayer an AlAs layer of about 10xa0nm was grown at 700°C and nitridized with the temperature ramping from 540 to 730°C. Then low-temperature GaN or AlN was grown as the buffer layer. The epilayers were characterized by using high-resolution X-ray diffraction (HRXRD), atomic force microscopy (AFM), and Raman scattering. By using AlN instead of GaN as the buffer layer, the GaN epilayer quality and morphology are significantly improved.