The influence of growth temperature and input V/III ratio on the initial nucleation and material properties of InN on GaN by MOCVD

The effects of growth temperature and V/III ratio on the InN initial nucleation of islands on the GaN (0 0 0 1) surface were investigated. It is found that InN nuclei density increases with decreasing growth temperature between 375 and 525 degrees C. At lower growth temperatures, InN thin films take the form of small and closely packed islands with diameters of less than 100 nm, whereas at elevated temperatures the InN islands can grow larger and well separated, approaching an equilibrium hexagonal shape due to enhanced surface diffusion of adatoms. At a given growth temperature of 500 degrees C, a controllable density and size of separated InN islands can be achieved by adjusting the V/III ratio. The larger islands lead to fewer defects when they are coalesced. Comparatively, the electrical properties of the films grown under higher V/III ratio are improved

Kinetically controlled InN nucleation on GaN templates by metalorganic chemical vapour deposition

This paper presents a study on the nucleation and initial growth kinetics of InN on GaN, especially their dependence on metalorganic chemical vapour deposition conditions. It is found that the density and size of separated InN nano-scale islands can be adjusted and well controlled by changing the V/III ratio and growth temperature. InN nuclei density increases for several orders of magnitude with decreasing growth temperature between 525 and 375 degrees C. At lower growth temperatures, InN thin films take the form of small and closely packed islands with diameters less than 100 nm, whereas at elevated temperatures the InN islands grow larger and become well separated, approaching an equilibrium hexagonal shape due to enhanced surface diffusion of adatoms. The temperature dependence of InN island density gives two activation energies of InN nucleation behaviour, which is attributed to two different kinetic processes related to In adatom surface diffusion and desorption, respectively

Investigation on the structural origin of n-type conductivity in InN films

This work presents a study of the correlation between the electrical properties and the structural defects in nominally undoped InN films. It is found that the density of edge-type threading dislocations (TDs) considerably affects the electron concentration and mobility in InN films. The Hall-effect measured electron concentration increases, while the Hall mobility decreases with the increase in the edge-type TD density. With the combination of secondary ion mass spectrometry and positron annihilation analysis, we suggest that donor-type point defects at the edge-type TD lines may serve as dominant donors in InN films and affect the carrier mobility

Suppression of indium droplet formation by adding CCl4 during metalorganic chemical vapor deposition growth of InN films

In this work, the influences of CCl4 on the metalorganic chemical vapor deposition (MOCVD) growth of InN were studied for the first time. It was found that the addition of CCl4 can effectively suppress the formation of metal indium (In) droplets during InN growth, which was ascribed to the etching effect of Cl to In. However, with increasing of CCl4 flow, the InN growth rate decreased but the lateral growth of InN islands was enhanced. This provides a possibility of promoting islands coalescence toward a smooth surface of the InN film by MOCVD. The influence of addition of CCl4 on the electrical properties was also investigated

Cathodoluminescence study on in composition inhomogeneity of thick InGaN layer

We have investigated the optical properties of thick InGaN film grown on GaN by cathodeluminescence (CL) spectroscopy. It is found that there is obvious In composition variation in both growth and lateral direction of InGaN film. The depth distribution of In composition is closely related to the strain relaxation process of InGaN film. Accompanied with the relaxation of compressive strain, the In composition of InGaN layer increases and the CL peak energy shifts towards red. Moreover, a rather apparent In composition fluctuation is found in the relaxed upper part of InGaN layer as confirmed by CL imaging

InGaN/GaN p-i-n Photodiodes Fabricated with Mg-Doped p-InGaN Layer

Mg-doped p-InGaN layers with In composition of about 10% are grown by metalorganic chemical vapor deposition (MOCVD). The effect of the annealing temperature on the p-type behavior of Mg-doped InGaN is studied. It is found that the hole concentration in p-InGaN increases with a rising annealing temperature in the range of 600 850 C, while the hole mobility remains nearly unchanged until the annealing temperature increases up to 750 C, after which it decreases. On the basis of conductive p-type InGaN growth, the p-In0.1Ga0.9N/i-In0.1Ga0.9N/n-GaN junction structure is grown and fabricated into photodiodes. The spectral responsivity of the InGaN/GaN p-i-n photodiodes shows that the peak responsivity at zero bias is in the wavelength range 350-400 nm

Investigation on the strain relaxation of InGaN layer and its effects on the InGaN structural and optical properties

The evolution of strain and structural properties of thick epitaxial InGaN layers grown on GaN with different thicknesses are investigated. It is found that, with increase in InGaN thickness, plastic relaxation via misfit dislocation generation becomes a more important strain relaxation mechanism. Accompanied with the relaxation of compressive strain, the In composition of InGaN layer increases and induces an apparent red-shift of the cathodoluminescence peak of the InGaN layer. On the other hand, the plastic relaxation process results in a high defect density, which degrades the structural and optical properties of InGaN layers. A transition layer region with both strain and In composition gradients is found to exist in the 450-nm-thick InGaN layer

Effects of grain size on the mosaic tilt and twist in InN films grown on GaN by metal-organic chemical vapor deposition

The structural property of InN films grown on Ga-face GaN layers by metal-organic chemical vapor deposition has been studied by high-resolution x-ray diffraction. The mosaic tilt and twist are found to be strongly dependent on the surface lateral grain size. The twist decreases with increasing grain size and finally approaches to a constant level. On the other hand, the mosaic tilt increases substantially when the grain size becomes large enough and exceeds the width of step terraces on the GaN surface, showing an important mechanism for the defect generation in the InN/GaN system with large out-of-plane lattice mismatch. (c) 2006 American Institute of Physics