52
4 Epitaxial of III-Nitride LED Materials
(2) Stabilizing the temperature after cooling to about 535 °C, and nitridating the
substrate surface using NH 3 . In other words, heat treatment of the substrate is
done in the environment of NH 3 . Sapphire and NH 3 will react under heating
to form AlN x O 1-x . The formation of such compound can reduce the lattice
mismatch between the substrate and the epitaxial layer.
(3) Low-temperature buffer layer growth is performed at about 535 °C. Since the
temperature is low, the surface diffusion coefficient of the atomic group is small.
This makes it easier to adhere to the surface of the nearby substrate, and thus
the density of the nucleation island is high and the reflectance increases. The
growth conditions of the buffer layer, such as thickness, temperature, pressure, etc. greatly affect the size and distribution of the nucleation islands, and
thereby affect the growth mode of the subsequent high temperature epitaxial
layer. Therefore, precise control and optimization of the growth conditions are
required. Its AFM image is shown in Fig. 4.7a. Low-temperature buffer layer
growth is performed at about 535 °C. Since the temperature is low, the surface
diffusion coefficient of the atomic group is small. This makes it easier to adhere
to the surface of the nearby substrate, and thus the density of the nucleation
island is high and the reflectance increases. The growth conditions of the buffer
layer, such as thickness, temperature, pressure, etc. greatly affect the size and
distribution of the nucleation islands, and thereby affect the growth mode of
the subsequent high temperature epitaxial layer. Therefore, precise control and
optimization of the growth conditions are required. Its AFM image is shown in
Fig. 4.7a.
Fig. 4.7 Surface AFM images during growth [21, 22]
4 Epitaxial of III-Nitride LED Materials
(2) Stabilizing the temperature after cooling to about 535 °C, and nitridating the
substrate surface using NH 3 . In other words, heat treatment of the substrate is
done in the environment of NH 3 . Sapphire and NH 3 will react under heating
to form AlN x O 1-x . The formation of such compound can reduce the lattice
mismatch between the substrate and the epitaxial layer.
(3) Low-temperature buffer layer growth is performed at about 535 °C. Since the
temperature is low, the surface diffusion coefficient of the atomic group is small.
This makes it easier to adhere to the surface of the nearby substrate, and thus
the density of the nucleation island is high and the reflectance increases. The
growth conditions of the buffer layer, such as thickness, temperature, pressure, etc. greatly affect the size and distribution of the nucleation islands, and
thereby affect the growth mode of the subsequent high temperature epitaxial
layer. Therefore, precise control and optimization of the growth conditions are
required. Its AFM image is shown in Fig. 4.7a. Low-temperature buffer layer
growth is performed at about 535 °C. Since the temperature is low, the surface
diffusion coefficient of the atomic group is small. This makes it easier to adhere
to the surface of the nearby substrate, and thus the density of the nucleation
island is high and the reflectance increases. The growth conditions of the buffer
layer, such as thickness, temperature, pressure, etc. greatly affect the size and
distribution of the nucleation islands, and thereby affect the growth mode of
the subsequent high temperature epitaxial layer. Therefore, precise control and
optimization of the growth conditions are required. Its AFM image is shown in
Fig. 4.7a.
Fig. 4.7 Surface AFM images during growth [21, 22]