54
4 Epitaxial of III-Nitride LED Materials
and the roughening layer have a great impact on the material properties of the high
temperature intrinsic GaN. The properties of GaN materials grown under different
initial growth conditions were characterized. The influence of the growth parameters of GaN on the properties of high temperature GaN materials was obtained. The
material properties of intrinsic GaN were improved by optimizing the initial growth
parameters.
4.5.1 Effect of Buffer Layer Growth Conditions on Material
Quality
4.5.1.1 Effect of Buffer Layer Thickness
The structural and electrical properties of intrinsic GaN materials grown with buffer
layers of different thicknesses (other growth conditions are the same) were investigated. It was found that when the thickness of the buffer layer is increased from
18 to 28 nm, the FWHM of the (002) and (102) peaks of the X-ray double crystal
diffraction of the material decreases gradually, the background carrier concentration
decreases, and the mobility increases.
According to Heinke et al. [23], Beaumont et al. [24], Ayers [25], the dislocation
density is proportional to the full width at half maximum of the X-ray diffraction
curve, as shown in Eq. (4.13):
ρ =
F W H M(hkl)
4.36b 2
(4.13)
where b is the Burgers Vector of the dislocation, FWHM (hkl) is the full width at
half maximum of the measured (hkl) plane, and ρ is the dislocation density. Thus, a
relatively large value FWHM from X-ray diffraction of the thin buffer layer indicates
an increase in dislocation density, which in turn leads to the degradation in the crystal
quality.
From the electrical properties of GaN with different buffer layers shown in
Table 4.2, the background carrier concentration of the sample increases and the
Table 4.2 Structure and electrical properties of intrinsic GaN grown by buffer layers of different
thickness
Sample
Buffer layer
thickness (nm)
Structural property
Electrical property
(002) FWHM
(arcsec)
(102) FWHM
(arcsec)
Carrier
concentration
(10 16 cm −3 )
Mobility
(cm 2 /Vs)
A
28
284
316
1.2
430
B
18
302
388
1.82
320
4 Epitaxial of III-Nitride LED Materials
and the roughening layer have a great impact on the material properties of the high
temperature intrinsic GaN. The properties of GaN materials grown under different
initial growth conditions were characterized. The influence of the growth parameters of GaN on the properties of high temperature GaN materials was obtained. The
material properties of intrinsic GaN were improved by optimizing the initial growth
parameters.
4.5.1 Effect of Buffer Layer Growth Conditions on Material
Quality
4.5.1.1 Effect of Buffer Layer Thickness
The structural and electrical properties of intrinsic GaN materials grown with buffer
layers of different thicknesses (other growth conditions are the same) were investigated. It was found that when the thickness of the buffer layer is increased from
18 to 28 nm, the FWHM of the (002) and (102) peaks of the X-ray double crystal
diffraction of the material decreases gradually, the background carrier concentration
decreases, and the mobility increases.
According to Heinke et al. [23], Beaumont et al. [24], Ayers [25], the dislocation
density is proportional to the full width at half maximum of the X-ray diffraction
curve, as shown in Eq. (4.13):
ρ =
F W H M(hkl)
4.36b 2
(4.13)
where b is the Burgers Vector of the dislocation, FWHM (hkl) is the full width at
half maximum of the measured (hkl) plane, and ρ is the dislocation density. Thus, a
relatively large value FWHM from X-ray diffraction of the thin buffer layer indicates
an increase in dislocation density, which in turn leads to the degradation in the crystal
quality.
From the electrical properties of GaN with different buffer layers shown in
Table 4.2, the background carrier concentration of the sample increases and the
Table 4.2 Structure and electrical properties of intrinsic GaN grown by buffer layers of different
thickness
Sample
Buffer layer
thickness (nm)
Structural property
Electrical property
(002) FWHM
(arcsec)
(102) FWHM
(arcsec)
Carrier
concentration
(10 16 cm −3 )
Mobility
(cm 2 /Vs)
A
28
284
316
1.2
430
B
18
302
388
1.82
320