58
4 Epitaxial of III-Nitride LED Materials
sample with a suitable-temperature for growth of buffer layer is significantly higher,
which is consistent with the results reported by Yi et al. [31]. It is believed that this is
resulted from a suitable buffer layer temperature which improves the quality of posthigh temperature growth GaN materials and reduces non-radiative recombination.
The optimized temperature for the buffer layer was 535 °C from our experiments.
There is 30 °C difference from the 505 °C reported by Yi et al. [31]. The difference
could be caused by the variation in growth equipment or temperature monitoring.
4.5.1.3 Effect of TMGa Flow for Buffer Layer
In experiments of different TMGa flow rates for the buffer layer, we found that the
slope of the buffer layer reflectance curve is larger for high TMGa flow. This indicates
that the Ga flow rate determines the growth rate in the buffer layer, and the buffer
layer is grown under N-rich condition. That is to say, the dissociation of NH 3 is
sufficient even at such a low temperature owing to the large V/III ratio (V/III ratio is
10,000). This also indicates that the growth rate of the buffer layer does not increase
with temperature, which is consistent with the results of Fig. 4.12 (the growth rate of
the buffer layers with different growth temperature is the same). In addition, when the
buffer layer is grown with a small Ga flow rate, the reflectance of the sample recovers
more rapidly during the roughening stage (with the same growth conditions in the
roughening stage). This can be explained by the faster island consolidation during
high temperature growth. Such a phenomenon is caused by the insufficient growth
of the nuclear islands and the resulted small size, high density, and small spacing
Fig. 4.12 In-situ monitoring curve of different Ga flow growth buffer layers
4 Epitaxial of III-Nitride LED Materials
sample with a suitable-temperature for growth of buffer layer is significantly higher,
which is consistent with the results reported by Yi et al. [31]. It is believed that this is
resulted from a suitable buffer layer temperature which improves the quality of posthigh temperature growth GaN materials and reduces non-radiative recombination.
The optimized temperature for the buffer layer was 535 °C from our experiments.
There is 30 °C difference from the 505 °C reported by Yi et al. [31]. The difference
could be caused by the variation in growth equipment or temperature monitoring.
4.5.1.3 Effect of TMGa Flow for Buffer Layer
In experiments of different TMGa flow rates for the buffer layer, we found that the
slope of the buffer layer reflectance curve is larger for high TMGa flow. This indicates
that the Ga flow rate determines the growth rate in the buffer layer, and the buffer
layer is grown under N-rich condition. That is to say, the dissociation of NH 3 is
sufficient even at such a low temperature owing to the large V/III ratio (V/III ratio is
10,000). This also indicates that the growth rate of the buffer layer does not increase
with temperature, which is consistent with the results of Fig. 4.12 (the growth rate of
the buffer layers with different growth temperature is the same). In addition, when the
buffer layer is grown with a small Ga flow rate, the reflectance of the sample recovers
more rapidly during the roughening stage (with the same growth conditions in the
roughening stage). This can be explained by the faster island consolidation during
high temperature growth. Such a phenomenon is caused by the insufficient growth
of the nuclear islands and the resulted small size, high density, and small spacing
Fig. 4.12 In-situ monitoring curve of different Ga flow growth buffer layers