5.4 Carrier Localization in InGaN/GaN Multiple Quantum Wells
85
Fig. 5.3 Schematic diagram of carrier localization model
strong localized states for combination luminescence. In addition, the corresponding
FWHM is reduced. After 70 K, as the temperature rise, carriers begin to occupy the
higher energy level of the local state, and the delocalized as well as non-radiative
combination increase. Under such circumstances, the peak position of the corresponding luminescence peak has a blue-shift. As the carriers occupy more high
energy levels, the corresponding FWHM increases. When the temperature rises to
150 K, the carriers confined in the local states will start to become free exciton states.
After 150 K, the common temperature thermal effect will become more and more
significant, and the energy of the luminescence peak has a red-shift due to the shrink
of forbidden band. Then, the corresponding FWHM gradually increases [28].
For most semiconductors (including GaN), in general, an increase in temperature
leads to a decrease in band edge transition energy and the band gap narrows. The
relationship between the band gap of the semiconductor and the temperature is in
accordance with the Varshni formula, which is the shrinkage effect of the band gap
with increasing temperature [29].
E g (T ) = E g (0) −
αT
2
β + T
(5.25)
where E g (T ) is the band gap at temperature T, E g (0) is the band gap at 0 K, and
constants α and β are Varshni thermal coefficients. Due to the fluctuation of the In
composition, the local state exists in the quantum well. Therefore, we use the bandtail model to modify the Varshni formula to study the variation of the peak position
with temperature.
85
Fig. 5.3 Schematic diagram of carrier localization model
strong localized states for combination luminescence. In addition, the corresponding
FWHM is reduced. After 70 K, as the temperature rise, carriers begin to occupy the
higher energy level of the local state, and the delocalized as well as non-radiative
combination increase. Under such circumstances, the peak position of the corresponding luminescence peak has a blue-shift. As the carriers occupy more high
energy levels, the corresponding FWHM increases. When the temperature rises to
150 K, the carriers confined in the local states will start to become free exciton states.
After 150 K, the common temperature thermal effect will become more and more
significant, and the energy of the luminescence peak has a red-shift due to the shrink
of forbidden band. Then, the corresponding FWHM gradually increases [28].
For most semiconductors (including GaN), in general, an increase in temperature
leads to a decrease in band edge transition energy and the band gap narrows. The
relationship between the band gap of the semiconductor and the temperature is in
accordance with the Varshni formula, which is the shrinkage effect of the band gap
with increasing temperature [29].
E g (T ) = E g (0) −
αT
2
β + T
(5.25)
where E g (T ) is the band gap at temperature T, E g (0) is the band gap at 0 K, and
constants α and β are Varshni thermal coefficients. Due to the fluctuation of the In
composition, the local state exists in the quantum well. Therefore, we use the bandtail model to modify the Varshni formula to study the variation of the peak position
with temperature.