We report the effects of rapid thermal annealing (RTA) and electron-blocking layers (EBL) on the optical properties of InGaP/InGaAlP multiple quantum well (MQW) structures for red resonant-cavity light-emitting diodes. The photoluminescence (PL) intensity is strongly dependent on the RTA temperature and time due to the annealing of non-radiative defect centers in QWs. The use of various EBL structures, such as p-InGaAlP, InAlP and p-InAlP, at the top and the top/bottom of MQWs increases the PL and electroluminescence (EL) intensities of InGaP/InGaAlP MQW structures by preventing electron overflow from the active region. For the as-grown sample with two EBLs of p-InAlP at the top/bottom of QWs, the PL intensity is approximately 14 times higher than that of the sample without an EBL. The additional RTA process at 720 • C for 240 s improves the PL intensity (i.e. 46 times) dramatically. For the device structure with two EBLs of p-InAlP on the annealed wafer, the EL intensity is improved by 12 times at 20 mA compared to the no-EBL structure.

We investigated the effect of dot size distribution and interlayer thickness on the optical property of closely stacked self-assembled InAs/GaAs quantum dot (QD) structures with growth interruption for 30 s using an As 2 source. The structural property was optimized by changing the growth parameters, such as growth temperature, growth time and group III/V ratio. As the stacking number was increased, the size of truncated pyramid-shaped QDs became larger in both height and width, maintaining an on-top vertical alignment with a dot density of ∼5.2-5.9 × 10 10 cm −2 . Compared to the single QD layer, five closely stacked QDs with the GaAs interlayer are found to exhibit a significant improvement of their photoluminescent (PL) intensity, indicating a slight shift of the PL peak position toward the high-energy side. The use of a thin GaAs interlayer of 3 nm in the QDs enhanced the blue shift, which is attributed to the dominant strain-induced intermixing or loss of indium atoms in the InAs QD layers. For the interlayer thicker than about 7 nm, the blue shifts are correlated to the dominant high-energy excited state transitions due to the successive state filling of the ground and higher excited states in the QDs. The energy separation of double PL peaks, originating from two different excited states, was kept at around 50 meV at room temperature. A possible mechanism concerning this phenomenon was also discussed.