At high V/III ratio, the available AsH3 molecules are far more than enough for group III species, thus the excess AsH3 may act as impurity-free ‘morphactants’ and raise the surface energy [17], leading to the suppression of QD formation. This effect becomes prominent with the increase of V/III ratio, finally causing the sudden decrease of QD density at V/III ratio of 200 (phase III). However, with further increase of V/III ratio, the QD density increases gently. The reasons are still not clear at this moment, but in this case, the partial pressure of group III species

becomes so low that the possibility of surface reconstruction, which is not detectable during MOCVD growth, may need to be considered. Further experimental works will be conducted to clarify this phenomenon. The PL measurements of selected samples were conducted PF-4708671 clinical trial and the results are shown in Figure 3. Figure 3a shows the photoluminescence from an ensemble of GaAs/InAs QD (V/III ratio

= 50)/60 nm GaAs cap measured at 300 K using excitation at 514 nm. The ground state (labeled as GS) emission peak and the excited state (labeled as ES) emission peak are identified by fitting the PL spectra with two Gaussians. The full width at half maximum of the GS emission peak is 63 nm, indicating that the uniformity of the QDs should be further improved by optimizing other growth parameters. Low-temperature (77 K) μPL using excitation at 514 nm was measured for the ensemble of GaAs/InAs QD (V/III ratio = selleck compound 35)/60 nm GaAs cap (Figure 3b). Verteporfin cell line The emission peak at 966.8 nm indicates that the ensemble has single QD emission characteristics, suggesting that this growth approach can be used for the fabrication of single-photon devices. Figure 3 Results of PL measurements of selected samples. (a) Room-temperature PL spectrum of GaAs/InAs QD (V/III ratio = 50)/60 nm GaAs cap measured at 300 K. (b) The μPL spectrum of GaAs/InAs

QD (V/III ratio = 35)/60 nm GaAs cap measured at 77 K. Conclusions In conclusion, we have described the effects of the V/III ratio on the density and sizes of InAs QDs. Due to the effects of several competing mechanisms resulting from increasing AsH3 partial pressure on coverage, In adatom migration length and surface energy, which are the complicated behaviors of QD formation, are observed. The results also demonstrate that the densities of InAs QDs can be manipulated easily in a wide range from 105 to 1010 cm−2 by varying the V/III ratio. Although the initial PL studies show that the optical performance of InAs QDs should be further improved, this V/III ratio-dependent InAs QDs growth approach may prove very useful for the MOCVD growth of different QDs-based device structures due to its simplicity and reproducibility. Authors’ information LSL, YLL, and JPZ are PhD students at Huazhong University of Science and Technology. QQC and SCS are Master’s degree students at Huazhong University of Science and Technology.